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  Subjects -> ENGINEERING (Total: 2281 journals)
    - CHEMICAL ENGINEERING (192 journals)
    - CIVIL ENGINEERING (186 journals)
    - ELECTRICAL ENGINEERING (102 journals)
    - ENGINEERING (1203 journals)
    - ENGINEERING MECHANICS AND MATERIALS (385 journals)
    - HYDRAULIC ENGINEERING (55 journals)
    - INDUSTRIAL ENGINEERING (68 journals)
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CIVIL ENGINEERING (186 journals)                     

Showing 1 - 186 of 186 Journals sorted alphabetically
ACI Structural Journal     Full-text available via subscription   (Followers: 17)
Acta Polytechnica : Journal of Advanced Engineering     Open Access   (Followers: 2)
Acta Structilia : Journal for the Physical and Development Sciences     Open Access   (Followers: 2)
Advances in Civil Engineering     Open Access   (Followers: 34)
Advances in Structural Engineering     Full-text available via subscription   (Followers: 27)
Ambiente Construído     Open Access   (Followers: 1)
American Journal of Civil Engineering and Architecture     Open Access   (Followers: 30)
Architectural Engineering     Open Access   (Followers: 4)
Archives of Civil and Mechanical Engineering     Full-text available via subscription   (Followers: 1)
Archives of Civil Engineering     Open Access   (Followers: 10)
Archives of Hydro-Engineering and Environmental Mechanics     Open Access   (Followers: 1)
ATBU Journal of Environmental Technology     Open Access   (Followers: 3)
Australian Journal of Structural Engineering     Full-text available via subscription   (Followers: 6)
Baltic Journal of Road and Bridge Engineering     Full-text available via subscription   (Followers: 1)
BER : Building and Construction : Full Survey     Full-text available via subscription   (Followers: 9)
BER : Building Contractors' Survey     Full-text available via subscription   (Followers: 4)
BER : Building Sub-Contractors' Survey     Full-text available via subscription   (Followers: 3)
BER : Survey of Business Conditions in Building and Construction : An Executive Summary     Full-text available via subscription   (Followers: 4)
Berkeley Planning Journal     Open Access   (Followers: 7)
Bioinspired Materials     Open Access   (Followers: 5)
Bridge Structures : Assessment, Design and Construction     Hybrid Journal   (Followers: 15)
Building and Environment     Hybrid Journal   (Followers: 15)
Building Women     Full-text available via subscription  
Built Environment Project and Asset Management     Hybrid Journal   (Followers: 15)
Bulletin of Pridniprovsk State Academy of Civil Engineering and Architecture     Open Access   (Followers: 6)
Canadian Journal of Civil Engineering     Hybrid Journal   (Followers: 11)
Case Studies in Engineering Failure Analysis     Open Access   (Followers: 8)
Case Studies in Nondestructive Testing and Evaluation     Open Access   (Followers: 10)
Case Studies in Structural Engineering     Open Access   (Followers: 9)
Cement and Concrete Composites     Hybrid Journal   (Followers: 17)
Challenge Journal of Concrete Research Letters     Open Access   (Followers: 2)
Challenge Journal of Structural Mechanics     Open Access   (Followers: 5)
Change Over Time     Full-text available via subscription   (Followers: 2)
Civil and Environmental Engineering     Open Access   (Followers: 7)
Civil And Environmental Engineering Reports     Open Access   (Followers: 5)
Civil and Environmental Research     Open Access   (Followers: 19)
Civil Engineering = Siviele Ingenieurswese     Full-text available via subscription   (Followers: 4)
Civil Engineering and Architecture     Open Access   (Followers: 17)
Civil Engineering and Environmental Systems     Hybrid Journal   (Followers: 3)
Civil Engineering and Technology     Open Access   (Followers: 9)
Civil Engineering Dimension     Open Access   (Followers: 8)
Cohesion and Structure     Full-text available via subscription   (Followers: 2)
Composite Structures     Hybrid Journal   (Followers: 257)
Computer-aided Civil and Infrastructure Engineering     Hybrid Journal   (Followers: 10)
Computers & Structures     Hybrid Journal   (Followers: 36)
Concrete Research Letters     Open Access   (Followers: 6)
Construction Economics and Building     Open Access   (Followers: 2)
Construction Engineering     Open Access   (Followers: 8)
Construction Management and Economics     Hybrid Journal   (Followers: 21)
Construction Science     Open Access   (Followers: 4)
Constructive Approximation     Hybrid Journal  
Curved and Layered Structures     Open Access   (Followers: 2)
DFI Journal : The Journal of the Deep Foundations Institute     Hybrid Journal   (Followers: 1)
Earthquake Engineering and Structural Dynamics     Hybrid Journal   (Followers: 16)
Enfoque UTE     Open Access   (Followers: 4)
Engineering Project Organization Journal     Hybrid Journal   (Followers: 7)
Engineering Structures     Hybrid Journal   (Followers: 13)
Engineering Structures and Technologies     Hybrid Journal   (Followers: 2)
Engineering, Construction and Architectural Management     Hybrid Journal   (Followers: 14)
Environmental Geotechnics     Hybrid Journal   (Followers: 5)
European Journal of Environmental and Civil Engineering     Hybrid Journal   (Followers: 8)
Fatigue & Fracture of Engineering Materials and Structures     Hybrid Journal   (Followers: 16)
Frattura ed Integrità Strutturale : Fracture and Structural Integrity     Open Access  
Frontiers in Built Environment     Open Access  
Frontiers of Structural and Civil Engineering     Hybrid Journal   (Followers: 6)
Geomaterials     Open Access   (Followers: 4)
Geosystem Engineering     Hybrid Journal   (Followers: 1)
Geotechnik     Hybrid Journal   (Followers: 3)
Géotechnique Letters     Hybrid Journal   (Followers: 6)
HBRC Journal     Open Access   (Followers: 2)
Hormigón y Acero     Full-text available via subscription  
HVAC&R Research     Hybrid Journal  
Indoor and Built Environment     Hybrid Journal   (Followers: 2)
Infrastructure Asset Management     Hybrid Journal   (Followers: 2)
Infrastructures     Open Access  
Ingenio Magno     Open Access   (Followers: 1)
Insight - Non-Destructive Testing and Condition Monitoring     Full-text available via subscription   (Followers: 22)
International Journal for Service Learning in Engineering     Open Access  
International Journal of 3-D Information Modeling     Full-text available via subscription   (Followers: 3)
International Journal of Advanced Structural Engineering     Open Access   (Followers: 16)
International Journal of Civil, Mechanical and Energy Science     Open Access   (Followers: 1)
International Journal of Concrete Structures and Materials     Open Access   (Followers: 13)
International Journal of Condition Monitoring     Full-text available via subscription   (Followers: 2)
International Journal of Construction Engineering and Management     Open Access   (Followers: 8)
International Journal of Geo-Engineering     Open Access   (Followers: 3)
International Journal of Geosynthetics and Ground Engineering     Full-text available via subscription   (Followers: 4)
International Journal of Masonry Research and Innovation     Hybrid Journal   (Followers: 1)
International Journal of Pavement Research and Technology     Open Access   (Followers: 4)
International Journal of Protective Structures     Hybrid Journal   (Followers: 6)
International Journal of Steel Structures     Hybrid Journal   (Followers: 2)
International Journal of Structural Engineering     Hybrid Journal   (Followers: 10)
International Journal of Structural Integrity     Hybrid Journal   (Followers: 2)
International Journal of Structural Stability and Dynamics     Hybrid Journal   (Followers: 7)
International Journal of Sustainable Built Environment     Open Access   (Followers: 4)
International Journal of Sustainable Construction Engineering and Technology     Open Access   (Followers: 8)
International Journal on Pavement Engineering & Asphalt Technology     Open Access   (Followers: 6)
International Journal Sustainable Construction & Design     Open Access  
Journal of Bridge Engineering     Full-text available via subscription   (Followers: 15)
Journal of Building Engineering     Hybrid Journal   (Followers: 1)
Journal of Building Materials and Structures     Open Access   (Followers: 2)
Journal of Building Performance Simulation     Hybrid Journal   (Followers: 6)
Journal of Civil Engineering and Construction Technology     Open Access   (Followers: 11)
Journal of Civil Engineering and Management     Hybrid Journal   (Followers: 7)
Journal of Civil Engineering and Science     Open Access   (Followers: 7)
Journal of Civil Engineering Research     Open Access   (Followers: 6)
Journal of Civil Society     Hybrid Journal   (Followers: 3)
Journal of Civil Structural Health Monitoring     Hybrid Journal   (Followers: 4)
Journal of Composites for Construction     Full-text available via subscription   (Followers: 13)
Journal of Computing in Civil Engineering     Full-text available via subscription   (Followers: 24)
Journal of Construction Engineering     Open Access   (Followers: 7)
Journal of Construction Engineering and Management     Full-text available via subscription   (Followers: 19)
Journal of Construction Engineering, Technology & Management     Full-text available via subscription   (Followers: 4)
Journal of Constructional Steel Research     Hybrid Journal   (Followers: 8)
Journal of Earth Sciences and Geotechnical Engineering     Open Access   (Followers: 4)
Journal of Fluids and Structures     Hybrid Journal   (Followers: 6)
Journal of Frontiers in Construction Engineering     Open Access   (Followers: 2)
Journal of Green Building     Full-text available via subscription   (Followers: 11)
Journal of Highway and Transportation Research and Development (English Edition)     Full-text available via subscription   (Followers: 12)
Journal of Infrastructure Systems     Full-text available via subscription   (Followers: 21)
Journal of Legal Affairs and Dispute Resolution in Engineering and Construction     Full-text available via subscription   (Followers: 5)
Journal of Marine Science and Engineering     Open Access   (Followers: 1)
Journal of Materials and Engineering Structures     Open Access   (Followers: 4)
Journal of Materials in Civil Engineering     Full-text available via subscription   (Followers: 10)
Journal of Nondestructive Evaluation     Hybrid Journal   (Followers: 11)
Journal of Offshore Structure and Technology     Full-text available via subscription  
Journal of Performance of Constructed Facilities     Full-text available via subscription   (Followers: 4)
Journal of Pipeline Systems Engineering and Practice     Full-text available via subscription   (Followers: 7)
Journal of Rehabilitation in Civil Engineering     Open Access   (Followers: 3)
Journal of Solid Waste Technology and Management     Full-text available via subscription   (Followers: 1)
Journal of Structural Engineering     Full-text available via subscription   (Followers: 39)
Journal of Structural Fire Engineering     Full-text available via subscription   (Followers: 6)
Journal of Sustainable Architecture and Civil Engineering     Open Access   (Followers: 3)
Journal of Sustainable Design and Applied Research in Innovative Engineering of the Built Environment     Open Access   (Followers: 1)
Journal of the South African Institution of Civil Engineering     Open Access   (Followers: 4)
Jurnal Spektran     Open Access   (Followers: 1)
Jurnal Teknik Sipil dan Perencanaan     Open Access  
Konstruksia     Open Access  
KSCE Journal of Civil Engineering     Hybrid Journal   (Followers: 2)
Latin American Journal of Solids and Structures     Open Access   (Followers: 4)
Materiales de Construcción     Open Access  
Mathematical Modelling in Civil Engineering     Open Access   (Followers: 3)
Nondestructive Testing And Evaluation     Hybrid Journal   (Followers: 17)
Obras y Proyectos     Open Access   (Followers: 1)
Open Journal of Civil Engineering     Open Access   (Followers: 6)
Photonics and Nanostructures - Fundamentals and Applications     Hybrid Journal   (Followers: 2)
Practice Periodical on Structural Design and Construction     Full-text available via subscription   (Followers: 4)
Proceedings of the Institution of Civil Engineers - Bridge Engineering     Hybrid Journal   (Followers: 7)
Proceedings of the Institution of Civil Engineers - Civil Engineering     Hybrid Journal   (Followers: 11)
Proceedings of the Institution of Civil Engineers - Management, Procurement and Law     Hybrid Journal   (Followers: 8)
Proceedings of the Institution of Civil Engineers - Municipal Engineer     Hybrid Journal   (Followers: 3)
Proceedings of the Institution of Civil Engineers - Structures and Buildings     Hybrid Journal   (Followers: 4)
Random Structures and Algorithms     Hybrid Journal   (Followers: 5)
Recent Trends In Civil Engineering & Technology     Full-text available via subscription   (Followers: 4)
Research in Nondestructive Evaluation     Hybrid Journal   (Followers: 7)
Revista IBRACON de Estruturas e Materiais     Open Access   (Followers: 1)
Road Materials and Pavement Design     Hybrid Journal   (Followers: 9)
Russian Journal of Nondestructive Testing     Hybrid Journal   (Followers: 6)
Science and Engineering of Composite Materials     Hybrid Journal   (Followers: 61)
Selected Scientific Papers - Journal of Civil Engineering     Open Access   (Followers: 3)
Slovak Journal of Civil Engineering     Open Access   (Followers: 2)
Soils and foundations     Full-text available via subscription   (Followers: 4)
Steel Construction - Design and Research     Hybrid Journal   (Followers: 3)
Structural and Multidisciplinary Optimization     Hybrid Journal   (Followers: 9)
Structural Concrete     Hybrid Journal   (Followers: 11)
Structural Control and Health Monitoring     Hybrid Journal   (Followers: 9)
Structural Engineering International     Full-text available via subscription   (Followers: 11)
Structural Safety     Hybrid Journal   (Followers: 7)
Structural Survey     Hybrid Journal  
Structure     Full-text available via subscription   (Followers: 23)
Structure and Infrastructure Engineering: Maintenance, Management, Life-Cycle Design and Performance     Hybrid Journal   (Followers: 12)
Structures     Hybrid Journal   (Followers: 1)
Study of Civil Engineering and Architecture     Open Access   (Followers: 8)
Superlattices and Microstructures     Hybrid Journal   (Followers: 2)
Surface Innovations     Hybrid Journal  
Technical Report Civil and Architectural Engineering     Open Access  
Teknik     Open Access  
The IES Journal Part A: Civil & Structural Engineering     Hybrid Journal   (Followers: 6)
The Structural Design of Tall and Special Buildings     Hybrid Journal   (Followers: 6)
Thin Films and Nanostructures     Full-text available via subscription   (Followers: 2)
Thin-Walled Structures     Hybrid Journal   (Followers: 4)
Transactions of the VŠB - Technical University of Ostrava. Construction Series     Open Access   (Followers: 1)
Transportation Geotechnics     Full-text available via subscription   (Followers: 1)
Transportation Infrastructure Geotechnology     Hybrid Journal   (Followers: 8)
Underground Space     Open Access  
Water Science & Technology     Partially Free   (Followers: 25)
Water Science and Technology : Water Supply     Partially Free   (Followers: 22)

           

Journal Cover Frattura ed Integrità Strutturale : Fracture and Structural Integrity
  [SJR: 0.349]   [H-I: 5]   [0 followers]  Follow
    
  This is an Open Access Journal Open Access journal
   ISSN (Print) 19718993
   Published by Italian Group of Fracture Homepage  [1 journal]
  • A review of thermographic techniques for damage investigation in
           composites

    • Authors: Laura Vergani, Chiara Colombo, Flavia Libonati
      Abstract: The aim of this work is a review of scientific results in the literature, related to the application of
      thermographic techniques to composite materials. Thermography is the analysis of the surface temperature of a
      body by infrared rays detection via a thermal-camera. The use of this technique is mainly based on the
      modification of the surface temperature of a material, when it is stimulated by means of a thermal or mechanical
      external source. The presence of defects, in fact, induces a localized variation in its temperature distribution and,
      then, the measured values of the surface temperature can be used to localize and evaluate the dimensions and
      the evolution of defects. In the past, many applications of thermography were proposed on homogeneous
      materials, but only recently this technique has also been extended to composites. In this work several
      applications of thermography to fibres reinforced plastics are presented. Thermographic measurements are
      performed on the surface of the specimens, while undergoing static and dynamic tensile loading. The joint
      analysis of thermal and mechanical data allows one to assess the damage evolution and to study the damage
      phenomenon from both mechanical and energetic viewpoints. In particular, one of the main issues is to obtain
      information about the fatigue behaviour of composite materials, by following an approach successfully applied
      to homogenous materials. This approach is based on the application of infrared thermography on specimens
      subjected to static or stepwise dynamic loadings and on the definition of a damage stress, 'D, that is correlated
      to the fatigue strength of the material. A wide series of experimental fatigue tests has been carried out to verify
      if the value of the damage stress, 'D, is correlated with the fatigue strength of the material. The agreement
      between the different values is good, showing the reliability of the presented thermographic techniques, to the
      study of composite damage and their fatigue behaviour.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • A review of using thermoelasticity for structural integrity assessment

    • Authors: L. Marsavina, R.A. Tomlinson
      Abstract: The advances in the use of thermoelastic stress analysis (TSA) for fracture mechanics assessment
      are reviewed. The development of techniques to determine stress intensity factor is presented followed by the
      application of these techniques to fatigue crack growth, crack closure and the study of mixed mode cracks.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • The application of the infrared thermography on titanium alloy for
           studying fatigue behavior

    • Authors: P. Hou, J. Fan, Q. Guo, X. Guo
      Abstract: The infrared thermography is an attractive tool for studying the fatigue behavior of materials. Based
      on two theoretical models of fatigue damage indicators, this work studied the fatigue properties of the virgin Ti-
      6Al-4V alloy. According to the two damage indicators and the energy theory, the relationship between the
      macro-phenomenon and the micro-structural evolution during fatigue process was discussed. The fatigue limit
      of the titanium alloy was rapidly determined based on the measured temperature increment signals. The
      capability of the infrared thermographic method on the evaluation of fatigue properties was validated.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • Energy dissipation and storage in iron under plastic deformation
           (experimental study and numerical simulation)

    • Authors: A. Kostina, A. Iziumova, O. Plekhov
      Abstract: The work is devoted to the experimental and numerical investigation of thermodynamic aspects of
      the plastic deformation in Armco iron. Dissipation and stored energies was calculated from processed
      experimental data of the surface temperature obtained by infrared thermography. An original mathematical
      model describing the process of mesoscopic defects accumulation was used for numerical simulation of the
      quasistatic loading of iron samples and for calculation of theoretical value of the stored energy. Experimental
      and modeled values of the stored energy are in a good agreement.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • Characterization of mechanical damage in granite

    • Authors: Minh-Phong Luong, Mehrdad Emami
      Abstract: This paper aims to illustrate the use of infrared thermography as a non-destructive and non-contact
      technique to observe the phenomenological manifestation of damage in granite under unconfined compression.
      It allows records and observations in real time of heat patterns produced by the dissipation of energy generated
      by plasticity. The experimental results show that this technique, which couples mechanical and thermal energy,
      can be used for illustrating the onset of damage mechanism by stress concentration in weakness zones.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • A theoretical model for predicting the Peak Cutting Force of conical picks

    • Authors: Gao Kuidong, Du Changlong, Jiang Hongxiang, Liu Songyong
      Abstract: In order to predict the PCF (Peak Cutting Force) of conical pick in rock cutting process, a
      theoretical model is established based on elastic fracture mechanics theory. The vertical fracture model of rock
      cutting fragment is also established based on the maximum tensile criterion. The relation between vertical
      fracture angle and associated parameters (cutting parameter n and ratio B of rock compressive strength to
      tensile strength) is obtained by numerical analysis method and polynomial regression method, and the
      correctness of rock vertical fracture model is verified through experiments. Linear regression coefficient
      between the PCF of prediction and experiments is 0.81, and significance level less than 0.05 shows that the
      model for predicting the PCF is correct and reliable. A comparative analysis between the PCF obtained from
      this model and Evans model reveals that the result of this prediction model is more reliable and accurate. The
      results of this work could provide some guidance for studying the rock cutting theory of conical pick and
      designing the cutting mechanism.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • Fracture failure analysis of baseplates in a fluidic amplifier made of
           WC-11Co cemented carbide

    • Authors: H. Liu, K. Yin, J.M. Peng, Q.L. Yin
      Abstract: A fluidic amplifier is a crucial automatic control component in a liquid jet hammer used to drill
      hard formations in the oil industry. This study aims to determine the true causes of the fracture failure of
      baseplates in a fluidic amplifier made of WC-11Co cemented carbide in a very short period of time.
      Computational fluid dynamics (CFD), theoretical estimation, and finite element analysis (FEA) were employed
      to analyze the effect of static and dynamic loads on the strength of the baseplates. Fractographic,
      metallographic, and processing defect analyses were also carried out. The FEA results showed that the static
      and dynamic loads caused stress concentrations at the actual fracture locations, and the effect of working loads
      on material strength was allowable and safe. Fracture surfaces exhibited typical characteristics of a brittle
      fracture. The metallographic analysis revealed that a specific amount of brittle eta-phase ('-phase) was present
      in the material. The microstructure of the processing cutting zone was inspected and the results revealed that
      some voids, pores, and microcracks were formed on the processing surface. The manufacturing and processing
      defects resulted in low stress fracture failure of the baseplates.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • Effects of the manufacturing process on fracture behaviour of cast TiAl
           intermetallic alloys

    • Authors: A. Brotzu, F. Felli, D. Pilone
      Abstract: The ' -TiAl based intermetallic alloys are interesting candidate materials for high-temperature
      applications with the efforts being directed toward the replacement of Ni-based superalloys. TiAl-based alloys
      are characterised by a density (3.5-4 g/cm3) which is less than half of that of Ni-based superalloys, and therefore
      these alloys have attracted broad attention as potential candidate for high-temperature structural applications.
      Specific composition/microstructure combinations should be attained with the aim of obtaining good
      mechanical properties while maintaining satisfactory oxidation resistance, creep resistance and high temperature
      strength for targeted applications.
      Different casting methods have been used for producing TiAl based alloys. In our experimental work,
      specimens were produced by means of centrifugal casting. Tests carried out on several samples characterised by
      different alloy compositions highlighted that solidification shrinkage and solid metal contraction during cooling
      produce the development of relevant residual stresses that are sufficient to fracture the castings during cooling
      or to produce a delayed fracture. In this work, crack initiation and growth have been analysed in order to
      identify the factors causing the very high residual stresses that often produce explosive crack propagation
      throughout the casting.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • Research on borehole stability of shale based on seepage-stress-damage
           coupling model

    • Authors: Xiaofeng Ran, Yuezhi Wang, Shanpo Jia
      Abstract: In oil drilling, one of the most complicated problems is borehole stability of shale. Based on the
      theory of continuum damage mechanics, a modified Mohr-Coulomb failure criterion according to plastic
      damage evolution and the seepage-stress coupling is established. Meanwhile, the damage evolution equation
      which is based on equivalent plastic strain and the permeability evolution equation of shale are proposed in this
      paper. The physical model of borehole rock for a well in China western oilfield is set up to analyze the
      distribution of damage, permeability, stress, plastic strain and displacement. In the calculation process, the
      influence of rock damage to elastic modulus, cohesion and permeability is involved by writing a subroutine for
      ABAQUS. The results show that the rock damage evolution has a significant effect to the plastic strain and
      stress in plastic zone. Different drilling fluid density will produce different damage in its value, range and type.
      This study improves the theory of mechanical mechanism of borehole collapse and fracture, and provides a
      reference for the further research of seepage-stress-chemical-damage coupling of wall rock.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • Study of spatial-time inhomogeneity of serrated plastic flow Al-Mg alloy:
           using DIC-technique

    • Authors: T. V. Tretyakova, V. E. Wildemann
      Abstract: The aim of the present paper is the investigation of temporal instabilities and spatial localization
      due to the Lüders behavior, the Portevin–Le Chatelier effect and the shoulder or necking effect during uniaxial
      tension tests of aluminum-magnesium alloy. This paper presents the brief description of the test procedure and
      experimental results of carrying out research by the combined use of a servo-hydraulic biaxial test system
      Instron 8850 and a non-contact 3-D digital image correlation measurement system Vic-3D. The digital image
      correlation is a highly effective computer-vision-based technique, which provides estimation of the
      displacement and strain fields on specimen surface by matching the reference subsets in the undeformed image
      (before loading) with the target subsets in the deformed images (captured during test). The evolution of
      inhomogeneous axial strain and axial strain rate fields has been illustrated for each stage of material’s
      deformation. To estimate the kinematics of serrated or jerky flow due to the strain bands propagation, the strain
      versus time curves and strain diagrams are given here. The experimental results show the recurrence in the
      strain distribution leveling along the specimen gauge. The changing between the macroscopic localization of the
      plastic flow, namely the running of the Lüders and PLC bands and the recovery of strain field homogeneity, has
      been observed.
      PubDate: 2013-12-23
      Issue No: Vol. 0 (2013)
       
  • Fatigue characterization of mechanical components in service

    • Authors: G. Fargione, D. Tringale, E. Guglielmino, G. Risitano
      Abstract: The quickly identify of fatigue limit of a mechanical component with good approximation is
      currently a significant practical problem not yet resolved in a satisfactory way. Generally, for a mechanical
      component, the fatigue strength reduction factor ( '
      i) is difficult to evaluate especially when it is in service.
      In this paper, the procedures for crack paths individuation and consequently damage evaluation (adopted in
      laboratory for stressed specimens with planned load histories) are applied to mechanical components, already
      failed during service. The energy parameters, proposed by the authors for the evaluation of the fatigue behavior
      of the materials [1-5], are defined on specimens derived from a flange bolts. The flange connecting pipes at high
      temperature and pressure. Due to the loss of the seal, the bolts have been subjected to a hot flow steam
      addition to the normal stress.
      The numerical analysis coupled experimental analysis (measurement of surface temperature during static and
      dynamic tests of specimens taken from damaged tie rods), has helped to determine the causes of failure of the
      tie rods.
      The determination of an energy parameter for the evaluation of the damage showed that factors related to the
      heat release of the material (loaded) may also help to understand the causes of failure of mechanical
      components.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Behaviour of a speargun with a novel muzzle Comportamento di un fucile
           subacqueo con testata innovativa

    • Authors: T. Ingrassia, M. Mucera, V. Nigrelli
      Abstract: The paper presents the results of a numerical and experimental investigation performed on a barrel
      of a speargun equipped with two kinds of muzzle. In particular, a standard muzzle for speargun (having an
      elastic propulsion) has been compared with an innovative one called ‘roller’. This new muzzle is equipped with
      two rollers and special bands. The rubber bands, fixed at the lower side of the barrel, run through the rollers
      and are engaged in suitable seats of the shaft. These bands are, therefore, longer than the traditional ones and,
      consequently, with equal force applied by the diver, the roller speargun has a longer range. Thanks to the
      particular geometry of the new muzzle, one of the front constraints of the elastic bands is moved to the lower
      part of the barrel or the handle.
      As a consequence, the scheme of the loads applied on the speargun remarkably changes passing from a standard
      muzzle to a roller one. All that has a great influence on the level of deformation of the barrel and, consequently,
      on the accuracy of the shot. Because of the low velocity of the spear (if compared with the firearms), in fact, the
      accuracy of the shoot if strongly influenced by the barrel bending due to the forces applied by means of the
      elastic bands...
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • High temperature initiation and propagation of cracks in 12%Cr-steel
           turbine disks

    • Authors: S. Foletti, A. Lo Conte, S. Salgarollo, F. Bassi, A. Riva
      Abstract: This work aims to study the crack propagation in 12%Cr steel for turbine disks. Creep Crack
      Growth (CCG) tests on CT specimens have been performed to define the proper fracture mechanics which
      describes the initiation of the crack propagation and the crack growth behaviour for the material at high
      temperature. Results have been used to study the occurrence of crack initiation on a turbine disk at the extreme
      working temperature and stress level experienced during service, and validate the use of C* integral in
      correlating creep growth rate on the disk component, in case C* is numerically calculated through FEM analysis
      or calculated by the use of reference stress concept.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Crack of a helicopter main rotor actuator attachment: failure analysis and
           lessons learned

    • Authors: L. Allegrucci, F. De Paolis, A. Coletta, M. Bernabei
      Abstract: A Light Utility Helicopter (LUH), in the course of a training flight, leaving the ground during the
      taxi to take off, went into an uncontrolled rolling to the right; consequently the helicopter gradually laid down
      on the right side. The impact with the runway destroyed the rotating blades up to the hubs rotor. The accident
      investigation focused on main rotor oscillatory plate servo actuators . These components, directly linked to the
      cloche movements, regulate main rotor blades plane tilt and pitch. Following the preliminary examination, only
      front servo actuator attachment was found to be broken in two parts. In detail, the present paper deals with the
      fracture analysis results. The servo actuator attachment material is a 2014 Aluminum alloy extrudate, undergone
      to T651 heat treatment. Fracture surfaces were examined by optical and electronic microscopy in order to
      determine the main morphological features and consequently to trace the origin of failure mechanism and
      causes. The accordance with the specification requirements about alloy composition was verified by quantitative
      elementary analysis through inductive coupled plasma spectroscopy (ICP); furthermore, semi-quantitative
      elementary analysis was locally verified by Energy dispersion spectroscopy X ray (EDS_RX). Finally, the
      hydrogen content of the material was evaluated by the total hydrogen analysis. Microstructural and
      technological alloy characteristics were verified as well by using metallographic microscopy and hardness testing
      of the material.
      Macroscopic fracture surfaces evidences were characterized by the lack of any significant plastic deformations
      and by the presence of symmetry compared to the servo actuator axis. Microscopic fracture features of both the
      investigated surfaces were not coherent to the hypothesis of an impact of the main rotor to the soil. Further
      achieved evidences, such as grain boundary fracture propagation, the presence of corrosion products, were all in
      accordance with a Stress Corrosion Cracking (SCC) progressive fracture mechanism.
      Finite Element Analysis (FEA) located the highest tensile stress value, when the servo actuator is in its nominal
      working condition, at the same points where the corrosion products were more concentrated (i.e. in the part of
      the fracture exposed to oxidative air effect for the longest time). The good agreement between FEA and
      morphological evidences allowed to determine the progressive fracture origin area, though it was not possible to
      individuate the crack initiation point. In fact, in correspondence to the initiation area of both the fracture
      surfaces, shining and flat morphology was found;. then there were evidence of plastic deformations, due to the
      detachment of a servo actuator part.The ICP analysis and hardness testing results were in accordance with the material specification requirements.
      However, the hydrogen content was one order of magnitude greater than the required value and many and
      unexpected globular formations were observed on the fracture surface. Part of these were dendritic formations,
      while the others looked smooth and shining. Further, FESEM boundary grain observation gave evidences of a
      high presence of precipitates on the investigated surfaces. Hence, observed microstructural characteristics,
      boundary grain precipitates and globular formations allowed to hypothesize possible overheating/eutectic
      melting phenomena, occurred during manufacturing processes.
      As widely reported in literature, the AA 2014 alloy is one of the aluminum-copper-magnesium-silicon type,
      employing copper aluminide (CuAl2 ) as the primary precipitation-hardening agent. The need for a maximum
      Cu phase dispersion in solid solution requires a heat treatment range with an upper limit (507°C) that is near to
      the melting of the eutectics (510°C). Moreover, since the 1960s, AA2014 has been defined as sensitive to SCC.
      This condition is mainly related to the presence of coarse-grained and aligned CuAl2 precipitates. This
      arrangement is due to an overheating (more than 507°C) or to a cooling process carried out too slowly.
      Microstructural analysis was carried out on three items: 1) a large portion of the broken actuator attachment; 2)
      on a servoactuator coming from the same production batch; 3) on a servo actuator coming from a different
      production batch.
      The microstructure from the broken actuator attachment showed a great amount of precipitates (second
      phases) lengthwise aligned to the boundary grain, pores, and also cavities and dendritic globular formations.
      Analysis results, morphology evidences and reference images available on scientific literature were found to be
      in excellent agreement and validated the embrittlement and subsequent SCC mechanism hypotesis
      (intergranular failure propagation).
      In conclusion, flight accident causes are attributable to main rotor actuator attachment failure.
      Failure mechanism is classifiable as SCC supported by microstructural anomalies of the material. The
      investigation of the manufacturing process highlighted how one of the servo actuator batches was not properly
      produced due to poor control and accuracy of heat treatment temperature and/or cooling time. This led to
      hydrogen embrittlement and to a microstructural problem (globular formations and boundary grain
      precipitates). The combination of those phenomena caused an increase of the SCC sensitivity and were the
      basic progressive failure driving forces.
      Nevertheless, as above mentioned, alloy composition was found compliant with the material specification
      requirements and this just because none of the scheduled quality control tests is able to determine the peculiar
      microstructural anomalies reported...
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Coupled FEM-DBEM method to assess crack growth in magnet system of
           Wendelstein 7-X

    • Authors: R. Citarella, M. Lepore, Joris Fellinger, Victor Bykov, Felix Schauer
      Abstract: The fivefold symmetric modular stellarator Wendelstein 7-X (W7-X) is currently under
      construction in Greifswald, Germany. The superconducting coils of the magnet system are bolted onto a central
      support ring and interconnected with five so-called lateral support elements (LSEs) per half module. After
      welding of the LSE hollow boxes to the coil cases, cracks were found in the vicinity of the welds that could
      potentially limit the allowed number N of electromagnetic (EM) load cycles of the machine. In response to the
      appearance of first cracks during assembly, the Stress Intensity Factors (SIFs) were calculated and
      corresponding crack growth rates of theoretical semi-circular cracks of measured sizes in potentially critical
      position and orientation were predicted using Paris’ law, whose parameters were calibrated in fatigue tests at
      cryogenic temperature. In this paper the Dual Boundary Element Method (DBEM) is applied in a coupled
      FEM-DBEM approach to analyze the propagation of multiple cracks with different shapes. For this purpose,
      the crack path is assessed with the Minimum Strain Energy density criterion and SIFs are calculated by the Jintegral
      approach. The Finite Element Method (FEM) is adopted to model, using the commercial codes Ansys
      or Abaqus;, the overall component whereas the submodel analysis, in the volume surrounding the cracked area,
      is performed by FEM (“FEM-FEM approach”) or alternatively by DBEM (“FEM-DBEM approach”). The
      “FEM-FEM approach” considers a FEM submodel, that is extracted from the FEM global model; the latter
      provide the boundary conditions for the submodel. Such approach is affected by some restrictions in the crack
      propagation phase, whereas, with the “FEM-DBEM approach”, the crack propagation simulation is
      straightforward. In this case the submodel is created in a DBEM environment with boundary conditions
      provided by the global FEM analysis; then the crack is introduced and a crack propagation analysis has been
      performed to evaluate the effects of the crack shape and of the presence of nearby cracks on the allowed
      number of EM load cycles.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Mode I Stress Intensity Factors for triangular corner crack nearby
           intersecting of cylindrical holes

    • Authors: E. Salvati, P. Livieri, R. Tovo
      Abstract: The paper deals with the Stress Intensity Factor assessment of cracks at the intersection of holes
      loaded by internal pressure.
      Triangular flaws are considered at the intersection of two holes inside a specific specimen. The research
      examines the influence of hole diameter ratio D1/D2 and the angle between their axes '. Numerical analysis is
      performed to determine the Stress Intensity Factors (SIF) of mode I in many different geometric
      configurations.
      The actual shape of a real crack nucleated at the intersection of two cylindrical holes is subject to variable
      internal pressure and is usually geometrically complex. The Stress Intensity Factor changes along the crack
      contour and the crack shape development is controlled by its local value, e.g. during a fatigue loading. In
      general, the estimation of the Stress Intensity Factors of cracks with a complex shape is made by means of
      numerical methods since closed form solutions in literature are limited. However, in order to solve the problem
      of crack propagation more quickly, in the case of a crack corner at the intersection between two cylindrical
      holes, we can assume, in agreement with scientific literature, a symmetrical triangular crack shape and the Stress
      Intensity Factor are only calculated at the middle of the crack. Obviously, this is a strong approximation, but
      this allows a reduction in the computation effort for crack growth rate assessments and safety evaluation.
      In this paper, the weight function technique is used by integrating the actual stress field evaluated in the uncracked
      model. The method of the weight function is of general validity and the weight function is related to the
      displacement components close to the crack front, as proposed by Bueckner and Rice. From a computational
      point of view, the use of the three-dimensional weight function is complex and in scientific literature a weight
      function of general validity is not available. Nevertheless, thanks to the work conducted by Petroski and
      Achenbach, Shen and Glinka, an efficient generalised weight function has been adopted and then developed by
      Sha and Yang [9], which considers a series expansion of non-singular terms. In this way, the integration of the
      weight function, multiplied by a nominal stress, is made along a line and not in a two-dimensional domain.
      In this preliminary work, according to Herz et al., we consider a weight function with three terms by assuming a
      priori the coefficients of the second and third non-singular terms. This contribution is essentially an extension
      of a previous paper by Herz et al. They only considered the case of D1/D2=1 and '=90° (Di are the diameters
      of the two cylindrical holes and a is the angle between their axis). Here, we extend the analysis to D1/D2 equal
      to 2, 4 and 8 with an ' of 60 and 45 degrees. With the aid of three-dimensional modelling, an accurate FE model of a triangular corner crack at different
      crack depths has been made. Subsequently, by using ANSYS finite element software, it is possible to employ the
      command KCAL that evaluates the Stress Intensity Factors in the middle of the crack. Subsequently, a
      comparison between numerical FE results and the analytical results, giving the values of the unknown
      coefficients of the weight function (the unknown coefficient is indicated in the paper as M1).
      As reported in the tables, the accuracy of the weight functions in SIF predictions is about 5% despite the strong
      simplification previously introduced in the model. This result is considerable because it is possible to determine
      the Stress Intensity Factor of a triangular shaped crack by a line integral of a stress profile in a model without
      considering the crack.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • A four-parameters model for fatigue crack growth data analysis

    • Authors: M. Grasso, F. Penta, P. Pinto, G.P. Pucillo
      Abstract: A four-parameters model for interpolation of fatigue crack growth data is presented. It has been
      validated by means of both data produced by the
      Authors and data collected from Literature. The proposed
      model is an enhanced version of a three-parameters model already discussed in a previous work that has been
      suitably modified in order to overcome some drawbacks raised when applied to a quite wider experimental data
      set. Results of validation study have also revealed that the new model, besides interpolating accurately crack
      growth data, allows to identify the presence of anomalies in the data sets. For this reason, by a suitable filter to
      be chosen depending on the size and number of anomalies, it can be used to remove them and obtain sigmoidal
      crack propagation curves smoother than those obtained when the current analysis techniques are used. In the
      end, possible model parameters correlations are analysed.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • About the certification of railway rails

    • Authors: A. De Iorio, M. Grasso, F. Penta, G.P. Pucillo
      Abstract: When the compliance with the European Code of some rail steel has to be verified, the need of
      carrying out the experimental activities in accordance with several testing Standards forces the operator both to
      solve the problems related to the choice of a suitable testing practice and often to interpret subjectively
      Standards guidelines. This does not facilitate the comparability and/or the quality of the results produced by
      several laboratories. With reference to a series of fatigue, fracture toughness and fatigue crack growth tests
      carried out by the authors on specimens extracted from rails, the main lacks in the current standards, related to
      both the choice of the control parameters and the testing procedures, are pointed out. Regarding the crack
      growth testing, several procedures to compute the crack growth rates to be compared with the limits prescribed
      by the Code are proposed. These procedures have been applied to a data set produced during the
      aforementioned testing activity, in order to highlight, by comparison of the results obtained by them, the
      significant differences in the crack growth rate estimates and the magnitude of the errors that can be done due
      to the lacks in the standard practices currently adopted.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Comparison between dog-bone and Gaussian specimens for size effect
           evaluation in gigacycle fatigue

    • Authors: A. Tridello, D.S. Paolino, G. Chiandussi, M. Rossetto
      Abstract: Gigacycle fatigue properties of materials are strongly affected by the specimen risk volume (volume
      of material subjected to a stress amplitude larger than the 90% of the maximum stress). Gigacycle fatigue tests,
      performed with ultrasonic fatigue testing machines, are commonly carried out by using hourglass shaped
      specimens with a small risk volume. The adoption of traditional dog-bone specimens allows for increasing the
      risk volume, even if the increment is quite limited. In order to obtain larger risk volumes, a new specimen shape
      is proposed (Gaussian specimen). The dog-bone and the Gaussian specimens are compared through Finite
      Element Analyses and the numerical results are validated experimentally by means of strain gages
      measurements. The range of applicability of the two different specimens in terms of available risk volume and
      stress concentration effects due to the cross section variation is determined.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Failure of steam line causes determined by NDT testing in power and
           heating plants

    • Authors: Srdjan Bulatovic, Vujadin Aleksic, Ljubica Milovic
      Abstract: This paper examines leakage and damages of steam and provides an overview of NDT testing in
      order to determine the cause of steam lines failure in power plants and heating plants. This approach may be
      applied to similar structures and its application in preventive maintenance would help extend the life of steam
      pipes.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Strength on cut edge and ground edge glass beams with the failure analysis
           method

    • Authors: Stefano Agnetti
      Abstract: The aim of this work is the study of the effect of the finishing of the edge of glass when it has a
      structural function.
      Experimental investigations carried out for glass specimens are presented. Various series of annealed glass beam
      were tested, with cut edge and with ground edge. The glass specimens are tested in four-point bending
      performing flaw detection on the tested specimens after failure, in order to determine glass strength. As a result,
      bending strength values are obtained for each specimen.
      Determining some physical parameter as the depth of the flaw and the mirror radius of the fracture, after the
      failure of a glass element, it could be possible to calculate the failure strength of that.
      The experimental results were analyzed with the LEFM theory and the glass strength was analyzed with a
      statistical study using two-parameter Weibull distribution fitting quite well the failure stress data.
      The results obtained constitute a validation of the theoretical models and show the influence of the edge
      processing on the failure strength of the glass. Furthermore, series with different sizes were tested in order to
      evaluate the size effect.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • An experimental study on flexural strength enhancement of concrete by
           means of small steel fibers

    • Authors: Abdoullah Namdar, Ideris Bin Zakaria, Azimah Bt Hazeli, Sayed Javid Azimi, Abdul Syukor Bin Abd. Razak, G. S. Gopalakrishna
      Abstract: Cost effective improvement of the mechanical performances of structural materials is an important
      goal in construction industry. To improve the flexural strength of plain concrete so as to reduce construction
      costs, the addition of fibers to the concrete mixture can be adopted. The addition of small steel fibers with
      different lengths and proportion have experimentally been analyzed in terms of concrete flexural strength
      enhancement. The main objectives of the present study are related to the evaluation of the influence of steel
      fibers design on the increase of concrete flexural characteristics and on the mode of failure. Two types of beams
      have been investigated. The force level, deflection and time to failure of beams have been measured. The shear
      crack, flexural crack and intermediate shear-flexural crack have been studied. The steel fiber content controlled
      crack morphology. Flexural strength and time to failure of fiber reinforce concrete could be further enhanced if,
      instead of smooth steel fibers, corrugated fibers were used.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Graphite nodules features identifications and damaging micromechanims in
           ductile irons

    • Authors: Alberto De Santis, Daniela Iacoviello, Vittorio Di Cocco, Francesco Iacoviello
      Abstract: Ductile irons mechanical properties are strongly influenced by the metal matrix microstructure and
      on the graphite elements morphology. Depending on the chemical composition, the manufacturing process and
      the heat treatments, these graphite elements can be characterized by different shape, size and distribution. These
      geometrical features are usually evaluated by the experts visual inspection, and some commercial softwares are
      also available to assist this activity. In this work, an automatic procedure based on an image segmentation
      technique is applied: this procedure is validated not only considering spheroidal graphite elements, but also
      considering other morphologies (e.g. lamellae).
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Investigation via morphological analysis of aluminium foams produced by
           replication casting

    • Authors: A. Boschetto, L. Bottini, F. Campana, L. Consorti, D. Pilone
      Abstract: Foams and porous materials with cellular structure have many interesting combinations of physical
      and mechanical properties coupled with low specific weight. By means of replication casting it is possible to
      manufacture foams from molten metal without direct foaming. A soluble salt is used as space holder, which is
      removed by leaching in water. This can be done successfully if the content of space holding fillers is so high that
      all the granules are interconnected. One of the main advantages of using the replication casting is a close control
      of pore sizes which is given by the distribution of particle sizes of the filler material. This contrasts with the
      pore size distribution of the materials foamed by other processes where a wider statistical distribution of pores
      is found. On the other hand, the maximum porosities that can be achieved using space holders are limited to
      values below 60%, whereas the other methods allow for porosities up to 98%. Temperature of the mould and
      infiltration pressure are critical process parameters: a typical problem encountered is the premature solidification
      of the melt, especially due to the high heat capacity of the salt.
      In this work foam properties such as cell shape, distribution and anisotropy and defect presence are investigated
      by using digital image processing technique. For this purpose replicated AlSi7Mg0.3 alloy foams are produced
      by infiltrating preforms of NaCl particles, varying the metal infiltration pressure and the mould preheating
      temperature.
      An original procedure based on image analysis has been set up to determine size, morphology and distribution
      of cells. The paper demonstrates that this methodology, coupled with microstructural analysis, is a useful tool
      for investigating the effects of process parameters on foam properties.
      PubDate: 2013-09-25
      Issue No: Vol. 0 (2013)
       
  • Extension of the CJP model to mixed mode I and mode II

    • Authors: C. J. Christopher, G. Laboviciute, M. N. James, E. A. Patterson
      Abstract: The present authors have previously proposed a novel ‘plastic inclusion’ approach for dealing with
      the local plasticity which occurs at the tip of a growing fatigue crack. This meso-scale model provides a
      modified set of crack tip stress intensity factors that include the magnitude of plastic wake-induced crack tip
      shielding and which have the potential to help resolve some long-standing controversies associated with
      plasticity-induced closure. The present work extends the CJP model to deal with the case of mixed Mode I and
      Mode II loading and thus opens up enhanced possibilities for testing it on inclined cracks in metallic specimens.
      This extension requires the addition of only one new force parameter to the model, i.e. an anti-symmetric shear
      force on either side of the crack.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Study of overload effects in bainitic steel by synchrotron X-ray
           diffraction

    • Authors: P. Lopez-Crespo, P.J. Withers, J. R. Yates, A. Steuwer, T. Buslaps, Y. H. Tai
      Abstract: This work presents an in-situ characterisation of crack-tip strain fields following an overload by
      means of synchrotron X-ray diffraction. The study is made on very fine grained bainitic steel, thus allowing a
      very high resolution so that small changes occurring around the crack-tip were captured along the crack plane at
      the mid-thickness of the specimen. We have followed the crack as it grew through the overload location. Once
      the crack-tip has progressed past the overload event there is strong evidence that the crack faces contact in the
      region of the overload event (though not in the immediate vicinity of the current locations of the crack tip) at
      Kmin even when the crack has travelled 1mm beyond the overload location. It was also found that at Kmax the
      peak tensile strain ahead of the crack-tip decreases soon after the overload is applied and then gradually
      recovers as the crack grows past the compressive region created by the overload.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • High magnification crack-tip field characterisation under biaxial
           conditions

    • Authors: B. Moreno, P. Lopez-Crespo, J. Zapatero
      Abstract: This work presents a novel methodology for characterising fatigue cracks under biaxial conditions.
      The methodology uses high magnification Digital Image Correlation (DIC) technique for measuring
      displacement and strain crack-tip fields. By applying micro-speckle pattern on the metal surface it is possible to
      achieve high magnification for DIC technique. The speckles were created by electro-spray technique. The
      validity of this novel technique is demonstrated by direct comparison with standard extensometer
      measurements, under tension-compression and torsion conditions. In order to image the correct region, the
      notch effect on the fatigue life was also evaluated.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Initiation and growth behavior of very-long microstructurally short
           fatigue cracks

    • Authors: P. Lorenzino, A. Navarro
      Abstract: The present paper describes a novel experimental technique recently presented that allows one to
      study interactions between the crack and microstructural barriers with an unprecedented level of ease and detail.
      The method consists in increasing the grain size of Al1050 Aluminium alloy until the centimetre scale by
      applying a series of mechanical and heat treatments. Once the thermo-mechanical treatment is completed and
      the desired microstructure obtained, a circular notch is machined on each specimen, and the samples are
      subjected to push-pull fatigue loading. Several combinations of notch and microstructural sizes have been
      tested. This method provides an easy way to record and analyse the effect of the microstructure upon crack
      growth rate. It was observed that the space between successive crack-tip arrests correlates well with the material
      grain size. Another interesting observation is that in the majority of the cases studied the cracks did not initiate
      at the point of maximum stress concentration. This is surprising since the classical methods of notched fatigue
      limit analysis clearly indicate the horizontal symmetry axis as the initiation and propagation direction for pushpull
      loading.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Role of plasticity-induced crack closure in fatigue crack growth

    • Authors: Jesús Toribio, Viktor Kharin
      Abstract: The premature contact of crack surfaces attributable to the near-tip plastic deformations under
      cyclic loading, which is commonly referred to as plasticity induced crack closure (PICC), has long been focused
      as supposedly controlling factor of fatigue crack growth (FCG). Nevertheless, when the plane-strain near-tip
      constraint is approached, PICC lacks of straightforward evidence, so that its significance in FCG, and even the
      very existence, remain debatable. To add insights into this matter, large-deformation elastoplastic simulations of
      plane-strain crack under constant amplitude load cycling at different load ranges and ratios, as well as with an
      overload, have been performed. Modeling visualizes the Laird-Smith conceptual mechanism of FCG by plastic
      blunting and re-sharpening. Simulation reproduces the experimental trends of FCG concerning the roles of
      stress intensity factor range and overload, but PICC has never been detected. Near-tip deformation patterns
      discard the filling-in a crack with material stretched out of the crack plane in the wake behind the tip as
      supposed PICC origin. Despite the absence of closure, load-deformation curves appear bent, which raises
      doubts about the trustworthiness of closure assessment from the compliance variation. This demonstrates
      ambiguities of PICC as a supposedly intrinsic factor of FCG and, by implication, favors the stresses and strains
      in front of the crack tip as genuine fatigue drivers.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Plastic zone evolution near a crack tip and its role in environmentally
           assisted cracking

    • Authors: Jesús Toribio, Viktor Kharin
      Abstract: This paper analyzes the effects of crack tip plastic strains and compressive residual stresses, created
      by fatigue pre-cracking, on environmentally assisted cracking of pearlitic steel subjected to localized anodic
      dissolution and hydrogen assisted fracture. In both situations, cyclic crack tip plasticity improves the behavior of
      the steel. In the respective cases, the effects are supposed to be due to accelerated local anodic dissolution of
      the cyclic plastic zone (producing chemical crack blunting) or to the delay of hydrogen entry into the metal
      caused by residual compressive stresses, thus increasing the fracture load in aggressive environment.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • On numerical integration for effective stress assessment at notches

    • Authors: Enrico Maggiolini, Paolo Livieri, Roberto Tovo
      Abstract: This paper presents a numerical method for non-local stress assessment by means of a general FE
      tool and the local stress field. Unlike usual calculations by means of a numerical PDE solver, a more general
      numerical integration is used. Different solutions are compared theoretically and numerically by evaluating the
      results obtained by two different FEM commercial software. The application of the non-local tension field is
      applied to the strength assessment of notches, welded joints and cracks.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Application of thermoelastic stress analysis for the experimental
           evaluation of the effective stress intensity factor

    • Authors: Francisco A. Díaz, Eann A. Patterson, John R. Yates
      Abstract: In recent years, the advent of staring array detectors has made Thermoelastic Stress Analysis (TSA)
      a technique with considerable potential for fatigue and fracture mechanics applications. The technique is noncontacting
      and provides full field stress maps from the surface of cyclically loaded components. In addition, the
      technique appears to have a great potential in the evaluation of the effective stress intensity factor range during
      fatigue since fracture mechanics parameters are derived directly from the temperature changes in the vicinity of
      the crack tip rather than from remote data. In the current work TSA is presented as a novel methodology for
      measuring the effective stress intensity factor from the analysis of thermoelastic images. 'K values inferred
      using TSA have been employed to estimate an equivalent opening/closing load at different R-ratios in a cracked
      aluminium 2024 CT specimen. Results have been compared with those obtained using the strain-offset
      technique showing a good level of agreement.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Pearlitic ductile cast iron: damaging micromechanisms at crack tip

    • Authors: F. Iacoviello, V. Di Cocco, A. Rossi, M. Cavallini
      Abstract: Ductile cast irons (DCIs) are characterized by a wide range of mechanical properties, mainly
      depending on microstructural factors, as matrix microstructure (characterized by phases volume fraction, grains
      size and grain distribution), graphite nodules (characterized by size, shape, density and distribution) and defects
      presence (e.g., porosity, inclusions, etc.). Versatility and higher performances at lower cost if compared to steels
      with analogous performances are the main DCIs advantages.
      In the last years, the role played by graphite nodules was deeply investigated by means of tensile and fatigue
      tests, performing scanning electron microscope (SEM) observations of specimens lateral surfaces during the
      tests (“in situ” tests) and identifying different damaging micromechanisms.
      In this work, a pearlitic DCIs fatigue resistance is investigated considering both fatigue crack propagation (by
      means of Compact Type specimens and according to ASTM E399 standard) and overload effects, focusing the
      interaction between the crack and the investigated DCI microstructure (pearlitic matrix and graphite nodules).
      On the basis of experimental results, and considering loading conditions and damaging micromechanisms, the
      applicability of ASTM E399 standard on the characterization of fatigue crack propagation resistance in ferritic
      DCIs is critically analyzed, mainly focusing the stress intensity factor amplitude role.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • On a kinked crack model to describe the influence of material
           microstructure on fatigue crack growth

    • Authors: Andrea Spagnoli, Andrea Carpinteri, Sabrina Vantadori
      Abstract: Threshold condition and rate of fatigue crack growth in both short and long crack regime appear to
      be significantly affected by the degree of crack deflection. In the present paper, a theoretical model of a
      periodically-kinked crack is presented to describe the influence of the degree of crack deflection on the fatigue
      behavior. The kinking of the crack is due to a periodic self-balanced microstress field having a length scale, d.
      By correlating the parameter d with a characteristic material length (e.g. average grain size in metals, maximum
      aggregate dimension in concrete), the possibility of using the present model to describe some experimental
      findings related to crack size effects in fatigue of materials is explored. Well-known experimental results
      concerning two different situations (fatigue threshold and fatigue crack growth in the Paris regime) are briefly
      analysed.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Gradient enriched linear-elastic crack tip stresses to estimate the static
           strength of cracked engineering ceramics

    • Authors: Harm Askes, Luca Susmel
      Abstract: According to Gradient Mechanics (GM), stress fields have to be determined by directly
      incorporating into the stress analysis a length scale which that takes into account the material microstructural
      features. This peculiar modus operandi results in stress fields in the vicinity of sharp cracks which are no longer
      singular, even though the assessed material is assumed to obey a linear-elastic constitutive law. Given both the
      geometry of the cracked component being assessed and the value of the material length scale, the magnitude of
      the corresponding gradient enriched linear-elastic crack tip stress is then finite and it can be calculated by taking
      full advantage of those computational methods specifically devised to numerically implement gradient elasticity.
      In the present investigation, it is first shown that GM’s length scale can directly be estimated from the material
      ultimate tensile strength and the plane strain fracture toughness through the critical distance value calculated
      according to the Theory of Critical Distances. Next, by post-processing a large number of experimental results
      taken from the literature and generated by testing cracked ceramics, it is shown that gradient enriched linearelastic
      crack tip stresses can successfully be used to model the transition from the short- to the long-crack
      regime under Mode I static loading.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Is notch sensitivity a stress analysis problem'

    • Authors: Jaime Tupiassú Pinho de Castro, Marco Antonio Meggiolaro
      Abstract: Semi–empirical notch sensitivity factors q have been widely used to properly account for notch
      effects in fatigue design for a long time. However, the intrinsically empirical nature of this old concept can be
      avoided by modeling it using sound mechanical concepts that properly consider the influence of notch tip stress
      gradients on the growth behavior of mechanically short cracks. Moreover, this model requires only wellestablished
      mechanical properties, as it has no need for data-fitting or similar ill-defined empirical parameters.
      In this way, the q value can now be calculated considering the characteristics of the notch geometry and of the
      loading, as well as the basic mechanical properties of the material, such as its fatigue limit and crack propagation
      threshold, if the problem is fatigue, or its equivalent resistances to crack initiation and to crack propagation
      under corrosion conditions, if the problem is environmentally assisted or stress corrosion cracking. Predictions
      based on this purely mechanical model have been validated by proper tests both in the fatigue and in the SCC
      cases, indicating that notch sensitivity can indeed be treated as a stress analysis problem.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Multi-parameter crack tip stress state description for estimation of
           fracture process zone extent in silicate composite WST specimens

    • Authors: Václav Veselý, Jakub Sobek, Lucie Šestáková, Petr Frantík, Stanislav Seitl
      Abstract: For wedge splitting test specimens, the stress and displacement fields both in the vicinity and also
      in larger distance from the crack tip are investigated by means of numerical methods. Several variants of
      boundary conditions were modeled. The stress intensity factor K, T-stress and even higher-order terms of
      William series were determined and subsequently utilized for analytical approximation of the stress field. A good
      fit between the analytical and numerical solution in dependence on the distance from the crack tip was shown,
      compared and discussed. Presented approach is considered as suitable for estimation of the fracture process
      zone extent in silicate composite materials.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Recent developments in multi-parametric three-dimensional stress field
           representation in plates weakened by cracks and notches

    • Authors: P. Lazzarin, M. Zappalorto, F. Berto
      Abstract: The paper deals with the three-dimensional nature and the multi-parametric representation of the
      stress field ahead of cracks and notches of different shape. Finite thickness plates are considered, under
      different loading conditions. Under certain hypotheses, the three-dimensional governing equations of elasticity
      can be reduced to a system where a bi-harmonic equation and a harmonic equation have to be simultaneously
      satisfied. The former provides the solution of the corresponding plane notch problem, the latter provides the
      solution of the corresponding out-of-plane shear notch problem. The analytical frame is applied to some
      notched and cracked geometries and its degree of accuracy is discussed comparing theoretical results and
      numerical data from 3D FE models.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Effect of crack propagation on crack tip fields

    • Authors: F.V. Antunes, A.G. Chegini, L.M. Correia, A.L. Ramalho
      Abstract: Crack closure influences fatigue crack growth rate and must be included in the design of
      components. Plasticity induced crack closure is intimately linked with the crack tip plastic deformation, which
      becomes residual as the crack propagates. The objective here is to study numerically the effect of crack
      propagation on crack tip fields. The transient effect observed at the beginning of crack propagation is linked to
      the hardening behavior of material. The effect of mesh refinement is studied, and a singular behavior is evident,
      which is explained by the sharp crack associated with mesh topology, composed of a regular pattern of square
      elements. The plastic zone size measured perpendicularly to crack flank in the residual plastic wake is quantified
      and compared with literature models. Finally, the removal of material at the first node behind crack tip with
      load cycling was observed for plane strain state and some hardening models in plane stress state.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • In situ 3D characterization of fatigue cracks displacement fields

    • Authors: Joel Lachambre, Jean-Yves Buffiere, Julien Réthoré, Arnaud Weck
      Abstract: The three dimensional growth of fatigue cracks in samples of nodular graphite cast iron is
      characterized using laboratory X-ray computed tomography. The cracks grow from laser machined artificial
      defects, their development is monitored in situ using laboratory X-ray computed tomography (lab. CT) and
      Digital Volume Correlation (DVC). The combination of both techniques gives access to the 3D displacement
      field at the tip of the crack (mainly mode I opening).
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Near tip strain evolution under cyclic loading

    • Authors: J. Tong, Y.-W. Lu, B. Lin, Y. H. Tai, J.R. Yates
      Abstract: The concept of ratchetting strain as a crack driving force in controlling crack growth has previously
      been explored at Portsmouth using numerical approaches for nickel-based superalloys. In this paper, we report
      the first experimental observations of the near-tip strain evolution as captured by the Digital Image Correlation
      (DIC) technique on a compact tension specimen of stainless steel 316L. The evolution of the near-tip strains
      with loading cycles was studied whilst the crack tip was maintained stationary. The strains were monitored over
      the selected distances from the crack tip for a given number of cycles under an incremental loading regime. The
      results show that strain ratchetting does occur with load cycling, and is particularly evident close to the crack tip
      and under higher loads. A finite element model has been developed to simulate the experiments and the
      simulation results are compared with the DIC measurements.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Subsurface metals fatigue cracking without and with crack tip

    • Authors: Andrey Shanyavskiy
      Abstract: Very-High-Cycle-Fatigue regime for metals was considered and mechanisms of the subsurface
      crack origination were introduced. In many metals first step of crack origination takes place with specific area
      formation because of material pressing and rotation that directed to transition in any volume to material ultrahigh-
      plasticity with nano-structure appearing. Then by the border of the nano-structure takes place volume
      rotation and fracture surface creates with spherical particles which usually named Fine-Granular-Area. In
      another case there takes place First-Smooth-Facet occurring in area of origin due to whirls appearing by the one
      of the slip systems under discussed the same stress-state conditions. Around Fine-Granular-Area or First-
      Smooth-Facet there plastic zone appeared and, then, subsurface cracking develops by the same manner as for
      through cracks. In was discussed quantum-mechanical nature of fatigue crack growth in accordance with Yang’s
      modulus quantization for low level of deformations. New simply equation was considered for describing
      subsurface cracking in metals out of Fine-Granular-Area or Fist-Smooth-Facet.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Sharp contact corners, fretting and cracks

    • Authors: D. A. Hills, R. C. Flicek, D. Dini
      Abstract: Contacts with sharp edges subject to oscillatory loading are likely to nucleate cracks from the
      corners, if the loading is sufficiently severe. To a first approximation, the corners behave like notches, where the
      local elastic behaviour is relieved by plasticity, and which in turn causes irreversibilities that give rise to crack
      nucleation, but also by frictional slip. One question we aim to answer here is; when is the frictional slip
      enveloped by plastic slip, so that the corner is effectively a notch in a monolithic material' We do this by
      employing the classical Williams asymptotic solution to model the contact corner, and, in doing so, we render
      the solution completely general in the sense that it is independent of the overall geometry of the components.
      We then re-define the independent parameters describing the properties of the Williams solution by using the
      inherent length scale, a procedure that was described at the first IJFatigue and FFEMS joint workshop [1]. By
      proceeding in this way, we can provide a self-contained solution that can be ‘pasted in’ to any complete contact
      problem, and hence the likelihood of crack nucleation, and the circumstances under which it might occur, can
      be classified. Further, this reformulation of Williams' solution provides a clear means of obtaining the strength
      (defined by crack nucleation conditions) of a material pair with a particular contact angle. This means that the
      results from a test carried out using a laboratory specimen may easily be carried over to any complicated contact
      problem found in engineering practice, and a mechanical test of the prototypical geometry, which may often be
      quite difficult, is avoided.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Determination of fracture mechanics parameters on a base of local
           displacement measurements

    • Authors: Yu. G. Matvienko, V.S. Pisarev, S. I. Eleonsky
      Abstract: New experimental technique for a determination of the stress intensity factor (SIF) and T-stress
      values is developed and verified. The approach assumes combining the crack compliance method and optical
      interferometric measurements of local deformation response on small crack length increment. Initial
      experimental information has a form of in-plane displacement component values, which are measured by
      electronic speckle-pattern interferometry at some specific points located near a crack tip. Required values of
      fracture mechanics parameters follow from the first four coefficients of Williams’ series. A determination of
      initial experimental data at the nearest vicinity of notch tip is the main feature of the developed approach. That
      is why it is not necessary to involve complex numerical models, which include global geometrical parameters,
      loading and boundary conditions of the object under study, in a stage of experimental data interpretation. An
      availability of high-quality interference fringe patterns, which are free from rigid-body motions, serves as a
      reliable indicator of real stress state around a crack tip. A verification of the technique is performed by
      comparing experimental results with analogous data of FEM modelling. Experimentally determined mode I SIF
      for DCB specimen with end crack is in 5 per cent agreement with the numerically simulated case. Proposed
      approach is capable of estimating an influence of the notch radius on fracture mechanics parameters.
      Comparing SIF and T-stress obtained for U-notches of different radius both in actual and residual stress field
      confirms this statement.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Combining experimental and numerical analysis to estimate stress fields
           along the surface crack front

    • Authors: A.S. Chernyatin, Yu.G. Matvienko, I.A. Razumovsky
      Abstract: Combining experimental and computational method for determination of the singular and the nonsingular
      stress terms along the front of the 3D surface crack is proposed. Evaluation of the terms is based on
      comprehensive comparison between deformation responses (for measurement points on the surface) obtained
      experimentally and from numerical solutions of the corresponding boundary problem of solid mechanics. The
      proposed approach allows carrying out an adequate and a comprehensive assessment of stress fields in the
      vicinity of the surface crack front.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Crack propagation mechanism and life prediction for very-highcycle fatigue
           of a structural steel in different environmental medias

    • Authors: Guian Qian, Chengen Zhou, Youshi Hong
      Abstract: The influence of environmental medias on crack propagation of a structural steel at high and veryhigh-
      cycle fatigue (VHCF) regimes is investigated based on the fatigue tests performed in air, water and 3.5%
      NaCl aqueous solution. Crack propagation mechanisms due to different crack driving forces are investigated in
      terms of fracture mechanics. A model is proposed to study the relationship between fatigue life, applied stress
      and material property in different environmental medias, which reflects the variation of fatigue life with the
      applied stress, grain size, inclusion size and material yield stress in high cycle and VHCF regimes. The model
      prediction is in good agreement with experimental observations.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • Characterisation of crack tip fields under non-uniform fatigue loading

    • Authors: D. Nowell, M.E. Kartal, P.F.P. de Matos
      Abstract: The paper analyses previously reported work, which uses digital image correlation to measure
      fatigue crack closure. As well as determining crack opening loads, the information on crack shape may be used
      to estimate the stress intensity factor, as well as other parameters in more complex models of crack tip fields. A
      number of specimens were subjected to single overload cycles, which produced a significant retardation in crack
      growth rate. The method previously applied to the analysis of constant amplitude loading is here used to
      analyse the single overload case. The stress intensity factor history is found to be very different in the two cases
      and the consequences of this observation for analysis of fatigue crack propagation are discussed.
      PubDate: 2013-04-11
      Issue No: Vol. 0 (2013)
       
  • The healing of damage after the plastic deformation of metals

    • Authors: S.V. Smirnov
      Abstract: The general regularities of damage healing during the annealing after cold deformation of metal materials are presented in this paper. In categories of damage mechanics the kinetic equations of damage healing during recovery and recrystallization are formulated. Diagrams of damage healing for some metal alloys are presented. The example of use of investigation results for optimization of industrial technology of pipes drawing is presented.
      PubDate: 2013-03-21
      Issue No: Vol. 0 (2013)
       
  • Relay-race deformation mechanism during uniaxial tension of cylindrical
           samples of carbon steel: using digital image correlation technique

    • Authors: T.V. Tretiakova, V.E. Vildeman
      Abstract: The work deals with experimental study of macro localization of plastic yielding occurrences of structural carbon steel, research of singularity of deformation wave processes by complex use of contemporary test equipment and high effective digital image correlation method. Evolution of nonuniform axial strain fields on surface of cylindrical samples during uniaxial tension was registered, time dependences were drawn, and a ‘relay-race’ mechanism of material deformation was found out at the stage of yield plateau forming. Strain concentration ratio was estimated for several material deformation stages.
      PubDate: 2013-03-21
      Issue No: Vol. 0 (2013)
       
  • Effect of weld parameter on mechanical and metallurgical properties of
           dissimilar joints AA6082–AA6061 in T6 condition produced by FSW

    • Authors: H. S. Patil, S. N. Soman
      Abstract: The effect of processing parameters on the mechanical and metallurgical properties of dissimilarjoints of AA6082–AA6061 produced by friction stir welding was analysed in this study. Different FSW sampleswere produced by varying the welding speeds of the tool as 50 and 62 mm/min and by varying the alloypositioned on the advancing side of the tool. In all the experiments the rotating speed is fixed at 1600rpm. Allthe welds were produced perpendicularly to the rolling direction for both the alloys. Microhardness (HV) andtensile tests performed at room temperature were used to evaluate the mechanical properties of the joints. Inorder to analyse the microstructural evolution of the material, the weld’s cross-sections were observed opticallyand SEM observations were made of the fracture surfaces. The corrosion tests of base alloy and welded jointswere carried out in 3.5%NaCl solution at a room temperature. Corrosion current and potential were determinedusing potentiostatic polarization measurements. It was found that the corrosion rates of welded joints werehigher than that of base alloy.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Impact loading of a space nuclear powerplant

    • Authors: Evgeny I. Kraus, Ivan I. Shabalin
      Abstract: Preferred formulation of the problem in two space dimensions are described for solving the threefundamental equations of mechanics (conservation of mass, conservation of momentum, and conservation ofenergy). Models of the behavior of materials provide the closure to the three fundamentals equations forapplications to problems in compressible fluid flow and solid mechanics. Models of fracture and damage aredescribed. A caloric model of the equation of state is proposed to describe thermodynamic properties of solidmaterials with the phase transitions. Two-dimensional problems of a high-velocity impact of a space nuclearpropulsion system reactor are solved. High-velocity impact problems of destruction of reactor are solved for thetwo cases:1) at its crash landing on the Earth surface (the impact velocity being up to 400 m/s);2) at its impact (with velocity up to 16 km/s) with the space debris fragments.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • The numerical simulation of ceramic composites failure at axial
           compression

    • Authors: P.V. Makarov, M.O. Eremin
      Abstract: On the basis of the developed model of quasibrittle medium the brittle and quasibrittle failure ofcomposite ceramic materials with zirconium dioxide matrix and various percentage of hardening particles ofcorundum are studied numerically. The theory of the damaged media is applied in the calculations. It is shownthat failure process educes in 2 stages - a relatively slow quasistationary phase of accumulation of inelasticdeformations and damages in all hierarchy of scales and superfast catastrophic phase - a blow-up regime whenthe failure process reaches the macro-scale and there is a macro-crack formation. The failure process in theproposed model assumes to be completed when the damage function reaches its maximum value and thestrength of the composite evolve to zero.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • The failure criterion based on hydrogen distribution ahead of the fatigue
           crack tip

    • Authors: Yu. G. Matvienko
      Abstract: The hydrogen effect on the fracture toughness and fatigue crack growth behaviour in themartensitic high strength steel is investigated. The secondary ion mass spectrometry method has beenemployed to analyse the distribution of hydrogen concentration in the zone of the crack tip and at its edges.Changes in hydrogen concentration are observed in the vicinity of the propagating crack tip and at a remotesite. The hydrogen peak H C is reduced and moves away from the fatigue crack tip with the increase of themaximum stress intensity factor max K . The concept of damage evolution is used to explain fatigue crackpropagation in connection with the hydrogen redistribution ahead of the crack tip. The physical failure criterionbased on the hydrogen peak in the vicinity of the fatigue crack tip and the maximum stress intensity factor hasbeen proposed. The criterion reflects changes in the hydrogen peak which resulted from the hydrogenredistribution due to the increase of the maximum stress intensity factor as the crack length increases underfatigue loading.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Temporal peculiarities of brittle fracture of rocks and concrete

    • Authors: Y. Petrov, I. Smirnov, A. Evstifeev, N. Selyutina
      Abstract: When we want to compare the strength of two materials, we compare the table values of quasistaticstrength. However results of some experiments show that the strength ratio of the materials can changewith increase in rate of loading. Such "substitution effect" of material strength at different strain rates is studiedin this paper. It is shown that one material can have a lower dynamic strength for a higher static strengthcompared to the other material. Tests of two different materials, tests of mortar and concrete, and tests ofconcrete with different water content are considered. It is shown that load-carrying capacity of materials and thesubstitution effect of material strength in a wide range of loading rates can be predicted by the incubation timecriterion.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Study of the conditions of fracture at explosive compaction of powders

    • Authors: Andrey E. Buzyurkin, Evgeny I. Kraus, Yaroslav L. Lukyanov
      Abstract: Joint theoretical and experimental investigations have allowed to realize an approach with use ofmathematical and physical modeling of processes of a shock wave loading of powder materials.In order to gain a better insight into the effect of loading conditions and, in particular, to study the effect ofdetonation velocity, explosive thickness, and explosion pressure on the properties of the final sample, wenumerically solved the problem about powder compaction in the axisymmetric case.The performed analysis shows that an increase in the decay time of the pressure applied to the sample due to anincrease of the explosive thickness or the external loading causes no shrinkage of the destructed region at afixed propagation velocity of the detonation wave. Simultaneously, a decrease in the propagation velocity of thedetonation wave results in an appreciable shrinkage of this region.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Tests in tension-torsion conditions with descending sections of strain
           curve construction

    • Authors: M.P. Tretiakov, V.E. Vildeman
      Abstract: The paper is devoted to theoretical and experimental investigation of materials behavior onpostcritical deformation stage (strain softening). Tests results, which confirm theoretical justification ofspecimen configuration impact on the possibility of creating descending sections of strain curve, are given. It isshown that, with sufficient stiffness of loading system, equilibrium postcritical deformation of materials ispossible. It is confirmed in uniaxial tension tests with unloading on postcritical deformation stage. Test resultson tension with torsion of thin-walled tubular specimens in strain softening conditions are adduced.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Research of the effectiveness of mechanical testing methods with analysis
           of features of destructions and temperature effects

    • Authors: A.V. Babushkin, D.S. Lobanov, A.V. Kozlova, I.D. Morev
      Abstract: In this paper is carried out the comparative analysis of effectiveness of test methods ofdetermination of stiffness and strength properties of highly filled unidirectional fiberglass (Direct "E" roving 0.7- orthophthalic polyester resin 0.3) via tensile testing along the reinforcement and three-point bending testing atseveral bases. The necessity of deviation from standard procedures is substantiated. Deformation and failurefeatures of the material under quasi-static loading, as well as at low and high temperatures, are shown.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Multiscale approach to description of deformation and fracture of brittle
           media with hierarchical porous structure on the basis of movable cellular
           automaton method

    • Authors: Ig. S. Konovalenko, A. Yu. Smolin; , S. G. Psakhie
      Abstract: An approach to multiscale description of deformation and fracture of brittle porous materials onthe basis of movable cellular automaton method was proposed. The material characterized by pore sizedistribution function having two maxima was considered. The core of the proposed approach consists infinding the automaton effective response function by means of direct numerical simulation of representativevolume of the porous material. A hierarchical two-scale model of mechanical behavior of ceramics undercompression and shear loading was developed. Zirconia based ceramics with pore size greater than the averagegrain size was considered. At the first scale of the model only small pores (corresponding to the first maximumof the pore size distribution function) were taking into account explicitly (by removing automata from the initialstructure). The representative volume and effective elastic properties of the porous material at this scale wereevaluated. At the second scale of the model, big pores were taking into account explicitly, the parameters of thematrix corresponded to the ones determined at the first scale. Simulation results showed that the proposedmultiscale model allows qualitatively and quantitatively correct describing of deformation and fracture of brittlematerial with hierarchical porous structure.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Optimization of fractional composition of the excipient in the elastomeric
           covering for asphalt highways

    • Authors: E.M. Nurullaev, A. S. Ermilov
      Abstract: The computational method of optimum fractional composition of a dispersible filler of polymericcomposite on the basis of three-dimensionally linked elastomer is developed according to non-linearprogramming. The coefficient of dynamic viscosity of polymeric suspension or the initial module of aviscoelasticity of the join solidification low-molecular rubbers with the final functional groups, filled by manyfractional dioxide of silicon are considered as criteria of optimization. Influence of the limiting volume filling onenergy of mechanical destruction was investigated. The elastomeric material is offered for use as a covering ofasphalt highways in the form of a frost-proof waterproofing layer, which allowing multiply to increase operatingproperties.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Fractal statistics of brittle fragmentation

    • Authors: M. Davydova, S. Uvarov
      Abstract: The study of fragmentation statistics of brittle materials that includes four types of experiments ispresented. Data processing of the fragmentation of glass plates under quasi-static loading and the fragmentationof quartz cylindrical rods under dynamic loading shows that the size distribution of fragments (spatial quantity)is fractal and can be described by a power law. The original experimental technique allows us to measure, apartfrom the spatial quantity, the temporal quantity - the size of time interval between the impulses of the lightreflected from the newly created surfaces. The analysis of distributions of spatial (fragment size) and temporal(time interval) quantities provides evidence of obeying scaling laws, which suggests the possibility of selforganizedcriticality in fragmentation.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Development of a formalism of movable cellular automaton method for
           

    • Authors: S. Psakhie, E. Shilko, A. Smolin, S. Astafurov, V. Ovcharenko
      Abstract: A general approach to realization of models of elasticity, plasticity and fracture of heterogeneousmaterials within the framework of particle-based numerical methods is proposed in the paper. It is based onbuilding many-body forces of particle interaction, which provide response of particle ensemble correctlyconforming to the response (including elastic-plastic behavior and fracture) of simulated solids. Implementationof proposed approach within particle-based methods is demonstrated by the example of the movable cellularautomaton (MCA) method, which integrates the possibilities of particle-based discrete element method (DEM)and cellular automaton methods. Emergent advantages of the developed approach to formulation of manybodyinteraction are discussed. Main of them are its applicability to various realizations of the concept ofdiscrete elements and a possibility to realize various rheological models (including elastic-plastic or visco-elasticplastic)and models of fracture to study deformation and fracture of solid-phase materials and media.Capabilities of particle-based modeling of heterogeneous solids are demonstrated by the problem of simulationof deformation and fracture of particle-reinforced metal-ceramic composites.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Fatigue crack propagation in turbine disks of EI698 superalloy

    • Authors: A.A. Shanyavskiy
      Abstract: In-service fatigue cracking of turbine disks of EI698 superalloy is discussed based on crack growthanalyses. In the bolt joint for disks to shaft connecting there is high level of stress-state, which directed to earlierin-disks fatigue crack origination in low-cycle-fatigue regime. Fracture surface pattern such as fatigue striationswere used for their spacing measurement and crack growth duration estimating. Developed disk tests on aspecial bench by the equivalent program to in-service cyclic loads have allowed discovering one-to-onecorrelation between fatigue striation spacing and crack increment in one flight. Number of fatigue striations andbeach-marks calculations permitted to estimate crack growth period for the different stages of in-service diskscracking. Equivalent stress level for in-service cracked disks was calculated and compared with stress-level intesteddisks under stress equivalent program to in-service operated cyclic loads. Based on this result nondestructiveinspection intervals were discussed and recommended for in-service disks in dependence on numberof their flights at the moment of developed inspection to exclude in-flight disks fast fracture.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • A study of the stored energy in titanium under deformation and failure
           using infrared data

    • Authors: A.Yu. Fedorova, M.V. Bannikov, O.A. Plekhov
      Abstract: The work is devoted to the experimental study of heat dissipation caused by plastic deformationand failure processes taking place in a titanium alloy Ti-4.2Al-1.6Mn. To investigate the spatial and timeevolution of temperature, a set of experiments has been carried out on plane titanium smooth specimens andspecimens with pre-grown centered fatigue cracks. The original mathematical algorithm for experimental dataprocessing has been applied to obtain the rate of heat dissipation generated by plastic deformation and storedenergy. It is shown that the stored energy is accumulated in titanium specimens undergoing fatigue tests, and atthe time of damage to fracture transition it is equal to zero.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • A consistent use of the Gurson-Tvergaard-Needleman damage model for the
           R-curve calculation

    • Authors: Gabriele Cricrì
      Abstract: The scope of the present work is to point out a consistent simulation procedure for the quasi-staticfracture processes, starting from the micro-structural characteristics of the material. To this aim, a local nineparametersGurson-Tvergaard-Needleman (GTN) damage law has been used. The damage parameters dependon the micro-structural characteristics and must be calculated, measured or opportunely tuned. This can bedone, as proposed by the author, by using an opportunely tuned GTN model for the representative volumeelement simulations, in order to enrich the original damage model by considering also the defect sizedistribution. Once determined all the material parameters, an MT fracture test has been simulated by a FE code,to calculate the R-curve in an aeronautical Al-based alloy. The simulation procedure produced results in a verygood agreement with the experimental data.
      PubDate: 2013-03-20
      Issue No: Vol. 0 (2013)
       
  • Wear surface damage of a Stainless Steel EN 3358 aeronautical component
           subjected to sliding

    • Authors: Ferdinando Felli, Andrea Brotzu, Cristian Vendittozzi, Antonio Paolozzi, Francesco Passeggio
      Abstract: The present paper describes the failure analysis of an aircraft component subjected to severalepisodes of in service failure, resulted in loss of the aircraft safety. Modern aircrafts are provided withmechanical systems which have the task to open not pressurized hatches during landing. The components ofsuch systems are subject to considerable mechanical stresses in harsh environment (presence of moisture andpollutants, significant and sudden temperature variations). The system is constituted by a sliding piston, arelated nipple and by a locking system consisting of 4 steel spheres which are forced into a countersinkmachined on the piston when the hatches is open. The whole system is activated by a preloaded spring. Themachined parts, nipple and piston, are made of EN3358 steel (X3CrNiMo13-8-2), a precipitation hardeningstainless steel with very low content of carbon often used in the aerospace. The samples provided by themanufacturer present different types of damage all referable to phenomena relative to the sliding of the pistoninside the nipple. The present paper describes the different damage observed and the microstructure of thematerial, then are reported the results obtained from the characterization of the material of the samples bymeans of optical and electronic microscopy, carried out to define the mechanisms involved in the systemseizure. In order to define the primary cause of failure and to propose solutions to be adopted, also analyzingthe criticality of using this PH stainless steel for this application, the results of different tests were comparedwith system design and working data.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Experimental methods for the characterization of fatigue in
           microstructures

    • Authors: G. De Pasquale, A. Somà
      Abstract: The mechanical fatigue behavior of gold microbeams is analyzed. Dedicated devices have beendesigned and built able to produce alternate loading on gold specimens; the electrostatic actuation is used asdriving force. Gold beams are tested under both bending and tensile alternate loadings. Results were used toplot S-N curves and fatigue Goodman-Smith diagram in order to estimate the fatigue limit of the material inpresence of mean and alternate stress conditions. The surface topography evolution is studied and failure modesare discussed.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • A numerical study of squeeze-film damping in MEMS-based structures
           including rarefaction effects

    • Authors: Maria F. Pantano, Leonardo Pagnotta, Salvatore Nigro
      Abstract: In a variety of MEMS applications, the thin film of fluid responsible of squeeze-film dampingresults to be rarefied and, thus, not suitable to be modeled though the classical Navier-Stokes equation. Thesimplest way to consider fluid rarefaction is the introduction of a slight modification into its ordinaryformulation, by substituting the standard fluid viscosity with an effective viscosity term. In the present paper,some squeeze-film damping problems of both parallel and torsion plates at decreasing pressure are studied bynumerical solving a full 3D Navier-Stokes equation, where the effective viscosity is computed according toproper expressions already included in the literature. Furthermore, the same expressions for the effectiveviscosity are implemented within known analytical models, still derived from the Navier-Stokes equation. In allthe considered cases, the numerical results are shown to be very promising, providing comparable or evenbetter agreement with the experimental data than the corresponding analytical results, even at low air pressure.Thus, unlike what is usually agreed in the literature, the effective viscosity approach can be efficiently applied atlow pressure regimes, especially when this is combined with a finite element analysis (FEA
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Electro-mechanical coupled design of self-powered sensing systems and
           performances comparison through experiments

    • Authors: A. Somà, G. B. De Pasquale
      Abstract: Recent advances in low-power sensors and electronic components open to innovative strategies instructural monitoring and real-time data processing, in particular for industrial and vehicular fields. Dedicateddevices for harvesting the energy dissipated by mechanical vibrations of machines are showing their applicabilityin supplying autonomous distributed sensing systems. The harvester will replace cables and storage batteries,with relevant benefits on the sensing system capillarity, accessibility and applicability. The design of theinterfaces of the electric, magnetic and structural coupled systems forming the harvester include static anddynamic modeling and simulation of the interactions involved; smart and effective architectures are need tosatisfy the general requirements of bandwidth, tunability and efficiency required by each application. This paperreports the research advances in this field as a result of laboratory tests and design studies, with particular focuson the design methodologies involved in the definition of energy harvesters.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Design and characterization of a fractal-inspired multi-frequency
           piezoelectric energy converter

    • Authors: Davide Castagnetti
      Abstract: A promising harvesting technique, in terms of simplicity and efficiency, is the conversion ofambient kinetic energy through piezoelectric materials. This work aims to design and investigate a piezoelectricconverter conform to a fractal-inspired, multi-frequency structure previously presented by the author. Aphysical prototype of the converter is built and experimentally examined, up to 120 Hz, in terms of modalresponse and power output. Three eigenfrequencies are registered and the power output is particularly good atthe fundamental eigenfrequency. Also the effect of the resistive load applied to the converter is investigated.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Effect of pressure on the physical properties of magnetorheological fluids

    • Authors: A. Spaggiari, E. Dragoni
      Abstract: To date, several applications of magnetorheological (MR) fluids are present in the industrial world,nonetheless system requirements often needs better material properties. In technical literature a previous workshows that MR fluids exhibit a pressure dependency called squeeze strengthen effect. Since a lot of MR fluidbased devices are rotary devices, this paper investigates the behaviour of MR fluids under pressure when arotation is applied to shear the fluid. The system is designed in order to apply both the magnetic field and thepressure and follows a Design of Experiment approach. The experimental apparatus comprises a cylinder inwhich a piston is used both to apply the pressure and to shear the fluid. The magnetic circuit is designed toprovide a nearly constant induction field in the MR fluid. The experimental apparatus measures the torque as afunction of the variables considered and the yield shear stress is computed. The analysis of the results showsthat there is a positive interaction between magnetic field and pressure, which enhances the MR fluidperformances more than twice.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • A magnetorheological clutch for efficient automotive auxiliary device
           actuation

    • Authors: F. Bucchi, P. Forte, F. Frendo, R. Squarcini
      Abstract: In this paper the results of a project funded by Regione Toscana aimed at reducing the powerabsorption of auxiliary devices in vehicles are presented. In particular the design, testing and application of amagnetorheological clutch (MR) is proposed, aimed at disengaging the vacuum pump, which draws in air fromthe power-brake booster chamber, in order to reduce the device power absorption.Several clutch preliminary studies done to choose the clutch geometry and the magnetic field supply areillustrated. The final choice consisted in an MR clutch with permanent magnet, which satisfied size, torque andfail-safe specifications. The clutch characteristics, in terms of torque versus slip, were obtained experimentallyfor three different clutch prototypes on an ad-hoc developed test bench.As result of a preliminary simulation, a comparison between the power absorption of a current productionvacuum pump, an innovative vacuum pump and both vacuum pumps coupled with the MR clutch is presented.The New European Driving Cycle is considered for simulating the vacuum pump operation both in urban andhighway driving. Results show that the use of the innovative vacuum pump reduces the device consumption ofabout 35%, whereas the use of MR clutch coupled with the innovative vacuum pump reduces it up to about44% in urban driving and 50% in highway driving.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Properties and applications of Magnetorheological fluids

    • Authors: A. Spaggiari
      Abstract: This brief introduction describes the mechanical, rheological and magnetic properties of themagnetorheological (MR) fluids for feasible engineering applications. The typical modes of exploiting thistechnology are shown and discussed. An increasing number of industrial applications illustrate how the MRfluids peculiar properties may be used to provide optimal performance in semi active damping and dissipativedevices.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Compliant actuation based on dielectric elastomers for a force-feedback
           device: modeling and experimental evaluation

    • Authors: R. Vertechy, M. Bergamasco, G. Berselli, V. Parenti Castelli, G. Vassura
      Abstract: Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE)seem to be a promising technology for the implementation of light and compact force-feedback devices such as,for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivialowing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changingdeformations. In this context, the present paper addresses the development of a force feedback controller foran agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliantmechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the viscohyperelasticnature of the DE material. The model is then linearized and employed for the design of a forcecontroller. The controller employs a position sensor, which determines the actuator configuration, and a forcesensor, which measures the interaction force that the actuator exchanges with the environment. In addition, anoptimum full-state observer is also implemented, which enables both accurate estimation of the time-dependentbehavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminaryexperimental results are provided to validate the proposed actuator-controller architecture
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Application of martensitic SMA alloys as passive dampers of GFRP laminated
           composites

    • Authors: M. Bocciolone, M. Carnevale, A. Collina, N. Lecis, A. Lo Conte, B. Previtali, C.A. Biffi, P. Bassani, A. Tuissi
      Abstract: This paper describes the application of SMA (Shape Memory Alloy) materials to enhance thepassive damping of GFRP (Glass Fiber Reinforced Plastic) laminated composite. The SMA has been embeddedas reinforcement in the GFRP laminated composite and a SMA/GFRP hybrid composite has been obtained.Two SMA alloys have been studied as reinforcement and characterized by thermo-mechanical tests. Thearchitecture of the hybrid composite has been numerically optimized in order to enhance the structural dampingof the host GFRP laminated, without significant changes of the specific weight and of the flexural stiffness. Thedesign and the resultant high damping material are interesting and will be useful in general for applicationsrelated to passive damping. The application to a new designed lateral horn of railway collector of the Italianhigh speed trains is discussed.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Functional fatigue of NiTi Shape Memory wires for a range of end loadings
           and constraints

    • Authors: G. Scirè Mammano, E. Dragoni
      Abstract: The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermalactivation (functional fatigue) is central to the rational design of smart actuators based on these materials. Testresults on SMAs under functional fatigue are scarce in the technical literature and the few data available aremainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased byelastic springs or by another SMA element, their stress state is far from constant in operation. The mismatchbetween actual working conditions and laboratory arrangements leads to suboptimal designs and underminesthe prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality. Fourtest procedures are planned, covering most of the typical situations occurring in practice: constant-stress,constant-strain, constant-stress with limited maximum strain and linear stress-strain variation with limitedmaximum strain. The paper describes the experimental apparatus specifically designed to implement the fourloading conditions and presents fatigue results obtained from commercial NiTi wires tested under all thoseprotocols.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Fracture mechanics of pseudoelastic NiTi alloys: review of the research
           activities carried out at University of Calabria

    • Authors: C. Maletta, F. Furgiuele, E. Sgambitterra
      Abstract: This paper reports a brief review of the research activities on fracture mechanics of nickel-titaniumbased shape memory alloys carried out at University of Calabria. In fact, this class of metallic alloys show aunusual fracture response due to the reversible stress-induced and thermally phase transition mechanismsoccurring in the crack tip region as a consequence of the highly localized stresses. The paper illustrates the mainresults concerning numerical, analytical and experimental research activities carried out by using commercialNiTi based pseudoelastic alloys. Furthermore, the effect of several thermo-mechanical loading conditions onthe fracture properties of NiTi alloys are illustrated.
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • On the preparation and characterization of thin NiTi shape memory alloy
           wires for MEMS

    • Authors: Riccardo Casati, Maurizio Vedani, Syed A. M. Tofail, Calum Dikinson, Ausonio Tuissi
      Abstract: Shape memory alloy (SMA) wires are employed as actuators in small devices for consumerelectronics, valves and automotive applications. Because of the continued miniaturization of all the industrialproducts, nowadays the tendency is to produce MEMS (micro electromechanical systems). Among the mostpromising functional MEMS materials, the thin SMA wires that are offering a rapid actuating response withhigh power/weigh ratio of the material, are attracting a world wide interest. This paper is aimed at showing theproduction process and the characterizations of thin NiTi shape memory wires. The activity was focused ondrawing procedure and on functional and TEM characterizations of the final products. In particular, it wasevaluated the performance of the SMA wires for actuators in terms of functional fatigue and thermo-mechanicalproperties by means of an experimental apparatus design ad hoc for these specific tests
      PubDate: 2012-12-28
      Issue No: Vol. 0 (2012)
       
  • Fracture toughness of TiAl-Cr-Nb-Mo alloys produced via centrifugal
           casting

    • Authors: A. Brotzu, F. Felli, D. Pilone
      Abstract: Fracture toughness of a TiAl base intermetallic alloy has been investigated at room temperature.The Ti-48Al-2.5Cr-0.5Nb-2Mo (at. %) alloy produced via centrifugal casting exhibits fine nearly lamellar microstructures, consisting mainly of fine lamellar grains, together with a very small quantity of residual ' phases along lamellar colony boundaries. In order to determine the alloy fracture toughness compact tension specimens were tested and the results were compared with those available in literature.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Rilievo in tempo reale di difetti superficiali su corpi in movimento a
           velocità elevata con ultrasuoni senza contatto

    • Authors: D. Cerniglia, V. Nigrelli, A. Mancuso, A. Alberti
      Abstract: Il rilievo di difetti superficiali durante le ispezioni periodiche è importante poiché in genere le sollecitazioni sono maggiori in superficie e possono accelerare la crescita delle discontinuità. I difetti superficiali possono essere rilevati utilizzando alcuni metodi tradizionali di controllo non distruttivo, quali correnti indotte, liquidi penetranti, polveri magnetiche ed ultrasuoni. Alcuni tra questi metodi possono essere usati solo in condizioni statiche; gli altri presentano delle limitazioni per l’ispezione dinamica. I progressi recenti nel campo dei sensori ultrasonori senza contatto ci hanno permesso di sviluppare un sistema semplice per l’ispezione in tempo reale di corpi in movimento a velocità elevata. Nel lavoro viene presentata la possibilità di usare, col sistema sviluppato, due metodologie, basate sugli ultrasuoni generati e ricevuti senza contatto con la struttura, per rilevare difetti superficiali su corpi in movimento a 100 km/h, così da poter effettuare l’ispezione anche in servizio. Una metodologia, basata sull’uso di laser e trasduttori senza contatto, utilizza i vantaggi delle onde superficiali generate con il laser; l’analisi viene fatta sull’onda riflessa, creata dall’interazione dell’onda superficiale con il difetto. Lo spessore superficiale ispezionato è selezionabile dalla lunghezza d’onda dell’onda superficiale generata. L’altra metodologia, basata sull’uso di trasduttori senza contatto, sfrutta gli svantaggi della trasmissione degli ultrasuoni all’interfaccia aria/metallo; l’analisi viene fatta sulla diffrazione dell’onda riflessa dalla superficie. L’esecuzione delle ispezioni risulta semplice con entrambe le tecniche. I risultati sperimentali indicano una buona efficienza delle due metodologie proposte per il rilievo, in tempo reale, di difetti superficiali su corpi in movimento ad alta velocità.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Design and realization of a multisamples rotating high cycle fatigue
           machine

    • Authors: Domenico Gentile, Massimo Martorelli
      Abstract: In this work the design and the technical characteristic of a Moore rotating bending machine are presented. The machine has been realized at the University of Cassino in order to run tests on multiple specimens at different temperature. The user can choose independently the load and the temperature for each specimen. The machine has been designed to produce in short time a several numbers of data of materials fatigue strength at low costs. The machine is in assembling step at the Laboratory of Industrial Design of the University of Cassino.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Contact between the components of a knee prosthesis: numerical and
           experimental study

    • Authors: D. Cerniglia, T. Ingrassia, L. D’Acquisto, M. Saporito, D. Tumino
      Abstract: The aim of this work is the analysis of the contact area in a knee prosthesis using two different approaches. In particular, the interface between the femoral component and the polyethylene insert has been studied both numerically and experimentally. The interest in studying the contact area is related to the fact that the wear of the polyethylene insert, due to the high contact pressures, represents one of the major causes of failure of the total knee prosthesis. The possibility to evaluate the contact area at different loads and mutual position between femur and tibia is, therefore, of fundamental importance to study the service life of a prosthesis and to improve its performance. The finite element numerical approach has required the acquisition, through reverse engineering, and CAD modelling of the prosthetic components. Then the FEM simulations have been developed considering two different load conditions. In order to compare the calculated data, the same load configurations have been used for experimental tests based on ultrasonic method. In this case, some preliminary tests were required to calibrate the system depending on the particular characteristics of materials, geometries and surface finish of the prosthesis.The results show a good correlation between the data obtained with the two different approaches and, consequently, a good level of reliability of the procedures developed for the numerical and experimental evaluation of the contact area. The numerical procedure can be used to determine the area for different angles and loads, but especially in the design phase. The ultrasonic technique can be used to validate the numerical data.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • A mechanical model for FRP-strengthened beams in bending

    • Authors: S. Bennati, N. Dardano, P. S. Valvo
      Abstract: We analyse the problem of a simply supported beam, strengthened with a fibre-reinforced polymer (FRP) strip bonded to its intrados and subjected to bending couples applied to its end sections. A mechanical model is proposed, whereby the beam and FRP strip are modelled according to classical beam theory, while the adhesive and its neighbouring layers are modelled as an interface having a piecewise linear constitutive law defined over three intervals (elastic response – softening response – debonding). The model is described by a set of differential equations with appropriate boundary conditions. An analytical solution to the problem is determined, including explicit expressions for the internal forces, displacements and interfacial stresses. The model predicts an overall non-linear mechanical response for the strengthened beam, ranging over several stages: from linearly elastic behaviour to damage, until the complete detachment of the FRP reinforcement.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Sn and Ti influences on intermetallic phases damage in hot dip galvanizing

    • Authors: V. Di Cocco
      Abstract: Protection against metallic materials corrosion is one of the most important means to reduce both maintenance costs and environmental impact. In the last years new studies on chemical baths compositions and fluxes have been performed in order to improve processes, corrosion resistance and mechanical behavior of Zn based coatings. Chemical bath composition is often improved by the Sn addition which increases the fluidity ofthe melt. Ti addition makes the coatings to change color under appropriate heat treatment. In this work a comparative microstructural analysis, in Zn-Sn and Zn-Ti coatings, is performed to evaluate intermetallic phases formation kinetics and the influence of intermetallic microstructure on coating damage under constant bending deformation.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Natural minerals mixture for enhancing concrete compressive strength

    • Authors: Abdoullah Namdar
      Abstract: The construction material quality is required to be improved in order to enhancing structure stability, optimizing construction cost and quality. The kaolin and bentonite have been mixed in equal quantity and treated by heat for 1 hour under 600 oC, 800 oC and 1000 oC to create new minerals under high temperature condition to introduce an acceptable concrete additive for achieving concrete compressive strength in early age.To study micro properties of additive-cement mixture, X-ray and FESEM experiments have been used. The results indicate that acceptable proportion of unheated kaolin-bentonite is improving the concrete compressive response. But if kaolin-bentonite mixture treated by heat under 800 oC and in quantity of 12 % has been used in concrete mixed design, then the concrete compressive strength of 7 days shows the best result. The result is due to the development of new minerals under high temperature condition in mineral mixture and also kaolin-bentonite additive change cement past crystal and lead to enhancement of nano structural cement bonding.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Fractography as a tool to assess the occurrence of fatigue fractures in
           complex microstructure structural components

    • Authors: D. Firrao, P. Matteis
      Abstract: Fractographic assessment of fatigue fractures may be difficult if they occur in metallic components characterized by low ductility complex microstructures. In these cases reconciliation of known fatigue rupture mechanisms with fractographic appearance of fatigue fractured surfaces is challenging. Special techniques coupled with theory development may be necessary. Pearlitic steels or steels with predominant pearliticmicrostructures are among the ones that are visited and their fatigue fractures interpreted. Analogously, fatigued Al foundry alloys, with hypoeutectic Al-Si compositions, are also illustrated.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Evaluation of stress intensity factor of multiple inclined cracks under
           biaxial loading

    • Authors: R. K. Bhagat, V. K. Singh, P. C. Gope, A.K. Chaudhary
      Abstract: A finite rectangular plate of unit thickness with two inclined cracks (parallel and non parallel) under biaxial mixed mode condition are modelled using finite element method. The finite element method is used for determination of stress intensity factors by ANYSIS software. Effects of crack inclination angle on stress intensity factors for two parallel and non parallel cracks are investigated. The significant effects of different crack inclination parameters on stress intensity factors are seen for lower and upper crack in two inclined crack.The present method is validated by comparing the results from available experimental data obtained by photo elastic method in same condition.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Cold spray technology: future of coating deposition processes

    • Authors: Harminder Singh, T.S. Sidhu, S.B.S. Kalsi
      Abstract: Cold spray (CS) belongs to a wide family of thermal spray technology with the difference that it is a solid state process in which spray particles are deposited via supersonic velocity impact at a temperature much below the melting point of the spray material. This paper briefly describes the various aspects of this rapidly emerging technology, with almost all the important parameters which affect the deposition behavior along withadvantages and limitations; applications and history of emergence of this process is also reviewed. Though this technology emerges three decades ago but still it could not establish itself as viable practical industrial technology. Hence, the efforts, along with funding from public/private sources are required to commercialize this coating process. It is expected that next decade will saw the growth of cold spray as a viable coating processaround the globe.
      PubDate: 2012-09-30
      Issue No: Vol. 0 (2012)
       
  • Interference fit effect on holed single plates loaded with tension-tension
           stresses

    • Authors: D. Croccolo, M. De Agostinis, N. Vincenzi
      Abstract: This paper deals with the influence of interference fit coupling on the fatigue strength of holed plates. The effect was investigated both experimentally and numerically. Axial fatigue tests have been carried out on holed specimens made of high performance steel (1075MPa of Ultimate strength and 990MPa of Yield strength) with or without a pin, made of the same material, press fitted into their central hole. Three different conditions have been investigated: free hole specimens, specimens with 0.6% of nominal specific interference and specimens with 2% of nominal specific interference. The experimental stress-life (S–N) curves pointed out an increased fatigue life of the interference fit specimens compared with the free hole ones. The numericalinvestigation was performed in order to analyse the stress fields by applying an elastic plastic 2D simulation witha commercial Finite Element software. The stress history and distribution along the contact interference of the fitted samples indicates a significant reduction of the local stress range due to the externally applied loading (remote stress) since a residual and compressive stress field is generated by the pin insertion.
      PubDate: 2012-06-29
      Issue No: Vol. 0 (2012)
       
  • Infrared thermography study of the fatigue crack propagation

    • Authors: A.Yu. Fedorova, M.V. Bannikov, M.V. Bannikov, O.A. Plekhov, E.V. Plekhova
      Abstract: The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone.
      PubDate: 2012-06-29
      Issue No: Vol. 0 (2012)
       
  • A numerical approach for the analysis of deformable journal bearings

    • Authors: D. Benasciutti, M. Gallina, M. Gh. Munteanu, F. Flumian
      Abstract: This paper presents a numerical approach for the analysis of hydrodynamic radial journal bearings. The effect of shaft and housing elastic deformation on pressure distribution within oil film is investigated. An iterative algorithm that couples Reynolds equation with a plane finite elements structural model is solved. Temperature and pressure effects on viscosity are also included with the Vogel-Barus model. The deformed lubrication gap and the overall stress state were calculated. Numerical results are presented with reference to atypical journal bearing configuration at two different inlet oil temperatures. Obtained results show the great influence of elastic deformation of bearing components on oil pressure distribution, compared with results for ideally rigid components obtained by Raimondi and Boyd solution.
      PubDate: 2012-06-29
      Issue No: Vol. 0 (2012)
       
  • Hydrogen Re-Embrittlement of Aerospace grade High Strength Steels

    • Authors: R. Valentini, C. Colombo, M. De Sanctis, G. Lovicu
      Abstract: Hydrogen Re-Embrittlement on anodically coated high strength steels is a relevant risk for aerospace structures due to the possibility of hydrogen uptake during the operative life of the components. AISI 4340 and Maraging 250 unnotched tensile specimens were subjected to SSRT in order to evaluate the influence of test environment on time to failure. Fracture surfaces were examined by SEM analysis to evaluate the degree of embrittlement and to correlate it with hydrogen diffusivity of the tested steels.
      PubDate: 2012-06-29
      Issue No: Vol. 0 (2012)
       
  • A three-parameter model for fatigue crack growth data analysis

    • Authors: A. De Iorio, M. Grasso, F. Penta, G.P. Pucillo
      Abstract: A three-parameters model for the interpolation of fatigue crack propagation data is proposed. It has been validated by a Literature data set obtained by testing 180 M(T) specimens under three different loading levels. In details, it is highlighted that the results of the analysis carried out by means of the proposed model are more smooth and clear than those obtainable using other methods or models. Also, the parameters of the model have been computed and some peculiarities have been picked out.
      PubDate: 2012-06-29
      Issue No: Vol. 0 (2012)
       
  • Indentation response of a NiTi shape memory alloy: modeling and
           experiments

    • Authors: C. Maletta, F. Furgiuele, E. Sgambitterra, M. Callisti, B. G. Mellor, R. J. K. Wood
      Abstract: The indentation response of a pseudoelastic nickel-titanium based shape memory alloy (SMA) has been analyzed. Indentation tests have been carried out at room temperature using a spherical diamond tip and indentation loads in the range 50-500 mN in order to promote a large stress-induced transformation zone in the indentation region and, consequently, to avoid local effects due to microstructural variations. The measured load-displacement data have been analyzed to obtain information on the pseudoelastic response of the alloy. To aid this analysis numerical simulations were performed, by using a commercial finite element (FE) softwarecode and a special constitutive model for SMAs, so as to understand better the microstructural evolution occurring during the indentation process. Finally, the FE model has been used to analyze the effects of temperature on the indentation response of the alloy. This analysis revealed a marked variation of both the maximum and residual penetration depths with increasing test temperature.
      PubDate: 2012-06-29
      Issue No: Vol. 0 (2012)
       
  • Case studies in numerical simulation of crack trajectories in brittle
           materials

    • Authors: H. Jasarevic, S. Gagula
      Abstract: Statistical Fracture Mechanics, formalism of few natural ideas is applied to simulation of cracktrajectories in brittle material. The “diffusion approximation” of the crack diffusion model represents cracktrajectories as a one-dimensional Wiener process with advantage of well-developed mathematical formalismand simplicity of creating computer generated realizations (fractal dimension d = 1.5). However, the most ofreported d values are in the range 1.1-1.3. As a result, fractional integration of Wiener processes is applied forlowering d and to generate computer simulated trajectories. Case studies on numerical simulation ofexperimentally observed crack trajectories in sandstone (discs tested in indirect tensile strength test) andconcrete (compact tension specimens tested in the quasi-static splitting tensile test) are presented here.
      PubDate: 2012-03-19
      Issue No: Vol. 0 (2012)
       
  • Analysis of the causes of failure in 5Cr-1Mo pipes mounted in a preheating
           furnace

    • Authors: Adelina Borruto, Giovanni Narducci, Pietro Pietrosanti
      Abstract: The oxidation resistance of iron-based alloys depends on the formation of thin protective films consisting ofreaction products between the alloys and the ambient atmosphere. The high corrosion resistance of Fe-Cr-Mo alloys hasbeen attributed to the rapid formation of a uniform, highly protective passive film. The pipes hardness and resistance tovarious forms of corrosion are determined by the composition of the oxide layer that plays an important role indetermining the lifetime of the pipes themselves. The thermal stability of the oxide layer is influenced by its compositionand thickness as well as by the bond to the underlying metal.Determining factors for the high temperature corrosion are generally: temperature, metallurgy, TAN (chloridric andnaphthenic acid), local flow conditions, sulphur compounds.
      PubDate: 2012-03-19
      Issue No: Vol. 0 (2012)
       
  • Current state of existing project risk modeling and analysis methods with
           focus on fuzzy risk assessment – Literature Review

    • Authors: Pejman Rezakhani
      Abstract: Risk modeling and analysis is one of the most important stages in project success. There are manyapproaches for risk assessment and an investigation of existing methods helps in developing new models . Thispaper is an extensive literature survey in risk modeling and analysis methods with main focus on fuzzy riskassessment.
      PubDate: 2012-03-19
      Issue No: Vol. 0 (2012)
       
  • Crack path dependence on inhomogeneities of material microstructure

    • Authors: Roberto Brighenti, Andrea Carpinteri, Andrea Spagnoli, Daniela Scorza
      Abstract: Crack trajectories under different loading conditions and material microstructural features play animportant role when the conditions of crack initiation and crack growth under fatigue loading have to beevaluated. Unavoidable inhomogeneities in the material microstructure tend to affect the crack propagationpattern, especially in the short crack regime. Several crack extension criteria have been proposed in the pastdecades to describe crack paths under mixed mode loading conditions. In the present paper, both the Sihcriterion (maximum principal stress criterion) and the R-criterion (minimum extension of the core plastic zone)are adopted in order to predict the crack path at the microscopic scale level by taking into account microstressfluctuations due to material inhomogeneities. Even in the simple case of an elastic behaviour under uniaxialremote stress, microstress field is multiaxial and highly non-uniform. It is herein shown a strong dependence ofthe crack path on the material microstructure in the short crack regime, while the microstructure of the materialdoes not influence the crack trajectory for relatively long cracks.
      PubDate: 2012-03-19
      Issue No: Vol. 0 (2012)
       
  • Mechanical properties of copper processed by Equal Channel Angular
           Pressing – a review

    • Authors: Ludvík Kunz, Luca Collini
      Abstract: The Equal Channel Angular Pressing is a hardening treatment with which ductile metals can beprocessed to refine their grain and sub-grain structure. This process enhances the mechanical strength of metalsin terms of tensile strength, stress-controlled fatigue strength, and fatigue crack growth resistance. In this paperthe authors draw a review of the major results of a wide research activity they carried out on a coppermicrostructure processed by Equal Channel Angular Pressing. The essential results are that tensile and fatiguestrengths of the so obtained refined structure are improved by a factor of two with respect to the originalcoarse-grained metal. The fatigue crack initiation mechanism and the stability of the refined microstructureunder cyclic loading are topics also discussed, evidencing the essential role of the process and of the materialparameter, as the content of impurities in the microstructure. In this review, the authors also underline somecritical aspects that have to be more investigated.
      PubDate: 2011-12-20
      Issue No: Vol. 0 (2011)
       
  • Micro void coalescence of ductile fracture in mild steel during tensile
           straining

    • Authors: P. K. Pradhan, P. S. Robi, Sankar K. Roy
      Abstract: The ductile fracture occurs mainly in three stages i.e. void nucleation, void growth and the voidcoalescence. The present work focuses on the study the coalescence of existing micro void in a ductile material,mild steel. The specimen with holes in square array at various angle to load axis have been tested. The holeswere machined in the specimen and assuming those hole as the voids. The growth and coalescence behavioursduring tensile straining were observed both in macro and micro levels. Since the existing facility is not adequateto make hole size in micron, this work has been carried out by making hole upto 500 micron. The results arecompared with other specimen with bigger size hole and without any hole. Also the effects of micro voids(present in the material) on the progress of crack have been studied. It is found that with same amount of voids,present in different positions, the mechanical properties of the material are altered.

      PubDate: 2011-12-20
      Issue No: Vol. 0 (2011)
       
  • Sulla stima di macro, micro e nano-durezza di materiali metallici mediante
           analisi elasto-plastiche agli elementi finiti

    • Authors: Luca Susmel, David Taylor
      Abstract: Il lavoro sintetizzato nel presente articolo si pone come obiettivo primario quello di investigare lapossibilita di stimare, mediante un approccio elasto-plastico agli elementi finiti, la durezza dei materiali metalliciconvenzionali, e questo sia a livello macroscopico, che a livello microscopico, che, infine, a livello nanoscopico.Per verificare validita e accuratezza della metodologia FEM sviluppata, sono state condotte una serie di analisisperimentali su tre materiali metallici aventi caratteristiche metallurgiche estremamente diverse: una legadfalluminio (Al 7075-T6), un acciaio a basso tenore di carbonio (BS970-En3B) e, infine, un acciaio austenitico(AISI 316L). Lfindentazione Vickers e stata simulata con analisi elasto.plastiche agli elementi finiti considerandocarichi di prova nellfintervallo tra 490 N e 490 ƒÊN e calibrando le simulazioni numeriche mediante curvemonotone tensione.deformazione ottenute da prove di trazione eseguite utilizzando provini sia di dimensioneconvenzionale che aventi larghezza della zona calibrata dellfordine dei 100 ƒÊm.La sistematica comparazione tra risultati sperimentali e simulazioni numeriche ha posto in evidenza comelfaumentare del valore della durezza misurata al diminuire della dimensione dellfimpronta possa essere imputataal ruolo giocato dalla reale morfologia del materiale, ruolo che diventa predominante sulla plasticitaconvenzionale quando le dimensioni della superficie indentata diventano comparabili con le dimensioni mediedella grana cristallina delle leghe esaminate. Tali fenomeni, pertanto, non hanno consentito di estenderelfutilizzo della meccanica del continuo fino ad un livello nanoscopico per determinare correttamente i valoridella durezza. Alla luce di questi risultati e stata, pero, proposta una semplice metodologia di correzione dellestime eseguite mediante gli elementi finiti che si e dimostrata un valido strumento da utilizzarsi in situazioni diinteresse pratico per stimare la durezza dei materiali metallici, indipendentemente dalla dimensione dellasuperficie indentata.
      PubDate: 2011-12-20
      Issue No: Vol. 0 (2011)
       
  • Structural integrity of hierarchical composites

    • Authors: Marco Paggi
      Abstract: Interface mechanical problems are of paramount importance in engineering and materials science.Traditionally, due to the complexity of modelling their mechanical behaviour, interfaces are often treated asdefects and their features are not explored. In this study, a different approach is illustrated, where the interfacesplay an active role in the design of innovative hierarchical composites and are fundamental for their structuralintegrity. Numerical examples regarding cutting tools made of hierarchical cellular polycrystalline materials areproposed, showing that tailoring of interface properties at the different scales is the way to achieve superior
      PubDate: 2011-12-20
      Issue No: Vol. 0 (2011)
       
  • Characterization of fracture properties of thin aluminuminclusions
           embedded in anisotropic laminate composites

    • Authors: Gabriella Bolzon, Vladimir Buljak, Emanuele Zappa
      Abstract: The fracture properties of thin aluminum inclusions embedded in anisotropic paperboardcomposites, of interest for food and beverage packaging industry, can be determined by performing tensile testson non-conventional heterogeneous specimens. The region of interest of the investigated material samples ismonitored all along the experiment by digital image correlation techniques, which allow to recover qualitativeand quantitative information about the metal deformation and about the evolution of the damaging processesleading to the detachment of the inclusion from the surrounding laminate composite. The interpretation of thelaboratory results is supported by the numerical simulation of the tests.
      PubDate: 2011-12-20
      Issue No: Vol. 0 (2011)
       
  • Damage localization and rupture with gradient damage models

    • Authors: K. Pham, J.-J. Marigo
      Abstract: We propose a method of construction of non homogeneous solutions to the problem of traction ofa bar made of an elastic-damaging material whose softening behavior is regularized by a gradient damage model.We show that, for sufficiently long bars, localization arises on sets whose length is proportional to the materialinternal length and with a profile which is also characteristic of the material. The rupture of the bar occurs at thecenter of the localization zone when the damage reaches there the critical value corresponding to the loss ofrigidity of the material. The dissipated energy during all the damage process up to rupture is a quantity c G whichcan be expressed in terms of the material parameters. Accordingly, c G can be considered as the usual surfaceenergy density appearing in the Griffith theory of brittle fracture. All these theoretical considerations areillustrated by numerical examples.
      PubDate: 2011-12-20
      Issue No: Vol. 0 (2011)
       
  • Experimental and numerical study of cemented bone-implant interface
           behavior

    • Authors: D. Kytyr, T. Doktor, O. Jirousek, P. Zlamal, D. Pokorny
      Abstract: Although the total hip replacement (THR) is a long-proven method of surgical treatment of diseases and disorders of the human hip, the surgery brings some risk of long-term instability of the joint. The aim of the research was to investigate the cemented bone-implant interface behavior. The main problems (cement layer degradation and bone-cement interface debonding) during physiological loading conditions have been investigated using a custom hip simulator. The experimental setup was designed to allow cyclic loading of the sample of pelvic bone with implanted cemented acetabular component. The hip contact force of required direction and magnitude was applied to the implant using a spherical femoral component head. The most unfavorable activity (downstairs walking) was simulated. The process of damage accumulation in the fixation was monitored by repeated scanning using high resolution micro Computed Tomography (µCT). Use of micro-focus source and large high-resolution flat panel detector allows investigation of structural changes and crack propagation both in the cement layer and the trabecular bone.
      PubDate: 2010-12-15
      Issue No: Vol. 0 (2010)
       
  • On the application of the Theory of Critical Distances for prediction of
           fracture in fibre composites

    • Authors: David Taylor
      Abstract: This paper is concerned with the fracture of composite materials containing stress concentration
      features such as notches and holes. In particular, it addresses the question of the use of the Theory of Critical
      Distances (TCD) – a method which is widely used for predicting notch effects in fatigue and fracture. The TCD
      makes use of a length constant, L, known as the critical distance, which is normally assumed to be a material
      property. However, many workers in the field of composite materials have suggested that the critical distance is
      not a constant, but rather is a function of notch size. I examined the evidence for this assertion, and concluded
      that it arises for four different reasons, two of which (process zone size and constraint) are real material effects
      whilst the other two (choice of test specimen and estimation of the stress field) arise due to errors in making the
      assessments. From a practical point of view, the assumption of a constant value for L leads to only small errors,
      so it is recommended for engineering design purposes.

      PubDate: 2009-12-30
      Issue No: Vol. 0 (2009)
       
  • Sommario

    • Authors: Francesco Iacoviello
      Abstract: -
      PubDate: 2009-10-05
      Issue No: Vol. 0 (2009)
       
  • Effetto delle dimensioni del cordone di saldatura sulla resistenza a
           fatica dei giunti a croce

    • Authors: B. Atzori, B. Rossi, G. Demelio
      Abstract: La scelta della dimensione da assegnare al cordone di saldatura nel caso di giunzioni saldate a croce può presentarsi problematica, specie quando gli spessori delle lamiere che formano il giunto sono differenti tra loro. Le normative di tipo tecnologico suggeriscono in genere di prevedere uno spessore del cordone di saldatura inferiore al minimo spessore della lamiera da collegare, mentre le normative di tipo strutturale non prevedono una dipendenza della resistenza del giunto, sia statica che a fatica, dalle dimensioni del cordone di saldatura, a meno che queste non siano tanto ridotte da portare a rotture che si inneschino e si propaghino non più nella lamiera base ma nel cordone di saldatura. Scopo del presente lavoro è la verifica, teorica e sperimentale, della variazione della resistenza a fatica al variare del rapporto tra lo spessore del cordone di saldatura e quello minimo delle lamiere da saldare.
      PubDate: 2009-07-01
      Issue No: Vol. 0 (2009)
       
  • On the influence of T-Stress on photoelastic analysis under pure mode II
           loading

    • Authors: Mahnaz Zakeri, Chiara Colombo
      Abstract: According to the classical definition for in-plane modes of crack deformation, the constant stress term T exists only in the presence of mode I. However, recent studies show that this term can exist in mode II conditions as well, and significantly affect the elastic stress field around the crack tip. These effects can be visualized using the experimental method of photoelasticity. Based on the analytical studies, presence of the T-stress in mode II cracks transforms the isochromatic fringe patterns from symmetric closed loops to asymmetric and discontinuous shapes. In this paper, presence of the T-stress in mode II cracks and its effects on the fringe patterns is experimentally investigated. The test specimens are Brazilian disks containing very sharp central cracks: experimental results indicate that these specimens contain negative values of T-stress. Experimental values are then compared to numerical results. To better understand the differences between experimental and numerical values, a thee dimensional analysis is performed with the finite element method: results show the influence of the real geometry of the crack front on the stress intensity factors.
      Issue No: Vol. 0
       
  • Densità di energia di deformazione locale e resistenza a fatica di giunti
           saldati di geometria complessa

    • Authors: M. Zappalorto, F. Berto, P. Lazzarin
      Abstract: A recent criterion based on the local strain energy density (SED) averaged over a given control volume is applied to well-documented experimental data taken from the literature, all related to steel welded joints of complex geometry. This small size volume embraces the weld root or the weld toe, both regions being modelled as sharp (zero notch radius) V-notches with different opening angles. The SED is evaluated from three-dimensional finite element models by using a circular sector with a radius equal to 0.28 mm. The data expressed in terms of the local energy fall in a scatter band recently reported in the literature, based on about 650 experimental data related to fillet welded joints made of structural steel with failures occurring at the weld toe or at the weld root.
      Issue No: Vol. 0
       
  • Analisi dell’anisotropia microstrutturale in materiali compositi
           rinforzati con fibre corte

    • Authors: A. Bernasconi, F. Cosmi, D. Dreossi
      Abstract: Synchrotron light microtomography has proved to be particularly efficient in order to analyze the microstructural characteristics in terms of reinforce fibre distribution and orientation in glass fibre reinforced composites. The spatial distribution of fibre within the polymeric matrix could be detected even in case of fibre characterized by a small diameter (10 micrometers average diameter). Differences in orientation distribution within a sample could be measured using the Mean Intercept Length (MIL) and the fabric tensor. The results presented herein refer to a sample of a 30% by weight glass fibre reinforced polyamide 6, extracted form a thin plate.
      Issue No: Vol. 0
       
  • Misure di tenacità a frattura su acciai utilizzando velocità di
           deformazione elevate

    • Authors: Enrico Lucon
      Abstract: The knowlegde of dynamic mechanical properties is useful in all cases where the strain ratesensitivity of metallic materials is an issue, and whenever the actual loading conditions for a structure (eitherin normal operation or under accidental circumstances) are different from static. Furthermore, in someinvestigations increasing the loading rate is used to simulate other embrittling mechanisms such as thermalaging or neutron exposure.This paper provides an overview of SCK•CEN experience on measuring fracture toughness of steels at elevatedloading rates, with specific emphasis on instrumented impact tests on precracked Charpy (PCVN)specimens.After briefly dwelling on the basic mechanisms which explain loading rate effects on cleavage and ductilefracture toughness, the experimental and analytical procedures for measuring fracture toughness at elevatedloading rates are addressed, both in terms of official ASTM and ISO test standards and considering standardizationefforts currently in progress under SCK•CEN coordination: revision of ASTM E1921 (MasterCurve methodology for measuring fracture toughness in the ductile-to-brittle transition region) and a future ISO standard on instrumented PCVN testing. This latter document is examined in more detail, focussing theattention on the dynamic evaluation of brittle fracture toughness (Impact Response Curve) and the determinationof crack resistance curves using multiple and single-specimen techniques.Finally, selected examples from SCK•CEN database of dynamic toughness measurements will be illustrated,mainly relevant to reactor pressure vessel (RPV) steels.
      Issue No: Vol. 0
       
  • Are the Paris’ law parameters dependent on each other'

    • Authors: Alberto Carpinteri, Marco Paggi
      Abstract: The question about the existence of a correlation between the parameters C and m of the Paris’ law is re-examined in this paper. According to dimensional analysis and incomplete self-similarity concepts applied to the linear range of fatigue crack growth, a power-law asymptotic representation relating the parameter C to m and to the governing variables of the fatigue phenomenon is derived. Then, from the observation that the Griffith-Irwin instability must coincide with the Paris’ instability at the onset of rapid crack growth, the exponents entering this correlation are determined. A fair good agreement is found between the proposed correlation and the experimental data concerning Aluminium, Titanium and steel alloys.
      Issue No: Vol. 0
       
  • Applicazione della meccanica della frattura viscoelastica alla previsione
           della vita di tubi in polibutene

    • Authors: Luca Andena, Marta Rink, Roberto Frassine
      Abstract: Isotactic polybutene-1 (i-PB1) is a polymer used for the manufacturing of pressurized pipes. In this work two grades of i-PB1 with a different degree of isotacticity have been investigated; they have been supplied by Basell Polyolefins. Fracture tests have been performed at various temperatures and testing speeds. Two configurations have been used, single edge notch bending (SENB) and double cantilever beam (DCB), the latter only to study crack propagation. Optical methods have been used to detect crack initiation and measure propagation speed. From the phenomenological point of view, the formation of highly stretched material regions has been observed during crack propagation. A continuous tearing of these regions as the crack advances has often been interrupted by their sudden rupture, with the load decreasing accordingly. This partial instability has been observed on both material grades, with both testing configurations. Results of the tests have been interpreted using the fracture mechanics framework; a time-temperature superposition scheme has been adopted to represent viscoelastic behavior over several decades. An analytical model has been applied to predict the lifetime of pressurized pipes. A good agreement has been reported between model predictions and experimental data obtained from tests on polybutene pipes.
      Issue No: Vol. 0
       
  • L’applicazione della diffrattometria dei raggi X per l’analisi del
           cedimento dei componenti meccanici

    • Authors: Mario Guagliano
      Abstract: X-ray diffraction is a well-known experimental technique for measuring residual stresses inmetallic materials. If XRD is applied to the fracture surface of a broken part it becomes a fractographicaltechnique, that is to say that it is possible to relate the results of the measures to the loading condition thatlead a component to fail. In this paper, after an introduction about the technique, XRD fractography is appliedto a fatigue failed diesel engine crankshaft. It was possible to determine the load that lead the crankshaftto fail and to evidence some original aspects about the application of this technique to real machineparts.
      Issue No: Vol. 0
       
  • Some practical crack path examples

    • Authors: Les P. Pook
      Abstract: It is well known that many engineering structures and components, as well as consumer items,contain cracks or crack-like flaws. It is widely recognised that crack growth must be considered both in designand in the analysis of failures. The complete solution of a crack growth problem includes determinationof the crack path. Macroscopic aspects of crack paths have been of industrial interest for a very long time.At the present state of the art the factors controlling the path taken by a crack are not completely understood.Eight brief case studies are presented. These are taken from the author’s professional and personal experienceof macroscopic crack paths over many years. They have been chosen to illustrate various aspects ofcrack paths. One example is in a component from a major structure, three examples are in laboratory specimens,and four are in nuisance failures. Such nuisance failures cause, in total, a great deal of inconvenienceand expensive, but do not normally receive much publicity.
      Issue No: Vol. 0
       
  • Sulla storia degli studi di frattura in Italia

    • Authors: Roberto L. Colombo, Donato Firrao
      Abstract: History of studies of fracture is inherently intermingled with the history of technology developments. In the beginning very little was written about. We must credit Leonardo and Galileo as the first ones that wrote about the problem and on how to measure and foresee rupture loads. Later, nineteenth century italian scientists distinguished themselves in attempting to establish material laws and multiple stresses rupture criteria. A review of the works of past centuries italian scientists is presented, along with a critical comparison with the work of other past european scientists.
      Issue No: Vol. 0
       
  • Numerical modelling in non linear fracture mechanics

    • Authors: Viggo Tvergaard
      Abstract: Some numerical studies of crack propagation are based on using constitutive models that accountfor damage evolution in the material. When a critical damage value has been reached in a materialpoint, it is natural to assume that this point has no more carrying capacity, as is done numerically in the elementvanish technique. In the present review this procedure is illustrated for micromechanically based materialmodels, such as a ductile failure model that accounts for the nucleation and growth of voids to coalescence,and a model for intergranular creep failure with diffusive growth of grain boundary cavities leadingto micro-crack formation. The procedure is also illustrated for low cycle fatigue, based on continuum damagemechanics. In addition, the possibility of crack growth predictions for elastic-plastic solids using cohesivezone models to represent the fracture process is discussed.
      Issue No: Vol. 0
       
  • Effetto supporto, tensione locale e gradiente relativo di tensione nella
           predizione della vita a fatica

    • Authors: B. Reggiani, A. Freddi
      Abstract: Obiettivo ultimo delle ricerche nelle quali si inquadra questo studio è superare, o almeno limitare, la necessità di complicate e costose prove sperimentali a favore di altri metodi predittivi della vita a fatica. Scopo specifico del presente lavoro è, dopo una analisi critica delle diverse soluzioni proposte in letteratura, la valutazione di una formulazione atta a predire, tramite analisi agli Elementi Finiti (FEM), la vita a fatica locale, nella regione ad alto numero di cicli, di componenti di forma complessa con una distribuzione irregolare di tensione. Concetto base di questa teoria è che il fenomeno della vita a fatica sia governato dal gradiente relativo di tensione nella zona maggiormente sollecitata del componente. Le simulazioni proposte per il calcolo della pendenza delle curve S-N e del limite di fatica sono verificate tramite il confronto con dati sperimentali tratti da letteratura. Mentre la formulazione per il calcolo del limite di fatica mostra un buon accordo con i dati sperimentali (errore medio percentuale del 7%), la pendenza valutata mediante l'equazione proposta risulta in alcuni casi sovrastimata (errore medio percentuale oltre il 100%). Nel presente lavoro si propone quindi una nuova formula che permette di ottenere un errore medio percentuale sulla pendenza dell'ordine del 20% nel confronto con i dati sperimentali.
      Issue No: Vol. 0
       
  • Effect of Carbon and Nitrogen content on deformation and fracture of AISI
           304 austenitic stainless steel

    • Authors: A. Molinari, M. Composta, C. Menapace
      Abstract: In questo lavoro è stato studiato l'effetto di modeste differenze nel contenuto di carbonio e di azoto sulla deformazione e il comportamento a frattura a temperatura ambiente di un acciaio inossidabile austenitico AISI 304. Nell'acciaio contenente il più basso contenuto degli elementi interstiziali si forma una maggiore quantità di martensite indotta dalla deformazione plastica dell'austenite; ne risulta un aumento dell'incrudimento, della deformazione uniforme e della deformazione totale. La presenza di aree martensitiche di dimensioni significative nella sezione resistente causa però localizzazione della deformazione all'interfaccia austenite/martensite, e questo promuove la nucleazione di cricche e la loro propagazione all'interfaccia stesso. Questo fenomeno determina una diminuzione di UTS. La trasformazione martensitica indotta dalla deformazione causa inoltre una diminuzione della "strain rate sensitivity".
      Issue No: Vol. 0
       
  • Dalla Frattura alla Scienza dei Metalli

    • Authors: M. Cavallini
      Abstract: La frattura inizia ad essere considerata oggetto di studio da Leonardo da Vinci e trova in Vannoccio Biringucci ed in Galileo Galilei i precursori di un approccio scientifico al come e perché si produce una rottura. Nell'arco di poco più di un secolo, il sedicesimo, si trovano i primi riferimenti scritti di esperienze e interpretazioni su cui lavorare: i limiti tecnologici e di conoscenza scientifica dei materiali allora disponibili hanno impedito una interpretazione soddisfacente del fenomeno della rottura. Sarebbero occorsi altri due secoli per collegare con una relazione lineare, prima forza e deformazione, e poi tensione e deformazione.
      Issue No: Vol. 0
       
  • A model for steady state stage III creep regime at low-high
           stress/temperature range

    • Authors: L. Esposito, N. Bonora
      Abstract: Although diffusional flow creep is often considered out of practical engineering applications, the need for a model capable to account for the resulting action of both diffusional and dislocation type creep is justified by the increasing demands of reliable creep design for very long lives (exceeding lOO.OOOh), high stress-low temperatures and high temperature-low stress regimes. In this paper, a creep model formulation, in which the change of the creep mechanism has been accounted for through an explicit dependence of the creep exponent n on stress and temperature, has been proposed. An application example of the proposed approach to high purity aluminum is given.
      Issue No: Vol. 0
       
  • Propagazione di fratture longitudinali in gasdotti caratterizzati da bassa
           duttilità

    • Authors: M. Minotti, P. Salvini, G. Demofonti
      Abstract: Il presente lavoro propone l'analisi di propagazione di una frattura fragile longitudinale di un gasdotto interrato basata sulla valutazione dell'energy release rate. Viene illustrata l'implementazione della suddetta metodologia all'interno di un codice proprietario agli elementi [miti con formulazione esplicita, illustrando gli interventi eseguiti sul preesistente algoritmo di propagazione stazionaria, e proponendo i risultati ottenuti a seguito di simulazioni dinamiche svolte su tubi in acciaio X80 e su provini SENB in pieno spessore sottoposti a prove DW1T.
      Issue No: Vol. 0
       
  • L'infragilimento da idrogeno. Un caso di studio In una barra di
           comandi di un velivolo dell'aviazione generale.

    • Authors: M. Amura, V. Di Paolo, M. Bernabei, M. Colavita, L. Aiello
      Abstract: La degradazione delle caratteristiche meccaniche di un materiale di impiego aeronautico ha pesanti ricadute sulla sicurezza del volo. Tale degradazione si può manifestare sia per l'effetto combinato tra l'ambiente nel quale il velivolo opera e le sollecitazioni cui è sottoposto sia che a causa di anomalie avvenute in fase produttiva che, dopo un periodo di incubazione, manifestano il loro pericoloso effetto: è questo il caso dell'infragilimento da idrogeno che, nel presente articolo che esamina sia i punti critici del processo di produzione che possono indudo che la morfologia delle superfici di rottora che ad esso si possono ricondurre. Viene infme presentato un caso di studio che ha interessato un velivolo dell'aviazione generale nel quale è stato individuato l'infragilimento da idrogeno di un componente in acciaio AISI 4130 è stata individuata quale causa primaria dell'incidente.
      Issue No: Vol. 0
       
  • Un approccio innovativo per l'analisi quantitativa delle superfici di
           frattura a fatica nelle ghise sferoidali mediante elaborazione di
           immagini.

    • Authors: A. De Santis, D. Iacoviello, V. Di Cocco, O. Di Bartolomeo
      Abstract: Le osservazioni al microscopio elettronico a scansione (SEM) delle superfici di fratturaottenute a seguito di rotture per fatica consentono di evidenziare alcuni meccanismi di avanzamento che dipendono dal materiale e dalla modalità di applicazione delle sollecitazioni. L'introduzione di moderne tecniche di analisi di immagine assistite al calcolatore permette di elaborare un numero di informazioni elevato che consente di porre in relazione le caratteristiche morfologiche locali con il comportamento meccanico macroscopico del materiale. In questo lavoro è stata implementata una tecnica innovativa di analisi di immagine basata sull'analisi della tessitura, valutando l'influenza delle condizioni di applicazione della sollecitazione (LlK applicato) sulla evoluzione del clivaggio rilevato sulle superfici di frattura a fatica di una ghisa sferoidale ferritoperlitica.
      Issue No: Vol. 0
       
  • On the relationship between J-integral and CTOD for CT and SENB specimens

    • Authors: S. K. Kudari, K.G. Kodancha
      Abstract: In this investigation the relationship between J-integral and CTOD is studied considering a Compact Tensile (CT) and Single edge notched bend (SENB) specimens using finite element analysis. The magnitude of CTOD is estimated by 90o-intercept method and also by plastic hinge model. The results indicate that there exists a discrepancy in estimation of CTOD by 90o-intercept method and by plastic hinge model. The CTOD values obtained by both the methods are found to be linearly proportional to J-integral. The linear proportionality constant dn between CTOD and J is found to strongly depend on the method of estimation of CTOD, specimen geometry and a/W ratio of the specimens.
      Issue No: Vol. 0
       
  • Inferenza bayesiana per l'analisi dei dati di prove di fatica

    • Authors: A. De Iorio, M. Guida, F. Penta, P. Pinto
      Abstract: Si prende in esame il problema della caratterizzazione a fatica dei materiali mediante campioni di dati poco numerosi. Se ne prospetta una soluzione che impiega la metodologia bayesiana. Per la vasta famiglia degli acciai al carbonio, laminati a caldo o bonificati che siano, utilizzando dati di letteratura ed alcune consolidate correlazioni tra proprietà di fatica e resistenza statica, è definita una funzione di densità di probabilità a priori in grado di condensare gran parte delle informazioni disponibili. Queste ultime, in uno con quelle fornite dalla sperimentazione diretta, da esaminare mediante il teorema di Bayes, permettono di identificare con grande accuratezza la resistenza a fatica del particolare acciaio provato. L’efficacia del metodo proposto è verificata con una sperimentazione virtuale su un ipotetico acciaio condotta con il metodo Montecarlo.
      Issue No: Vol. 0
       
  • A new method for the experimental study of fatigue behaviour of
           thermoplastic materials

    • Authors: M. Basso, A. Crevatin, M. Celotto, M. Sanità
      Abstract: Nowadays most industrial realities undergo a strong push to improve cost-effectiveness, productivity and quality of manufactured products. In particular we focussed our attention in the area of design of plastic structural components, including both optimization of existing structures and design of new ones. In this case, but the following considerations have a more general value, these needs could be translated into demanding requirements of cost-effectiveness, weight reduction, reduced time-to-market with guarantee reliability. From a material perspective this means demanding mechanical performances, attention to safety margins and need of a better control of key design parameters. To obtain these results, we need to develop a new approach and effective tools in the design of plastic materials and components aimed at tailoring part behaviour to endurance and performance requirements. The target of the project is to find effective tools for predicting life endurance and damage evolution of plastic materials and components under mechanical/thermal service loading, in order to support the development of new material formulations and the design and optimization of structural components. In a particular way, we focussed our work in the characterization and modellization of materials durability and damage mechanisms. One of the main problems related to materials durability is due to fatigue failure. Fatigue process is a progressive weakening of a component with increasing time under load such that loads to be supported satisfactorily for short duration produce failure after long durations [1, 2, 3]. Fatigue failure should not be thought only as the breaking of the specimen into two separated pieces, but as a progressive material damage accumulation [2]. Material damage during fatigue loading manifests as progressive reduction of stiffness and as creep [5]. As standard fatigue testing are expensive in terms of money and time, it is essential to develop new approaches less time consuming and simpler to be implemented. One of the most important goals of the present work is the setting of an investigation method (Accelerated Fatigue Test) very simple to be implemented that is able to differentiate damage accumulation and durability performances of various material formulations in reduced time.
      Issue No: Vol. 0
       
  • Effects of surfaces nanocrystallization induced by shot peening on
           material properties : a Review

    • Authors: Sara Bagheri Fard, Mario Guagliano
      Abstract: A brief description of surface nanosrystallization process via severe plastic deformation is presented. To come to the point different shot peening methods which have proved to be able to create nanocrystalline layers are demonstrated clarifying the actual state of the art. Then the influence of the process is reviewed on material behavior and a wide range of affected properties are investigated. On this basis some possible addresses for future research in this field are drawn and underlined.
      Issue No: Vol. 0
       
  • Il modello della fessura coesiva in trazione e compressione per la
           valutazione della duttilità degli elementi strutturali in calcestruzzo
           armato

    • Authors: Alberto Carpinteri, Mauro Corrado, Giuseppe Mancini, Marco Paggi
      Abstract: Il problema della valutazione della duttilità degli elementi in calcestruzzo armato soggetti a flessione o presso-flessione è stato largamente studiato negli ultimi decenni, sia da un punto di vista sperimentale che analitico. Data l’influenza di numerosi parametri di progetto sulla duttilità, tuttavia, è difficile sviluppare un modello in grado di descrivere completamente la risposta meccanica di elementi strutturali, tenendo conto di tutti gli effetti dovuti alla non-linearità dei materiali. Nel passato, in particolare, si è studiato in maniera approfondita l’effetto della classe di duttilità dell’acciaio, mentre il ruolo degli effetti di scala, evidenziato da più campagne sperimentali, non è stato ancora del tutto chiarito. Una delle ragioni principali è l’inadeguatezza dei modelli tradizionali, basati su leggi costitutive tra tensioni e deformazioni. Nel presente lavoro, si propone un nuovo modello basato sul concetto della localizzazione delle deformazioni, capace di descrivere la propagazione della fessura e l’avanzamento del crushing durante il processo di carico. In tale contesto, il comportamento non-lineare del calcestruzzo in compressione è modellato attraverso l’Overlapping Crack Model, modello analogo a quello coesivo valido per la trazione, che descrive la localizzazione delle deformazioni dovuta al danneggiamento del calcestruzzo mediante una compenetrazione del materiale. Con questo nuovo algoritmo è possibile cogliere l’effettiva risposta flessionale di elementi strutturali in calcestruzzo armato al variare della percentuale di armatura e della scala dimensionale. Applicazioni numeriche riguardano l’analisi della risposta post-picco di provini in calcestruzzo soggetti a compressione e la valutazione delle rotazioni plastiche di travi in calcestruzzo armato soggette a flessione su tre punti. Si propone infine un ampio confronto con i risultati di prove sperimentali, con lo scopo di dimostrare la validità del nuovo approccio.
      Issue No: Vol. 0
       
  • Distribuzioni di tensione per intagli soggetti a torsione in condizioni
           elastiche ed elastoplastiche

    • Authors: Michele Zappalorto, Paolo Lazzarin
      Abstract: Il lavoro riporta delle soluzioni analitiche in forma chiusa per le distribuzioni di tensione generate da intagli circonferenziali in componenti assialsimmetrici soggetti a torsione, in condizioni lineari elastiche ed elastoplastiche. Il problema teorico in condizioni lineari elastiche è stato impostato e risolto utilizzando la teoria dei potenziali nel dominio complesso e una serie di opportuni sistemi di riferimento in coordinate curvilinee, evitando l’uso di mappature conformi. Le soluzioni proposte hanno un ampio range di applicabilità, in termini di dimensioni e forma dell’intaglio e di diametro dell’albero. Il problema elastoplastico è stato invece risolto utilizzando la tecnica delle trasformazioni odografiche, al fine di rendere lineari le equazioni nonlineari fondamentali del problema. Il contributo rappresenta la sintesi di una serie di lavori più ampi a cura degli stessi autori.
      Issue No: Vol. 0
       
  • Experimental investigation on possible dependence of plastic zone size on
           specimen geometry

    • Authors: S. K. Kudari, B. Maiti, K. K. Ray
      Abstract: In this investigation the extent of the plastic zone size ahead of a crack-tip in single edge notched tension (SENT), compact tension (CT) specimens has been examined experimentally by micro-hardness technique and by elastic-plastic finite element analyses at different applied load levels. The magnitudes of the plastic zone size (PZS), rp ahead of crack-tip in the investigated specimens have been compared using normalized J-integral (J/a'y, where, a-crack length and 'y-yield stress of the material). The results show the dependence of PZS on specimen geometry due to varied in-plane crack-tip constraint. The results also demonstrate that the existing analytical models do not explain the experimental results of PZS satisfactorily.
      Issue No: Vol. 0
       
  • High-cycle fatigue strength of a pultruded composite material

    • Authors: C. Colombo, M. Guagliano, L. Vergani
      Abstract: Dealing with composites in polymeric matrix, the pultruded ones are among the more suitable for large production rates and volumes. For this reason, their use is increasing also in structural applications in civil and mechanical engineering. However, their use is still limited by the partial knowledge of their fatigue behaviour; in many applications it is, indeed, required a duration of many millions of cycles, while most of the data that can be found in literature refer to a maximum number of cycles equal to 3 millions. In this paper a pultruded composite used for manufacturing structural beams is considered and its mechanical behaviour characterized by means of static and high-cycle fatigue tests. The results allowed to determine the S-N curve of the material and to assess the existence of a fatigue limit. Observations at the scanning electronic microscope (SEM) allowed to evaluate the damage mechanisms involved in the static and fatigue failure of the material.
      Issue No: Vol. 0
       
  • Bearing capacity of mixed soil model

    • Authors: Abdoullah Namdar, Mehdi Khodashenas Pelkoo
      Abstract: The main objective of this research is the improvement of red soil by the addition of construction materials. This method could provide a scientific way to create a soil foundation with sufficient stability against geo-technical problems or instabilities. Laboratory tests have been conducted to characterize the behavior of red soil when amended with different types of gravels, soils and sand under compacted conditions with Optimum Moisture Content (OMC). Safe bearing capacity of all models have been calculated to identify the best and worst soil mixed model.
      Issue No: Vol. 0
       
  • Elementi di interfaccia per l’analisi di strutture murarie

    • Authors: Elio Sacco, Jessica Toti
      Abstract: The present paper deals with the modelling of the mechanical behaviour of masonry elements regarded as heterogeneous systems, made of mortar, bricks and interfaces. Thus, the adopted computational strategy consists in modelling the brick units, the mortar joints and the interfaces responsible for the mortarbrick decohesion mechanisms; to this end, a special interface model combining damage and friction is proposed. A numerical procedure, based on the backward Euler time-integration scheme, is introduced; the time step is solved adopting a displacement driven predictor-corrector scheme. Some numerical applications are performed in order to assess the performances of the proposed model and algorithm in reproducing the nonlinear response of masonry material due to damage localization. Finally, a masonry arch model is studied, comparing the numerical results with experimental ones; it is show the ability of the proposed model to simulate the global behaviour of the arch structure in term of ultimate load and collapse mechanism.
      Issue No: Vol. 0
       
  • Evaluation of seismic mitigation of embankment mode

    • Authors: Abdollah Namdar
      Abstract: Conducting experiment on embankment model by shaking table could be an accurate method to evaluate the behavior of embankment or any structures under seismic loading. In this research work, in order to assess the function of seismic force and accurate placement of dense zone in the embankment model,  the results of three experiments have been considered. To evaluate the reaction of the embankment model, it was measured the stress in the system and photographs were taken. The results of three experiments indicated that suitable arrangement of dense zone is the main factor at the play in embankment stability, and in predicting the possibility of embankment behavior.
      Issue No: Vol. 0
       
  • Coating by the Cold Spray Process: a state of the art

    • Authors: Ramin Ghelichi, Mario Guagliano
      Abstract: A brief description of cold spray coating process is presented. This paper intends to review some the previous works which are mostly about the influences of the cold spray parameters, mostly the surface of the substrate, on the deposition efficiency (DE). Almost all the important parameters, with more focus on the roughness of the substrate, on increasing the DE are briefly studied; this review also includes a description of application of cold spray and of some important effect of this method on substrate properties. On this basis, some possible development in this field of research are drawn and discussed.
      Issue No: Vol. 0
       
  • Variation of stress intensity factor and elastic T-stress along the
           crack-front in finite thickness plates

    • Authors: K. G. Kodancha, S. K. Kudari
      Abstract: Non-singular terms in the series expansion of the elastic crack-tip stress fields, commonly referred to as the T-stress. The T-stress is as an additional stress field characterizing parameter to stress intensity factor (K) in the analysis of cracked bodies. T-stress is used as an important constraint parameter in the fracture analysis. In this investigation, three-dimensional finite element analyses have been conducted to compute the elastic T-stress considering a single edge notched tensile (SENT) specimen with varied thickness and a/W ratio. The results indicate that the T-stress depends on the specimen thickness and significantly varies along the crackfront from surface to centre of the specimen. The T-stress results obtained in the present analysis together with corresponding KI values can be used for analysis of constraint effects in a fracture specimen.
      Issue No: Vol. 0
       
  • Structural durability assessment of welded offshore K-nodes by different
           local design concepts

    • Authors: C. M. Sonsino
      Abstract: The structural durability design of complex welded structures should not rely only on one single design method but should apply different methods for assuring the reliability of the assessment. In this context the application of the structural stress concept, notch stress concept and crack propagation concept are discussed through the example of K-nodes used in energetic offshore constructions like oil platforms or wind power plants, presenting the state of the art.

      Issue No: Vol. 0
       
  • Comportamento a fatica dei giunti saldati in funzione della densità di
           energia di deformazione locale: influenza dei campi di tensione singolari
           e non singolari

    • Authors: Paolo Lazzarin
      Abstract: In the Strain Energy Density (SED) approach for fatigue strength assessments of welded joints a well-defined control volume is considered. This volume surrounds the weld root or weld toe, both modelled like sharp (zero radius) V-notches with different opening angles. The volume becomes a circular sector under plane strain conditions, with the radius being about 0.3 mm for welded joints made of structural steel. The mean value of the SED mainly depends on the singular stress fields when the main plate thickness is large enough, whereas the influence of the T-stress component cannot be neglected in the case of thin-walled welded joints. Both contributions are directly accounted for by using finite element models, also when the relevant meshes are quite coarse. This fact makes the application of the SED approach easier than any stress-based approach in the case of complex structures.
      Due to three-dimensional effects, a non conventional out-of-plane singular mode can be present, in addition with respect to modes I and II of the Williams’ solution. This out-of-plane mode, analogous to the Mode III, is discussed here with reference to welded (seam) lap joints under tensile-shear loads.
      Issue No: Vol. 0
       
  • Resistenza a fatica di strutture in leghe di alluminio: normative a
           confronto e verifica sperimentale

    • Authors: B. Atzori, G. Meneghetti, B. Rossi
      Abstract: Le problematiche relative all’utilizzo delle normative nell’ambito della progettazione a fatica di strutture in leghe di alluminio sono state di recente affrontate in numerosi lavori che hanno messo in luce sia le difficoltà legate al passaggio da normative oramai obsolete ad altre di nuova concezione, ma di caratteristiche e struttura completamente diverse, che la sostanziale carenza anche all’interno delle più recenti normative europee, quale l’Eurocodice 9, di molti risultati e metodi sviluppati in anni di ricerca scientifica e ormai indiscutibilmente consolidati. Il presente lavoro si propone di approfondire entrambe le tematiche tramite il confronto tra risultati sperimentali tratti da letteratura e le corrispondenti curve di resistenza proposte rispettivamente dalla normativa italiana UNI 8634, di recente ritirata, e dall’Eurocodice 9. In questo modo verranno messe in luce le differenze tra i valori di resistenza proposti dalle due norme e verrà illustrata sia la corrispondenza a volte poco soddisfacente con i risultati sperimentali che le conseguenze dovute alla mancata applicazione di assodati risultati teorici.
      Issue No: Vol. 0
       
  • Fatigue life estimation in welded joints under multiaxial loadings

    • Authors: Andrea Carpinteri, Andrea Spagnoli, Sabrina Vantadori
      Abstract: Welded joints are frequently locations for cracks initiation and propagation that may cause fatigue failure of engineering structures. Biaxial or triaxial stress-strain states are present in the vicinity of welded joints, due to local geometrical constraints, welding processes and/or multiaxial external loadings. Fatigue life evaluation of welded joints under multiaxial proportional (in-phase) cyclic loading can be performed by using conventional hypotheses (e.g. see the von Mises criterion or the Tresca criterion) on the basis of local approaches. On the contrary, the fatigue life predictions of welded joints under non-proportional (out-of-phase) cyclic loading are generally unsafe if these conventional hypotheses are used. A criterion initially proposed by the authors for smooth and notched structural components has been extended to the fatigue assessment of welded joints. In more detail, fatigue life of welded joints under multiaxial stress states can be evaluated by considering a nonlinear combination of the shear stress amplitude (acting on the critical plane) and the amplitude and the mean value of the normal stress (acting on the critical plane). In the present paper, fatigue lifetimes predicted through the proposed criterion are compared with experimental fatigue life data available in the literature, related to fatigue biaxial tests.
      Issue No: Vol. 0
       
  • Modellazione efficiente agli elementi finiti per l’analisi a collasso di
           strutture incollate complesse

    • Authors: D. Castagnetti, A. Spaggiari, E. Dragoni
      Abstract: Il lavoro verifica l’applicabilità di un modello semplificato agli elementi finiti per l’analisi a collasso post elastico di strutture incollate complesse in parete sottile. Al fine di superare le limitazioni dei modelli di letteratura come l’uso di elementi speciali, il lavoro sfrutta un modello ridotto già presentato dagli autori in campo elastico. Tale modello è basato sulla rappresentazione degli aderendi mediante elementi semistrutturali (piastre o gusci) e dell’adesivo per mezzo di speciali elementi coesivi. La continuità strutturale tra aderendi e adesivo è ottenuta mediante vincoli interni (tied mesh) che accomunano i gradi di libertà dei nodi mutuamente affacciati di aderendi ed adesivo. La struttura analizzata è un simulacro di incollaggio industriale e produce nella strato adesivo una sollecitazione complessa, analizzabile solo con modelli numerici. Si considera una struttura tubolare in parete sottile a sezione quadrata, fatta di due spezzoni posti testa a testa e incollati con fazzoletti di lamiera sui quattro lati. La struttura è sottoposta a flessione a tre punti fino al cedimento e la zona incollata posta disassata rispetto al punto di applicazione del carico riceve una sollecitazione indiretta. I risultati dell’analisi FEM, confrontati direttamente con le curve sperimentali forza-spostamento, evidenziano una buona accuratezza del metodo, in termini di rigidezza, forza massima e comportamento post elastico della struttura, accompagnati da ridotte dimensioni del modello e tempi di calcolo molto contenuti. Grazie a questi vantaggi, la procedura si presta ad effettuare l’analisi di strutture incollate complesse, altrimenti ingestibili se affrontate con una modellazione agli elementi finiti tradizionale.
      Issue No: Vol. 0
       
  • Verifica a fatica dei giunti saldati sulla base di misure di deformazione
           locale

    • Authors: V. Dattoma, R. Nobile, F.W. Panella
      Abstract: Lo studio della resistenza a fatica delle giunzioni saldate rappresenta un campo di prova molto interessante dal punto di vista scientifico, con ricadute pratiche altrettanto importanti. Si tratta in generale di fornire dei metodi di verifica e progetto deterministici, come è proprio dell’ingegneria, per revedere il comportamento meccanico di un materiale che, quando è sotto forma di saldatura, cambia le sue proprietà meccaniche e microstrutturali rispetto al materiale base, si dispone in una geometria locale del cordone estremamente variabile e non definibile a priori, è infine affetto da campi di tensione residua  non proprio trascurabili. In questo lavoro, partendo da una breve panoramica sui principali indicatori e metodi che sono stati utilizzati nel corso degli anni per la stima dello stato di sollecitazione in un giunto saldato e della vita residua a fatica, si presenta l’approccio basato sulla misura della deformazione locale che è stato seguito da diversi autori nel corso degli anni, evidenziandone i vantaggi ma anche le limitazioni rilevate attraverso le numerose attività sperimentali direttamente eseguite.

      Issue No: Vol. 0
       
  • Fatigue design of welded joints using the finite element method and the
           2007 ASME Div. 2 Master curve

    • Authors: T. Marin, G. Nicoletto
      Abstract: Fatigue design of welded structures is primarily based on a nominal stress; hot spot stress methods or local approaches each having several limitations when coupled with finite element modeling. An alternative recent structural stress definition is discussed and implemented in a post-processor. It provides an effective means for the direct coupling of finite element results to the fatigue assessment of welded joints in complex structures. The applications presented in this work confirm the main features of the method: mesh-insensitivity, accurate crack location and life to failure predictions.
      Issue No: Vol. 0
       
  • Utilizzo della tensione di picco per la verifica a fatica dei giunti
           saldati d’angolo con il metodo degli elementi finiti

    • Authors: G. Meneghetti
      Abstract: In questo lavoro viene applicato il metodo della tensione di picco per l’analisi della resistenza a fatica di giunti saldati con cordone d’angolo limitatamente al caso di rottura al piede del cordone di saldatura. Il metodo è un’applicazione ingegneristica dell’approccio locale basato sul fattore di intensificazione delle tensioni per intagli (Notch-Stress Intensity Factor, N-SIF) di modo I, che assimila il profilo del piede del cordone di saldatura ad un intaglio a V con raggio di raccordo pari a zero. Inoltre si basa sull’utilizzo della tensione di picco singolare calcolata al piede del cordone mediante un’analisi agli elementi finiti lineare elastica con elementi aventi una prefissata dimensione, assunta pari a 1 mm in questo lavoro. La relativa semplicità di utilizzo e la robustezza del metodo lo rendono adatto all’applicazione in ambito industriale.

      Issue No: Vol. 0
       
  • Simulazione della propagazione di difetti a fatica mediante il modello di
           zona coesiva

    • Authors: A. Pirondi, F. Moroni
      Abstract: Le giunzioni incollate guadagnano sempre più mercato, nel campo delle costruzioni in genere, dove è necessario un alleggerimento delle strutture. Nel caso di geometrie di giunto semplici il dimensionamento avviene attraverso relazioni analitiche che restituiscono il valore massimo delle tensioni, il quale deve essere inferiore al limite di utilizzo dell’adesivo stesso. Quando le geometrie sono complesse l’approccio analitico diventa impraticabile, di conseguenza si provvede a verificare la correttezza della soluzione mediante analisi agli elementi finiti (EF). L’introduzione del modello di zona coesiva nell'analisi EF permette di simulare il danneggiamento ed il cedimento del giunto in condizioni quasi-statiche e impulsive. In questo articolo si vuole implementare il modello per la simulazione della propagazione a fatica di difetti, utilizzando il software agli elementi finiti ABAQUS assieme a subroutine esterne interagenti con il modello EF stesso. Un punto focale dell'implementazione sarà il calcolo automatico del tasso di rilascio di energia G in modo indipendente dalla geometria del difetto stesso. I parametri del modello ricavati da prove di tenacità a frattura e propagazione di difetti a fatica in modo I, saranno utilizzati come riferimento per la convalida dell'implementazione.
      Issue No: Vol. 0
       
  • Fatigue failure of welded connections at orthotropic bridges

    • Authors: Z.H. Qian, D. Abruzzese
      Abstract: Orthotropic decks were applied to the long span bridges after World War II due to several advantages, such as light weight, high strength, few deck joints, durability, rapid construction, life-cycle economy. The fatigue problem of orthotropic decks was realized twenty years ago since fatigue failure was found. In the past two decades large amount of studies and investigations were carried out and fruitful achievements were obtained. It was found that most of the fatigue cracks were occurred at the welded connection details, such as rib-to-deck plate, rib-to-diaphragm, and rib-to-diaphragm-to-deck plate (RDDP). These connections are sensitive to fatigue cracking due to high concentrated stress and residual stress at welded connections. In this paper practical fatigue failure cases at the welded connections, ease to occur fatigue cracking, are presented, and analyzed through a numerical modeling of orthotropic deck via FE (finite element) software. Furthermore, the improvement technologies of fatigue are also discussed. The results of the analysis can be contributed to the evaluation of the fatigue design for the orthotropic deck.
      Issue No: Vol. 0
       
  • L’importanza del “parametro energetico” temperatura per la
           caratterizzazione dinamica dei materiali

    • Authors: A. Risitano, G. Risitano
      Abstract: Le esperienze maturate nel campo dell’analisi termica di materiali utilizzati nelle costruzioni meccaniche [1,2,3] hanno permesso di evidenziare come il rilievo della temperatura (terzo parametro) in prove statiche e dinamiche costituisca un indicatore molto importante ai fini della caratterizzazione dinamica del materiale. Essendo il rilascio termico funzione dell’energia applicata per portare a rottura il materiale, il rilievo di parametri ad esso legati, induce a nuovi ipotesi e definizioni di limiti di fatica e resistenza a tempo. Mediante l’analisi termica è possibile valutare anche parametri correlabili con il valore limite di energia a rottura El del materiale. In [4] era stato già messo in evidenza da A. Risitano e Altri che, in prove statiche di trazione, l’inizio della zona di prima plasticizzazione del materiale, in termine di tensione, era osservabile dalla curva di variazione di temperatura deltaT con il procedere della prova. Nello stesso lavoro si evidenziava come la velocità di prova avesse poca influenza sui valori della variazione di temperatura specialmente durante la fase elastica. Operando con sensori sempre più precisi e per obbiettivi rivolti alla ricerca dell’energia limite a rottura è stato osservato dagli autori che il seguire la variazione della temperatura sulla superficie del provino, in prove statiche di trazione, permette di legare i classici valori di resistenza all’oscillazione '0 con una “temperatura limite” T0 corrispondente all’inizio di andamenti non lineari della stessa. In questa sede si evidenzia un modello di comportamento fisico del materiale durante le prova di trazione che giustifica, in modo semplice, la capacità di risalire, attraverso la conoscenza sperimentale del limite di comportamento termo-elastico, ai classici parametri di resistenza a fatica. Viene riportato, a titolo di esempio, il risultato relativo a provini piatti forati in acciaio facenti parte di una serie utilizzati per altri scopi (formeranno oggetto di altra pubblicazione) con i quali anche mediante prova statica si è determinata la loro resistenza all’oscillazione.
      Issue No: Vol. 0
       
  • Sulla stima della vita a fatica di giunti saldati soggetti a carichi
           multiassiali ad ampiezza variabile

    • Authors: L. Susmel, R. Tovo, D. Benasciutti
      Abstract: Nel presente articolo viene proposta una nuova metodologia di progettazione a fatica, basata sull’utilizzo del metodo delle Curve di Wöhler Modificate, per la previsione della vita a fatica di giunzioni saldate, sia in acciaio che in alluminio, soggette a carichi multiassiali ad ampiezza variabile. In particolare, il criterio delle Curve di Wöhler Modificate è stato applicato determinando l’orientazione del piano critico mediante il Metodo della Massima Varianza, ovvero definendo il piano critico come quello contenente la direzione che sperimenta la massima varianza della tensione tangenziale risolta. L’accuratezza della metodologia di progettazione a fatica proposta nella presente memoria è stata valutata mediante due serie di dati sperimentali di letteratura ottenute sollecitando, sia ad ampiezza costante che variabile, giunti saldati tubo-piastra in acciaio e lega di alluminio con carichi di flesso/torsione in fase e sfasati di 90°. Il criterio delle Curve di Wöhler Modificate, applicato in concomitanza con il Metodo della Massima varianza, si è dimostrato capace di fornisce stime accurate della durata a fatica anche in presenza di sollecitazioni multiassiali ad ampiezza variabile, e questo sia quando applicato in termini di tensioni nominali che in termini di tensioni di “hot-spot”.
      Issue No: Vol. 0
       
  • Il gradiente implicito nella verifica a fatica di giunzioni saldate
           sollecitate a fatica

    • Authors: R. Tovo, P. Livieri
      Abstract: L’incremento delle potenzialità di strumenti per la progettazione assistita (come modellatori solidi e strumenti per FEA in grado di gestire modelli molto complessi) permette di ipotizzare lo sviluppo di strumenti numerici specifici per la previsione della resistenza a fatica delle giunzioni saldate. Tali strumenti potrebbero essere in grado di valutare l’influenza di geometria e carichi senza la necessità di elaborazioni successive, e spesso, del progettista (come nelle tensioni di Hot Spot). Il presente lavoro propone una metodologia di calcolo adatta alla previsione della vita a fatica di giunzioni saldate complesse. Un indice di resistenza è ottenuto innanzitutto risolvendo il problema tensionale completamente in modo numerico (agli elementi finiti) . La previsione della resistenza a fatica, è calcolata facendo uso di un modello analitico basato sul gradiente implicito che assume come tensione efficace la tensione equivalente non locale derivante dalla tensione principale. Dapprima verrà tarato il metodo su prove sperimentali eseguite su giunzioni saldate a croce, successivamente il metodo verrà utilizzato per la verifica a fatica di giunzioni saldate più complesse a sviluppo tridimensionale.
      Issue No: Vol. 0
       
  • Analisi basata sugli sforzi locali della resistenza a fatica di giunzioni
           incollate di materiali compositi

    • Authors: S. Beretta, A. Bernasconi, A. Pirondi, F. Moroni
      Abstract: Il lavoro prende spunto dai risultati di un’analisi sperimentale del comportamento a fatica di giunzioni incollate di materiali compositi laminati di elevato spessore formati da strati di unidirezionale e di tessuto di fibra di carbonio. I giunti sono stati realizzati in modo tale da saggiare l’influenza della lunghezza di sovrapposizione (da 25,4 mm a 110,8 mm), della forma del giunto (con e senza rastremazione), e della composizione degli aderendi (sostituzione di uno degli aderendi in composito con uno in acciaio). Mediante analisi 2D elastiche con il metodo degli elementi finiti sono state ricavate le distribuzioni degli sforzi all’interno dello strato di adesivo, al fine di individuare un parametro utile alla descrizione del comportamento a fatica in termini di sforzi locali - numero di cicli a rottura. Il ruolo della fase di propagazione viene discusso alla luce di osservazioni dell’avanzamento della frattura, condotta su alcuni dei giunti testati.
      Issue No: Vol. 0
       
  • The theory of critical distances applied to problems in fracture and       />fatigue of bone

    • Authors: David Taylor, Saeid Kasiri, Emma Brazel
      Abstract: The theory of critical distances (TCD) has been applied to predict notch-based fracture and fatigue in a wide range of materials and components. The present paper describes a series of projects in which we applied this approach to human bone. Using experimental data from the literature, combined with finite element analysis, we showed that the TCD was able to predict the effect of notches and holes on the strength of bone failing in brittle fracture due to monotonic loading, in different loading regimes. Bone also displays short crack effects, leading to R-curve data for both fracture toughness and fatigue crack propagation thresholds; we showed that the TCD could predict this data. This analysis raised a number of questions for discussion, such as the significance of the L value itself in this and other materials. Finally, we applied the TCD to a practical problem in orthopaedic surgery: the management of bone defects, showing that predictions could be made which would enable surgeons to decide on whether a bone graft material would be needed to repair a defect, and to specify what mechanical properties this material should have.
      Issue No: Vol. 0
       
  • Failure prediction of T-peel adhesive joints by different cohesive laws
           and modelling approaches

    • Authors: Alessandro Pirondi
      Abstract: In this work, Cohesive Zone Modelling (CZM) was used to simulate failure of T-peel bonded joints with 1.5mm thick adherends, respectively, bonded toghether with Loctite Multibond 330 adhesive. The fracture toughness and load-opening behaviour recorded in previous experiments on bonded Double Cantilever Beam (DCB) specimens were taken as reference to calibrate CZM parameters. Two-dimensional models were analysed using the FE code ABAQUS. The failing interface was modeled with the cohesive elements available in this software. The influence of: i) different cohesive law shapes, ii) modeling the presence of the adhesive layer explicitly, was studied.
      Issue No: Vol. 0
       
  • Sismabeton: a new frontier for ductile concrete

    • Authors: Bernardino Chiaia, Alessandro P. Fantilli, Paolo Vallini
      Abstract: The high ductility of Fiber Reinforced Self-consolidating concrete (called Sismabeton) can be developed not only in tension but also in compression. This aspect is evidenced in the present paper by measuring the mechanical response of normal concrete (NC), plain self-compacting concrete (SC) and Sismabeton cylindrical specimens under uniaxial and triaxial compression. The post-peak behaviour of these specimens is defined by a non-dimensional function that relates the inelastic displacement and the relative stress during softening. Both for NC and SC, the increase of the fracture toughness with the confinement stress is observed. Conversely, Sismabeton shows, even in absence of confinement, practically the same ductility measured in normal and self-compacting concretes with a confining pressure. Thus, the presence of Sismabeton in compressed columns is itself sufficient to create a sort of active distributed confinement.
      Issue No: Vol. 0
       
  • Numerical analysis of soil bearing capacity by changing soil
           characteristics

    • Authors: Abdoullah Namdar, Mehdi Khodashenas Pelko
      Abstract: In this research work by changing different parameters of soil foundation like density, cohesion and foundation depth and width of square foundation at angle of friction of 0° to 50° with increment of 5°, numerically safe bearing capacity of soil foundation is calculated and it is attempted to assess economical dimension of foundation as well as understanding variation range of bearing capacity at different degree. It could help of civil engineering in design of foundations at any situation.
      Issue No: Vol. 0
       
  • A dimensional analysis approach to fatigue in quasi-brittle materials

    • Authors: Marco Paggi
      Abstract: In this study, a generalized Barenblatt and Botvina dimensional analysis approach to fatigue crack growth is proposed in order to highlight and explain the deviations from the classical power-law equations used to characterize the fatigue behaviour of quasi-brittle materials. According to this theoretical approach, the microstructural-size (related to the volumetric content of fibres in fibre-reinforced concrete), the crack-size, and the size-scale effects on the Paris’ law and the Wöhler equation are presented within a unified mathematical framework. Relevant experimental results taken from the literature are used to confirm the theoretical trends and to determine the values of the incomplete self-similarity exponents. All these information are expected to be useful for the design of experiments, since the role of the different dimensionless numbers governing the phenomenon of fatigue is herein elucidated.
      Issue No: Vol. 0
       
  • Mechanical characterization of metal-ceramic composites

    • Authors: G. Bolzon, M. Bocciarelli, E.J. Chiarullo
      Abstract: Metal-ceramic composites represent a class of quasi-brittle materials for advanced structural applications that require adequate mechanical characterization. Difficulties and costs associated with material production and specimen extraction prevent the execution of a statistically meaningful number of standard laboratory tests. Parameter calibration methodologies based on instrumented indentation and inverse analysis represent fast and reliable identification procedures in the present context, as shown by the present contribution, based on some experience achieved in the framework of the European Network of Excellence on ‘Knowledge-based Multi-component Materials for durable and safe performance’ (KMM-NoE).
      Issue No: Vol. 0
       
  • Complexity: a new paradigm for fracture mechanics

    • Authors: A. Carpinteri, S. Puzzi
      Abstract: The so-called Complexity Sciences are a topic of fast growing interest inside the scientific community. Actually, researchers did not come to a definition of complexity, since it manifests itself in so many different ways [1]. This field itself is not a single discipline, but rather a heterogeneous amalgam of different techniques of mathematics and science. In fact, under the label of Complexity Sciences we comprehend a large variety of approaches: nonlinear dynamics, deterministic chaos theory, nonequilibrium thermodynamics, fractal geometry, intermediate asymptotics, complete and incomplete similarity, renormalization group theory, catastrophe theory, self-organized criticality, neural networks, cellular automata, fuzzy logic, etc. Aim of this paper is at providing insight into the role of complexity in the field of Materials Science and Fracture Mechanics [2-3]. The presented examples will be concerned with the snap-back instabilities in the structural behaviour of composite structures (Carpinteri [4-6]), the occurrence of fractal patterns and self-similarity in material damage and deformation of heterogeneous materials, and the apparent scaling on the nominal mechanical properties of disordered materials (Carpinteri [7,8]). Further examples will deal with criticality in the acoustic emissions of damaged structures and with scaling in the time-to-failure (Carpinteri et al. [9]). Eventually, results on the transition towards chaos in the dynamics of cracked beams will be reported (Carpinteri and Pugno [10,11]).
      Issue No: Vol. 0
       
  • Modello di tenuta della flangia bullonata, senza guarnizione, mediante
           l’analogia della meccanica della frattura di una fessura parzialmente
           aperta

    • Authors: M. Beghini, L. Bertini, C. Santus, C. Cagnarini, P. Romanello
      Abstract: I compressori centrifughi di elevate dimensioni non permettono l’utilizzo di guarnizioni deformabili, per cui le due metà della flangia di connessione sono forzate mediante bullonatura e la tenuta è affidata al contatto completo delle due superfici. La previsione della pressione di perdita è un aspetto di progetto di notevole interesse per questa tecnologia. L’azione della pressione interna sollecita la separazione delle superfici della flangia, che invece è contrastata dall’azione di serraggio dei bulloni. Il presente lavoro propone un modello per prevedere la condizione di perdita, basato sulla meccanica della frattura. Dato che le due superfici della flangia sono semplicemente a contatto, esse costituiscono una vera e propria fessura parzialmente aperta. Come ben noto il fattore di intensificazione di una fessura parzialmente aperta è nullo. Imponendo che le due superfici siano parzialmente separate ad una distanza fino al bordo del foro del bullone (che offre un canale di fuoriuscita per il fluido in pressione), e imponendo la condizione di fattore di intensificazione nullo, è possibile determinare la pressione di perdita, analiticamente, mediante la tecnica delle “weight functions” (o “funzioni peso”). Il presente lavoro riporta una positiva validazione del modello proposto mediante sia simulazione numerica sia risultati sperimentali in piena scala e in scala ridotta. Il modello analitico proposto offre uno strumento di progetto di immediata implementazione per comparare diverse geometrie di flangia bullonata.
      Issue No: Vol. 0
       
  • Valutazione della capacità di rientro alla base di un elicottero in
           presenza di danno balistico ad un albero di trasmissione della linea
           rotore di coda

    • Authors: L. Giudici, A. Manes, M. Giglio
      Abstract: Nella progettazione di un elicottero militare, destinato ad operare a bassa quota e in ambiente
      ostile, il danneggiamento di componenti critici, conseguente ad impatto balistico, riveste un ruolo primario nella
      valutazione delle possibilità di sopravvivenza dell’intera macchina. In questo articolo è quindi proposto uno
      studio sperimentale, suddiviso in diverse fasi, riguardante la verifica della capacità di un elicottero di portare a
      termine una missione di rientro alla base a potenza ridotta e in presenza di danneggiamento balistico ad un
      albero di trasmissione della linea rotore di coda.
      Il lavoro ha richiesto dapprima l’esecuzione, su esemplari del componente in esame, di prove sperimentali di
      impatto balistico, condotte utilizzando un proiettile calibro 7.62 NATO. Successivamente su ciascun albero
      danneggiato sono state eseguite prove torsionali statiche ed a fatica, il cui scopo è stato verificare la resistenza
      residua del componente all’applicazione di opportuni carichi rappresentativi delle sollecitazioni riscontrate
      durante la missione di rientro.

      Issue No: Vol. 0
       
  • Modello coesivo per l’avanzamento di fratture mediante rilascio nodale
           di strutture discretizzate con elementi finiti

    • Authors: M. Minotti, P. Salvini, G. Mannucci
      Abstract: La simulazione numerica della propagazione di una frattura in MODO I, viaggiante ad elevata
      velocità in un acciaio a comportamento duttile è realizzata attraverso un modello coesivo che governa la
      distribuzione delle forze di rilascio nodale. Come noto, la ricerca di un valore di tensione all’apice non ha alcun
      senso nel caso elastico; infatti, la tensione può essere valutata solo mediante fattori di campo. Nel caso elasto-
      plastico, incrudimento e softening di origine geometrica o legato al progressivo danneggiamento influiscono
      decisamente sull’andamento esponenziale del campo tensionale. È possibile comunque individuare un valore di
      riferimento, di entità finita, mediante estrapolazione delle tensioni elasto-plastiche nella zona di inizio softening
      della frattura. Tale grandezza può essere presa come fattore di riferimento per il calcolo delle forze di rilascio
      coesive e quindi dell’energia dissipata. Nel lavoro viene discusso come determinare, dal campo di tensione
      elasto-plastico locale, il valore che governa la zona coesiva al variare del T-stress.

      Issue No: Vol. 0
       
  • Modello numerico per la simulazione e l’ottimizzazione di controlli non
           distruttivi con ultrasuoni

    • Authors: A. Pantano, D. Cerniglia
      Abstract: I controlli non distruttivi basati sull’impiego di ultrasuoni sono ampiamente usati per la loro efficacia e affidabilità nel rilevamento di difetti. La generazione di onde ultrasonore e la propagazione in strutture di forma non regolare sono difficili da analizzare, soprattutto se la sorgente impiegata è un laser. Le tecniche numeriche per la simulazione del fenomeno reperibili in letteratura mostrano limiti di applicabilità per frequenze nel campo dei MHz e lunghezze d’onda molto corte. In questo lavoro presentiamo un metodo numerico in grado di risolvere accuratamente ed efficientemente problemi di generazione di onde ultrasonore tramite laser, con frequenze nel range dei MHz, e di propagazione in corpi relativamente estesi. La ricezione viene simulata con la propagazione degli ultrasuoni in aria, al fine di poter ottimizzare la configurazione completa per controlli non distruttivi con ultrasuoni senza contatto. Diverse configurazioni di ispezione sono state prima simulate tramite l’analisi numerica e poi riprodotte sperimentalmente per confrontare i risultati.
      Issue No: Vol. 0
       
  • Caratterizzazione microstrutturale e prove di resilienza su giunti
           Friction Stir Welding e Linear Friction Welding di compositi a matrice
           metallica

    • Authors: L. Ceschini, A. Morri, F. Rotundo, G.L. Garagnani, M. Merlin
      Abstract: In questo studio sono stati caratterizzati giunti Friction Stir Welding e Linear Friction Welding su
      compositi a matrice in lega di alluminio e rinforzo particellare ceramico. Il processo FSW è stato applicato a due
      compositi ottenuti con processo fusorio, quindi estrusi e trattati termicamente T6: AA6061/20%vol.Al2O3p e
      AA7005/10%vol.Al2O3p. I giunti LFW sono stati invece realizzati su un composito con matrice in lega di
      alluminio e rinforzo particellare in carburo di silicio, ottenuto mediante metallurgia delle polveri, quindi forgiato
      e trattato termicamente T4: AA2124/25%vol.SiCp. Sono stati esaminati gli effetti della saldatura sulle
      caratteristiche microstrutturali dei giunti, avvalendosi di tecniche di microscopia ottica con analisi di immagine e
      di microscopia elettronica in scansione (SEM) con microsonda a dispersione di energia (EDS). Sono state
      quindi condotte prove di resilienza con pendolo strumentato Charpy. Lo studio dei meccanismi di
      danneggiamento è stato effettuato mediante analisi al SEM delle superfici di frattura. Entrambi i processi di
      saldatura hanno portato a giunti sostanzialmente esenti da difetti. La microstruttura dei cordoni è risultata
      dipendente sia dalle caratteristiche microstrutturali iniziali dei compositi considerati, sia dalla tipologia di
      processo di saldatura. Nel caso dei compositi AA6061/20%Al2O3p e AA7005/10%Al2O3p saldati FSW si è
      osservato un sostanziale incremento di resilienza, rispetto al materiale base, in conseguenza dell’affinamento dei
      grani della matrice, della riduzione della dimensione media delle particelle di rinforzo e della loro spigolosità,
      indotte dal processo di saldatura. Il composito AA2124/25%SiCp saldato LFW ha presentato valori di resilienza
      confrontabili con quelli del materiale base, in conseguenza, soprattutto, dei limitati effetti della saldatura su
      dimensione e distribuzione delle particelle di rinforzo.
      Issue No: Vol. 0
       
  • An approach for the modeling of interface-body coupled nonlocal damage

    • Authors: S. Marfia, E. Sacco, J. Toti
      Abstract: Fiber Reinforced Plastic (FRP) can be used for strengthening concrete or masonry constructions.
      One of the main problem in the use of FRP is the possible detachment of the reinforcement from the support
      material. This paper deals with the modeling of the FRP-concrete or masonry damage interface, accounting for
      the coupling occurring between the degradation of the cohesive material and the FRP detachment. To this end,
      a damage model is considered for the quasi-brittle material. In order to prevent strain localization and strong
      mesh sensitivity of the solution, an integral-type of nonlocal model based on the weighted spatial averaging of a
      strain-like quantity is developed. Regarding the interface, the damage is governed by the relative displacement
      occurring at bond. A suitable interface model which accounts for the mode I, mode II and mixed mode of
      damage is developed. The coupling between the body damage and the interface damage is performed
      computing the body damage on the bond surface. Numerical examples are presented.
      Issue No: Vol. 0
       
  • La modellazione microstrutturale di materiali a struttura eterogenea:
           princìpi ed applicazioni

    • Authors: Luca Collini
      Abstract: Molti problemi della Meccanica e Fisica dei Solidi e della Scienza dei Materiali, non sono
      facilmente risolvibili con gli approcci tradizionali. Oltre allo studio delle proprietà effettive dei solidi eterogenei,
      vi è la crescente necessità di incorporare un maggiore numero di informazioni sui meccanismi di deformazione e
      danneggiamento generati alla microscala, anche per i materiali abitualmente considerati omogenei.
      Micromeccanismi di cavitazione e concentrazioni locali di tensione e deformazione, sono indispensabili per
      spiegare fenomeni non-lineari come la rottura di fatica o il cedimento duttile, altrimenti non inquadrabili con
      approcci classici di tensioni e deformazioni medie. La micromeccanica si occupa della determinazione precisa, o
      di una stima accurata, di grandezze di campo microstrutturali locali. In questo lavoro sono illustrati i princìpi
      che sono alla base dell’approccio micromeccanico, come i concetti di multiscala, di distribuzione statistica delle
      fasi, di descrizione mediante volumi di riferimento e di omogeneizzazione e localizzazione, e, attraverso alcune
      applicazioni pratiche delle principali tecniche di modellazione, sono illustrati e discussi criticamente i risultati
      della ricerca effettuata su varie strutture di ghisa nodulare.
      Issue No: Vol. 0
       
  • Proposta di utilizzo di metodologie termografiche per il controllo di
           qualità di componenti meccanici

    • Authors: Carmelo Clienti, Guido La Rosa, Antonino Risitano, Roberto D’Andrea
      Abstract: In base all’esperienza maturata in anni di sperimentazione sull’analisi delle caratteristiche
      meccaniche dei materiali mediante indagine termografica, nel presente lavoro è proposta una procedura per il
      controllo di qualità di componenti meccanici in linea di produzione, che è già stata argomento di brevetto.
      Lo sviluppo di questo lavoro si colloca nell’ambito del progetto FIRB “Sistemi di produzione intelligenti,
      flessibili e riconfigurabili”. L’attività svolta dal DIIM riguarda il controllo avanzato dell’affidabilità di
      componenti meccanici per l’industria automobilistica. Viene proposta, quindi, la realizzazione di una cella di
      controllo in linea di produzione capace di valutare la presenza di eventuali componenti difettosi attraverso
      l’analisi termica degli stessi, sollecitati secondo un modello predefinito.
      L’attività, svolta in questa prima fase in laboratorio, è facilmente trasferibile in linea di produzione,
      considerando la possibilità di realizzare celle di prova in ambiente controllato, con condizioni praticamente
      identiche a quelle di laboratorio, eliminando gli effetti di disturbo che possono influenzare la risposta
      dell’indagine termografica in ambiente non strutturato.
      Issue No: Vol. 0
       
  • Analisi del cedimento strutturale del braccio di una gru portuale

    • Authors: Francesco Frendo
      Abstract: Nel presente lavoro vengono discusse le cause del cedimento strutturale del braccio di una gru
      portuale a portata variabile. L’ispezione delle sezioni di rottura ha mostrato in particolare la presenza di una
      grossa fessura preesistente al momento del crollo, che si estendeva per circa metà sezione di uno degli elementi
      tubolari principali che costituiscono il traliccio del braccio.
      Al fine di stabilire le modalità del crollo, nel lavoro vengono presentati un modello per l’analisi della
      propagazione della fessura, che fa uso del metodo delle weight functions ed un modello per l’analisi di collasso
      della sezione. Le analisi condotte hanno permesso di concludere che il crollo si è verificato per collasso plastico
      della sezione ed hanno messo in evidenza come la fessura in esame, per una parte considerevole della vita, sia
      propagata in condizioni stabili con velocità di avanzamento circa costante.
      Issue No: Vol. 0
       
  • Tsunami numerical modeling and mitigation

    • Authors: Abdoullah Namdar, Asima Nusrath
      Abstract: The numerical modeling and wave theory are used in tsunami mitigation analysis. It is assumed sea
      forest is simulating offshore structure submitted to wave loads. The sea forest acts simulate break waves in
      conservation of coastal territory and facility installed over there. The result reveal that mathematical modeling
      and numerical simulation can be used to understand tsunami ability in design and urban construction, the
      research indicates reduction of water deep by sea forest resulted in reducing geometry and all wave ability.
      Issue No: Vol. 0
       
  • Numerical experiments in 2D variational fracture

    • Authors: M. Angelillo, A. Fortunato, E. Babilio, M. Lippiello, L. Cardamone
      Abstract: In the present work we present some results of numerical experiments obtained with a variational
      model for quasi-static Griffith-type brittle fracture. Essentially the analysis is based on a recent formulation by
      Francfort and Marigo the main difference being the fact that we rely on local rather than on global
      minimization. Propagation of fracture is obtained by minimizing, in a step by step process, a form of energy
      that is the sum of bulk and interface terms. To solve the problem numerically we adopt discontinuous finite
      elements based on variable meshes and search for the minima of the energy through descent methods. We use a
      sort of mesh dependent relaxation of the interface energy to get out of small energy wells. The relaxation
      consists in the adoption of a carefully tailored cohesive type interface energy, tending to the Griffith limit as the
      mesh size tends to zero.
      Issue No: Vol. 0
       
  • Previsione della resistenza a fatica in saldature per punti attraverso
           modellazione solida

    • Authors: R. Tovo, P. Livieri, S. Capetta
      Abstract: Nel presente lavoro vengono messi a confronto due metodi idonei per la verifica di giunzioni
      saldate per punti: il metodo del raggio di raccordo fittizio ed il metodo del gradiente implicito. Il primo impone
      un raggio di raccordo diverso da zero al piede o alla radice del cordone di saldatura, il secondo, invece,
      considera più semplicemente la saldatura come un intaglio acuto. Il confronto è fatto sulla capacità di prevedere
      l’affidabilità di giunti saldati per punti in acciaio aventi spessore variabile da 0.8 a 1.5 mm. Tali giunti sono
      sollecitati a taglio (giunti a semplice sovrapposizione) o a trazione (giunti a tazza). Infine, è discussa la
      condizione di convergenza delle analisi numeriche necessarie, in entrambi i metodi, per il calcolo di una tensione
      equivalente da porre a confronto direttamente con la di resistenza a fatica del materiale.
      Issue No: Vol. 0
       
  • Analisi termica per la valutazione del comportamento a fatica di provini
           soggetti a successive serie di carichi

    • Authors: Antonino Risitano, Giacomo Risitano
      Abstract: Partendo dalla osservazione che provini precedentemente danneggiati hanno un limite di fatica
      differente (vedi Miner) viene esaminato il comportamento di un acciaio soggetto a serie di carichi affaticanti al
      fine di verificare la conseguente risposta termica.
      L’esame, mediante analisi termica, delle prove di fatica su provini di acciaio C40 danneggiati a diverso grado, da
      interessanti indicazioni sul ruolo dei carichi applicati in relazione alla possibilità di produrre danno nel materiale.
      Viene messo in evidenza come la temperatura, conseguenza dell’energia consumata dal provino, possa essere
      elemento indicativo dello stato del materiale. Vengono riportate le curve di fatica e le curve di temperatura di
      provini lisci sottoposti a storie di carico diverse. Da esse si può evincere che mentre è valida la legge di linearità
      del danno ('ini/Ni= cost), la curva definita secondo la regola del Miner-Manson ('ini/Ni=1), che tiene solo
      conto del numero di volte in cui la tensione supera il limite di fatica del materiale (provini lisci), invece, non
      sempre rispecchia il reale stato di danno. Questo specialmente quando si è in presenza di carichi prossimi al
      limite di fatica che, per la sequenza dell’applicazione, possono diventare carichi affaticanti.
      Issue No: Vol. 0
       
  • Ductile cast irons: microstructure influence on fatigue crack propagation
           resistance

    • Authors: Francesco Iacoviello, Vittorio Di Cocco, Mauro Cavallini
      Abstract: Microstructure influence on fatigue crack propagation resistance in five different ductile cast irons
      (DCI) was investigated. Four ferrite/pearlite volume fractions were considered, performing fatigue crack
      propagation tests according to ASTM E647 standard (R equals to 0.1, 0.5 and 0.75, respectively). Results were
      compared with an austempered DCI. Damaging micromechanisms were investigated according to the following
      procedures:
      - “traditional” Scanning Electron Microscope (SEM) fracture surfaces analysis;
      - SEM fracture surface analysis with 3D quantitative analysis;
      - SEM longitudinal crack profile analysis
      - Light Optical Microscope (LOM) transversal crack profile analysis;
      Issue No: Vol. 0
       
  • Studio del danneggiamento mediante tomografia in luce del sincrotrone:
           impatto di un cono d’ombra sulla qualità finale delle ricostruzioni

    • Authors: Francesca Cosmi, Salvatore Scozzese, Andrea Bernasconi
      Abstract: Un’accurata osservazione della geometria tridimensionale di cricche e difetti è necessaria per lo
      studio dei meccanismi alla base del processo di danneggiamento. I metodi convenzionali utilizzati a questo
      scopo sono distruttivi o non possiedono una sufficiente risoluzione. Le tecniche di imaging che utilizzano la
      luce di sincrotrone, ed in particolare la microtomografia (micro-CT) a raggi X, invece, uniscono i vantaggi di una
      tecnica non distruttiva ad un’elevata risoluzione spaziale e risultano quindi particolarmente interessanti. Un
      limite all’applicazione di questa tecnica è costituito dalla propensione della cricca a richiudersi una volta rimosso
      il carico che ha provocato il danneggiamento, superabile attraverso l’impiego di un dispositivo in grado di
      esercitare un carico di trazione durante l’acquisizione dei dati. Facendo riferimento al set-up sperimentale della
      linea SYRMEP di Elettra, il sincrotrone di Trieste, e tralasciando per il momento i vincoli legati a pesi e
      ingombri, è possibile pensare di inserire tra camera di ionizzazione e CCD una macchina per prove di trazione
      mono-colonna commerciale, in grado di mantenere aperto il difetto per tutta la durata della tomografia. In
      questo lavoro viene valutato l’impatto di questo vincolo sulla qualità finale delle ricostruzioni.
      Issue No: Vol. 0
       
  • Analysis of the influence of the anisotropy induced by cold rolling on
           duplex and super-austenitic stainless steels

    • Authors: Angelo Finelli, Martino Labanti
      Abstract: This report contains the results obtained from the mechanical characterization tests carried out on two different stainless steel (duplex 6%Ni, 22%Cr and super-austenitic 31%Ni, 28%Cr) used for the manufacturing of pipes which are employed in the oil production. The activity has been performed in order to evaluate the effects of anisotropy, induced by cold rolling, on the mechanical characteristics of the investigated steels, measured in the three main directions. Considering the small size of the component, the method and the specimens used for the tests were not the standard one. The procedure carried out provided the strain measurement of the specimen during testing by means of resistive strain gages, bonded on the specimens.
      Issue No: Vol. 0
       
  • Investigation of crack propagation in single optical fiber composite with
           thermal influence by finite element method

    • Authors: Ahanchian Mohammad, Arzumanyan Hovhannes, Verlinski Sergey
      Abstract: Two parallel comparative ‘Conventional Method and Computer Simulation using ANSYS software’
      for prediction of crack growth and its behavior in optical fiber are studied and presented in this work.
      Corresponding finite element analysis was performed to determine the evolution of stress and strain states. The
      method is developed and combined with the modified J-integral theory to deal with this problem. The effects of
      crack length, temperature and mechanical forces are investigated by Finite Element Method in the cracked
      body. The conditions where the Mode I stress intensity factor motivate fracture occurrence is investigated and
      variations of the different cases are discussed. The most deleterious situation is found to be that wherein the
      entire model reaches rupture at some stage. The accuracy of the method is investigated through comparison of
      numerical results with computerized simulation using commercial ANSYS software.
      Issue No: Vol. 0
       
  • Analysis of crack-tip plastic zone in a Compact Tensile Shear (CTS)
           Specimen

    • Authors: C.M. Sharanaprabhu, S.K. Kudari
      Abstract: The minimum plastic zone radius (MPZR) criterion is one of the recent criterions to estimate crack initiation direction under mixed mode loading. The MPZR theory is based on the theoretical computations of plastic zone size (PZS). In this investigation, the shape and size of crack-tip plastic zones have been estimated by analytical and the elastic finite element computations in a Compact Tensile Shear (CTS) specimen under mixed mode (I/II) loading according to von Mises yield criteria. The theoretical and the finite element analysis results are compared to analyze the minimum plastic zone radius (MPZR) criterion for crack-initiation angle with reference to the loading angle and stress intensity factor.

      Issue No: Vol. 0
       
  • The interface between metallurgy and mechanics in material performance

    • Authors: M. N. James, M. Newby
      Abstract: This paper considers an important topic, and one that is often poorly understood or misinterpreted, but which is a determining factor in many aspects of the service performance of metals (and other materials). Engineering components and structures must, of necessity, provide a bridge between the macroscopic, homogeneous and generally continuum aspects of applied load and displacement, and the microscopic, heterogeneous and often non-continuum reality of material structure and behaviour. This bridge can take the form of a genuine interface between material and environment, e.g. at a surface, or can be a virtual one where the differing philosophies of design have to be merged. The interface has particular importance in circumstances where environmental influences have a key role in determining performance characteristics (e.g. creep, environmentally-assisted cracking, or corrosion), where performance is dominated by fatigue or fracture, where welding is used to join components, or where tribology plays a role. The paper focuses on the problems associated with cracking and uses case study examples drawn from engineering practice to illustrate the role of metallurgical factors in mechanical performance of materials.
      Issue No: Vol. 0
       
  • Influence of mean stress on the fatigue strength of ASTM A743 CA6NM alloy
           steel

    • Authors: B. Lobato da Silva, J. L. de Almeida Ferreira, F. Oliveira, J. A. Araújo
      Abstract: The objective of this work is to evaluate the effects of mean stress on the fatigue behavior of ASTM A743 CA6NM alloy steel. It is used in several hydrogenator turbine components. In order to achieve it, 33 specimens were experimentally evaluated under axial loads with stress ratio of - 1 and more 60 specimens were tested under stress ratio 0, 1/3 and 2/3. Based on the obtained results it was possible to determine parameters that describe the fatigue behavior of the evaluated material, obtain its S-N curves, its endurance limit and its scatter bands. In the assessment of the mean stress effects of fatigue life, Goodman, Gerber, Walker and Kwofie’s relations were tested in order to evaluate the validity of the use of such rules for the tested material. According to the obtained results it was possible to verify that Goodman and Gerber’s relations do not model correctly the reduction effect fatigue life and presented high scatter. The predictions of Walker and Kwofie’s relation are consistent and the Walker’s relation presented smaller scatter than Kwofie’s relation. Walker’s relation makes it possible to evaluate in a consistent way the effect of the presence of mean stresses on fatigue strength.

      Issue No: Vol. 0
       
  • High-cycle notch sensitivity of alloy steel ASTM A743 CA6NM used in
           hydrogenator turbine components

    • Authors: B. Lobato da Silva, J. L. de Almeida Ferreira, José Alexander Araújo
      Abstract: The presence of notches and other stress concentrations in turbine blades and other notch hydraulic components is a current problem in engineering. It causes a reduction of endurance limit of material. In that sense, specimens of the ASTM A743 CA6NM alloy steel using in several hydrogenator turbine components was tested. The specimens were tested under uniaxial fatigue loading with a load ratio equal to -1, and the considered stress concentration factors, Kt, values, calculated with respect to net area, were 1.55, 2.04 and 2.42. In order to determine the fatigue limit for such notch type, a reduction data method by Dixon and Mood, Staircase method was used. This approach is based on the assumed target distribution of the fatigue limit. For such geometry at least 8 specimens were tested. In addition, the Peterson and Neuber’s notch fatigue factor were compared through fatigue notch reduction factor, Kf, obtained from experimental data. According to results obtained it was possible to conclude that the tested material is less sensitive to notches than the prediction of the Peterson and Neuber’s empirical models.

      Issue No: Vol. 0
       
  • Numerical study of fracture arrest on snow cover

    • Authors: B. M. Chiaia, B. Frigo
      Abstract: Under the hypothesis of a perfectly brittle phenomenon, avalanche triggering can be investigated numerically by means of Linear Elastic Fracture Mechanics (LEFM). Since, however, the real phenomenon is intrinsically dynamical, another aspect to investigate is represented by dynamic fracture propagation. In this paper, we model dynamic crack propagation into a dry snow slab and we investigate the possibility to arrest the crack propagation through the presence of weak zones distributed along the extension of the snow slope. Assuming that the weak layer is almost collapsed, we simulate the efficiency of artificial voids in the slab to arrest fracture propagation, into the framework of Dynamical Fracture Mechanics. We put forward here a new philosophy for the use of artificial discontinuities (void) into the snowpack able to perform as crack arresters  distributed along the snow slope area: the target is to split a large avalanche slab into smaller slabs, causing small avalanches to propagate with less catastrophic effects.

      Issue No: Vol. 0
       
  • Influence of dipping time on cracking during bending of hot dip galvanized
           coatings with Sn and Ti contents

    • Authors: V. Di Cocco, L. Zortea
      Abstract: In the last years, the attention to environmental topics led a new approach solution in classical protection techniques, introducing innovative way oriented to optimize different coating properties. Hot-dip galvanizing is a classical process aimed to generate coatings on iron-based surfaces, used unchanged since 200 years: some chemical elements are added in the bath with different aims (e.g., Pb is really important for its fluidizing properties, sometimes replaced by Sn) but sometimes these elements are dangerous for human health (e.g. … Pb!).
      In this work, the influence of dipping time and coatings chemical compositions on damaging micromechanisms was investigated considering different Sn and Ti contents. Main damaging micromechanisms in hot dip zinc coated ipersandelin steel specimens were investigated by means of bending tests. Longitudinal sections of bended specimens were observed by means of a LOM (Light Optical Microscope): main damage micromechanisms were identified as longitudinal and radial cracks.

      Issue No: Vol. 0
       
  • Microstructural characterisation related to hot tearing of Al-Cu sand
           mould castings

    • Authors: M. Merlin
      Abstract: In this paper, the hot tearing behaviour in Al-(4.8'6)%Cu sand mould castings was preliminary investigated by means of microstructural examination and image analysis. A dog-bone pattern was employed for the realisation of the castings and three Al-Cu alloys with different Cu and Si contents were used. The effects of the alloy composition and of different pouring temperatures on the hot tearing behaviour of the castings were evaluated. The quantity of the eutectic phase available during solidification is considered a very important parameter for the crack healing phenomenon, in fact the eutectic liquid flows into the hot tear areas and covers parts of the cracks. The hot tear paths and surfaces were observed by means of optical and scanning electron microscopes, which showed that the fracture surfaces were dominated by bridged grain boundaries and the presence of a liquid film, in particular at higher copper concentrations. Several samples were also drawn from the zones characterised by the maximum cross-section variation and the micrographs from the optical microscope were statistically analysed by means of commercially available image analysis software. The quantitative microstructural parameters of percentage, mean area and distribution of the eutectic phase were evaluated and correlated to the capacity of the eutectic liquid to heal open fractures caused by hot tearing for the examined alloys.

      Issue No: Vol. 0
       
  • Liquefaction mathematical analysis for improvement structures stability

    • Authors: A. Namdar, A. K. Pelko, A. Nusrath
      Abstract: The stability of any structure is possible if foundation is appropriately designed. The Bandar abbas is the largest and most important port of Iran, with high seismicity and occurring strong earthquakes in this territory, the soil mechanical properties of different parts of city have been selected as the subject of current research. The data relating to the design of foundation for improvement of structure at different layer of subsoil have been collected and, accordingly, soil mechanical properties have been evaluated. The results of laboratory experiments can be used for evaluation of geotechnical characteristics of urban area for development a region with high level of structural stability. Ultimately, a new method for calculation of liquefaction force is suggested. It is applicable for improving geotechnical and structure codes and also for reanalysis of structure stability of previously constructed buildings.

      Issue No: Vol. 0
       
  • The way the mistery of the Mattei’s case was solved

    • Authors: D. Firrao, G. Ubertalli, P. Matteis, C. Pozzi
      Abstract: Enrico Mattei, the President of the Italian oil conglomerate, ENI, was about to land in Milan Linate Airport on October 27, 1962 when his airplane crashed on the ground due to a then unexplained accident. The investigation, reopened more than 30 years later, implied complete re-examining of the theories on macroscopic and lattice deformations under high velocity waves emanating from a small charge explosion.
      Various macro- and micro-structural changes are induced by an explosion and by the resulting shear stresses in metals exposed to it. At the microstructural level multiple slip bands or mechanical twins, induced from the pressure wave caused by an explosion, can be observed. The occurrence of either ones depend on the type of metal, the pressure and the strain rate. The temperature wave may also cause surface alterations. Different situations regarding stainless steels, aluminium, copper and gold alloys are analysed.
      Calculations to evaluate which deformation mechanism is eligible for different FCC metals and alloys are reported. Results of field explosion experiments are incorporated into the evaluation of microstructural signs possibly induced on metal targets by an unknown explosive event.
      Revisited theories were applied to the Mattei forensic case, reaching the conclusion that the aircraft had fallen following an on board small charge explosion.

      Issue No: Vol. 0
       
  • Esistenza del modo O in piastre tridimensionali con fori circolari ed
           ellittici soggette a modo II

    • Authors: F. Berto, C. Marangon
      Abstract: On the mode O existence in three-dimensional plates weakened by circular and elliptical holes under mode II loading It is known for long time that in a cracked plate subjected to anti-symmetric plane loading, the Poisson’s effect leads to the generation of a coupled out-of-plane singular mode (Mode O). Recent theoretical and numerical analyses have shown that this effect is present also in plates weakened by pointed V-notches and might play a role in failure initiation phenomena in plates under mode II loading particularly in the presence of large opening angle. Since the degree of singularity characterising the mode O is greater than that of mode II, the mutual incidence of the two modes depends on the component size. Dealing with circular and elliptic holes, the presence or not of the out-of-plane mode has never been discussed in the literature. The main aim of this work is to demonstrate the existence of a three-dimensional effect tied to mode O. On the basis of a large bulk of numerical results the following conclusions can be drawn: - An out-of-plane mode is present in plates weakened by U-notches and subjected to Mode II loading, as previously demonstrated for plates weakened by cracks and pointed V-notches; its intensity is not negligible also for finite values of the notch radius. - Out-of-plane mode results in a shear stress distribution symmetric with respect to the mid-plane. The intensity of this stress component strongly depends on the Poisson’s ratio. It increases as increases. - The strain energy density averaged on a given control volume which should, in principle, be material dependent is a parameter suitable for the natural of capture all three dimensional effects occurring through the plate thickness. It is surely a powerful tool in practical cases where the role played by three-dimensionality is not negligible, or is not known in detail.
      Issue No: Vol. 0
       
  • Crack propagation in micro-chevron-test samples of direct bonded
           silicon-silicon wafers

    • Authors: K. Vogel, D. Wuensch, A. Shaporin, J. Mehner, D. Billep, M. Wiemer
      Abstract: Wafer bonding describes all technologies for joining two or more substrates directly or using certain intermediate layers. Current investigations are focused on so-called low temperature bonding as a special direct bonding technology. It is carried out without intermediate layers and at temperatures below 400 °C. In addition to the wafer materials, the toughness of the bonded interface also depends on the bonding process itself. It can vary for different pre-treatments. Furthermore, an increase of the annealing temperature leads to a higher toughness of the bonded interface. The fracture toughness is a suitable value to describe the damage behaviour of the bonded interface. Based on a micro-chevron-specimen, the fracture toughness can be determined either numerically or by combining numerical analysis with experimental measurement of the maximum force. The maximum force is measured during a micro-chevron-test using a Mode I loading. The minimum of the stress intensity coefficient can be determined by a FE-simulation only. One possibility to estimate the stress intensity coefficient is the compliance method. The compliance of the whole specimen increases with a growing crack. The stress intensity coefficient can be directly derived from the simulated compliance and the crack length itself. The paper is focused on the micro-chevron-test for direct bonded silicon-silicon wafers. Additional to the estimation of dimensionless stress intensity coefficient as a function of geometry, the influence of different pre-treatments and annealing temperatures on the measured maximum force are analysed and discussed.
      Issue No: Vol. 0
       
  • Design and experimental characterization of a 350 W High Temperature PEM
           fuel cell stack

    • Authors: N. Zuliani
      Abstract: High Temperature Proton Exchange Membrane (HT PEM) fuel cell based on polybenzimidazole (PBI) polymer and phosphoric acid, can be operated at temperature between 120 °C and 180 °C. Reactants humidification is not required and CO content up to 2% in the fuel can be tolerated, affecting only marginally performance. This is what makes HT PEM very attractive, as low quality reformed hydrogen can be used and water management problems are avoided. Till nowadays, from experimental point of view, only few studies relate to the development and characterization of high temperature stacks. The aim of this work is to present the main design features and the performance curves of a 25 cells HT PEM stack based on PBI and phosphoric acid membranes. Performance curves refer to the stack operating with two type of fuels: pure hydrogen and a gas mixture simulating a typical steam reformer output. The stack voltage distribution analysis and the stack temperature distribution analysis suggest that cathode air could be used as coolant leading to a better thermal management. This could simplify stack design and system BOP, thus increasing system performance
      Issue No: Vol. 0
       
  • Fracture mechanics analyses of the slip-side joggle regions of
           wing-leading-edge panels

    • Authors: I. S. Raju, N. F. Knight, K. Song, D. R. Phillips
      Abstract: The Space Shuttle wing-leading edge consists of panels that are made of reinforced carbon-carbon. Coating spallation was observed near the slip-side region of the panels that experience extreme heating. To understand this phenomenon, a root-cause investigation was conducted. As part of that investigation, fracture mechanics analyses of the slip-side joggle regions of the hot panels were conducted. This paper presents an overview of the fracture mechanics analyses.
      Issue No: Vol. 0
       
  • Studio delle prestazioni di giunzioni incollate ibride (Strength
           evaluation of structural hybrid bonded joints)

    • Authors: F. Moroni
      Abstract: The idea of “hybrid joints” arises from the need of joining together materials, producing a tough, stiff and lightweight joint. The core concept is: use two different joining techniques, with the aim to increase the strength and gather the advantages of each technique, reducing the drawbacks. In this work hybrid joints consist in joints produced with two different kinds of joining techniques: one of them being adhesive bonding and the other being one among Resistance Spot Welding, Pop Riveting, Clinching, Self Piercing Riveting. The performance of hybrid joints are compared with those of traditional joints for the single lap joint geometry, for different geometric (plates thickness, pitch of the mechanical fastening) and environmental condition (temperature and ageing). The experimental tests are planned and therefore their results analyzed by means of Design of Experiment techniques. Results show that hybrid joints allow a significant performances enhancement with respect to simple joints when the two simple joining techniques give similar performances, while the performance of hybrid joints are only equal or lower than the those of the strongest joint when the performances of the two joining techniques are significantly different.
      Issue No: Vol. 0
       
  • Cyclic bend tests for the reliability evaluation of printed circuit boards
           under dynamic loads

    • Authors: P.F. Fuchs, Z. Major
      Abstract: The reliability of printed circuit boards under dynamic loads is a key issue in the handheld electronic products industry. In order to predict the performance of the boards in their application lifetime, different tests were developed. The current industry-wide standard testing method is a board level drop test. In this test, the boards are dropped under defined conditions until a failure in the board is detected. The main failure driver is a flexural oscillation of the board due to the impact event. As this test method has a number of drawbacks, an alternative test method was evaluated in this study. A board level cyclic bend test was used and the results of both tests were compared. A very good correlation between the methods could be observed, supporting the suitability of the board level cyclic bend test for the determination of the drop test performance. The advantages of the alternative test method were shorter testing times, better adaptability and test simulations at lower computing time. In future analysis, test simulations will be used to generate Wöhler curves related to the local stresses.
      Issue No: Vol. 0
       
  • On the overall accuracy of the Modified Wöhler Curve Method in estimating
           high-cycle multiaxial fatigue strength

    • Authors: Luca Susmel
      Abstract: The aim of the present paper is to systematically investigate the accuracy of the so-called Modified Wöhler Curve Method (MWCM) in estimating high-cycle fatigue strength of plain and notched engineering materials damaged by in-service multiaxial load histories. In more detail, the MWCM, which is a bi-parametrical critical plane approach, postulates that initiation and Stage I propagation of fatigue cracks occur on those material planes experiencing the maximum shear stress amplitude (this being assumed to be always true independently from the degree of multiaxiality of the applied loading path). Further, the fatigue damage extent is hypothesised to depend also on the maximum stress perpendicular to the critical plane, the mean normal stress being corrected through the so-called mean stress sensitivity index (i.e., a material constant capable of quantifying the sensitivity of the assessed material to the presence of superimposed static stresses). In the present investigation, the overall accuracy of the MWCM in estimating high-cycle fatigue strength was checked through 704 endurance limits taken from the literature and generated, under multiaxial fatigue loading, by testing both plain and notched samples made of 71 different materials. Such a massive validation exercise allowed us to prove that the MWCM is highly accurate, resulting in 95% of the estimates falling within an error interval equal to ±15%.
      Issue No: Vol. 0
       
  • The use of thermally expandable microcapsules for increasing the toughness
           and heal structural adhesives

    • Authors: Guillaume Pesquet, Lucas F. M. da Silva, Chiaki Sato
      Abstract: In this research, the effect of thermally expandable microcapsules (TEMs) on mode I fracture toughness of structural adhesives were investigated. The single-edge-notch bending (SENB) test was used. Firstly, a standard toughness test was performed on adhesives with microcapsules. Secondly, since TEMs start their expansion at approximately 60ºC, the next specimens were fatigue tested expecting a local heating in the notch leading to the desired expansion before being statically loaded for fracture toughness determination. Thirdly, a manual local heating at 90ºC was applied in the notch before the fracture static test. The experimental results were successfully cross-checked through a numerical analysis using the virtual crack closure technique (VCCT) based on linear elastic fracture mechanics (LEFM). The major conclusion is that fracture toughness of the modified adhesives increased as the mass fraction of the TEMs increased.
      Issue No: Vol. 0
       
  • Damages to stent stabilized left ventricular pacemaker electrodes during
           simulated lead extraction

    • Authors: Romola Laczkó, Tibor Balázs, Eszter Bognár, János Ginsztler
      Abstract: During biventricular pacemaker implantation stents can be applied for coronary sinus lead stabilization to prevent lead dislocations. A lot of issues have been raised in connection with the use of the stent. In some cases the implanted left ventricular lead must be explanted. It is crucial to avoid any injury to the heart when the electrode is removed. Another very important question concerns the type of injuries the electrode may cause during the removal process. An extraction model has been prepared using a special curve and a polymer tube. After the pacemaker leads were extracted, various microscopic examinations were executed. The findings may to make such intervention methods more successful, helping to better stabilize the electrode and to keep injuries during interventions to a minimum.
      Issue No: Vol. 0
       
  • Damage tolerance analysis of aircraft reinforced panels

    • Authors: F. Carta, A. Pirondi
      Abstract: This work is aimed at reproducing numerically a campaign of experimental tests performed for the development of reinforced panels, typically found in aircraft fuselage. The bonded reinforcements can significantly reduce the rate of fatigue crack growth and increase the residual strength of the skin. The reinforcements are of two types: stringers and doublers. The former provides stiffening to the panel while the latter controls the crack growth between the stringers. The purpose of the study is to validate a numerical method of analysis that can predict the damage tolerance of these reinforced panels. Therefore, using a fracture mechanics approach, several models (different by the geometry and the types of reinforcement constraints) were simulated with the finite element solver ABAQUS. The bonding between skin and stiffener was taken either rigid or flexible due to the presence of adhesive. The possible rupture of the reinforcements was also considered. The stress intensity factor trend obtained numerically as a function of crack growth was used to determine the fatigue crack growth rate, obtaining a good approximation of the experimental crack propagation rate in the skin. Therefore, different solutions for improving the damage tolerance of aircraft reinforced panels can be virtually tested in this way before performing experiments.
      Issue No: Vol. 0
       
  • Use of a gray level co-occurrence matrix to characterize duplex stainless
           steel phases microstructure

    • Authors: F. R. Renzetti, L. Zortea
      Abstract: Duplex stainless steels are widely used in industry. This is due to their higher strength compared to austenitic steels and to their higher toughness than ferritic steels. They also have good weldability and high resistance to stress corrosion cracking. These steels are characterized by two-phase microstructures composed by almost the same level of ferrite and austenite. Duplex steel 2205 samples evaluated are: as received, cold rolled (33%) and heat-treated at 800°C for 10 hours. A metallographic etching with 10% oxalic acid has been carried out to highlight the phases morphology. Some photos have been taken by SEM microscope and submitted to image analysis. The analysis carried out is based on the determination of co-occurrence matrix and on the following interpretation of appropriate indicators. Through these indicators is possible to estimate the features of images objectively.
      Issue No: Vol. 0
       
  • Numerical modelling of intergranular fracture in polycrystalline materials
           and grain size effects

    • Authors: M. Paggi, P. Wriggers
      Abstract: In this paper, the phenomenon of intergranular fracture in polycrystalline materials is investigated using a nonlinear fracture mechanics approach. The nonlocal cohesive zone model (CZM) for finite thickness interfaces recently proposed by the present authors is used to describe the phenomenon of grain boundary separation. From the modelling point of view, considering the dependency of the grain boundary thickness on the grain size observed in polycrystals, a distribution of interface thicknesses is obtained. Since the shape and the parameters of the nonlocal CZM depend on the interface thickness, a distribution of interface fracture energies is obtained as a consequence of the randomness of the material microstructure. Using these data, fracture mechanics simulations are performed and the homogenized stress-strain curves of 2D representative volume elements (RVEs) are computed. Failure is the result of a diffuse microcrack pattern leading to a main macroscopic crack after coalescence, in good agreement with the experimental observation. Finally, testing microstructures characterized by different average grain sizes, the computed peak stresses are found to be dependent on the grain size, in agreement with the trend expected according to the Hall-Petch law.
      Issue No: Vol. 0
       
  • Analysis of the fatigue strength under two load levels of a stainless
           steel based on energy dissipation

    • Authors: B. Atzori, G. Meneghetti, M. Ricotta
      Abstract: In this paper the fatigue behaviour of a stainless steel AISI 304L is analysed. In the first part of the work the results obtained under constant amplitude fatigue are presented and synthesised in terms of both stress amplitude and energy released to the surroundings as heat by a unit volume of material per cycle, Q. Then some specimens have been fatigued in variable amplitude, two different load level tests: the first level was set higher while the second was lower than the constant amplitude fatigue limit. The Q values, evaluated during the second part of the fatigue test, have been compared with those calculated under constant amplitude fatigue at the same load level. The comparison allowed us to notice that the Q parameter is sensitive to the fatigue damage accumulated by the material during the first part of the fatigue test.
      Issue No: Vol. 0
       
  • A brittle fracture criterion for PMMA V-notches tensile specimens based on
           a length-enriched eXtended Finite Element approach

    • Authors: E. Benvenuti, R. Tovo, P. Livieri
      Abstract: A criterion for the prediction of the static failure loads in tensile PMMA specimens with sharp notches is presented. The proposed criterion is based on a regularized version of the eXtended Finite Element Method (XFEM), which has been previously applied to concrete-like materials. The main feature of the proposed approach is that the cracking process is not treated as a local process, but it is modeled by assuming that macro-cracks stem from the interaction of micro-cracks within a finite width process zone. The case of a brittle materials with thin process zone is tackled by assuming one layer of enriched finite elements. Preliminary results concerning PMMA specimens subjected to mode-one loading are presented.
      Issue No: Vol. 0
       
  • Computed Tomography analysis of damage in composites subjected to impact
           loading

    • Authors: V. Crupi, G. Epasto, E. Guglielmino
      Abstract: The composites, used in the transportation engineering, include different classes with a wide range of materials and properties within each type. The following different typologies of composites have been investigated: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches. Aim of this paper was the analysis of low-velocity impact response of such composites and the investigation of their collapse modes. Low velocity impact tests were carried out by a drop test machine in order to investigate and compare their structural response in terms of energy absorption capacity. The failure mode and the internal damage of the impacted composites have been, also, investigated using 3D Computed Tomography.
      Issue No: Vol. 0
       
  • The variational theory of fracture: diffuse cohesive energy and
           elastic-plastic rupture

    • Authors: Gianpietro Del Piero, Giovanni Lancioni, Riccardo March
      Abstract: This communication anticipates some results of a work in progress [1], addressed to explore the efficiency of the diffuse cohesive energy model for describing the phenomena of fracture and yielding. A first local model is partially successful, but fails to reproduce the strain softening regime. A more robust non-local model, obtained by adding an energy term depending on the deformation gradient, describes many typical features of the inelastic response observed in experiments, including strain localization and necking. Fracture occurs as the result of extreme strain localization. The model predicts different fracture modes, brittle and ductile, depending on the analytical form of the cohesive energy function.
      Issue No: Vol. 0
       
  • Fatigue behaviour of titanium dental endosseous implants

    • Authors: Ferdinando Felli, Daniela Pilone, Alessandro Scicutelli
      Abstract: In this work two different titanium dental implants are analyzed in order to evaluate their mechanical strength. An ad-hoc designed experimental apparatus is prepared to test against fatigue these implants in a way that approximates as much as possible the actual stresses occurring during mastication motion. The results of these endurance tests are summarized in the form of Wohler-type diagrams showing the duration of a specific implant for different applied loads. These plots show a fatigue limit below which the implants could resist indefinitely. Other aspects of this research concern the influence of a potentially corrosive medium and the analysis of the deformation and failure of the specimens. During fatigue cycling, the titanium implants do not seem to be affected by a more aggressive environment, such as a saline solution. The analysis of the broken specimen allowed the crack initiation sites and the type of fracture propagation to be investigated in depth. In all the considered implants fatigue cracks were seen to initiate preferentially from sites in which the tensile stress concentration is the highest. The results of a finite element analysis performed on one of the specimens is in good agreement with the failure mode observed after the tests. The SEM fracture surface analysis shows a clear similarity between the fracture mode of the tested implants and of the actual implants broken after a certain operating period.
      Issue No: Vol. 0
       
  • A coupled interface-body nonlocal damage model for the analysis of FRP
           strengthening detachment from cohesive material

    • Authors: S. Marfia, E. Sacco, J. Toti
      Abstract: In the present work, a new model of the FRP-concrete or masonry interface, which accounts for the coupling occurring between the degradation of the cohesive material and the FRP detachment, is presented; in particular, a coupled interface-body nonlocal damage model is proposed. A nonlocal damage and plasticity model is developed for the quasi-brittle material. For the interface, a model which accounts for the mode I, mode II and mixed mode of damage and for the unilateral contact and friction effects is developed. Two different ways of performing the coupling between the body damage and the interface damage are proposed and compared. Some numerical applications are carried out in order to assess the performances of the proposed model in reproducing the mechanical behavior of the masonry elements strengthened with external FRP reinforcements.
      Issue No: Vol. 0
       
  • Carbon nanotubes cement composites

    • Authors: Giuseppe Ferro, Jean-Marc Tulliani, Simone Musso
      Abstract: The present paper reviews the current state of the art of carbon nanotubes cement-based composites and the possible applications. The influence of carbon nanotubes additions onto cement paste mechanical and electrical properties are discussed in detail. Though promising, several challenges have still to be solved before the introduction of these new materials into the public sphere through civil infrastructures.
      Issue No: Vol. 0
       
  • Structural transitions in a NiTi alloy: a multistage loading-unload cycle

    • Authors: V. Di Cocco, C. Maletta, S. Natali
      Abstract: NiTi shape memory alloys (SMAs) are increasingly used in many engineering and medical applications, because they combine special functional properties, such as shape memory effect and pseudoelasticity, with good mechanical strength and biocompatibility. However, the microstructural changes associated with these functional properties are not yet completely known. In this work a NiTi pseudo-elastic alloy was investigated by means of X-ray diffraction in order to assess micro-structural transformations under mechanical uniaxial deformation. The structure after complete shape recovery have been compared with initial state.
      Issue No: Vol. 0
       
  • Fracture toughness and fatigue resistance of quenched and tempered steels
           with microstructures deriving from a slant quench. Consequences on
           technical standards

    • Authors: D. Firrao, P. Matteis
      Abstract: Mechanical components fabbricated with quenched and tempered steels, exhibiting mixed microstructures as derived from slant quench conditions, are frequently encountered in the industrial practice, owing to a tendency to employ quite low alloy steels or due to quite large sections. The low notch strength of mixed microstructure steel samples was already emphasized in the 1950s; yet, it has never been investigated again. Also, technical standards have not addressed the risk deriving from the use of steel components with mixed microstructures. When pearlite and ferrite are present alongside tempered martensite and bainite, the fracture toughness of steel pieces diminishes to very dangerous levels. Results of an experimental program on the fracture toughness of plastic mould steels are reported, singling out microstructure mixtures with too a low toughness. In addition, the fatigue crack propagation rate is adversely affected by inhomogeneous metallographic structures. It is inferred that experimental results and ensuing considerations should be taken into account when formulating technical norms.
      Issue No: Vol. 0
       
  • Notiziario n. 18 - Luglio 2007

    • Authors: Gruppo Italiano Frattura
      Abstract: IN QUESTO NUMERO
      1) Editoriale del Presidente IGF;
      2) Cariche sociali biennio 2005-2007;
      3) Verbale dell’Assemblea Annuale dei Soci 2006;
      4) Verbali dei Consigli di Presidenza;
      5) Resoconti delle attività del 2006;
      6) XIX Convegno Nazionale IGF – Milano 2007;
      7) Convocazione Assemblea Annuale dei Soci 2007;
      8) Calendario congressi internazionali ;
      9) Modulo di iscrizione IGF-ESIS.
      Issue No: Vol. 0
       
  • Notiziario IGF n.19

    • Authors: Francesco Iacoviello
      Abstract: 1) Editoriale del Segretario IGF;2) Verbale dell'Assemblea Annuale dei Soci 2007;3) Verbali dei Consigli di Presidenza;4) Cariche sociali biennio 2007-2009;5) Resoconti delle attività TC-ESIS nel 2007;6) Summer School IGF 2008;7) Convocazione Assemblea Annuale dei Soci 2008;8) Calendario congressi internazionali  
      Issue No: Vol. 0
       
  • Workshop IGF "Fatica nelle giunzioni saldate (...e non)"

    • Authors: Francesco Iacoviello
      Abstract: -
      Issue No: Vol. 0
       
  • Notiziario IGF

    • Authors: Francesco Iacoviello
      Abstract: -
      Issue No: Vol. 0
       
  • Notiziario

    • Authors: F. Iacoviello
      Abstract: -
      Issue No: Vol. 0
       
 
 
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