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PHYSICS (623 journals)            First | 1 2 3 4 5 6 7 | Last

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Theoretical and Applied Fracture Mechanics     Hybrid Journal   (6 followers)

  First | 1 2 3 4 5 6 7 | Last

Theoretical and Applied Fracture Mechanics    [8 followers]  Follow    
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 0167-8442
     Published by Elsevier Homepage  [2556 journals]   [SJR: 0.78]   [H-I: 32]
  • STRESS-INTENSITY FACTORS AT THE INTERFACE EDGE OF A PARTIALLY DETACHED
           FIBRE
    • Abstract: Publication date: Available online 23 January 2014
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Roberto Brighenti , Andrea Carpinteri , Daniela Scorza
      Fibre-reinforced composites (FRCs) are multiphase materials characterised by high engineering performances. However, some degrading effects in such materials (the loss of their bearing capacity, related to the matrix-fibre detaching phenomenon also known as debonding, fibre breaking, matrix cracking) must be carefully taken into account in the assessment of the FRC safety and durability. In the present paper, the fibre-matrix detaching phenomenon is examined from the fracture mechanics point of view. The stress singularity arising at the extremities of a perfectly bonded fibre is studied, and the related Stress-Intensity Factors (SIFs) are used to assess the detachment initiation up to the appearance of a debonded region at the two ends of the fibre. The circular shape boundary line representing the edge of the debonded region is analysed as a 3D crack front located between two different materials, and the Stress-Intensity Factors are determined for different remote loadings and composite characteristics.


      PubDate: 2014-01-24T12:04:23Z
       
  • Effect of electrostatic tractions on the fracture behavior of a
           piezoelectric material under mechanical and/or electric loading
    • Abstract: Publication date: Available online 17 January 2014
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Tao Xie , CuiYing Fan , HaiTao Liu , MingHao Zhao , Tong-Yi Zhang
      The pre-cracked parallel-plate capacitor model is further developed to study analytically the effect of electrostatic tractions induced by Maxwell stress and piezoelectricity on the fracture behavior of a piezoelectric material under mechanical and/or electric loading. The results indicate that the Maxwell stress and piezoelectricity induced tractions are independent and dependent on the direction of an applied electric field, respectively. Hysteresis loops in the curves of crack opening (or closing) versus applied mechanical strain and in the curves of crack opening (or closing) versus applied electric field occur under positive fields much easier than negative fields due to the piezoelectricity. Because of the potential presence of hysteresis loops, the fracture criterion must be composed of two parts: the energy release rate must exceed a critical value and the mechanical load must be higher than the critical value for crack opening.


      PubDate: 2014-01-20T12:05:13Z
       
  • Singular stresses due to adhesion defect on intersection line along which
           a semi-infinite thin plate is attached to an infinite thin plate by
           eigenfunction expansion method
    • Abstract: Publication date: Available online 9 January 2014
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): D.H. Chen , K. Ushijima
      In this paper, the stress singularity due to adhesion defect on intersection line along which a semi-infinite thin plate (Plate 1) is attached to an infinite thin plate (Plate 2) is studied by the eigenfunction expansion method. For Plate 2 the stress is approximated as plane stress state, and for Plate 2 the stress is treated as a two-dimensional problem, in which the anti-plane deformation is also taken into account besides the plane stress. The eigenequation for the asymptotic behavior of stresses around the defect tip is given in an explicit form. This eigenequation is different from the analysis where the anti-plane deformation of Plate 2 is ignored. Specifically, it is found that the eigenvalue in consideration of the anti-plane deformation becomes a complex value with a real part equal to 0.5. Also, the singular stress around the defect tip is given in an explicit form. The obtained results are verified through comparison with numerical results of the finite element method.


      PubDate: 2014-01-12T12:08:25Z
       
  • On 3-D Crack Problems in Offshore Pipeline with Large Plastic Deformation
    • Abstract: Publication date: Available online 10 January 2014
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Y.M. Zhang , Z.M. Xiao , W.G. Zhang , D.K. Yi
      Offshore pipelines consist of short pipeline segments connected by girth welding method. Surface and embedded elliptical cracks are often observed at welding zone which pose a potential threat to the reliability of the offshore pipelines. In this paper, three-dimensional nonlinear elastic-plastic stress investigation for the fracture responses of such offshore pipeline with surface or embedded elliptical cracks has been carried out. Based on the reference strain method, strain-based estimation formulas for crack tip opening displacement (CTOD) are proposed for the flawed pipelines under pure bending. Furthermore, based on the proposed estimation formulations, two failure assessment diagrams (FAD) for strain-based fracture are established to perform fracture assessment on the specific pipelines.


      PubDate: 2014-01-12T12:08:25Z
       
  • A Mode III Interfacial Crack under Nonuniform Ferro-elastic Domain
           Switching
    • Abstract: Publication date: Available online 7 January 2014
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Xiaodong Xia , Yuanqing Cui , Zheng Zhong
      This paper deals with a mode III interfacial crack while considering the effect of domain switching. The analysis will focus on the variation of stress intensity factor caused by domain switching. Due to the mismatch of material properties, an asymmetric nonuniform domain switching zone around the interfacial crack is achieved under the nonuniform domain switching criterion. Employing the weight function method, we obtain analytic forms of mono-domain and multi-domain toughening effects about stationary and quasi-static steady-state growing cracks, respectively. Three coupling parameters are proposed to evaluate the influences of elastic and ferroelectric bimaterial properties. In conclusion, domain switching of mode III quasi-static steady-state growing interfacial crack can toughen the material. The research will give us ideas on material and initial poling orientation selection to maximize the ferro-elastic toughening effect.


      PubDate: 2014-01-08T13:32:24Z
       
  • Effect of Projectile Diameter on Ballistic Resistance and Failure
           Mechanism of Single and Layered Aluminum Plates
    • Abstract: Publication date: Available online 4 January 2014
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): K. Senthil , M.A. Iqbal
      Finite element analysis has been carried out to study the effect of diameter of ogive nosed projectile on the ballistic resistance of 1mm thick monolithic and 0.5 mm thick double-layered in contact plates of 1100-H12 aluminum alloy. The size of the projectile was varied by varying its shank diameter as 15, 19 and 24 mm, keeping the length constant. Thus, the length to diameter ratio varied as 2, 2.6 and 3.3. The ABAQUS/Explicit finite element code in conjunction with Johnson-Cook elasto-viscoplastic material model was employed to perform the simulation study. The numerical results were compared with available experiments. The ballistic resistance has been found to increase with increase in the projectile diameter. For a given diameter, the monolithic target has been found to offer better resistance. However, the influence of target configuration was dominant against the larger projectile diameter. The projectile was considered rigid and deformable to study its influence on the failure mechanism and ballistic limit. Friction effect between the projectile and target was also studied and its influence thereon the ballistic performance is discussed.


      PubDate: 2014-01-08T13:32:24Z
       
  • Scalability and homogenization of transitional functions: Effects of
           non-equilibrium and non-homogeneity
    • Abstract: Publication date: Available online 29 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): G.C. Sih
      Monoscale functions refer to the individual scale range of the SI system of measurement. Coarseness of the segmented scale was dictated by state-of-the-art of technology at that time. By to-day’s standard, non-equilibrium and non-homogeneity (NENH) are first order considerations whereby scales must be refined to include micro, nano and pico effects. The conventional technology applies to monoscaling, confined to equilibrium and homogeneity (E&M). Their conversion to multiscaling requires the use of transitional functions. The ultra high strength and light weight structural materials rely on the absorption of energy at more than one scale. For considerations are effects at microscopic, nanoscopic and picoscopic scales. The irony is that NENH are subject to eventual homogenization for otherwise the multiscale effects could not be transferred to improve and modify the monoscale rules in practices. To this end, additional Postulate and Corollary are needed to account for scale directionality of energy transfer, prevalent to NENH. Direction-dependency differentiates the transition of macro→micro and micro→macro. Transitional functions are not the same when they traverse up and down the scale. Homogenization averages out NENH effects such that corrections may be applied to monoscaling. Transitional functions can lock-in the load, material and geometry effects of the the macro-micro test data to produce the nano-pico data. This is related to the obtainment of small crack data from large crack test data. To this end, the volume energy density factor (VEDF) or the volume energy density (VED) can be used as the transitional functions as a form-invariant criterion such that multiscale effects can be used to correct and modify monoscale results. When NENH effects are highly localized and cannot be averaged out, the time rate of VEDF and VED or the equivalent of the power energy density must be used. The scalar correction for NENH is derived for the macro-micro cracking of a line crack subject to the combined effects of loading, material and geometry. Two correction factors Λ and Ω are used, one for macro→micro and another for micro→macro. The outcome can be checked by results for crack length and/or crack growth rate.


      PubDate: 2013-12-31T13:33:52Z
       
  • Effects of Small Defects, Matrix Structures and Loading Conditions on the
           Fatigue Strength of Ductile Cast Irons
    • Abstract: Publication date: Available online 25 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Masahiro Endo , Keiji Yanase
      The fatigue strength of ductile cast iron is influenced by microstructural inhomogeneities (i.e., graphite, casting defects and matrix structures composed of different phases). In particular, the presence of small casting defects such as micro-shrinkage cavity can frequently cause not only significant deterioration but also large scatter in fatigue strength. Therefore, the laboratory fatigue tests with a limited number of small-sized specimens could result in a non-conservative estimation. For such a material, the prediction for the lower bound of the scatter in fatigue strength is essential from a practical perspective. In this study, a novel method is presented to predict the lower bound based upon the information of microstructural inhomogeneities and loading conditions. This method offers such an advantage that the lower bound can be reasonably predicted without conducting time-consuming fatigue tests. The predictive capability of the method was verified by comparing to the experimental results obtained in rotating-bending, torsion and combined tension-torsion fatigue tests of ductile cast irons with ferritic, pearlitic and bulls-eye structures.


      PubDate: 2013-12-27T18:04:22Z
       
  • Phase-field modeling of fracture in linear thin shells
    • Abstract: Publication date: Available online 25 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): F. Amiri , D. Millán , Y. Shen , T. Rabczuk , M. Arroyo
      We present a phase-field model for fracture in Kirchoff-Love thin shells using the local maximum-entropy (LME) meshfree method. Since the crack is a natural outcome of the analysis it does not require an explicit representation and tracking, which is advantage over techniques as the extended finite element method that requires tracking of the crack paths. The geometric description of the shell is based on statistical learning techniques that allow dealing with general point set surfaces avoiding a global parametrization, which can be applied to tackle surfaces of complex geometry and topology. We show the flexibility and robustness of the present methodology for two examples: plate in tension and a set of open connected pipes.


      PubDate: 2013-12-27T18:04:22Z
       
  • Efficient Coarse Graining in Multiscale Modeling of Fracture
    • Abstract: Publication date: Available online 27 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Pattabhi R. Budarapu , Robert Gracie , Shih-Wei Yang , Xiaoying Zhuang , Timon Rabczuk
      We propose a coarse-graining technique to reduce a given atomistic model into an equivalent coarse grained continuum model. The developed technique is tailored for problems involving complex crack patterns in 2D and 3D including crack branching and coalescence. Atoms on the crack surface are separated from the atoms not on the crack surface by employing the centro symmetry parameter. A rectangular grid is superimposed on the atomistic model. Atoms on the crack surface in each cell are used to estimate the equivalent coarse-scale crack surface of that particular cell. The crack path in the coarse model is produced by joining the approximated crack paths in each cell. The developed technique serves as a sound basis to study the crack propagation in multiscale methods for fracture.


      PubDate: 2013-12-27T18:04:22Z
       
  • The fracture analysis of an arbitrarily oriented crack in the functionally
           graded material under in-plane impact loading
    • Abstract: Publication date: Available online 27 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Sheng-Hu Ding , Xing Li
      The plane problem for a infinite functionally graded material containing a finite crack subjected to the dynamic impact loads is studied. The crack arbitrarily oriented with respect to the direction of property gradient is considered. The transient crack problem is reduced to solving a system of Cauchy-type singular integral equation in the Laplace transform domain by using the Laplace and Fourier integral transforms. The crack-tip response in the physical domain is recovered via the inverse Laplace transform and the values of dynamic stress intensity factors are obtained as a function of time. The effects come from the crack orientation and the nonhomogeneous material parameter on the dynamic stress intensity factors are discussed graphically.


      PubDate: 2013-12-27T18:04:22Z
       
  • A mass matrix formulation for cohesive surface elements
    • Abstract: Publication date: Available online 27 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Jack Hetherington , Harm Askes
      A well-known method for modelling crack propagation in structural finite element analysis is the use of interface elements employing the theory of cohesive surfaces. However, the use of cohesive surfaces in explicit dynamics is problematic since they have zero mass and must initially be very stiff in order to avoid the introduction of artificial compliance. These properties lead to an often drastic reduction in the critical time step of the analysis. In this paper we use the bipenalty method to derive a mass matrix for a 2D cohesive surface interface element that does not add net physical mass to the overall system. This allows for cohesive surfaces with very high initial stiffness that have no effect on the critical time step of the analysis. Not only does this lead to a more robust and stable system, it also greatly simplifies the choice of parameters since there is no need to adjust the time step, and no need to limit the initial penalty stiffness according to time step stability considerations.


      PubDate: 2013-12-27T18:04:22Z
       
  • A meshless sub-region radial point interpolation method for accurate
           calculation of crack tip fields
    • Abstract: Publication date: Available online 16 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Xiaoying Zhuang , Yongchang Cai , Charles Augarde
      A new meshless sub-region radial point interpolation method (MS-RPIM) is proposed for linear elastic fracture mechanics. The Williams expansions of stress field for mode I/II crack is used as the trial functions in crack tip region, the meshless radial point interpolation is used for the rest of domain, and a mixed variational principle is used for discretisation. In contrast to existing meshless formulations, the present MS-RPIM requires only very few nodes around the crack tip to obtain smooth stress and accurate results and the SIFs can be directly obtained as part of the solution and no additional effort via post-processing.


      PubDate: 2013-12-19T12:05:41Z
       
  • An unconditionally convergent iterative algorithm for the intersection of
           Neuber’s and Molski-Glinka’s rules with the Ramberg-Osgood
           stress-strain relationship
    • Abstract: Publication date: Available online 12 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): A. Navarro
      An iterative calculation scheme for solving the intersection between Neuber’s rule hyperbola or Molski-Glinka’s strain energy density equation with Ramberg-Osgood stress-strain laws is presented. It is a fixed-point type algorithm and it is shown to be unconditionally convergent.


      PubDate: 2013-12-15T21:01:30Z
       
  • Rock fracture toughness study using cracked chevron notched Brazilian disc
           specimen under pure modes I and II loading- A statistical approach
    • Abstract: Publication date: Available online 11 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): M.R.M. Aliha , M.R. Ayatollahi
      Fracture toughness of a white marble is studied experimentally using several cracked chevron notched Brazilian disc (CCNBD) specimens under pure mode I and pure mode II loading. Even in the presence of natural scatters in the test data, it was observed that the average mode II fracture toughness K IIc was considerably larger than that of mode I fracture toughness K Ic such that the mean fracture toughness ratio (K IIc/K Ic) was about 2. Using the generalized maximum tangential stress theory, the obtained mode II test results were estimated in terms of mode I fracture toughness data. The enhanced K IIc value in the CCNBD specimen could be related to the influence of very large negative T-stress value that exists in the mode II CCNBD specimens. The statistical analyses of test data were performed successfully to predict the Weibull parameters of mode II results in terms of mode I Weibull parameters.


      PubDate: 2013-12-15T21:01:30Z
       
  • Numerical model for the zonal disintegration of the rock mass around deep
           underground workings
    • Abstract: Publication date: Available online 11 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): S.C. Li , X.D. Feng , S. C. Li
      Deep underground excavation can produce zonal disintegration in the surrounding rock under certain conditions. This phenomenon has mainly been studied in a qualitative manner using in situ investigations or laboratory experiments. Researchers have also derived analytical solutions, which resulted in the formation conditions for zonal disintegration. However, the analytic solutions developed to date are not suitable for practical engineering applications because of the stringent model requirements and complicated boundary conditions. To investigate the mechanism of zonal disintegration, a numerical method is proposed to model the phenomenon. The following concepts are incorporated into FLAC3D via its built-in FISH. First, coal mine (or tunnel) excavation is considered as a dynamic process. Second, the element failure criteria are developed based on the maximum tensile stress criterion and strain energy density theory. Third, the mechanical damage is modeled through a decrease in the multi-step elastic modulus, i.e., the non-linear stress-strain behavior is approximated by the multi-linear elastic softening model. Two practical cases with zonal disintegration are simulated using the proposed method. Both simulations predict the same number of fractured zones at the same location as those obtained through in situ monitoring.


      PubDate: 2013-12-15T21:01:30Z
       
  • Crack tip field in thermoelectric media
    • Abstract: Publication date: Available online 11 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): A.B. Zhang , B.L. Wang
      The crack problem in a medium possessing coupled thermoelectric effect under thermal-electric loads is considered in this paper. The crack surfaces boundary conditions are assumed to be electrically and thermally impermeable. The general two dimensional solutions are presented in closed-form based on the complex variable method. Expressions for thermal flux, electric flux and stress fields in the vicinity of crack tip are derived. It is found that these fields exhibit traditional square-root singularity at the crack tip. For this, some essential fracture mechanics parameters, such as the thermal flux, electric flux and stress intensity factors at the crack tip are obtained. The results show that the electric flux intensity factor and thermal flux intensity factor depend on the far-field electric flux loads and the applied total energy flux loads, respectively. For the homogeneous isotropic thermoelectric material, only mode II stress intensity factor develops if the thermal-electric loads are applied.


      PubDate: 2013-12-15T21:01:30Z
       
  • Analysis of functionally graded magneto-electro-elastic layer with
           multiple cracks
    • Abstract: Publication date: Available online 12 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): S.M. Mousavi , J. Paavola
      In this paper, the distributed dislocation technique (DDT) is developed to be utilized for the analysis of a cracked functionally graded piezoelectric-piezomagnetic (FGPP) layer under anti-plane mechanical and in-plane electric and magnetic fields. By using the Fourier transformation, the closed-form expressions for the shear stress, electric displacement and magnetic displacement components are obtained for a generalized Volterra-type screw dislocation. The generalized dislocation in FGPP layer contains dislocation in the displacement component and jump in the electric and magnetic potentials. The expressions of generalized stress intensity factor are derived in the DDT. The solution of the dislocation problem is utilized in the DDT to solve the problem of arbitrary configurations of multiple embedded and edge cracks. The generalized intensity factors of the cracked layer are obtained. Numerical results for generalized intensity factors of straight and curved cracks are presented. The DDT is proved to be useful in the analysis of the interaction of the embedded and edge cracks in an FGPP layer.


      PubDate: 2013-12-15T21:01:30Z
       
  • A new continuous-discontinuous damage model: cohesive cracks via an
           accurate energy-transfer process
    • Abstract: Publication date: Available online 14 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Elena Tamayo-Mas , Antonio Rodríguez-Ferran
      A new continuous-discontinuous strategy to describe failure of quasi-brittle materials is presented. For the early stages of the failure process, a gradient-enhanced model based on smoothed displacements is employed. As soon as the damage parameter exceeds a critical value D crit < 1 , a cohesive crack is introduced. A new criterion to estimate the energy not yet dissipated by the bulk when switching models —from continuous to continuous-discontinuous— is proposed. Then, this energy is transferred to the cohesive crack thus ensuring that the continuous and the continuous-discontinuous strategies are energetically equivalent. Compared to other existing techniques, this new strategy accounts for the different unloading branches of damage models and thus, a more accurate estimation of the energy that has to be transferred is obtained. The performance of this technique is illustrated with one- and two-dimensional examples.


      PubDate: 2013-12-15T21:01:30Z
       
  • Transient thermal cracking of a brittle half space medium with a
           semi-elliptical surface crack
    • Abstract: Publication date: Available online 8 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): D.M. CHANG , X.F. LIU
      The paper conducts the cracking study of a brittle half space medium with a semi-elliptical surface crack. The transient thermal stress intensity factors are obtained and are graphically presented. Effects of thermal shock time, crack size, and crack shape on the crack growth and thermal shock resistance behavior of the medium are investigated in details. A thermal shock resistance analysis methodology is established, allowing us to study the fracture strength of brittle media subjected to thermal shock.


      PubDate: 2013-12-11T16:31:25Z
       
  • Macro and microscopical approach to the damaging micromechanisms analysis
           in a ferritic ductile cast iron
    • Abstract: Publication date: Available online 4 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Vittorio Di Cocco , Francesco Iacoviello , Alessandra Rossi , Daniela Iacoviello
      The influence of the graphite nodules morphology (shape, dimension and distribution) on ductile cast irons (DCIs) mechanical properties is experimentally confirmed both in static, quasi static and cyclic loading conditions. According to the most recent results, these graphite elements cannot be merely considered as “microvoids embedded in a metal matrix”, but their presence implies a modification of the damaging micromechanisms, depending on the metal matrix microstructure. In this work, a fully ferritic DCI has been investigated: tensile tests have been performed on notched mini tensile specimens. Specimens lateral surfaces have been observed by means of a Scanning Electron Microscope (SEM) during the tests (“in situ” tests) at different magnifications. Considering the results obtained at low magnification, quantitative image analysis has been applied in order to investigate the triaxiality evolution during the test.


      PubDate: 2013-12-07T12:04:56Z
       
  • Load Sequence Effects on Fatigue Crack Growth in Notched Tubular Specimens
           Subjected to Axial and Torsion Loadings
    • Abstract: Publication date: Available online 6 December 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Maksym Gladskyi , Ali Fatemi
      Fatigue crack growth behavior of tubular specimens with a through thickness circular hole made of a carbon steel subjected to axial and torsional loads was investigate. Loading sequence effect on crack growth rate was also studied by alternating between axial and torsion cycles in a loading block. Mode I crack growth was observed. Torsion fatigue crack growth lives were shorter and crack growth rates were higher than for axial loading. This is explained by a larger plastic zone size produced by a compressive tangential stress acting parallel to the crack growth path. In block loading with dominated torsion cycles crack grown rate was slower in comparison with pure torsion, while in block loading with dominated axial cycles a faster crack growth rate occurred in comparison with pure axial loading. Effects of the stress state on the plane of crack growth and of one pair of cracks on a second pair are considered to explain these observations. Crack growth rates were correlated with stress intensity factor range with or without considering the T-stress effect. Short crack growth behavior near the threshold region is also discussed.


      PubDate: 2013-12-07T12:04:56Z
       
  • Crystallographic analysis for fatigue small crack growth behaviors of a
           nickel-based single crystal by in-situ SEM observation
    • Abstract: Publication date: Available online 28 November 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Yangyang Zhang , Hui-Ji Shi , Jialin Gu , Changpeng Li , Kai Kadau , Oliver Luesebrink
      Small fatigue crack growth behaviors of a nickel-base single crystal (SX) are studied by in-situ observations with scanning electron microscope (SEM). Two different crack propagation modes are identified, i.e., cracks at room temperature and 3000C prefer non-crystallographic propagation mode, while those at a higher temperature of 6000C propagate preferentially along crystallographic slip systems, besides, evident “small crack anomaly” has been partly found. Further computation of crack growth rate reveals that conventional Paris law is found no longer capable of characterizing the crystallographic crack propagation behaviors. Subsequently, with the help of finite element analysis (FEA), the crack tip stress fields are reconstructed and resolved shear stresses in each octahedral slip systems are calculated. It is found that the maximum resolved shear stress intensity parameter, first proposed by Chen and Liu, is able to characterize the growth behaviors of those small cracks.


      PubDate: 2013-11-29T12:04:59Z
       
  • Strain energy density prediction of crack propagation for 2D linear
           elastic materials
    • Abstract: Publication date: Available online 16 November 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): A. Boulenouar , N. Benseddiq , M. Mazari
      When the loading or the geometry of a structure is not symmetrical about the axis of the crack, the rupture occurs in mixed mode loading, and the crack does not propagate in a straight line. It is then necessary to use kinking criteria to determine the new direction of crack propagation. The aim of this work is to present a numerical modeling of crack propagation under mixed mode loading conditions. This work is based on the implementation of the displacement extrapolation method (DEM) and the strain energy density theory in a finite element code. At each crack increment length, the kinking angle is evaluated as a function of stress intensity factors (SIFs). In this paper, we analyzed the mechanical behavior of inclined cracks by evaluating the stress intensity factors. Then, we present the examples of crack propagation in structures containing inclusions and cavities.


      PubDate: 2013-11-17T12:06:17Z
       
  • Transient Response of a Crack in a Functionally Graded Piezoelectric Strip
           between Two Dissimilar Piezoelectric Strips
    • Abstract: Publication date: Available online 5 November 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Jeong Woo Shin , Young-Shin Lee , Sung Joon Kim
      Transient response of a crack in a functionally graded piezoelectric material (FGPM) interface layer between two dissimilar homogeneous piezoelectric layers under anti-plane shear is analyzed using integral transform approaches. The properties of the FGPM layer vary continuously along the thickness. The FGPM layer and two homogeneous piezoelectric layers are connected weak-discontinuously. Laplace and Fourier transforms are used to reduce the problem to two sets of dual integral equations, which are then expressed to the Fredholm integral equations of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGPM to show the effects on electric loading, gradient of the material properties, and thickness of the layers. Computed results yield following conclusions: (a) the DERR increases with the increase of the gradient of the material properties of the FGPM layer; (b) certain direction and magnitude of the electric impact loading impedes crack extension; (c) increase of the thickness of the FGPM layer and the homogeneous piezoelectric layer which has larger material properties than those of the crack plane are beneficial to increase of the resistance of transient fracture of the FGPM layer.


      PubDate: 2013-11-09T13:33:48Z
       
  • Mode i stress intensity factor for cracked thin-walled composite beams
    • Abstract: Publication date: Available online 22 October 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Franco E. Dotti , Víctor H. Cortínez , Florencia Reguera
      In this paper, we present an analytical method to determine the mode I stress intensity factor for thin-walled beams made of laminated composites. The technique relies on the concept of crack surface widening energy release rate, which is expressed in terms of the G∗ integral and thin-walled beam theory. In the vicinity of the crack tip, a solution of the G∗ integral is obtained employing stress and displacement fields derived for materials with general orthotropy. The effect of warping is taken into account. This is a common feature in thin-walled beams which cannot be neglected, especially when flexural-torsional loads are present. The model shows a good agreement with finite element results. It is shown that, although the approaches developed for isotropic materials may be useful in the treatment of orthotropic problems, they may not yield good results for some typical lamination sequences.


      PubDate: 2013-10-24T12:32:45Z
       
  • Fatigue Life Prediction of AZ31B Magnesium Alloy and Its Welding Joint
           through Infrared Thermography
    • Abstract: Publication date: Available online 16 October 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): LIU Xiao-qing , ZHANG Hong-xia , YAN Zhi-feng , WANG Wen-xian , ZHOU Ya-guo , ZHANG Qian-ming
      This paper presents an experimental approach to predict the fatigue life of AZ31B magnesium alloy and its butt joints based on infrared thermography. The thermographic technique was used to monitor the temperature evolution of the specimen during the fatigue testing. Temperature evolution during high-cycle fatigue testing can be divided into five stages: initial rapid increase stage, steep decrease stage, steady-state stage, abrupt increase stage and final drop stage. The heat generating mechanisms of five stages have been analyzed. It is found that the temperature evolution was closely related with fatigue life. The gradient of the initial rapid increase stage was used as an index of fatigue life prediction, with the prediction of fatigue life in good agreement with the experimental result.


      PubDate: 2013-10-16T14:03:09Z
       
  • A Dynamic Piecewise-exponential Model for Transient Crack Problems of
           Functionally Graded Materials with Arbitrary Mechanical Properties
    • Abstract: Publication date: Available online 23 September 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Xiao-Ming Bai , Li-Cheng Guo , Zhi-Hai Wang , Su-Yang Zhong
      A dynamic piecewise-exponential model (DPE model) is developed to investigate the transient fracture problems of functionally graded materials (FGMs) with arbitrary mechanical properties. In this model, a new approximate method for the graded modulus and mass density is presented; therefore, the problem can be solved analytically. The influences of graded ratios and variation forms of the modulus and mass density on the dynamic stress intensity factors (DSIFs) are investigated, respectively. It is found that the ratio and variation form of the modulus have pronounced influences on the peak value, steady value and overshoot characteristics of the DSIFs, while those of the mass density have relatively slight influences.


      PubDate: 2013-09-26T15:35:21Z
       
  • Editorial Board
    • Abstract: Publication date: June 2013
      Source:Theoretical and Applied Fracture Mechanics, Volume 65




      PubDate: 2013-07-02T11:06:00Z
       
  • Thermally conducting collinear cracks engulfed by thermomechanical field
           in a material with orthotropy
    • Abstract: Publication date: Available online 6 June 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Xian-Ci Zhong , Bing Wu , Ke-Shi Zhang
      The problem of two collinear cracks in an orthotropic solid is investigated under applied mechanical and uniform heat flow loadings. The thermal medium crack model is applied to address the effects of the medium inside cracks. Applying the Fourier transform technique, the boundary-valve problem is reduced to solving triple integral equations, then to solving singular integral equations with the Cauchy kernel. The thermoelastic fields involving of the strain energy density (SED) factors, the stress intensity factors, the jumps of temperature and elastic displacements across the cracks are given in closed forms. Numerical results are carried out to show the influences of applied mechanical loading and thermal conductivity of crack interior on the thermal stress intensity factors, the temperature change across crack faces and the strain energy density factors. The results reveal that the crack-tip thermoelastic fields are dependent on applied thermo-mechanical loadings and the thermophysical properties of crack interior. The crack-face thermal property is important and it should not be disregarded in analyzing thermoelastic problems of a cracked solid under a thermal loading.


      PubDate: 2013-06-08T11:04:35Z
       
  • Transmissibility of microwaves to ELF waves compatible to brain rhythms
    • Abstract: Publication date: Available online 5 June 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): G.C. Sih
      Brain function can be affected by electromagnetic waves having very long wave length if the frequency is kept very low. There is no known means of shielding such disturbances that happen to coincide with the frequency range of the brain waves. The quality of wave transmissibility determines the sustainability the threshold and the time span of waveform lock-on. A postulate is proposed for assessing the permanent set and lock-on time. A transmissibility constant b is defined in accordance with the surface energy density SEDELF related to the extreme low frequency (ELF) waves. The SEDELF for the gamma, beta, alpha, theta and delta waves at their average frequencies is found to dwell in a very narrow band for microwave frequency in the range of 1,000-2,400 MHz. The band width is negligibly small up to 1,800 MHz, after which the SEDELF increased only 15 mW/cm2 at 2,400 MHz. Approximately the same SEDELF for all the five brain waves can be used at each microwave frequency within the range mentioned earlier. The transmissibility constant b varied from 2.2x10-16 to 5.0x10-21 mW(V)2/cm2. The five orders of magnitude change in b is indicative of its capability to cover an extremely wide range of transmission of thousands of MHz to to a few Hz. Brain waves are most vulnerable to artificial alterations in the range 6-10 Hz. This work explores the quality of wave transmissibility by using ELG and EEG (electroencephalography) data on brain waves.


      PubDate: 2013-06-08T11:04:35Z
       
  • Rock Failure Induced by Dynamic Unloading under 3D StressState
    • Abstract: Publication date: Available online 6 June 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): Ming Tao , Xibing Li , Diyuan Li
      A commercial finite element program, LS-DYNA, was employed to simulate the unloading process of rocks under three dimensional (3D) stresses. The continuous surface cap model (CSCM), was used to model rock behaviour. Using this model, the unloading failure mechanisms of hard rock in a confined state were investigated during the unloading process. The results indicated that when rocks under 3D stress state experience unloading, the process is dominated by strain energy density (SED) rate. The effects of different unloading paths and different confining stresses can be characterised by the SEDrate. A significant finding of this study is that the SED rate can quantify the unloading process.Based on the findings, rock failure can be induced by rapid unload of initial stress. In the practical underground excavation engineering, dynamically controlling the SED rate can increase the excavation potential of rocks, minimising the required external excavation energy by using the energy of the stressed rock.


      PubDate: 2013-06-08T11:04:35Z
       
  • Dwelling time of normal and abnormal brain waves connected with their
           transformability and sustainability
    • Abstract: Publication date: Available online 3 June 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): G.C. Sih , K.K. Tang
      Normality and abnormality of EEG brain waves are associated with the transformability and sustainability time of the five waves types, namely gamma, beta, alpha, theta and delta in the order of their descending frequencies. Normal brain waves are transformable from one type to another with sustainable time in the order of seconds and minutes, while the transformability and sustainability time of abnormal brains may be of the order of months and years for situations where abnormalities are recoverable. Many of the exceptions caused by rhythmic irregularities and/or inappropriate EEG measurements can be identified with their respective wave type and sustainability time. This is done by using the least variance principle (LVP) where abnormalities in frequencies and amplitudes are captured by the variances and their sustaining time. The general notion is that normal waves would have less irregularities and are more predictable by the EEG wave frequencies and phase angles. Normal waves are not only more stable but they have a longer sustainable dwelling time. Waves with abnormally small (abs) and abnormally large (abl) frequencies on the other hand are more persistent on distinct dwelling times that can also affect the waveform stability. Dwelling time intervals of 0-6 min. and 4-10 min. are selected for abnormal waves in contrast to 0-10 min. for normal waves. The average frequencies are decreased from those for gamma waves to delta waves for determining the degree of persistency of dwelling times. Results from LVP show that the time occurrence of abnormally small (abs) and abnormally large (abl) frequencies affects the quality of the waveforms for the same dwelling time.


      PubDate: 2013-06-04T12:37:01Z
       
  • Fatigue damage and sensor development for aircraft structural health
           monitoring
    • Abstract: Publication date: Available online 3 June 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): S.R. Ignatovich , A. Menou , M.V. Karuskevich , P.O. Maruschak
      It was shown by tests conducted at the National Aviation University (Kiev, Ukraine) that fatigue damage of metal structures may be estimated by sensors with the surface relief pattern to indicate the accumulated fatigue damage. The nature of the deformation relief has been investigated by the light, scan and transmission microscopy, as well as by a new nano-interferometer, developed at the National Aviation University. Fractal analysis of the surface patterns based on box-counting method has proved the efficiency of fractal geometry application for additional quantitative description of such surface structures. The evolution of deformation relief parameters on the sensors surface is determined by the process of the sensor and construction fatigue damage accumulation.


      PubDate: 2013-06-04T12:37:01Z
       
  • Simulated flow model of fractured anisotropic media: Permeability and
           fracture
    • Abstract: Publication date: Available online 27 May 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): C.Y. Ma , Y.T. Liu , J.L. Wu
      This paper is typically studied the fracture flow in the anisotropic media in consider with the stress sensitivity of permeability. Combined with anisotropy percolation characteristics of permeability, laboratory full tensor permeability test method is established by means of the expandable polystyrene (EPS) cystosepiment, and the non-linear flow physical simulation in fractured anisotropic media is studied. Through numerical calculation and physical experiment, the variation mechanism of full tensor permeability with stress sensitivity in fractured anisotropic media is revealed. Based on percolation theory, tensor theory and coordinate transformation principle, the full permeability tensor model for single and multiple group fracture is presented. It is extended to the reservoir in-situ condition, and the mathematical model of the full tensor permeability for multiple group and pressure-sensitive fractured anisotropic media is established. The results have a significant impact in understanding the seepage law in the fracture.


      PubDate: 2013-05-31T11:04:46Z
       
  • Friction Stir Welded Joints of Al-Li Alloys for Aeronautical Applications:
           Butt-joints and Tailor Welded Blanks
    • Abstract: Publication date: Available online 27 May 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): S.M.O. Tavares , J.F. dos Santos , P.M.S.T. de Castro
      Structural design for safety critical components, as airframes, requires comprehensive characterization of the materials and joints properties. This characterization must take into account a large amount of variables required for accurate design to ensure structural integrity during the different phases of the product life cycle of an aircraft. One of the most important variables in this characterization is fatigue behavior due to the cyclic loads during the life of an airframe. The application of welding processes to replace riveted joints in aeronautical structures is an attractive option, since it allows joints with less stress concentration points and might be applied efficiently without overlapping the two joining parts (with a butt-joint configuration), reducing the joint weight. This weight reduction can have a small impact in production costs, but has a huge impact in the life cycle costs. Friction stir is the most appealing welding process in aeronautical structures since it has been shown to produce joints with excellent properties when applied to aluminum alloys and can deal with hardened precipitated aluminum alloys, since it is a semi-solid state process. Furthermore, this joining process allows to join dissimilar materials and plates with different thicknesses, creating in this way tailor welded blanks, which support the manufacturing of optimized panels by tailoring their strength in function of their needs. This article presents a mechanical characterization of friction stir welds of last generation aluminum-lithium alloys, including tailor welded blanks with different thicknesses, with potential applications in aeronautical and aerospace components. Mechanical characterization with crack initiation and fatigue crack growth tests were included in this study for an enhanced assessment of these alloys behavior, and was preceded by welding parameter calibration.


      PubDate: 2013-05-31T11:04:46Z
       
  • Uncertainties of stress intensification near broken fibers of
           unidirectional composite with random fiber spacing
    • Abstract: Publication date: Available online 28 May 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): B. Bouhamida , Z. Sereir , A. Chateauneuf
      This paper aims at developing a probabilistic model of unidirectional composite with random fiber spacing, in order to predict the stress concentration at the broken and neighboring fibers. Micromechanical technique with random fiber spacing is used in the development of a new formulation of load sharing between broken and nearest neighbors fibers. By the development of a 3D finite difference scheme with random fibers spacing, a new governing system of coupled equations is obtained for fibers displacement and stresses concentration. Using the Monte Carlo, the sensitivities of the mechanical response are evaluated regarding the uncertainties in the design variables, namely fiber spacing, radius and Young’s modulus of fibers and matrix.


      PubDate: 2013-05-31T11:04:46Z
       
  • Stability and sustainability: Efficacy of ATP (Adenosine triphosphate)
           
    • Abstract: Publication date: Available online 27 May 2013
      Source:Theoretical and Applied Fracture Mechanics
      Author(s): G.C. Sih
      The unstable bonds of ATP (Adenosine triphosphate) are investigated in relation to those for the GTP, CTP and UTP. Two existing efficacies Eff A: GTP> UTP > CTP > ATP and Eff B: ATP > UTP>CTP>GTP can be substantiated, respectively, by two least variance inequalities Var A: ΔRGTP>ΔRUTP>ΔRCTP>ΔRATP and Var B: ΔRATP>ΔRUTP>ΔRCTP>ΔRGTP . The verification involves computing the R-integrals and their variances ΔR from the nanometer displacements of the molecules of the S49 wild-type lymphoma cells. They are relevant to the coupling of the β2-adrenoreceptor (β2AR) to Gs protein, expressed as β2AR-Gαs. Application of the least variance principle, Eff A and B is identified with the NTP (Nucleoside 5′-triphosphates). They can enhance or inhibit the agonist-stimulated AC (Adenylyl cyclase) activity. Eff A is found to be more stable with a longer sustaining time than Eff B. These findings are consistent with the behavior of potentially reactive molecules. Corrective measures of ATP production can be used as an adjustment at the molecular scale to compensate for the unstable character of the ATP molecules. Quantitative assessment of the reactive process of ATP can also provide information on the breakdown of RNA and DNA. A possible approach is to couple the use of energy-release and non-equilibrium thermodynamics with the principle of least variance.


      PubDate: 2013-05-31T11:04:46Z
       
  • Editorial Board
    • Abstract: Publication date: February–April 2013
      Source:Theoretical and Applied Fracture Mechanics, Volumes 63–64




      PubDate: 2013-04-25T11:04:56Z
       
  • Editorial Board
    • Abstract: December 2012
      Publication year: 2012
      Source:Theoretical and Applied Fracture Mechanics, Volume 62




      PubDate: 2013-03-24T12:03:59Z
       
  • Fuzzy Variable Method for Characterizing Flaw Sizes
    • Abstract: Available online 22 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      Most of the discovery and measurement of the flaw sizes are using non-destructive testing (NDT) detection method. NDT detected flaw size with apparent randomness and fuzziness. This paper presents a fuzzy possibility distribution of flaw sizes based on the fuzzy theory of NDT and fuzzy variable method. This distribution is closer to the flaws’ real sizes and is more convenient to use, and can be used to cracks’ Monte Carlo simulation and other aspects of fracture mechanics analysis.


      PubDate: 2013-03-24T12:03:59Z
       
  • A synthesis of data from steel spot welded joints of reduced thickness by
           means of local SED
    • Abstract: Available online 22 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      In some previous works two fatigue scatterbands were given in terms of the local strain energy density (SED) for welded joints made of structural steel and aluminium alloy. The material-dependent radius R 0 of the control volume was identified with reference to conventional arc welding processes. It resulted equal to 0.28 mm for welded joints made of structural steel tested under prevailing mode I, with fatigue failures both at the weld root and the weld toe. The scatter band did not include data from thin welded joints, the main plate thickness being greater than 6 mm. The SED approach is used here to summarise more than 400 fatigue data from steel spot welds in lap-shear joints, coach-peel specimens and cross-tension specimens of small thickness. Due to the typical crack initiation and propagation phases, an appropriate choice to summarise the data in a narrow scatterband seems to be the use of a toroidal control volume. The volume circumferentially encapsulates the slit tip along the weld spot nugget. The SED value at 2 million cycles is found to match that of the previous scatterband for welded joints of higher thicknesses.


      PubDate: 2013-03-24T12:03:59Z
       
  • On-off switching of theta-delta brain waves related to falling asleep and
           awakening
    • Abstract: Available online 14 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      The monoscale time span transitions from minutes-to-minutes are examined in relation to the interaction of delta and theta waves. Sustainability and stability of the delta and theta waves are evaluated by the severity of the oscillatory behavior of the least variance, a principle established for ranking cell growth. The relative order or disorder of delta and theta waves can be applied to distinguish the difference between falling asleep (FA) and awakening (AW). The brain wave frequency, amplitude and phase angles are regarded as the governing parameters in conjunction with the concept of synchronicity via the weighting functions. Awakening (AW) is found to be more controllable with a shorter time of sustainability as compared to falling asleep (FA). This corresponds to theta waves stabilizes at a shorter time interval of 0-5min than delta waves at 0-10min. These results are based on the least variances averaged over the time span depicted. They are presented to encourage additional experiments on FA and AW. The monoscale time span study of delta-theta waves should be further reinforced by a dual scale time span of seconds-minutes with reference to the NREM and REM cycle of FA and AW. In particular, the direction of arrow from K-Complex (KC) to sleep spindle (SS) such as KC→SS deserves attention in relation to the reverse order of SS→KC. The reversal behavior may be associated with the N1 to N3 segment and N3 to REM segment of the FA-AW cycle. The monoscale study provides the impetus to further study the multiscale time span behavior of brain waves in general.


      PubDate: 2013-03-16T12:06:02Z
       
  • Crack tip strain localisation on mechanics of fracture of heat resistant
           steel after hydrogenation
    • Abstract: Available online 14 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      The fracture toughness of steel 15Kh2MFA(ІІ) after the PTL was investigated. It was established that the crack start is a multilevel process, in which the defining role is played by the turning modes of deformation. Regardless of the PTL modes in air and in the aggressive medium (electrolytic hydrogen), the resistance to brittle failure of the steel investigated increases as compared to static fracture toughness of the material in the initial state.


      PubDate: 2013-03-16T12:06:02Z
       
  • Propagation of interactive parallel flat elliptical cracks inclined to
           shear stress
    • Abstract: Available online 14 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      The propagation and interaction of parallel arrays of cracks embedded in rock mass have critical impact on the stability of rock mass subjected to earthquake. To investigate the propagation of these embedded cracks under shear stress, three-dimensional element partition method (3D-EPM) is used to model the pre-existing cracks in conjunction with the augmented virtual internal bond(AVIB) constitutive model to describe the rock matrix. By 3D-EPM, the contact effect of crack faces can be automatically accounted in the original mesh scheme. By AVIB, the failure criterion would be implicitly invoked by the micro fracture mechanism. It is revealed that the propagation pattern of embedded flat cracks to shear stress is related to the inclination of crack relative to the shear force. When the inclination is smaller than 90 degree, the father crack firstly propagates in wrapping wing pattern. Then, many parallel arrays of descendent cracks, which are vertical to the relative slip of the father crack faces, anti-symmetrically initiate on part of the upper and the lower father crack faces, respectively. With the inclination increasing, the distribution area of the descendent cracks moves from the lower to the upper part of the father crack face. With shear stress increasing, a prior propagation path, vertical to the father crack face, is formed near the middle transect of the father crack. Finally, these prior extended descendent cracks adjacent to different father cracks coalesce together in zigzag at rock bridges. However, when the inclination is bigger than 90 degree, the father cracks only independently propagate along their minor axis directions. The extended crack is coplanar with the father crack. In all inclination cases, no apparent tensile fracture propagates at the two major axis tips of the original crack. It is also found that the shear strength of the cracked specimen is strongly dependent on the inclination of embedded cracks. When the inclination varies from 0 to 40 degree or from 180 to 120 degrees, the shear strength remarkably decreases while when the inclination varies from 40 to 120 degrees, the shear strength changes very little. The features of crack propagation obtained and the conclusions drawn in the present paper are significantly valuable for the evaluation of jointed rock slope stability and land slide.


      PubDate: 2013-03-16T12:06:02Z
       
  • Dynamic fracture of an interfacial crack in a two-layered functionally
           graded piezoelectric strip
    • Abstract: Available online 14 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      The transient response of an interfacial crack between two functionally graded piezoelectric strips was investigated. The layered functionally graded piezoelectric material (FGPM) was subjected to uniform anti-plane mechanical and in-plane electric displacement impacts on the upper and lower free surfaces. An integral transform, Cauchy singular integral equation, and Chebyshev polynomial expansions were applied to obtain stress intensity factors and energy density factors in the Laplace transform domain. The Durbin method was then used to implement numerical inversion. The accuracy of the numerical results was examined, and superior parameters for Durbin inversion were suggested. The results show that the functionally graded parameters of the two-layered FGPM can either increase or decrease the value of the dynamic stress intensity factor and the dynamic energy density factor, thereby retarding or promoting the propagation of interfacial cracks.


      PubDate: 2013-03-16T12:06:02Z
       
  • Laser beam welding residual stresses of cracked T-joints
    • Abstract: Available online 14 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      A damage tolerance analysis methodology for Laser Beam Welded (LBW) structures is proposed. The Residual Stresses (RS) of LBW T-joints are initially calculated through the thermo-mechanical simulation of the LBW process. Through cracks of variable length are considered in the vicinity of the weld and the calculated RS field is introduced in the numerical calculation of the Stress Intensity Factors (SIF). As the Finite Element (FE) models used for the thermo-mechanical simulation cannot be the same to those required for the fracture analysis, a special numerical routine based on interpolation techniques is applied for the transfer of RS field to the fracture mechanics FE model. The computation of SIFs at the crack front is performed for mode-I external loading. The RS effect of various cracked T-joint configurations on the SIF values at different through-the-thickness locations is studied. It is shown that both the RS field, as well as the other studied parameters, have a significant influence on the calculated Stress Intensity Factor values.


      PubDate: 2013-03-16T12:06:02Z
       
  • Damage mechanism and mode of square reinforced concrete slab subjected to
           blast loading
    • Abstract: Available online 14 March 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      Reinforcement concrete is the principle material for military engineering and nuclear power plant. However, impact and explosions could completely destroy such structures, causing tremendous casualties and property loss. Therefore, analyzing the damage mechanism and mode of the structures under blast loading is significant. The objective of this paper is to investigate the dynamics response and damage mechanism of three 1000 mm × 1000 mm × 400 mm reinforcement concrete slabs subjected to 400 mm standoff distance close-in explosions using LS-DYNA software and compare with experimental tests. A three-dimensional material model including explosive, air and reinforcement concrete slab with separated modeling method taking into account Arbitrary Lagrange-Euler, multiple materials algorithms and fluid-structure coupling interaction, is created to simulate the experiments. The sophisticated concrete and reinforcement bar material models, considering the strain rate effects, dynamic increasing factor and equation of state for concrete, are applied in simulating the damage mechanism and dynamic response. From the numerical results and comparison of the experimental data, it can be seen that the numerical results and experimental data shows a favorable agreement and the present model can still give a reliable prediction of the damage characteristic for the reinforcement concrete slabs. It also observed that the increase of the amount of the explosive can change the failure mode of the slab.


      PubDate: 2013-03-16T12:06:02Z
       
  • Sustainable time and stability of hippocampal and cortical EEG theta waves
    • Abstract: Available online 25 January 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      Sinusoidal wave function is used to quantify brain rhythms characterized by the interaction of frequency, amplitude, and phase angle (FAP). Their combinations have been differentiated in terms of gamma, beta, alpha, theta, and delta waves, in accordance with test data obtained from electroencephalography (EEG) at different locations of the scalp, and hence neurons at the different locations of the brain. The standard wave-type classifications, however, refer to a wide range of situations that are changeable according to variations of the sensory stimuli such that one wave type may switch into another. Even for the same wave type, say theta, a perturbation of frequency and/or amplitude can alter the sustainable time of the wave. The Least Variance Principle (LVP) is applied to determine the stable and reliable state of the “hippocampal” and “cortical” EEG theta waves having the, respective, frequency ranges of 7-9 Hz and 4-7 Hz. The sustainable time of the hippocampal waves are longer and more stable while those of the cortical waves are shorter and less stable. These findings are in general agreement with the available experimental results obtained from small mammals and humans. Also keep in mind of the difference in the method of recording the EEG waves. Seven different cases are reported from the LVP model. They are characterized by a comparative scheme for testing the sensitivity of the frequency and phase angle changes. Using the average frequencies of 8.0Hz for the hippocampal waves and a higher phase angle and 5.5Hz for the cortical waves and a lower phase angle, the, respective, sustainable times are found to be 2.2 sec and 0.5 sec. The hippocampal waves were found to be more stable. These results correspond precisely to test measurements where perturbation of the frequencies and phase angles can correspond to large variations in the sustainable time of the hippocampal and cortical theta waves. In general, larger frequencies and phase angles favor longer sustainable and stable time. That is perturbation of the theta wave frequency and phase angle can result in appreciable change of the sustainable time of the theta wave. These features are exhibited consistently by the results for seven different FAPs. Other situations can be generated to propose additional theta wave oscillation experiments.


      PubDate: 2013-01-27T15:03:43Z
       
  • Ballistic resistance analysis of double-layered composite material
           structures
    • Abstract: Available online 10 January 2013
      Publication year: 2013
      Source:Theoretical and Applied Fracture Mechanics

      The spherical cavity expansion theory is applied. Considered are the effects of the resistance of the projectile nose and the friction of the projectile shank on the penetration depths and residual velocities of the projectiles. By progressively increasing the depth of penetration into double-layered composite targets, we adopted numerical calculation manner to develop the analytical model that determined the residual velocities, ballistic limit velocities, and penetration depths of the ogival nose projectiles during normal impact with double-layered composite targets of varying thicknesses. We also used NATO 0.30” armor piercing (AP) bullets to strike double-layered composite targets made from 6061-T651 aluminum, 5083-H116 aluminum, polycarbonate (PC), and polymethylmethacrylate (PMMA) plates for the ballistic tests. The analytical model predictions show well agreement with experimental results from Dey et al. (Int. J. Solids Struct. 44 (2007) 6701-6723.), Børvik et al. (Proceedings of the SEM Annual Conference, 2009), and the present ballistic tests.


      PubDate: 2013-01-11T15:03:57Z
       
 
 
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