Showing papers on "Fracture mechanics published in 2001"
TL;DR: In this paper, a finite element analysis of delamination in laminated composites is addressed using interface elements and an interface damage law, where the principles of linear elastic fracture mechanics are indirectly used by equating the area underneath the traction/relative displacement curve to the critical energy release rate of the mode under examination.
Abstract: The finite element analysis of delamination in laminated composites is addressed using interface elements and an interface damage law. The principles of linear elastic fracture mechanics are indirectly used by equating, in the case of single-mode delamination, the area underneath the traction/relative displacement curve to the critical energy release rate of the mode under examination. For mixed-mode delamination an interaction model is used which can fulfil various fracture criteria proposed in the literature. It is then shown that the model can be recast in the framework of a more general damage mechanics theory. Numerical results are presented for the analyses of a double cantilever beam specimen and for a problem involving multiple delamination for which comparisons are made with experimental results. Issues related with the numerical solution of the non-linear problem of the delamination are discussed, such as the influence of the interface strength on the convergence properties and the final results, the optimal choice of the iterative matrix in the predictor and the number of integration points in the interface elements. Copyright © 2001 John Wiley & Sons, Ltd.
1,169 citations
TL;DR: This review assesses the current understanding of the resistance of graded materials to contact deformation and damage, and outlines future research directions and possible applications for graded materials.
Abstract: The mechanical response of materials with spatial gradients in composition and structure is of considerable interest in disciplines as diverse as tribology, geology, optoelectronics, biomechanics, fracture mechanics, and nanotechnology. The damage and failure resistance of surfaces to normal and sliding contact or impact can be changed substantially through such gradients. This review assesses the current understanding of the resistance of graded materials to contact deformation and damage, and outlines future research directions and possible applications for graded materials.
741 citations
TL;DR: In this paper, the eXtended Finite Element Method (X-FEM) is used to discretize the equations, allowing for the modeling of cracks whose geometry is independent of the finite element mesh.
546 citations
TL;DR: In this paper, the influence of casting defects on the room temperature fatigue performance of a Sr-modified A356-T6 casting alloy has been studied using unnotched polished cylindrical specimens.
510 citations
TL;DR: In this paper, the authors revisited the maximum tensile stress (MTS) criterion to predict brittle fracture of polymethylmethacrylate (PMMA) using angled cracked plates.
Abstract: The purpose of this paper is to revisit the maximum tensile stress (MTS) criterion to predict brittle fracture for mixed mode conditions. Earlier experimental results for brittle fracture of polymethylmethacrylate (PMMA) using angled cracked plates are also re-examined. The role of the T-stress in brittle fracture for linear elastic materials is emphasized. The generalized MTS criterion is described in terms of mode I and II stress intensity factors, K I and K II and the T-stress (the stress parallel to the crack), and a fracture process zone, r c . The generalized MTS criterion is then compared with the earlier experimental results for PMMA subjected to mixed mode conditions. It is shown that brittle fracture can be controlled by a combination of singular stresses (characterized by K) or non-singular stress (T-stress). The T-stress is also shown to have an influence on brittle fracture when the singular stress field is a result of mode II loading.
501 citations
TL;DR: In this paper, the authors investigated the crack coalescence and peak strength of rock-like materials containing three parallel frictional flaws and found that the failure mechanism strongly depends on the cracks coalescence pattern between pre-existing flaws.
497 citations
TL;DR: In this paper, a ductile phase containing bulk metallic glass composites is prepared via an in situ method by rapid quenching of a homogenous Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 melt.
447 citations
TL;DR: In this article, the use of cohesive theories of fracture, in conjunction with the explicit resolution of the near-tip plastic fields and the enforcement of closure as a contact constraint, for the purpose of fatigue-life prediction is investigated.
Abstract: We investigate the use of cohesive theories of fracture, in conjunction with the explicit resolution of the near-tip plastic fields and the enforcement of closure as a contact constraint, for the purpose of fatigue-life prediction. An important characteristic of the cohesive laws considered here is that they exhibit unloading-reloading hysteresis. This feature has the important consequence of preventing shakedown and allowing for steady crack growth. Our calculations demonstrate that the theory is capable of a unified treatment of long cracks under constant-amplitude loading, short cracks and the effect of overloads, without ad hoc corrections or tuning.
417 citations
Book•
23 Mar 2001
TL;DR: In this paper, linear elastic fracture mechanics and elastic-plastic fracture mechanics are discussed. And they are combined with adhesion fracture and delamination fracture mechanics to form elastic elastic fracture.
Abstract: Chapter Headings. Linear elastic fracture mechanics. Elastic-plastic fracture mechanics. Adhesion fracture mechanics. Delamination fracture mechanics.
340 citations
TL;DR: In this paper, the grain boundary distributions were analyzed with special emphasis on grain boundary character along intergranular stress corrosion cracks and at crack arrest points, and it was established that only coherent twin Σ3 boundaries could be considered as special boundaries with regard to crack resistance.
15 Nov 2001-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the microstructure and fatigue properties of three model AS7G03 cast aluminium alloys containing artificial pore have been studied by using Synchrotron X-ray tomography.
Abstract: The microstructure and fatigue properties of three model AS7G03 cast aluminium alloys containing artificial pores have been studied. Synchrotron X-ray tomography has been used to characterise in three dimensions the pore population in the alloys. The development of fatigue cracks in relation with local crystallography has been studied by means of electron back scattered diffraction (EBSD). Both the average number of cycles to failure and the lifetime scatter depend on the pore content specially at high stress level. The mechanism leading to the initiation of a crack from a pore has been identified. The crack propagation at high stress level appears to be quite insensitive to microstructural barriers and can be reasonably well described by a Paris type law. At low stresses, however, short cracks are often observed to be stopped at grain boundaries and the fatigue life is no longer predicted by a simple propagation law.
TL;DR: In this article, a mode-dependent embedded process zone (EPZ) model has been developed and used to simulate the mixed-mode fracture of plastically deforming adhesive joints, which can provide quantitative predictions of the deformation and fracture of mixedmode geometries.
Abstract: A mode-dependent embedded-process-zone (EPZ) model has been developed and used to simulate the mixed-mode fracture of plastically deforming adhesive joints. Mode-I and mode-II fracture parameters obtained from previous work have been combined with a mixed-mode failure criterion to provide quantitative predictions of the deformation and fracture of mixed-mode geometries. These numerical calculations have been shown to provide excellent quantitative predictions for two geometries that undergo large-scale plastic deformation: asymmetric T-peel specimens and single lap-shear joints. Details of the deformed shapes, loads, displacements and crack propagation have all been captured reasonably well by the calculations.
TL;DR: In this article, the brittle failure of polycrystalline ice at temperatures > 0.8Tmp and strain rates (∼10−7−10−1 s−1) is discussed.
TL;DR: In this article, a fatigue crack driving force parameter, (K max ) α (Δ K + ) 1− α with load ratio effects on crack growth modeling is proposed, and the predictions are compared with the experimental data from the literature and the agreement is found to be fairly good.
TL;DR: In this article, a study on the accuracy of cohesive models for capturing dynamic fragmentation of ceramic microstructures is presented, which consists of a combined experimental/numerical approach in which microcracking and damage kinetics are examined by means of plate impact recovery experiments.
TL;DR: In this paper, a microfabric discrete element modeling (MDEM) approach is presented for modeling asphalt concrete microstructure, in which various material phases (e.g., aggregates, mastic) are modeled with clusters of very small, discrete elements.
Abstract: Micromechanical modeling has tremendous potential benefits in the field of asphalt technology for reducing or eliminating costly tests to characterize asphalt-aggregate mixtures for the design and control of flexible pavement structures and materials. In time, these models could provide a crucial missing link for the development of true performance-related specifications for hot-mix asphalt. A microfabric discrete element modeling (MDEM) approach is presented for modeling asphalt concrete microstructure. The technique is a straightforward extension of a traditional discrete element modeling (DEM) analysis, in which various material phases (e.g., aggregates, mastic) are modeled with clusters of very small, discrete elements. The MDEM approach has all the benefits of traditional DEM (e.g., the ability to handle complex, changing contact geometries and the suitability for modeling large displacements and crack propagation). These models also allow for the simulation of specimen assembly (e.g., laboratory com...
TL;DR: In this article, an isotropic damage model for concrete is presented, where the main features of the model are: limited number of constitutive parameters required; independent modelling of tension and compression behaviour by means of two damage variables and two separate activation criteria (bi-dissipative model); independent definition of tension/compression fracture energies; consistent modelling of the unilateral effect upon transition from tension to compression; and the effectiveness of fracture energy based regularization strategy.
TL;DR: In this article, a cohesive formulation of fracture is taken as a basis for the simulation of processes of combined tension-shear damage and mixed-mode fracture in specimens subjected to dynamic loading, and the model accurately captures the experimentally observed fracture patterns and displacement fields, as well as crack paths and cracktip velocities, as a function of pre-crack geometry and loading conditions.
Abstract: A cohesive formulation of fracture is taken as a basis for the simulation of processes of combined tension-shear damage and mixed-mode fracture in specimens subjected to dynamic loading. Our three-dimensional finite-element calculations account explicitly for crack nucleation, microcracking, the development of macroscopic cracks and inertia. In particular, a tension-shear damage coupling arises as a direct consequence of slanted microcrack formation in the process zone. We validate the model against the three-point-bend concrete beam experiments of Guo et al. (International Journal of Solids and Structures 1995; 32(17/18):2951–2607), John (PhD Thesis, Northwestern University, 1988), and John and Shah (Journal of Structural Engineering 1990; 116(3):585–602) in which a pre-crack is shifted from the central cross-section, leading to asymmetric loading conditions and the development of a mixed-mode process zone. The model accurately captures the experimentally observed fracture patterns and displacement fields, as well as crack paths and crack-tip velocities, as a function of pre-crack geometry and loading conditions. In particular, it correctly accounts for the competition between crack-growth and nucleation mechanisms.
15 May 2001-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a finite element method (FEM) is used to calculate stress development during thermal loading and these results can then be introduced into a crack propagation model to estimate crack development during the thermal cycling operation.
Abstract: A widely used method to produce thermal barrier coating (TBC) systems is the vacuum plasma spraying of a highly dense bondcoat layer with a defined surface roughness and the atmospheric plasma spraying (APS) of a porous (10–15%) Y 2 O 3 -stabilized zirconia top coat. In thermal cycling operation these systems often fail by crack initiation and propagation close to the bondcoat–top coat interface. This failure is attributed to stresses arising from the formation of a thermally grown oxide (TGO) layer on the rough bondcoat surface. The actual stress situation is rather complex due to TGO formation, creep effects in both bondcoat and top coat and due to the roughness of the bondcoat. All these factors have been take into account in the present work by using a finite element method (FEM) to calculate stress development during thermal loading. These results can then be introduced into a crack propagation model to estimate crack development during the thermal cycling operation. The predictions of this approach are compared to experimental results on the influence of bondcoat roughness on coating life. In these experiments TBC systems with bondcoat layers having three different levels of roughness were cycled in a gas burner rig until failure.
TL;DR: In this article, a new mechanical driving force parameter for long and short-crack growth rate correlation is proposed, which does not utilize disputable crack closure data, instead it is calculated as a geometric mean of the positive part of the applied stress intensity factor (SIF) range, ΔK+, and the corresponding maximum value of the SIF, Kmax.
TL;DR: In this article, a detailed three-dimensional finite-element study was conducted to explore near-field stress paths during the progressive advancement of a tunnel face, and the authors demonstrated that as the tunnel face approaches and passes through a unit volume of rock, the spatial and temporal evolution of the 3D stress field encompasses a series of deviatoric stress increases and/or decreases as well as several rotations of the principal stress axes.
TL;DR: In this article, a microstructural model for the mechanical behavior of quasi-brittle materials is developed and verified for concrete and bone specimens, based on interface elements equipped with a constitutive law representing non-linear fracture, while continuum elements remain linear elastic.
Abstract: A microstructural model for the mechanical behaviour of quasi-brittle materials is developed and verified for concrete and bone specimens. The model is based on interface elements equipped with a constitutive law representing non-linear fracture, while continuum elements remain linear elastic. The interface constitutive model is implemented with a sub-stepping scheme. Non-linear geometric effects due to large displacements are included in the model by means of an incremental Lagrangian formulation, although strains in the continuum and relative displacements in the interfaces are assumed to remain small. An arc-length procedure is used to ensure convergence during the highly non-linear behaviour in the post-peak regime. Concrete and bone specimens are idealized as two-phase particle composites and are discretized into finite elements, including interface elements along the main potential crack paths. The numerical results in tension and compression are described and compared with experimental observations. The need of considering non-linear geometric effects in this type of calculations is also discussed. Copyright © 2001 John Wiley & Sons, Ltd.
TL;DR: In this article, the formation of cup-cone fracture in round bars and of slant fracture in plane strain specimens using the finite element (FE) method was studied using the Rousselier model and the Gurson model.
TL;DR: In this article, a cohesive zone model for fatigue crack initiation and growth in quasibrittle materials is proposed, where the softening material in the cohesive zone and cracks are modeled as internal singular surfaces in the elastic body.
TL;DR: In this article, an edge crack in a strip of a functionally graded material (FGM) was studied under transient thermal loading conditions, where the FGM is assumed having constant Young's modulus and Poisson's ratio, but the thermal properties of the material vary along the thickness direction of the strip.
Abstract: An edge crack in a strip of a functionally graded material (FGM) is studied under transient thermal loading conditions. The FGM is assumed having constant Young's modulus and Poisson's ratio, but the thermal properties of the material vary along the thickness direction of the strip. Thus the material is elastically homogeneous but thermally nonhomogeneous. This kind of FGMs include some ceramic/ceramic FGMs such as TiC/SiC, MoSi2/Al2O3 and MoSi2/SiC, and also some ceramic/metal FGMs such as zirconia/nickel and zirconia/steel. A multi-layered material model is used to solve the temperature field. By using the Laplace transform and an asymptotic analysis, an analytical first order temperature solution for short times is obtained. Thermal stress intensity factors (TSIFs) are calculated for a TiC/SiC FGM with various volume fraction profiles of the constituent materials. It is found that the TSIF could be reduced if the thermally shocked cracked edge of the FGM strip is pure TiC, whereas the TSIF is increased if the thermally shocked edge is pure SiC.
TL;DR: In this paper, a combination of micro-structural observations of cracking and established mechanics of fracture of GaN films was used to examine the effect of tensile growth stresses on thin GaN GaN film growing on sapphire.
Abstract: Cracking of thick GaN films grown on sapphire is reexamined on the basis of a combination of microstructural observations of cracking and established mechanics of fracture of films. It is argued that cracking is motivated by tensile growth stresses once a critical thickness is reached. Subsequent growth on the cracked films occurs, perpetuating the cracked structure until the crack surfaces approach one another and touch. Continued film growth buries the crack. Once the crack faces touch, there are conditions under which it is energetically favorable for the cracks to close and heal. Crack healing can be kinetically limited. Whether the crack healing is complete within the growth time depends on several factors including, it is suggested, whether impurities have adsorbed to the surface during growth. Conditions under which cracks that have extended into the sapphire substrate during film growth can act as critical flaws for fracture of the substrate on cooling are also presented.
TL;DR: De Gennes and Okumura as mentioned in this paper constructed a coarse-grained elastic energy for such an anisotropic system and presented an analytic solution for a notch crack normal to the stratified sheets.
Abstract: Nacre, stratified ceramic layers surrounded by organic matrix, is a tough material found inside certain seashells. We construct a coarse-grained elastic energy for such an anisotropic system and present an analytic solution for a notch crack normal to the stratified sheets. This analysis proves the reduction in stress concentration which was announced in our earlier work (P. G. de Gennes and K. Okumura, C. R. Acad. Sci. Paris 1, Ser. IV, 257 (2000)) and the related increase in toughness.
TL;DR: In this paper, the authors performed simulations of the tensile deformation of cubic cubic metals and found that the strain to fracture is lower with the BCC materials than the FCC materials and that the radius of the neck increases with an increase in the deformation and decreases as the ductility of the material decreases.
TL;DR: In this paper, a mesh-free mesh-based fracture model is proposed for modeling brittle fracture, which is based on a cohesive view of materials, meaning that a finite material strength and work to fracture are included in the material description.