The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Marc Bonnet - One of the best experts on this subject based on the ideXlab platform.
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An adaptive algorithm for cohesive zone model and arbitrary Crack propagation
Revue Européenne de Mécanique Numérique European Journal of Computational Mechanics, 2012Co-Authors: Vincent Chiaruttini, Dominique Geoffroy, Vincent Riolo, Marc BonnetAbstract:This paper presents an approach to the numerical simulation of Crack propagation with cohesive models for the case of structures subjected to mixed mode loadings. The evolution of the Crack path is followed by using an adaptive method: with the help of a macroscopic branching criterion based on the calculation of an energetic integral, the evolving Crack path is remeshed as the Crack evolves in the simulation. Special attention is paid to the unknown fields transfer approach that is crucial for the success of the computational treatment. This approach has been implemented in the finite element code Z-Set (jointly developed by Onera and Ecole des Mines) and is tested on two examples, one featuring a Straight Crack path and the other involving a complex Crack propagation under critical monotonous loading monotonous.
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Fast identification of Cracks using higher-order topological sensitivity for 2-D potential problems
Engineering Analysis with Boundary Elements, 2011Co-Authors: Marc BonnetAbstract:This article concerns an extension of the topological sensitivity (TS) concept for 2D potential problems involving insulated Cracks, whereby a misfit functional $J$ is expanded in powers of the characteristic size $a$ of a Crack. Going beyond the standard TS, which evaluates (in the present context) the leading $O(a^{2})$ approximation of $J$, the higher-order TS established here for a small Crack of arbitrarily given location and shape embedded in a 2-D region of arbitrary shape and conductivity yields the $O(a^{4})$ approximation of $J$. Simpler and more explicit versions of this formulation are obtained for a centrally-symmetric Crack and a Straight Crack. A simple approximate global procedure for Crack identification, based on minimizing the $O(a^{4})$ expansion of $J$ over a dense search grid, is proposed and demonstrated on a synthetic numerical example. BIE formulations are prominently used in both the mathematical treatment leading to the $O(a^{4})$ approximation of $J$ and the subsequent numerical experiments.
Y. Yokoyama - One of the best experts on this subject based on the ideXlab platform.
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Fatigue pre-Cracking and toughness of the Zr55Cu30Al10Ni5 bulk metallic glass for two oxygen levels
Scripta Materialia, 2007Co-Authors: V. Keryvin, Y. Nadot, Y. YokoyamaAbstract:Samples of a Zr-based bulk metallic glass with a small (1000 appm) or very small (less than 300 appm) oxygen content are pre-Cracked by fatigue and tested for toughness evaluation. It is shown that oxygen trapped in oxide dendrites eases the initiation of a Straight Crack and embrittles the glass even at such low concentrations. In contrast, when oxygen is dissolved in the glass, fatigue Crack initiation becomes difficult and it is not possible to get a Crack passing Straight through the glass. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Solveig Melin - One of the best experts on this subject based on the ideXlab platform.
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Growth from a Straight Crack subjected to arbitrary remote loading
Engineering Fracture Mechanics, 1993Co-Authors: Solveig MelinAbstract:Growth from Straight Cracks is studied, both for loading in pure mode I or II and for mixed mode loading. Small scale yielding and a plane condition are assumed. Growth is assumed to take place in either mode I or mode II. Loss of directional stability sometimes occurs even from Cracks that seem destined for continued growth Straight forward. A striking example is the case of collinear Cracks under symmetric remote loading growing toward each other: before coalescence they deflect from their Straight paths and avoid each other instead of running together tip to tip as expected. One single Crack growing in mode I under symmetric loading conditions might suffer from loss of directional stability. Directional stability is here defined to prevail if the angle formed by the Straight line between the Crack tips and the original Crack direction eventually decreases during growth. This is shown to be the case if, and only if, the principal stress perpendicular to the original Crack is the largest of the two in-plane stresses. Another, although less logical, candidate for definition of directional stability is also discussed. It concentrates on the position of the Crack tips rather than on the main direction of the Crack and it is in this case assumed that directional stability prevails if the Crack tips eventually move closer toward the line along the original Crack. This definition leads to directional stability when the principal stress in the original Crack direction is smaller than the fraction 1 -π/4 of the other in-plane stress. For a Crack under mixed mode loading conditions an abrupt deviation from the Straight path is expected. Comparison of theoretically obtained values of the mode I and II stress intensity factors at the tips of the Crack, after introduction of an infinitesimal disturbance, with experimental results indicates that mode I growth is preferred before mode II in the absence of a confining pressure, at least if the ratio between the critical mode II and I stress intensity factors is larger than 0.38-0.81, depending on the load situation. Thus also a Straight Crack, originally directed favourably for extension Straight forward in mode II, will exhibit directional instability and mode I growth will take over after kink formation at the tips of the Crack. Eventually the growth approaches a direction perpendicular to the largest in-plane principal stress. (Less)
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Directional stability of an originally Straight Crack
International Journal of Fracture, 1992Co-Authors: Solveig MelinAbstract:The directional stability of an originally Straight Crack under symmetric remote loading is studied after introduction of an infinitesimal disturbance at one or both tips of the Crack. The Crack is assumed to grow slowly under vanishing mode II stress intensity factor. Directional stability is defined to prevail if the angle formed by the Straight line between the Crack tips and the original Crack direction eventually decreases during Crack growth. This is shown to be the case if, and only if, the principal stress perpendicular to the original Crack is the largest of the two in-plane stresses. Another candidate for definition of directional stability is also discussed, even though it appears less logical, since it concentrates on the position of the Crack tips rather than on the main direction of the Crack. It assumes that directional stability prevails if the Crack tips eventually move closer toward the line along the original Crack. This definition leads to directional instability when the principal stress in the original Crack direction is larger than the fraction 1-π/4 of the other in-plane stress.
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Directional stability of an originally Straight Crack
International Journal of Fracture, 1992Co-Authors: Solveig MelinAbstract:The directional stability of an originally Straight Crack under symmetric remote loading is studied after introduction of an infinitesimal disturbance at one or both tips of the Crack. The Crack is assumed to grow slowly under vanishing mode II stress intensity factor. Directional stability is defined to prevail if the angle formed by the Straight line between the Crack tips and the original Crack direction eventually decreases during Crack growth. This is shown to be the case if, and only if, the principal stress perpendicular to the original Crack is the largest of the two in-plane stresses. Another candidate for definition of directional stability is also discussed, even though it appears less logical, since it concentrates on the position of the Crack tips rather than on the main direction of the Crack. It assumes that directional stability prevails if the Crack tips eventually move closer toward the line along the original Crack. This definition leads to directional instability when the principal stress in the original Crack direction is larger than the fraction 1-/4 of the other in-plane stress. (Less)
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Which is the most unfavourable Crack orientation
International Journal of Fracture, 1991Co-Authors: Solveig MelinAbstract:The most unfavourable orientation of a Straight Crack of given length is investigated, assuming mode I growth. It is shown that this orientation is not always the one perpendicular to the largest principal stress. If the smallest in-plane principal stress is compressive and its magnitude more than about one third of the largest (tensile) in-plane stress, then some other orientations are more unfavourable. Crack growth then takes place after kinking.
Jan Sokolowski - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Crack singularities in an aging elastic material
ESAIM: Mathematical Modelling and Numerical Analysis, 2006Co-Authors: Martin Costabel, Monique Dauge, Sergei A. Nazarov, Jan SokolowskiAbstract:Version 10.03.2005International audienceWe consider a quasistatic system involving a Volterra kernel modelling an hereditarily-elastic aging body. We are concerned with the behavior of displacement and stress fields in the neighborhood of Cracks. In this paper, we investigate the case of a Straight Crack in a two-dimensional domain with a possibly anisotropic material law. We study the asymptotics of the time dependent solution near the Crack tips. We prove that, depending on the regularity of the material law and the Volterra kernel, these asymptotics contain singular functions which are simple homogeneous functions of degree \frac12 or have a more complicated dependence on the distance variable r to the Crack tips. In the latter situation, we observe a novel behavior of the singular functions, incompatible with the usual fracture criteria, involving super polynomial functions of \ln(r) growing in time
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Analysis of Crack singularities in an aging elastic material
ESAIM: Mathematical Modelling and Numerical Analysis, 2006Co-Authors: Martin Costabel, Monique Dauge, Sergei A. Nazarov, Jan SokolowskiAbstract:We consider a quasistatic system involving a Volterra kernel modelling an hereditarily-elastic aging body. We are concerned with the behavior of displacement and stress fields in the neighborhood of Cracks. In this paper, we investigate the case of a Straight Crack in a two-dimensional domain with a possibly anisotropic material law. We study the asymptotics of the time dependent solution near the Crack tips. We prove that, depending on the regularity of the material law and the Volterra kernel, these asymptotics contain singular functions which are simple homogeneous functions of degree \frac12 or have a more complicated dependence on the distance variable r to the Crack tips. In the latter situation, we observe a novel behavior of the singular functions, incompatible with the usual fracture criteria, involving super polynomial functions of \ln(r) growing in time.
Alvin C.k. Lai - One of the best experts on this subject based on the ideXlab platform.
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Comparison of Three Approaches to Model Particle Penetration Coefficient through a Single Straight Crack in a Building Envelope
Aerosol Science and Technology, 2010Co-Authors: Bin Zhao, Chun Chen, Xinyan Yang, Alvin C.k. LaiAbstract:In this study, we present three approaches to predict particle penetration coefficients through a single Straight Crack in building envelops. The three approaches are an analytical approach, an Eulerian approach, and a Lagrangian approach, respectively. The particle penetration coefficient through an idealized Straight Crack (smooth inner surfaces) and a strand board Crack (rough inner surfaces) were modeled by the three presented approaches. The calculated results were compared with the literature results. The comparison shows that for the idealized smooth Crack, the modeled results by the Eulerian approach match the experiments best for the entire range of particle sizes studied among the three approaches. The predicted results by the analytical approach also match the experiments reasonable well. Results modeled by the Lagrangian approach are less satisfied for fine particles (d p < 0.1 μm). Overall, all the three approaches agree well with the experiments for particle sizes ranging from 0.4–1.2 μm. Fo...