The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Alan Needleman - One of the best experts on this subject based on the ideXlab platform.
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Discrete Dislocation Predictions of Single Crystal Fatigue Crack Growth
Solid Mechanics and its Applications, 2020Co-Authors: Vikram Deshpande, Alan Needleman, Van Der Erik GiessenAbstract:A framework for analysis of crack growth under cyclic loading conditions is discussed where plastic flow arises from the motion of large numbers of discrete dislocations and the fracture properties are embedded in a Cohesive Surface constitutive relation. The formulation is the same as used to analyze crack growth under monotonic loading conditions, differing only in the remote loading being a cyclic function of time. Fatigue, i.e. crack growth in cyclic loading at a driving force for which the crack would have arrested under monotonic loading, emerges in the simulations as a consequence of the evolution of internal stresses associated with the irreversibility of the dislocation motion. The predictions for the qualitative features of fatigue crack growth are in remarkable accord with experimental observations.
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The Cohesive band model: a Cohesive Surface formulation with stress triaxiality
International Journal of Fracture, 2013Co-Authors: Joris J. C. Remmers, René Borst, Clemens V. Verhoosel, Alan NeedlemanAbstract:In the Cohesive Surface model Cohesive tractions are transmitted across a two-dimensional Surface, which is embedded in a three-dimensional continuum. The relevant kinematic quantities are the local crack opening displacement and the crack sliding displacement, but there is no kinematic quantity that represents the stretching of the fracture plane. As a consequence, in-plane stresses are absent, and fracture phenomena as splitting cracks in concrete and masonry, or crazing in polymers, which are governed by stress triaxiality, cannot be represented properly. In this paper we extend the Cohesive Surface model to include in-plane kinematic quantities. Since the full strain tensor is now available, a three-dimensional stress state can be computed in a straightforward manner. The Cohesive band model is regarded as a subgrid scale fracture model, which has a small, yet finite thickness at the subgrid scale, but can be considered as having a zero thickness in the discretisation method that is used at the macroscopic scale. The standard Cohesive Surface formulation is obtained when the Cohesive band width goes to zero. In principle, any discretisation method that can capture a discontinuity can be used, but partition-of-unity based finite element methods and isogeometric finite element analysis seem to have an advantage since they can naturally incorporate the continuum mechanics. When using interface finite elements, traction oscillations that can occur prior to the opening of a Cohesive crack, persist for the Cohesive band model. Example calculations show that Poisson contraction influences the results, since there is a coupling between the crack opening and the in-plane normal strain in the Cohesive band. This coupling holds promise for capturing a variety of fracture phenomena, such as delamination buckling and splitting cracks, that are difficult, if not impossible, to describe within a conventional Cohesive Surface model.
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3988 - MODELING FATIGUE CRACK GROWTH IN CRYSTALLINE SOLIDS WITH DISCRETE DISLOCATION PLATICITY
2013Co-Authors: Daniel S. Balint, Vikram Deshpande, Alan Needleman, E Van Der GiessenAbstract:Analyses of crack growth under cyclic loading conditions are discussed where plastic flow arises from the motion of large numbers of discrete dislocations and the fracture properties are embedded in a Cohesive Surface constitutive relation. The formulation is the same as used to analyse crack growth under monotonic loading conditions, differing only in the remote loading being a cyclic function of time. Fatigue, i.e. crack growth in cyclic loading at a driving force for which the crack would have arrested under monotonic loading, emerges in the simulations as a consequence of the evolution of internal stresses associated with the irreversibility of the dislocation motion. A fatigue threshold, Paris law behaviour, striations, the accelerated growth of short cracks and the scaling with material properties are outcomes of the calculations. Results for single crystals and polycrystals will be discussed.
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Fast crack growth along interfaces
Latin American Journal of Solids and Structures, 2005Co-Authors: Alan Needleman, Demirkan CokerAbstract:ANALYSES OF DYNAMIC CRACK GROWTH ALONG INTERFACES ARE DISCUSSED. THE MATERIAL ON EACH SIDE OF THE BOND LINE IS CHARACTERIZED BY AN ELASTIC CONSTITUTIVE RELATION. A Cohesive Surface CONSTITUTIVE RELATION THAT ALLOWS FOR THE CREATION OF NEW FREE Surface IS ALSO SPECIFIED ACROSS HE BOND LINE. THE RESISTANCE TO CRACK INITIATION AND THE CRACK SPEED HISTORY ARE THEN PREDICTED WITHOUT INVOKING ANY ADDITIONAL FAILURE CRITERION. TWO DIMENSIONAL MODELS, BOTH PLANE STRAIN AND PLANE STRESS, OF THE CON¯GURATION USED IN EXPERIMENTS OF ROSAKIS AND CO-WORKERS RE ANALYZED. THE FOCUS IS ON THE EMERGENCE OF CRACK SPEEDS GREATER THAN A CHARACTERISTIC WAVE SPEED AND ON THE NATURE OF CRACK TIP ¯ELDS AT SUCH INTERSONIC CRACK SPEEDS.
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A discrete dislocation analysis of rate effects on mode I crack growth
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: H.h.m. Cleveringa, Van Der Erik Giessen, Alan NeedlemanAbstract:The mesoscopic growth of a crack in an elastic-plastic single crystal under mode I loading conditions is studied using a formulation involving discrete dislocation dynamics and Cohesive Surfaces. A two-dimensional analysis is carried out with the dislocations all of edge character and modeled as line singularities in an elastic material. At each stage of loading, superposition is used to represent the solution in terms of solutions for edge dislocations in a half-space and a complementary solution that enforces the boundary conditions. The latter is non-singular and obtained from a finite element solution. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated into the formulation through a set of constitutive rules. The Cohesive Surface methodology allows crack growth to emerge naturally from the boundary value problem solution. Material parameters representative of aluminum are employed. This study focuses on the influence of dislocation nucleation rate and loading rate on the course of crack growth.
Francisco A. Gilabert - One of the best experts on this subject based on the ideXlab platform.
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Macro- and micro-modeling of crack propagation in encapsulation-based self-healing materials: Application of XFEM and Cohesive Surface techniques
Materials and Design, 2017Co-Authors: Francisco A. Gilabert, D. Garoz, W. Van PaepegemAbstract:Encapsulation-based materials are produced introducing some small healing fluid-filled capsules in a matrix. These materials can self-heal when internal cracks intercept and break the capsules. If the healing agent is released, the crack can be sealed. However, this is not always the case. These capsules need to be designed with the adequate shape and material to be properly broken. This paper presents two application models based on the combination of eXtended Finite Element Method (XFEM) elements and Cohesive Surfaces technique (CS) to predict crack propagation. Two types of encapsulated systems are considered: a concrete beam in a three-point bending test, and a micro-scale model of a representative volume element of a polymer subjected to a uniaxial tensile test. Despite both systems relying on different capsule shapes and different constituent materials, the models predict a similar non-linear response of the overall material strength governed by the coupled effect of the interface strength and the capsule radii-to-thickness ratio. Furthermore, even if an inadequate material and geometry combination is used, it is found that the mere presence of capsules might achieve, under certain conditions, an interesting overall reinforcement effect. This effect is discussed in terms of clustering and volume fraction of capsules.
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Numerical study of transitional brittle-to-ductile debonding of a capsule embedded in a matrix
Composite Interfaces, 2016Co-Authors: Francisco A. Gilabert, D. Garoz, W. Van PaepegemAbstract:AbstractThis work presents a numerical study that addresses the role of the interfacial fracture energy on the debonding process of a capsule embedded in an elastic matrix, which undergoes a uniaxial far-field stress. The motivation of this work is to analyze and to understand the effects of this energy in the framework of the so-called encapsulation-based self-healing cementitious materials, where glass capsules filled with a fluid healing agent are embedded in a cement-based matrix. A two-dimensional plane strain model based on a combination of the classical finite element method and Cohesive Surface techniques implemented in the commercial code Abaqus® has been used. It has been found that there exist three types of debonding regimes, ranging from a perfect brittle response up to a ductile-limited response, and whose range of validity is governed by a straightforward dimensionless number able to predict the type of debonding as a function of flexural properties of the capsule and the interface strength.
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Stress concentrations and bonding strength in encapsulation-based self-healing materials
Materials and Design, 2015Co-Authors: Francisco A. Gilabert, D. Garoz, Wim Van PaepegemAbstract:In encapsulation-based self-healing materials, filled capsules with the healing agent are embedded in a matrix. But between the capsule and the matrix an interface always exists. The strength of the interface between both components is proved to play a crucial role in the correct working of the self-healing. This paper analyzes numerically the role of the interface bonding strength and the stress concentration around a cylindrical capsule embedded in a homogeneous, isotropic and elastic matrix, which undergoes a uniform and uniaxial far-field stress. Geometry and load condition make it to use a two-dimensional plane strain model. This model is based on a combination of the classical Finite Element Method and Cohesive Surface techniques implemented in the commercial code Abaqus. Two types of interfaces have been studied: perfect and imperfect bonding. A detailed validation of the model against analytical expressions has been conducted in order to guarantee a correct behavior of the interface elements. The influence of the elastic mismatch between the capsule and the matrix on the stress concentrations has been assessed, as well as the possibility of using capsules with different thicknesses. In order to prevent debonding, a study to provide the optimum combination of material elasticities, capsule thicknesses and bonding strength has been performed. The initiation and propagation of the interfacial crack have been also fully addressed. In that direction, once a crack is initiated, the role of the elastic mismatch and the capsule thickness is also assessed. This model can predict the suitability of the mechanical performance of the interface and whose role is typically underestimated during the preparation process of encapsulated self-healing materials.
E Van Der Giessen - One of the best experts on this subject based on the ideXlab platform.
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3988 - MODELING FATIGUE CRACK GROWTH IN CRYSTALLINE SOLIDS WITH DISCRETE DISLOCATION PLATICITY
2013Co-Authors: Daniel S. Balint, Vikram Deshpande, Alan Needleman, E Van Der GiessenAbstract:Analyses of crack growth under cyclic loading conditions are discussed where plastic flow arises from the motion of large numbers of discrete dislocations and the fracture properties are embedded in a Cohesive Surface constitutive relation. The formulation is the same as used to analyse crack growth under monotonic loading conditions, differing only in the remote loading being a cyclic function of time. Fatigue, i.e. crack growth in cyclic loading at a driving force for which the crack would have arrested under monotonic loading, emerges in the simulations as a consequence of the evolution of internal stresses associated with the irreversibility of the dislocation motion. A fatigue threshold, Paris law behaviour, striations, the accelerated growth of short cracks and the scaling with material properties are outcomes of the calculations. Results for single crystals and polycrystals will be discussed.
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Simulation of fracture of cementitious composites with explicit modeling of microstructural features
Engineering Fracture Mechanics, 2001Co-Authors: M G A Tijssens, L J Sluys, E Van Der GiessenAbstract:Abstract Fracture of cementitious composites is analyzed numerically using the Cohesive Surface methodology. The presence of aggregates in the cement matrix is explicitly accounted for. The composite is modeled in two dimensions as a three-phase material, the third phase being the weak interfacial transition zone in between aggregates and cement matrix. The bulk material is regarded as elastic and fracture is described with Cohesive Surfaces. The Cohesive Surface constitutive model is motivated by experimental observations regarding the loading-rate sensitivity of cementitious composites and analytical studies regarding fracture of planar microcracks. The model predicts the important toughening mechanism of crack face bridging occurring in cementitious composites.
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Indentation-induced interface delamination of a strong film on a ductile substrate
Thin Solid Films, 2001Co-Authors: A. Abdul-baqi, E Van Der GiessenAbstract:Abstract The objective of this work is to study indentation-induced delamination of a strong film from a ductile substrate. To this end, spherical indentation of an elastic–perfectly plastic substrate coated by an elastic thin film is simulated, with the interface being modeled by means of a Cohesive Surface. The constitutive law of the Cohesive Surface includes a coupled description of normal and tangential failure. Cracking of the coating itself is not included and residual stresses are ignored. Delamination initiation and growth are analyzed for several interfacial strengths and properties of the substrate. It is found that delamination occurs in a tangential mode rather than a normal one and is initiated at two to three times the contact radius. It is also demonstrated that the higher the interfacial strength, the higher the initial speed of propagation of the delamination and the lower the steady state speed. Indentation load vs. depth curves are obtained where, for relatively strong interfaces, the delamination initiation is imprinted on this curve as a kink.
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Simulation of mode I crack growth in polymers by crazing
International Journal of Solids and Structures, 2000Co-Authors: M G A Tijssens, E Van Der Giessen, L J SluysAbstract:Crazing in amorphous polymers under mode I loading conditions is simulated using the concept of embedded Cohesive Surfaces with a recently proposed model. The dependence of the predicted crack growth resistance on the crazing material parameters is studied. In general, for constant loading rate, a lower fracture toughness is predicted for shorter craze lengths. However, since the widening of the craze is of a viscoplastic nature, this trend can be reversed for increasing loading rate. The parameter variations indicate that the perfectly plastic Dugdale Cohesive zone model is not applicable to crazing. Mesh sensitivity with respect to length and orientation of the Cohesive Surface elements is also studied. Convergence of crack growth resistance and crack path predictions can only be expected for very fine, randomly oriented meshes.
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modeling of crazing using a Cohesive Surface methodology
Mechanics of Materials, 2000Co-Authors: M G A Tijssens, E Van Der Giessen, L J SluysAbstract:A novel Cohesive Surface model for crazing in polymers is developed. The model incorporates the initiation, growth and breakdown of crazes based on micromechanical considerations. The initiation of crazes is controlled by the stress state, in particular by the hydrostatic stress and Cohesive Surface normal traction. The widening of a craze is based on a rate-dependent viscoplastic formulation and failure of the craze occurs when the fibrils reach a material-dependent maximum extension. Crazing is simulated using a high density of Cohesive Surfaces immersed in the continuum. The finite element method is used to discretize both Cohesive Surfaces and continuum separately. The capabilities of the method to describe multiple crazing is demonstrated with an example.
M G A Tijssens - One of the best experts on this subject based on the ideXlab platform.
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an efficient parallel procedure for the simulation of crack growth using the Cohesive Surface methodology
International Journal for Numerical Methods in Engineering, 2001Co-Authors: Frederik Jan Lingen, M G A TijssensAbstract:Simulations of crack growth that are based on the Cohesive Surface methodology typically involve ill-conditioned systems of equations and require much processing time. This paper shows how these systems of equations can be solved efficiently by adopting the domain decomposition approach in which the finite element mesh is partitioned into multiple blocks. The system of equations is then reduced to a much smaller system of equations that is solved with an iterative algorithm in combination with a powerful two-level preconditioner. Although the solution algorithm is more efficient than a direct solution algorithm on a single-processor computer, it becomes really attractive when used on a parallel computer. This is demonstrated for a large scale simulation of crack growth in a polymer using a Cray T3E with 64 processors. Copyright © 2001 John Wiley & Sons, Ltd.
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Simulation of fracture of cementitious composites with explicit modeling of microstructural features
Engineering Fracture Mechanics, 2001Co-Authors: M G A Tijssens, L J Sluys, E Van Der GiessenAbstract:Abstract Fracture of cementitious composites is analyzed numerically using the Cohesive Surface methodology. The presence of aggregates in the cement matrix is explicitly accounted for. The composite is modeled in two dimensions as a three-phase material, the third phase being the weak interfacial transition zone in between aggregates and cement matrix. The bulk material is regarded as elastic and fracture is described with Cohesive Surfaces. The Cohesive Surface constitutive model is motivated by experimental observations regarding the loading-rate sensitivity of cementitious composites and analytical studies regarding fracture of planar microcracks. The model predicts the important toughening mechanism of crack face bridging occurring in cementitious composites.
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Simulation of mode I crack growth in polymers by crazing
International Journal of Solids and Structures, 2000Co-Authors: M G A Tijssens, E Van Der Giessen, L J SluysAbstract:Crazing in amorphous polymers under mode I loading conditions is simulated using the concept of embedded Cohesive Surfaces with a recently proposed model. The dependence of the predicted crack growth resistance on the crazing material parameters is studied. In general, for constant loading rate, a lower fracture toughness is predicted for shorter craze lengths. However, since the widening of the craze is of a viscoplastic nature, this trend can be reversed for increasing loading rate. The parameter variations indicate that the perfectly plastic Dugdale Cohesive zone model is not applicable to crazing. Mesh sensitivity with respect to length and orientation of the Cohesive Surface elements is also studied. Convergence of crack growth resistance and crack path predictions can only be expected for very fine, randomly oriented meshes.
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modeling of crazing using a Cohesive Surface methodology
Mechanics of Materials, 2000Co-Authors: M G A Tijssens, E Van Der Giessen, L J SluysAbstract:A novel Cohesive Surface model for crazing in polymers is developed. The model incorporates the initiation, growth and breakdown of crazes based on micromechanical considerations. The initiation of crazes is controlled by the stress state, in particular by the hydrostatic stress and Cohesive Surface normal traction. The widening of a craze is based on a rate-dependent viscoplastic formulation and failure of the craze occurs when the fibrils reach a material-dependent maximum extension. Crazing is simulated using a high density of Cohesive Surfaces immersed in the continuum. The finite element method is used to discretize both Cohesive Surfaces and continuum separately. The capabilities of the method to describe multiple crazing is demonstrated with an example.
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Computational Modeling of Failure Processes in Polymers
1999Co-Authors: E Van Der Giessen, R. Estevez, K.g.w. Pijnenburg, M G A TijssensAbstract:This paper deals with the modeling of the key mechanisms involved in the fracture of polymers: shear yielding and crazing. Along with the continuum model for shear yielding, we will discuss a recently proposed Cohesive Surface model for crazing. Applications to be presented include the study of the competition between the two mechanisms during growth of a mode I crack, and a numerical investigation of the role of localized deformations in failure of a polymer blend.
D. Garoz - One of the best experts on this subject based on the ideXlab platform.
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Macro- and micro-modeling of crack propagation in encapsulation-based self-healing materials: Application of XFEM and Cohesive Surface techniques
Materials and Design, 2017Co-Authors: Francisco A. Gilabert, D. Garoz, W. Van PaepegemAbstract:Encapsulation-based materials are produced introducing some small healing fluid-filled capsules in a matrix. These materials can self-heal when internal cracks intercept and break the capsules. If the healing agent is released, the crack can be sealed. However, this is not always the case. These capsules need to be designed with the adequate shape and material to be properly broken. This paper presents two application models based on the combination of eXtended Finite Element Method (XFEM) elements and Cohesive Surfaces technique (CS) to predict crack propagation. Two types of encapsulated systems are considered: a concrete beam in a three-point bending test, and a micro-scale model of a representative volume element of a polymer subjected to a uniaxial tensile test. Despite both systems relying on different capsule shapes and different constituent materials, the models predict a similar non-linear response of the overall material strength governed by the coupled effect of the interface strength and the capsule radii-to-thickness ratio. Furthermore, even if an inadequate material and geometry combination is used, it is found that the mere presence of capsules might achieve, under certain conditions, an interesting overall reinforcement effect. This effect is discussed in terms of clustering and volume fraction of capsules.
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Numerical study of transitional brittle-to-ductile debonding of a capsule embedded in a matrix
Composite Interfaces, 2016Co-Authors: Francisco A. Gilabert, D. Garoz, W. Van PaepegemAbstract:AbstractThis work presents a numerical study that addresses the role of the interfacial fracture energy on the debonding process of a capsule embedded in an elastic matrix, which undergoes a uniaxial far-field stress. The motivation of this work is to analyze and to understand the effects of this energy in the framework of the so-called encapsulation-based self-healing cementitious materials, where glass capsules filled with a fluid healing agent are embedded in a cement-based matrix. A two-dimensional plane strain model based on a combination of the classical finite element method and Cohesive Surface techniques implemented in the commercial code Abaqus® has been used. It has been found that there exist three types of debonding regimes, ranging from a perfect brittle response up to a ductile-limited response, and whose range of validity is governed by a straightforward dimensionless number able to predict the type of debonding as a function of flexural properties of the capsule and the interface strength.
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Stress concentrations and bonding strength in encapsulation-based self-healing materials
Materials and Design, 2015Co-Authors: Francisco A. Gilabert, D. Garoz, Wim Van PaepegemAbstract:In encapsulation-based self-healing materials, filled capsules with the healing agent are embedded in a matrix. But between the capsule and the matrix an interface always exists. The strength of the interface between both components is proved to play a crucial role in the correct working of the self-healing. This paper analyzes numerically the role of the interface bonding strength and the stress concentration around a cylindrical capsule embedded in a homogeneous, isotropic and elastic matrix, which undergoes a uniform and uniaxial far-field stress. Geometry and load condition make it to use a two-dimensional plane strain model. This model is based on a combination of the classical Finite Element Method and Cohesive Surface techniques implemented in the commercial code Abaqus. Two types of interfaces have been studied: perfect and imperfect bonding. A detailed validation of the model against analytical expressions has been conducted in order to guarantee a correct behavior of the interface elements. The influence of the elastic mismatch between the capsule and the matrix on the stress concentrations has been assessed, as well as the possibility of using capsules with different thicknesses. In order to prevent debonding, a study to provide the optimum combination of material elasticities, capsule thicknesses and bonding strength has been performed. The initiation and propagation of the interfacial crack have been also fully addressed. In that direction, once a crack is initiated, the role of the elastic mismatch and the capsule thickness is also assessed. This model can predict the suitability of the mechanical performance of the interface and whose role is typically underestimated during the preparation process of encapsulated self-healing materials.