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  Subjects -> ENGINEERING (Total: 2268 journals)
    - CHEMICAL ENGINEERING (190 journals)
    - CIVIL ENGINEERING (183 journals)
    - ELECTRICAL ENGINEERING (103 journals)
    - ENGINEERING (1201 journals)
    - ENGINEERING MECHANICS AND MATERIALS (380 journals)
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CIVIL ENGINEERING (183 journals)                     

Showing 1 - 183 of 183 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: 35)
Advances in Structural Engineering     Full-text available via subscription   (Followers: 28)
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: 2)
ATBU Journal of Environmental Technology     Open Access   (Followers: 4)
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: 10)
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)
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: 12)
Case Studies in Engineering Failure Analysis     Open Access   (Followers: 8)
Case Studies in Nondestructive Testing and Evaluation     Open Access   (Followers: 11)
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: 10)
Civil Engineering Dimension     Open Access   (Followers: 8)
Cohesion and Structure     Full-text available via subscription   (Followers: 2)
Composite Structures     Hybrid Journal   (Followers: 266)
Computer-aided Civil and Infrastructure Engineering     Hybrid Journal   (Followers: 11)
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: 9)
Construction Management and Economics     Hybrid Journal   (Followers: 22)
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: 9)
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: 14)
International Journal of Condition Monitoring     Full-text available via subscription   (Followers: 2)
International Journal of Construction Engineering and Management     Open Access   (Followers: 9)
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: 5)
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: 12)
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: 4)
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 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: 13)
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: 5)
Journal of Materials in Civil Engineering     Full-text available via subscription   (Followers: 10)
Journal of Nondestructive Evaluation     Hybrid Journal   (Followers: 11)
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: 40)
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 Civil Engineering Forum     Open Access  
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   (Followers: 1)
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: 7)
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)
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: 10)
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: 13)
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]
  • 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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