The Experts below are selected from a list of 1689 Experts worldwide ranked by ideXlab platform
Noël Challamel - One of the best experts on this subject based on the ideXlab platform.
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A localization analysis of a non-uniform Damage lattice in presence of strength gradient
International Journal of Fracture, 2018Co-Authors: Benjamin Hérisson, Noël Challamel, Vincent Picandet, Arnaud PerrotAbstract:The failure of a non-uniform axial Damage chain under uniform tension is studied both with discrete Damage mechanics (DDM) and continuum Damage mechanics (CDM). It is shown that a micomechanics-based Nonlocal CDM Model may be built from a DDM formulation, that may include material heterogeneities. DDM is based on a microstructured Model consisting in multiples elastic-Damage springs, whose elastic yield threshold is variable and depends on the position along the chain. We aim to develop a Nonlocal CDM Model as a relevant continuous formulation of the lattice DDM system. To do this, we rely upon a continualisation procedure applied to the difference formulation of the lattice problem, which gives us a Nonlocal propagating Damage Model. The boundary conditions of the Nonlocal CDM problem are equivalent to a finite length Damage cohesive law. Analytical and numerical results show a strong proximity of the discrete and enriched continuous approaches for this heterogeneous bar problem, as well as the effectiveness of the Nonlocal Damage Model to capture the softening localization phenomenon in heterogeneous quasi-brittle fields.
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A variationally based Nonlocal Damage Model to predict diffuse microcracking evolution
International Journal of Mechanical Sciences, 2010Co-Authors: Noël ChallamelAbstract:Abstract We explore a variationally based Nonlocal Damage Model, based on a combination of a Nonlocal variable and a local Damage variable. The Model is physically motivated by the concept of “Nonlocal” effective stress. The energy functional which depends on the displacement and the Damage fields is given for a one-dimensional bar problem. The higher-order boundary conditions at the boundary of the elasto-Damaged zone are rigorously derived. We show that the gradient Damage Models can be obtained as particular cases of such a formulation (as an asymptotic case). Some new analytical solutions will be presented for a simplified formulation where the stress–strain Damage law is only expressed in a local way. These Continuum Damage Mechanics Models are well suited for the tension behaviour of quasi-brittle materials, such as rock or concrete materials. It is theoretically shown that the Damage zone evolves with the load level. This dependence of the localization zone to the loading parameter is a basic feature, which is generally well accepted, from an experimental point of view. The computation of the Nonlocal inelastic problem is based on a numerical solution obtained from a nonlinear boundary value problem. The numerical treatment of the nonlinear Nonlocal Damage problem is investigated, with some specific attention devoted to the Damageable interface tracking. A bending cantilever beam is also studied from the new variationally based Nonlocal Damage Model. Wood’s paradox is solved with such a Nonlocal Damage formulation. Finally, an anisotropic Nonlocal tensorial Damage Model with unilateral effect is also introduced from variational arguments, and numerically characterized in simple loading situations.
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A variationally based Nonlocal Damage Model to predict diffuse microcracking evolution
International Journal of Mechanical Sciences, 2010Co-Authors: Noël ChallamelAbstract:We explore a variationally based Nonlocal Damage Model, based on a combination of a Nonlocal variable and a local Damage variable. The Model is physically motivated by the concept of ''Nonlocal'' effective stress. The energy functional which depends on the displacement and the Damage fields is given for a one-dimensional bar problem. The higher-order boundary conditions at the boundary of the elasto-Damaged zone are rigorously derived. We show that the gradient Damage Models can be obtained as particular cases of such a formulation (as an asymptotic case). Some new analytical solutions will be presented for a simplified formulation where the stress-strain Damage law is only expressed in a local way. These Continuum Damage Mechanics Models are well suited for the tension behaviour of quasi-brittle materials, such as rock or concrete materials. It is theoretically shown that the Damage zone evolves with the load level. This dependence of the localization zone to the loading parameter is a basic feature, which is generally well accepted, from an experimental point of view. The computation of the Nonlocal inelastic problem is based on a numerical solution obtained from a nonlinear boundary value problem. The numerical treatment of the nonlinear Nonlocal Damage problem is investigated, with some specific attention devoted to the Damageable interface tracking. A bending cantilever beam is also studied from the new variationally based Nonlocal Damage Model. Wood's paradox is solved with such a Nonlocal Damage formulation. Finally, an anisotropic Nonlocal tensorial Damage Model with unilateral effect is also introduced from variational arguments, and numerically characterized in simple loading situations. (C) 2010 Elsevier Ltd. All rights reserved.
Jacky Mazars - One of the best experts on this subject based on the ideXlab platform.
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Stress-based Nonlocal Damage Model
International Journal of Solids and Structures, 2011Co-Authors: Cédric Giry, Frédéric Dufour, Jacky MazarsAbstract:Abstract Progressive microcracking in brittle or quasi-brittle materials, as described by Damage Models, presents a softening behavior that in turn requires the use of regularization methods in order to maintain objective results. Such regularization methods, which describe interactions between points, provide some general properties (including objectivity and the non-alteration of a uniform field) as well as drawbacks (Damage initiation, free boundary). A modification of the Nonlocal integral regularization method that takes the stress state into account is proposed in this contribution. The orientation and intensity of Nonlocal interactions are modified in accordance with the stress state. The fundamental framework of the original Nonlocal method has been retained, making it possible to maintain the method’s advantages. The modification is introduced through the weight function, which in this modified version depends not only on the distance between two points (as for the original Model) but also on the stress state at the remote point. The efficiency of this novel approach is illustrated using several examples. The proposed modification improves the numerical solution of problems observed in numerical simulations involving regularization techniques. Damage initiation and propagation in mode I as well as shear band formation are analyzed herein.
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Stress-based Nonlocal Damage Model
International Journal of Solids and Structures, 2011Co-Authors: Cédric Giry, Frédéric Dufour, Jacky MazarsAbstract:International audienc
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Stress state influence on Nonlocal interactions in Damage Modelling
2010Co-Authors: Cédric Giry, Frédéric Dufour, Jacky Mazars, Panagiotis KotronisAbstract:This paper presents a modification of an integral Nonlocal Damage Model used to describe concrete behaviour. It aims at providing a better treatment of areas close to a boundary and a fracture process zone where the interactions between points should vanish. Modifications on the original integral Nonlocal Model are introduced by considering the stress state of points in the weight function used to compute the Nonlocal variables. Computations show that local information such as strain or Damage profiles are significantly different, leading to a narrower region where Damage equal to 1 in the case of the modified Nonlocal Model. It allows to better approach a discontinuity of the displacement field upon failure and thus, improves the estimation of the crack opening that has been developed in post-processing for this type of calculation.
M.f. Nahan - One of the best experts on this subject based on the ideXlab platform.
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A simple Nonlocal Damage Model for predicting failure in a composite shell containing a crack
Composite Structures, 1997Co-Authors: T.c. Kennedy, M.f. NahanAbstract:The design of commercial aircraft structures composed of composite materials requires the ability to predict failure loads in laminated shells containing cracks. A Damage zone of considerable influence is known to develop in advance of the crack tip in a composite material. The objective of this investigation was to develop a computational Model that simulates progressive Damage growth around cracks and allows the prediction of failure loads in complex laminated shell structures. This was accomplished through the use of a relatively simple, Nonlocal Damage Model that incorporates strain-softening. The Model was implemented in a finite element shell program. An analysis was performed on a section of a composite aircraft fuselage containing a crack and subjected to internal pressure loading. Reasonably good agreement was found between the calculations and the results from a test.
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A simple Nonlocal Damage Model for predicting failure of notched laminates
Composite Structures, 1996Co-Authors: T.c. Kennedy, M.f. NahanAbstract:The ability to predict failure loads in notched composite laminates is a requirement in a variety of structural design circumstances. A complicating factor is the development of a zone of Damaged material around the notch tip. The objective of this study was to develop a computational technique that simulates progressive Damage growth around a notch in a manner that allows the prediction of failure over a wide range of notch sizes. This was accomplished through the use of a relatively simple, Nonlocal Damage Model that incorporates strain-softening. This Model was implemented in a two-dimensional finite element program. Calculations were performed for two different laminates with various notch sizes under tensile loading, and the calculations were found to correlate well with experimental results.
L.f. Pereira - One of the best experts on this subject based on the ideXlab platform.
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simulation of compaction and crushing of concrete in ballistic impact with a new Damage Model
International Journal of Impact Engineering, 2018Co-Authors: L.f. Pereira, J Weerheijm, L J SluysAbstract:Although many aspects of the fracturing process of concrete are now well understood and successfully simulated with various Models, it is still very difficult to properly simulate the different failure mechanisms observed in a concrete structure induced by ballistic impact. In this paper, an enhanced version of the effective-rate-dependent Nonlocal Damage Model [Eng. Fracture Mechanics, 176 (2017)] is proposed to simulate the response of concrete in such events. Hydrostatic Damage has been added to the formulation in order to take the Damage of the material matrix observed while porosity reduces during compaction into account. Besides controlling the evolution of the nonlinear volumetric response of the material, this new Damage variable contributes to the deterioration of the material stiffness upon confinement. It is demonstrated that the description of the nonlinear volumetric response of concrete by an equation of state (EOS) as a plasticity phenomenon, as it is commonly done in hydrodynamic constitutive Modeling, is unrealistic for concrete. Such formulations fail to represent the effect of the loss of cohesion observed during compaction on the deviatoric response of the material. By taking this phenomenon into consideration, the proposed Model systematically predicts the relevant failure modes (cratering, tunneling, radial cracking and spalling) observed during ballistic impact on a concrete plate as a function of the projectile velocity and plate thickness. © 2017 Elsevier Ltd
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A numerical study on crack branching in quasi-brittle materials with a new effective rate-dependent Nonlocal Damage Model
Engineering Fracture Mechanics, 2017Co-Authors: L.f. Pereira, Jaap Weerheijm, Lambertus J. SluysAbstract:Abstract This contribution presents a numerical study towards the propagation and branching of cracks in quasi-brittle materials, using a new effective rate-dependent Damage Model, enhanced by a stress-based Nonlocal (SBNL) regularization scheme. This phenomenological Model is mesh objective and reproduces the major phenomena associated with crack propagation and branching in quasi-brittle materials. It is discussed and demonstrated that the branching phenomenon is not controlled by a specific, material dependent, crack speed. Instead, it is governed by the evolution of the principal stresses at the crack tip, which are controlled by the evolution of Damage. It is demonstrated that, with increasing crack speeds, the principal stresses at the crack tip tend to evolve from a mode-I to a mixed-mode state. Beyond a certain (critical) crack speed, the stress distribution around the crack tip reaches a critical state at which a single crack is no longer stable. When this condition is met, crack branching occurs whenever the stress field at the crack tip is destabilized by either a physical discontinuity or an interfering stress wave reflected at the specimen boundaries.
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A new rate-dependent stress-based Nonlocal Damage Model to simulate dynamic tensile failure of quasi-brittle materials
International Journal of Impact Engineering, 2016Co-Authors: L.f. Pereira, Jaap Weerheijm, Lambertus J. SluysAbstract:The development of realistic numerical tools to efficiently Model the response of concrete structures subjected to close-in detonations and high velocity impact has been one of the major quests in defense research. Under these loading conditions, quasi-brittle materials undergo a multitude of failure (Damage) mechanisms. Dynamic tensile failure (e.g. spalling), characterized by a significant strength increase associated with loading rate, has revealed to be particularly challenging to represent. In this contribution, a rate-dependent stress-based Nonlocal Damage Model has been introduced for the simulation of dynamic tensile failure of quasi-brittle materials. The recently proposed stress-based Nonlocal criterion has been updated in order to be consistently combined with a rate-dependent version of the well-known Mazars Damage Model. The Model was implemented in LS-DYNA using a fully explicit computational scheme. Two sets of numerical examples have been presented. First, one-dimensional numerical analyses were conducted to evaluate the Model capabilities, applicability and limitations. Second, the Model has been validated against experimental results. It has been shown that the proposed Model, in addition to correcting spurious mesh sensitivity, also provides a more realistic representation of Damage initiation and growth, in particular around discontinuities (notches and free boundaries) and Damaged areas.
Cédric Giry - One of the best experts on this subject based on the ideXlab platform.
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Stress-based Nonlocal Damage Model
International Journal of Solids and Structures, 2011Co-Authors: Cédric Giry, Frédéric Dufour, Jacky MazarsAbstract:Abstract Progressive microcracking in brittle or quasi-brittle materials, as described by Damage Models, presents a softening behavior that in turn requires the use of regularization methods in order to maintain objective results. Such regularization methods, which describe interactions between points, provide some general properties (including objectivity and the non-alteration of a uniform field) as well as drawbacks (Damage initiation, free boundary). A modification of the Nonlocal integral regularization method that takes the stress state into account is proposed in this contribution. The orientation and intensity of Nonlocal interactions are modified in accordance with the stress state. The fundamental framework of the original Nonlocal method has been retained, making it possible to maintain the method’s advantages. The modification is introduced through the weight function, which in this modified version depends not only on the distance between two points (as for the original Model) but also on the stress state at the remote point. The efficiency of this novel approach is illustrated using several examples. The proposed modification improves the numerical solution of problems observed in numerical simulations involving regularization techniques. Damage initiation and propagation in mode I as well as shear band formation are analyzed herein.
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Stress-based Nonlocal Damage Model
International Journal of Solids and Structures, 2011Co-Authors: Cédric Giry, Frédéric Dufour, Jacky MazarsAbstract:International audienc
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Stress state influence on Nonlocal interactions in Damage Modelling
2010Co-Authors: Cédric Giry, Frédéric Dufour, Jacky Mazars, Panagiotis KotronisAbstract:This paper presents a modification of an integral Nonlocal Damage Model used to describe concrete behaviour. It aims at providing a better treatment of areas close to a boundary and a fracture process zone where the interactions between points should vanish. Modifications on the original integral Nonlocal Model are introduced by considering the stress state of points in the weight function used to compute the Nonlocal variables. Computations show that local information such as strain or Damage profiles are significantly different, leading to a narrower region where Damage equal to 1 in the case of the modified Nonlocal Model. It allows to better approach a discontinuity of the displacement field upon failure and thus, improves the estimation of the crack opening that has been developed in post-processing for this type of calculation.
