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John W. Gillespie - One of the best experts on this subject based on the ideXlab platform.
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Inter-molecular interactions in ultrahigh molecular weight polyethylene single crystals
Computational Materials Science, 2020Co-Authors: Sanjib C. Chowdhury, Subramani Sockalingam, John W. GillespieAbstract:Abstract This paper investigates the inter-molecular interactions during tensile loading in ultrahigh molecular weight polyethylene (UHWMPE) single crystals at the atomistic scale. Molecular dynamics (MD) simulations of velocity controlled chain pullout are employed to study inter-molecular load transfer mechanisms. The transfer of tensile load is governed by van der Waals forces that dominate the inter-molecular shear interactions. The tensile stress build up occurs over a length of approximately 40c, where c is the lattice constant along the chain axis. Atomistic MD models incorporate the influence of surrounding neighboring atoms. Therefore, a nonlocal shear lag continuum model is developed for the first time to bridge length scales by extending the classical shear lag model of stress transfer in composites. The nonlocal model predictions correlate better with the MD results compared to the classical shear lag formulation. Combining the MD and shear lag model results, a bilinear mode II Cohesive Traction-separation behavior is identified to describe the inter-molecular interactions of the continuum with interface stiffness (2.38 GPa/nm), peak Traction (0.14 GPa) and mode II fracture toughness (17 mJ/m2).
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Modeling the Fibrillation of Kevlar® KM2 Single Fibers Subjected to Transverse Compression
Fibers and Polymers, 2018Co-Authors: Jeffrey M. Staniszewski, Subramani Sockalingam, Travis A. Bogetti, John W. GillespieAbstract:In this work, fibrillation is introduced as an energy absorbing mechanism in the modeling of Kevlar® KM2 single fibers subjected to quasi-static transverse compression. Fibrillation is simulated using a finite element model of the fiber cross-section containing discrete fibrils connected by interfibrillar Cohesive zones. Model predictions of nominal stress-strain response for an assumed bilinear Cohesive Traction-separation interfibrillar behavior are compared to experimental data. Analysis shows that modeling of the microstructural fibril network, represented by a distribution of strong Cohesive interactions, is necessary to capture the experimental response. The model provides valuable insight into the unique deformation mechanisms governing fiber fibrillation under transverse compression.
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Silica–silane coupling agent interphase properties using molecular dynamics simulations
Journal of Materials Science, 2017Co-Authors: Sanjib C. Chowdhury, John W. GillespieAbstract:In this paper, strength of the interphase between silica and glycidoxypropyltrimethoxy silane (GPS) coupling agent has been studied using molecular dynamics (MD) simulations. Silica–GPS interphase model is created by coupling the hydroxylated silica surface with monolayer-hydroxylated GPS molecules. The interphase model is subjected to mode-I (normal), mode-II (shear) and mixed-mode (normal–shear) mechanical loading to determine the interphase Cohesive Traction–separation (T–S) response (i.e., Cohesive Traction law). In MD simulations, atomic interactions are modeled with the reactive force field ReaxFF. Effects of interphase thickness and GPS bond density on the T–S response are studied. Simulation results indicate that interphase strength decreases with increase in the interphase thickness before attaining a plateau level at higher thickness. For a particular thickness, strength improves significantly with increase in the GPS bond density with the silica surface. Damage mode is adhesive at the silica interface at lower thickness and transitions to mixed mode and Cohesive failure within the silane interphase at higher thickness. Mixed-mode T–S responses are bounded by the mode-I and mode-II responses. Characteristic parameters of the continuum-level potential-based Cohesive zone model (PPR–CZM) are determined by fitting the MD-based mode-I and mode-II T–S responses with PPR–CZM functional. Development of the PPR–CZM parameters enables bridging length scales from the MD to the continuum scale for fracture modeling of the fiber–matrix interphase in composites subjected to mixed-mode loading. Results on mode-I and mode-II unloading are also presented.
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Dynamic effects of single fiber break in unidirectional glass fiber-reinforced composites
Journal of Composite Materials, 2016Co-Authors: Raja Ganesh, Subramani Sockalingam, Bazle Z. Haque, John W. GillespieAbstract:In a unidirectional composite under static tensile loading, breaking of a fiber is shown to be a locally dynamic process that leads to stress concentrations in the interface, matrix and neighboring fibers that can propagate at high speed over long distances. To gain better understanding of this event, a fiber-level finite element model of a two-dimensional array of S2-glass fibers embedded in an elastic epoxy matrix with interfacial Cohesive Traction law is developed. The brittle fiber fracture results in release of stored strain energy as a compressive stress wave that propagates along the length of the broken fiber at speeds approaching the axial wave-speed in the fiber (6 km/s). This wave induces an axial tensile wave with a dynamic tensile stress concentration in adjacent fibers that diminishes with distance. Moreover, dynamic interfacial failure is predicted where debonding initiates, propagates and arrests at longer distances than predicted by models that assume quasi-static fiber breakage. In the c...
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Finite element analysis of the microdroplet test method using Cohesive zone model of the fiber/matrix interface
Composites Part A: Applied Science and Manufacturing, 2014Co-Authors: Subramani Sockalingam, John W. Gillespie, Moutushi Dey, Michael KeefeAbstract:Abstract This paper presents a finite element (FE) modeling methodology to simulate and assess the importance of various factors affecting the failure mechanisms in the microdroplet test used to measure the interface shear strength (IFSS) of S-glass fiber epoxy matrix. These factors include the effect of processing-induced residual thermal stresses, progressive debonding with interfacial friction, unstable crack propagation and frictional fiber sliding on mixed-mode loading at the interface. Cohesive zone modeling approach is employed to simulate the crack propagation and interfacial failure. Mode II dominated Traction separation laws are determined through numerical simulations of microdroplet test results. The importance of including the effect of residual stresses and interfacial friction in determining the Cohesive Traction–separation laws is illustrated. The sensitivity of the results for mode I Traction–separation parameters is studied. The developed holistic modeling methodology allows for accurate determination of Traction–separation behavior of the interface. This modeling effort also attempts to identify improvements to the microdroplet test method which is widely used to assess the degree of fiber/matrix adhesion.
Kim Lau Nielsen - One of the best experts on this subject based on the ideXlab platform.
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Cohesive Traction–separation relations for tearing of ductile plates with randomly distributed void nucleation sites
International Journal of Fracture, 2020Co-Authors: R. G. Andersen, C. Tekoğlu, Kim Lau NielsenAbstract:Cohesive zone Traction-separation relations, and the related phenomenological parameters, for steady-state ductile plate tearing, are strongly tied to the micro-mechanics governing the void nucleation and growth process leading to localized deformation and micro-crack formation. The effects of such local variations on the damage evolution and Cohesive zone parameters, respectively, are brought out in this study. A 2D plane strain model setup, first considered in Nielsen and Hutchinson (Int J Impact Eng 48:15–23 (2012)], is adopted, but here by discretely modeling a finite number of finite-size void nucleation sites distributed randomly in the plate material. It is found that the heterogeneous material conditions, resulting from the nucleation process, strongly affect the localization of damage and fracture, which influence the Cohesive energy. By considering a number of realizations of the random distribution for each material configuration, it is concluded that: (i) the peak force in the Cohesive Traction-separation relation is, essentially, unaffected by the heterogeneity coming into play through the damage-related microstructure, while (ii) the Cohesive energy decreases when either increasing the number or the size of the nucleation sites. The Cohesive energy is found to be in the range of those previously reported for homogeneous materials, but a direct comparison should be made with caution. The results imply that care should be taken if the actual material configuration diverges from a homogeneous microstructure such as when considering very thin plates and for plates with a few void nucleation sites.
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Cohesive Traction separation relations for tearing of ductile plates with randomly distributed void nucleation sites
International Journal of Fracture, 2020Co-Authors: R. G. Andersen, C. Tekoğlu, Kim Lau NielsenAbstract:Cohesive zone Traction-separation relations, and the related phenomenological parameters, for steady-state ductile plate tearing, are strongly tied to the micro-mechanics governing the void nucleation and growth process leading to localized deformation and micro-crack formation. The effects of such local variations on the damage evolution and Cohesive zone parameters, respectively, are brought out in this study. A 2D plane strain model setup, first considered in Nielsen and Hutchinson (Int J Impact Eng 48:15–23 (2012)], is adopted, but here by discretely modeling a finite number of finite-size void nucleation sites distributed randomly in the plate material. It is found that the heterogeneous material conditions, resulting from the nucleation process, strongly affect the localization of damage and fracture, which influence the Cohesive energy. By considering a number of realizations of the random distribution for each material configuration, it is concluded that: (i) the peak force in the Cohesive Traction-separation relation is, essentially, unaffected by the heterogeneity coming into play through the damage-related microstructure, while (ii) the Cohesive energy decreases when either increasing the number or the size of the nucleation sites. The Cohesive energy is found to be in the range of those previously reported for homogeneous materials, but a direct comparison should be made with caution. The results imply that care should be taken if the actual material configuration diverges from a homogeneous microstructure such as when considering very thin plates and for plates with a few void nucleation sites.
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Cohesive Traction-separation relations for plate tearing under mixed mode loading
European Journal of Mechanics - A Solids, 2018Co-Authors: R. G. Andersen, Pawel Woelke, Kim Lau NielsenAbstract:Abstract The present study investigates a sequence of failure events related to steady-state tearing of large-scale ductile plates by employing the micro-mechanics based Gurson-Tvergaard-Needleman (GTN) model. The fracture process in front of an advancing crack is approximated by a series of 2D plane strain finite element models to facilitate a comprehensive study of mixed mode fracture behavior as well as a parameter study of the Cohesive energy and Tractions involved in the process. The results from the conducted GTN model simulations are used to define Cohesive zone models suitable for plate tearing simulations at large scale. It is found that mixed mode loading conditions can have a significant effect on the Cohesive energy as well as relative displacement (in reference to pure mode I loading), while peak Traction is practically unaffected. Specifically, increasing mode II contribution leads to monotonic increase of the Cohesive energy. In contrast, the effect of mode III is more complicated as it leads to reduction of the mixed mode Cohesive energy (in reference to pure mode I loading) at low to medium levels of mode mixity ratios (0–0.3). However, increasing mode III contribution beyond the mode mixity ratio of 0.3, reverses this trend with Cohesive energy potentially exceeding the pure mode I level when at mode mixity ratio of 0.6 or higher. This behavior cannot be captured by the interactive Cohesive zone models that rely on a simple rotational sweep of mode I Traction-separation relation. Depending on the shear mode contribution, i.e., mode II or mode III, these models can lead to overly conservative (mode II) or unconservative (mode III) prediction of the crack growth resistance.
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Cohesive Traction separation laws for tearing of ductile metal plates
International Journal of Impact Engineering, 2012Co-Authors: Kim Lau Nielsen, John W. HutchinsonAbstract:Abstract The failure process ahead of a mode I crack advancing in a ductile thin metal plate or sheet produces plastic dissipation through a sequence of deformation steps that include necking well ahead of the crack tip and shear localization followed by a slant fracture in the necked region somewhat closer to the tip. The objective of this paper is to analyze this sequential process to characterize the Traction–separation behavior and the associated effective Cohesive fracture energy of the entire failure process. The emphasis is on what is often described as plane stress behavior taking place after the crack tip has advanced a distance of one or two plate thicknesses. Traction–separation laws are an essential component of finite element methods currently under development for analyzing fracture of large scale plate or shell structures. The present study resolves the sequence of failure details using the Gurson constitutive law based on the micromechanics of the ductile fracture process, including a recent extension that accounts for damage growth in shear. The fracture process in front of an advancing crack, subject to overall mode I loading, is approximated by a 2D plane strain finite element model, which allows for an intensive study of the parameters influencing local necking, shear localization and the final slant failure. The deformation history relevant to a Cohesive zone for a large scale model is identified and the Traction–separation relation is determined, including the dissipated energy. For ductile structural materials, the dissipation generated during necking prior to the onset of shear localization is the dominant contribution; it scales with the plate thickness and is mesh-independent in the present numerical model. The energy associated with the shear localization and fracture is secondary; it scales with the width of the shear band, and inherits the finite element mesh dependency of the Gurson model. The Cohesive Traction–separation laws have been characterized for various material conditions.
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Cohesive Traction–separation laws for tearing of ductile metal plates
International Journal of Impact Engineering, 2012Co-Authors: Kim Lau Nielsen, John W. HutchinsonAbstract:Abstract The failure process ahead of a mode I crack advancing in a ductile thin metal plate or sheet produces plastic dissipation through a sequence of deformation steps that include necking well ahead of the crack tip and shear localization followed by a slant fracture in the necked region somewhat closer to the tip. The objective of this paper is to analyze this sequential process to characterize the Traction–separation behavior and the associated effective Cohesive fracture energy of the entire failure process. The emphasis is on what is often described as plane stress behavior taking place after the crack tip has advanced a distance of one or two plate thicknesses. Traction–separation laws are an essential component of finite element methods currently under development for analyzing fracture of large scale plate or shell structures. The present study resolves the sequence of failure details using the Gurson constitutive law based on the micromechanics of the ductile fracture process, including a recent extension that accounts for damage growth in shear. The fracture process in front of an advancing crack, subject to overall mode I loading, is approximated by a 2D plane strain finite element model, which allows for an intensive study of the parameters influencing local necking, shear localization and the final slant failure. The deformation history relevant to a Cohesive zone for a large scale model is identified and the Traction–separation relation is determined, including the dissipated energy. For ductile structural materials, the dissipation generated during necking prior to the onset of shear localization is the dominant contribution; it scales with the plate thickness and is mesh-independent in the present numerical model. The energy associated with the shear localization and fracture is secondary; it scales with the width of the shear band, and inherits the finite element mesh dependency of the Gurson model. The Cohesive Traction–separation laws have been characterized for various material conditions.
Glaucio H. Paulino - One of the best experts on this subject based on the ideXlab platform.
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Assessment of Cohesive Traction-separation relationships in ABAQUS: A comparative study
Mechanics Research Communications, 2016Co-Authors: Kyoungsoo Park, Habeun Choi, Glaucio H. PaulinoAbstract:Abstract The definition of a Traction-separation relationship is essential in Cohesive zone models because it describes the nonlinear fracture process zone. A few models are investigated in this paper and a comparative study is conducted. Among various Traction-separation relationships, the one in Abaqus is assessed by evaluating the Cohesive Traction and its tangent stiffness according to a given separation path. The results demonstrate that the Traction-separation relationship in Abaqus can lead to non-physical responses because of a pathological positive tangent stiffness under softening condition. This is reflected in Cohesive Tractions that increase and decrease repeatedly while the Cohesive separation monotonically increases. Thus, together with supporting information, this paper conveys the message that a Traction-separation relationship should be developed and selected with great caution, especially under mixed-mode conditions.
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Cohesive zone models a critical review of Traction separation relationships across fracture surfaces
Applied Mechanics Reviews, 2011Co-Authors: Kyoungsoo Park, Glaucio H. PaulinoAbstract:One of the fundamental aspects in Cohesive zone modeling is the definition of the Traction-separation relationship across fracture surfaces, which approximates the nonlinear fracture process. Cohesive Traction-separation relationships may be classified as either nonpotential-based models or potential-based models. Potential-based models are of special interest in the present review article. Several potential-based models display limitations, especially for mixed-mode problems, because of the boundary conditions associated with Cohesive fracture. In addition, this paper shows that most effective displacement-based models can be formulated under a single framework. These models lead to positive stiffness under certain separation paths, contrary to general Cohesive fracture phenomena wherein the increase of separation generally results in the decrease of failure resistance across the fracture surface (i.e., negative stiffness). To this end, the constitutive relationship of mixed-mode Cohesive fracture should be selected with great caution.
Subramani Sockalingam - One of the best experts on this subject based on the ideXlab platform.
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Inter-molecular interactions in ultrahigh molecular weight polyethylene single crystals
Computational Materials Science, 2020Co-Authors: Sanjib C. Chowdhury, Subramani Sockalingam, John W. GillespieAbstract:Abstract This paper investigates the inter-molecular interactions during tensile loading in ultrahigh molecular weight polyethylene (UHWMPE) single crystals at the atomistic scale. Molecular dynamics (MD) simulations of velocity controlled chain pullout are employed to study inter-molecular load transfer mechanisms. The transfer of tensile load is governed by van der Waals forces that dominate the inter-molecular shear interactions. The tensile stress build up occurs over a length of approximately 40c, where c is the lattice constant along the chain axis. Atomistic MD models incorporate the influence of surrounding neighboring atoms. Therefore, a nonlocal shear lag continuum model is developed for the first time to bridge length scales by extending the classical shear lag model of stress transfer in composites. The nonlocal model predictions correlate better with the MD results compared to the classical shear lag formulation. Combining the MD and shear lag model results, a bilinear mode II Cohesive Traction-separation behavior is identified to describe the inter-molecular interactions of the continuum with interface stiffness (2.38 GPa/nm), peak Traction (0.14 GPa) and mode II fracture toughness (17 mJ/m2).
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Modeling the Fibrillation of Kevlar® KM2 Single Fibers Subjected to Transverse Compression
Fibers and Polymers, 2018Co-Authors: Jeffrey M. Staniszewski, Subramani Sockalingam, Travis A. Bogetti, John W. GillespieAbstract:In this work, fibrillation is introduced as an energy absorbing mechanism in the modeling of Kevlar® KM2 single fibers subjected to quasi-static transverse compression. Fibrillation is simulated using a finite element model of the fiber cross-section containing discrete fibrils connected by interfibrillar Cohesive zones. Model predictions of nominal stress-strain response for an assumed bilinear Cohesive Traction-separation interfibrillar behavior are compared to experimental data. Analysis shows that modeling of the microstructural fibril network, represented by a distribution of strong Cohesive interactions, is necessary to capture the experimental response. The model provides valuable insight into the unique deformation mechanisms governing fiber fibrillation under transverse compression.
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Dynamic effects of single fiber break in unidirectional glass fiber-reinforced composites
Journal of Composite Materials, 2016Co-Authors: Raja Ganesh, Subramani Sockalingam, Bazle Z. Haque, John W. GillespieAbstract:In a unidirectional composite under static tensile loading, breaking of a fiber is shown to be a locally dynamic process that leads to stress concentrations in the interface, matrix and neighboring fibers that can propagate at high speed over long distances. To gain better understanding of this event, a fiber-level finite element model of a two-dimensional array of S2-glass fibers embedded in an elastic epoxy matrix with interfacial Cohesive Traction law is developed. The brittle fiber fracture results in release of stored strain energy as a compressive stress wave that propagates along the length of the broken fiber at speeds approaching the axial wave-speed in the fiber (6 km/s). This wave induces an axial tensile wave with a dynamic tensile stress concentration in adjacent fibers that diminishes with distance. Moreover, dynamic interfacial failure is predicted where debonding initiates, propagates and arrests at longer distances than predicted by models that assume quasi-static fiber breakage. In the c...
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Finite element analysis of the microdroplet test method using Cohesive zone model of the fiber/matrix interface
Composites Part A: Applied Science and Manufacturing, 2014Co-Authors: Subramani Sockalingam, John W. Gillespie, Moutushi Dey, Michael KeefeAbstract:Abstract This paper presents a finite element (FE) modeling methodology to simulate and assess the importance of various factors affecting the failure mechanisms in the microdroplet test used to measure the interface shear strength (IFSS) of S-glass fiber epoxy matrix. These factors include the effect of processing-induced residual thermal stresses, progressive debonding with interfacial friction, unstable crack propagation and frictional fiber sliding on mixed-mode loading at the interface. Cohesive zone modeling approach is employed to simulate the crack propagation and interfacial failure. Mode II dominated Traction separation laws are determined through numerical simulations of microdroplet test results. The importance of including the effect of residual stresses and interfacial friction in determining the Cohesive Traction–separation laws is illustrated. The sensitivity of the results for mode I Traction–separation parameters is studied. The developed holistic modeling methodology allows for accurate determination of Traction–separation behavior of the interface. This modeling effort also attempts to identify improvements to the microdroplet test method which is widely used to assess the degree of fiber/matrix adhesion.
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finite element analysis of the microdroplet test method using Cohesive zone model of the fiber matrix interface
Composites Part A-applied Science and Manufacturing, 2014Co-Authors: Subramani Sockalingam, John W. Gillespie, Michael KeefeAbstract:Abstract This paper presents a finite element (FE) modeling methodology to simulate and assess the importance of various factors affecting the failure mechanisms in the microdroplet test used to measure the interface shear strength (IFSS) of S-glass fiber epoxy matrix. These factors include the effect of processing-induced residual thermal stresses, progressive debonding with interfacial friction, unstable crack propagation and frictional fiber sliding on mixed-mode loading at the interface. Cohesive zone modeling approach is employed to simulate the crack propagation and interfacial failure. Mode II dominated Traction separation laws are determined through numerical simulations of microdroplet test results. The importance of including the effect of residual stresses and interfacial friction in determining the Cohesive Traction–separation laws is illustrated. The sensitivity of the results for mode I Traction–separation parameters is studied. The developed holistic modeling methodology allows for accurate determination of Traction–separation behavior of the interface. This modeling effort also attempts to identify improvements to the microdroplet test method which is widely used to assess the degree of fiber/matrix adhesion.
Kyoungsoo Park - One of the best experts on this subject based on the ideXlab platform.
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Assessment of Cohesive Traction-separation relationships in ABAQUS: A comparative study
Mechanics Research Communications, 2016Co-Authors: Kyoungsoo Park, Habeun Choi, Glaucio H. PaulinoAbstract:Abstract The definition of a Traction-separation relationship is essential in Cohesive zone models because it describes the nonlinear fracture process zone. A few models are investigated in this paper and a comparative study is conducted. Among various Traction-separation relationships, the one in Abaqus is assessed by evaluating the Cohesive Traction and its tangent stiffness according to a given separation path. The results demonstrate that the Traction-separation relationship in Abaqus can lead to non-physical responses because of a pathological positive tangent stiffness under softening condition. This is reflected in Cohesive Tractions that increase and decrease repeatedly while the Cohesive separation monotonically increases. Thus, together with supporting information, this paper conveys the message that a Traction-separation relationship should be developed and selected with great caution, especially under mixed-mode conditions.
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Cohesive zone models a critical review of Traction separation relationships across fracture surfaces
Applied Mechanics Reviews, 2011Co-Authors: Kyoungsoo Park, Glaucio H. PaulinoAbstract:One of the fundamental aspects in Cohesive zone modeling is the definition of the Traction-separation relationship across fracture surfaces, which approximates the nonlinear fracture process. Cohesive Traction-separation relationships may be classified as either nonpotential-based models or potential-based models. Potential-based models are of special interest in the present review article. Several potential-based models display limitations, especially for mixed-mode problems, because of the boundary conditions associated with Cohesive fracture. In addition, this paper shows that most effective displacement-based models can be formulated under a single framework. These models lead to positive stiffness under certain separation paths, contrary to general Cohesive fracture phenomena wherein the increase of separation generally results in the decrease of failure resistance across the fracture surface (i.e., negative stiffness). To this end, the constitutive relationship of mixed-mode Cohesive fracture should be selected with great caution.