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Pablo D. Zavattieri - One of the best experts on this subject based on the ideXlab platform.

  • mixed mode Cohesive Zone models for fracture of an adhesively bonded polymer matrix composite
    Engineering Fracture Mechanics, 2006
    Co-Authors: Suyi Li, Jessica A Schroeder, M D Thouless, Anthony M Waas, Pablo D. Zavattieri
    Abstract:

    Abstract As a direct extension of previous mode-I work on the adhesion of composite joints, this paper uses a Cohesive-Zone approach to model the mixed-mode fracture of adhesive joints made from a polymer–matrix composite. Mode-II Cohesive-Zone parameters were obtained using sandwich end-notch flexure specimens. These parameters were used directly with the previously determined mode-I parameters to predict the fracture and deformation of mixed-mode geometries. It was shown that numerical simulations provided quantitative predictions for these geometries, including predictions for both the strengths of the joints and for the failure mechanisms. In conjunction with the earlier work, these results demonstrate the use of Cohesive-Zone approaches for the design of adhesively bonded composite joints, and indicate approaches for determining the relevant material properties to describe mixed-mode fracture.

  • use of mode i Cohesive Zone models to describe the fracture of an adhesively bonded polymer matrix composite
    Composites Science and Technology, 2005
    Co-Authors: Suyi Li, Jessica A Schroeder, M D Thouless, Anthony M Waas, Pablo D. Zavattieri
    Abstract:

    In this paper, the use of a Cohesive-Zone approach to model the mode-I fracture of adhesive joints made from a polymer-matrix composite is demonstrated. Cohesive-Zone parameters were obtained by matching numerical results to experimental observations. It is shown that there is a distinction between the characteristic strength of the interface associated with the toughness, and the intrinsic Cohesive strength of the interface. While the characteristic strength and toughness are often sufficient to describe fracture in the presence of a crack, the intrinsic Cohesive strength is also required to analyze some geometries that have very small characteristic dimensions or crack lengths. It is shown that Cohesive-Zone models accurately predict the behavior of the joints studied. In particular, not only are the strengths and deformations accurately described, but the transition between failure of the composite and failure of the interface can also be predicted. This mode-I transition cannot be predicted by conventional fracture mechanics as it depends on both the energy-based and strength-based failure parameters associated with Cohesive-Zone models.

Anthony M Waas - One of the best experts on this subject based on the ideXlab platform.

  • multiple solutions in Cohesive Zone models of fracture
    Engineering Fracture Mechanics, 2017
    Co-Authors: Anthony M Waas
    Abstract:

    Abstract The use of Cohesive Zone models (CZM) for studying crack initiation and propagation can lead to non-unique deformed configurations. This situation can lead to solution branches that may be non-physical, leading to difficulty in interpreting computed results. These aspects are studied in this paper using the double cantilever beam (DCB) specimen first and next in the context of a mode I center crack in a thin sheet of infinite extent subjected to remote tensile loading. Analytical solutions to the CZM that employ constant stress and linear softening laws are presented, and it is shown that when the linear softening Cohesive law is used, two Cohesive Zone sizes are valid for the same external loads, leading to two equally possible deformed configurations, satisfying all the field equations and boundary conditions. The smaller of the two Cohesive Zones has a lower energy which proposed as a criterion to render a unique solution.

  • predictions of delamination of a stiffened panel using a Cohesive Zone model
    51st AIAA ASME ASCE AHS ASC Structures Structural Dynamics and Materials Conference<BR> 18th AIAA ASME AHS Adaptive Structures Conference<BR&, 2010
    Co-Authors: Peter A Gustafson, Anthony M Waas
    Abstract:

    The ability of a nite element Cohesive Zone model to predict delamination in a sti ened structural component is investigated. A sti ened panel was proposed as a validation test for T650/AFR-PE4/FM680-1 material system Cohesive Zone parameters that were determined in coupon level tests. Models of the panel were constructed using two methods including the discrete Cohesive Zone element and the Abaqus R COH3D8 element to simulate adhesive failure. The test was found to be insensitive for validation of implicit models. The model and experimental failure loads were found to over-predict the experimental failure load by about 10%; the displacement at failure over-predicted by a larger margin. The discrepancies are discussed. The coupon level tests for determining the adhesive parameters are also summarized.

  • the influence of Cohesive Zone modeling on the stress field and energy release rates in a cracked elastic body
    51st AIAA ASME ASCE AHS ASC Structures Structural Dynamics and Materials Conference<BR> 18th AIAA ASME AHS Adaptive Structures Conference<BR&, 2010
    Co-Authors: Pavana Prabhakar, Anthony M Waas
    Abstract:

    that varies with distance, r, from the crack tip as r 1 2 . In this paper, a traction free plane stress wedge with a discrete Cohesive Zone along the intended crack-path is studied. Of interest is the in uence of the Cohesive Zone on the crack tip stress eld. Further, the in uence of the Cohesive Zone on the strain energy release rate is also investigated. Two example problems are studied; a double cantilever beam and an in nitely wide plate with a through-the-thickness crack. The objective of this paper is to examine the conditions under which a Cohesive Zone model can be used to represent an intended crack-path without unduly altering the original problem being investigated.

  • mixed mode Cohesive Zone models for fracture of an adhesively bonded polymer matrix composite
    Engineering Fracture Mechanics, 2006
    Co-Authors: Suyi Li, Jessica A Schroeder, M D Thouless, Anthony M Waas, Pablo D. Zavattieri
    Abstract:

    Abstract As a direct extension of previous mode-I work on the adhesion of composite joints, this paper uses a Cohesive-Zone approach to model the mixed-mode fracture of adhesive joints made from a polymer–matrix composite. Mode-II Cohesive-Zone parameters were obtained using sandwich end-notch flexure specimens. These parameters were used directly with the previously determined mode-I parameters to predict the fracture and deformation of mixed-mode geometries. It was shown that numerical simulations provided quantitative predictions for these geometries, including predictions for both the strengths of the joints and for the failure mechanisms. In conjunction with the earlier work, these results demonstrate the use of Cohesive-Zone approaches for the design of adhesively bonded composite joints, and indicate approaches for determining the relevant material properties to describe mixed-mode fracture.

  • use of mode i Cohesive Zone models to describe the fracture of an adhesively bonded polymer matrix composite
    Composites Science and Technology, 2005
    Co-Authors: Suyi Li, Jessica A Schroeder, M D Thouless, Anthony M Waas, Pablo D. Zavattieri
    Abstract:

    In this paper, the use of a Cohesive-Zone approach to model the mode-I fracture of adhesive joints made from a polymer-matrix composite is demonstrated. Cohesive-Zone parameters were obtained by matching numerical results to experimental observations. It is shown that there is a distinction between the characteristic strength of the interface associated with the toughness, and the intrinsic Cohesive strength of the interface. While the characteristic strength and toughness are often sufficient to describe fracture in the presence of a crack, the intrinsic Cohesive strength is also required to analyze some geometries that have very small characteristic dimensions or crack lengths. It is shown that Cohesive-Zone models accurately predict the behavior of the joints studied. In particular, not only are the strengths and deformations accurately described, but the transition between failure of the composite and failure of the interface can also be predicted. This mode-I transition cannot be predicted by conventional fracture mechanics as it depends on both the energy-based and strength-based failure parameters associated with Cohesive-Zone models.

Huang Yuan - One of the best experts on this subject based on the ideXlab platform.

  • assessment of low cycle fatigue crack growth under mixed mode loading conditions by using a Cohesive Zone model
    International Journal of Fatigue, 2015
    Co-Authors: Huang Yuan
    Abstract:

    Abstract Most Cohesive Zone models were used to reproduce fatigue crack growth under small scale yielding and failed to predict elastic–plastic fatigue crack growth. In the present work a new Cohesive Zone model is introduced to give a uniform description of both fatigue crack growth and elastoplastic rupture. Damage accumulation of the Cohesive model contains both monotonic damage as well as cyclic damage and validated by corresponding mixed-mode fracture and fatigue experiments of an austenitic stainless steel. Computations confirm that the present Cohesive Zone model may provide a uniform description for the whole fatigue crack growth regimes.

  • Effects of the Cohesive law on ductile crack propagation simulation by using Cohesive Zone models
    Engineering Fracture Mechanics, 2014
    Co-Authors: Huang Yuan
    Abstract:

    Abstract The Cohesive Zone model has been applied in different computational fracture mechanical investigations. However, effects of the Cohesive law on crack simulation results have not been systematically and quantitatively studied. To quantify the influence of the Cohesive law, a special Cohesive element has been developed and implemented into the commercial FEM code ABAQUS. The detailed computational investigation of compact tension (CT) specimens confirms that the load vs. load line displacement curve hardly depends on the initial Cohesive stiffness of the Cohesive Zone, but the fracture parameters, such as δ 5 , may deviate up to 5%. A significant difference is observed in prediction of crack propagation, which exceeds 35% for a given load line displacement in CT specimens. To diminish artificial influence of the Cohesive Zone model, one has to increase the specific Cohesive stiffness. The J -integral as the critical energy release rate generally differs from the Cohesive energy. The elastic unloading and plastic reloading around the Cohesive Zone affect the fracture energy amount. The difference between the Cohesive energy and the critical energy release rate depends on the Cohesive law as well as the ductility of the material, vanishes only in an elastic specimen and exceeds 40% for ductile materials. The discrepancy between J and the Cohesive energy grows and is stagnated for the Cohesive strength larger by three times the initial yield stress. To obtain realistic computational results by using Cohesive Zone models, one has to build the Cohesive law with proper parameters.

  • applications of normal stress dominated Cohesive Zone models for mixed mode crack simulation based on extended finite element methods
    Engineering Fracture Mechanics, 2011
    Co-Authors: Yangjian Xu, Huang Yuan
    Abstract:

    Abstract In conventional Cohesive Zone models the traction-separation law starts from zero load, so that the model cannot be applied to predict mixed-mode cracking. In the present work the Cohesive Zone model with a threshold is introduced and applied for simulating different mixed-mode cracks in combining with the extended finite element method. Computational results of cracked specimens show that the crack initiation and propagation under mixed-mode loading conditions can be characterized by the Cohesive Zone model for normal stress failure. The contribution of the shear stress is negligible. The maximum principal stress predicts crack direction accurately. Computations based on XFEM agree with known experiments very well. The shear stress becomes, however, important for uncracked specimens to catch the correct crack initiation angle. To study mixed-mode cracks one has to introduce a threshold into the Cohesive law and to implement the new Cohesive Zone based on the fracture criterion. In monotonic loading cases it can be easily realized in the extended finite element formulation. For cyclic loading cases convergence of the inelastic computations can be critical.

Suyi Li - One of the best experts on this subject based on the ideXlab platform.

  • mixed mode Cohesive Zone models for fracture of an adhesively bonded polymer matrix composite
    Engineering Fracture Mechanics, 2006
    Co-Authors: Suyi Li, Jessica A Schroeder, M D Thouless, Anthony M Waas, Pablo D. Zavattieri
    Abstract:

    Abstract As a direct extension of previous mode-I work on the adhesion of composite joints, this paper uses a Cohesive-Zone approach to model the mixed-mode fracture of adhesive joints made from a polymer–matrix composite. Mode-II Cohesive-Zone parameters were obtained using sandwich end-notch flexure specimens. These parameters were used directly with the previously determined mode-I parameters to predict the fracture and deformation of mixed-mode geometries. It was shown that numerical simulations provided quantitative predictions for these geometries, including predictions for both the strengths of the joints and for the failure mechanisms. In conjunction with the earlier work, these results demonstrate the use of Cohesive-Zone approaches for the design of adhesively bonded composite joints, and indicate approaches for determining the relevant material properties to describe mixed-mode fracture.

  • use of mode i Cohesive Zone models to describe the fracture of an adhesively bonded polymer matrix composite
    Composites Science and Technology, 2005
    Co-Authors: Suyi Li, Jessica A Schroeder, M D Thouless, Anthony M Waas, Pablo D. Zavattieri
    Abstract:

    In this paper, the use of a Cohesive-Zone approach to model the mode-I fracture of adhesive joints made from a polymer-matrix composite is demonstrated. Cohesive-Zone parameters were obtained by matching numerical results to experimental observations. It is shown that there is a distinction between the characteristic strength of the interface associated with the toughness, and the intrinsic Cohesive strength of the interface. While the characteristic strength and toughness are often sufficient to describe fracture in the presence of a crack, the intrinsic Cohesive strength is also required to analyze some geometries that have very small characteristic dimensions or crack lengths. It is shown that Cohesive-Zone models accurately predict the behavior of the joints studied. In particular, not only are the strengths and deformations accurately described, but the transition between failure of the composite and failure of the interface can also be predicted. This mode-I transition cannot be predicted by conventional fracture mechanics as it depends on both the energy-based and strength-based failure parameters associated with Cohesive-Zone models.

Edward H. Glaessgen - One of the best experts on this subject based on the ideXlab platform.

  • molecular dynamics simulation based Cohesive Zone representation of intergranular fracture processes in aluminum
    Journal of The Mechanics and Physics of Solids, 2006
    Co-Authors: V Yamakov, Dawn R. Phillips, Erik Saether, Edward H. Glaessgen
    Abstract:

    Abstract A traction–displacement relationship that may be embedded into a Cohesive Zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics (MD) simulations. An MD model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat Σ 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element—an atomistic analog to a continuum Cohesive Zone model element—the results from the MD simulation are recast to obtain an average continuum traction–displacement relationship to represent Cohesive Zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion.

  • molecular dynamics simulation based Cohesive Zone representation of intergranular fracture processes in aluminum
    Journal of The Mechanics and Physics of Solids, 2006
    Co-Authors: V Yamakov, Dawn R. Phillips, Erik Saether, Edward H. Glaessgen
    Abstract:

    Abstract A traction–displacement relationship that may be embedded into a Cohesive Zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics (MD) simulations. An MD model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat Σ 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element—an atomistic analog to a continuum Cohesive Zone model element—the results from the MD simulation are recast to obtain an average continuum traction–displacement relationship to represent Cohesive Zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion.

  • molecular dynamics simulation based Cohesive Zone representation of intergranular fracture processes in aluminum
    Journal of The Mechanics and Physics of Solids, 2006
    Co-Authors: V Yamakov, Dawn R. Phillips, Erik Saether, Edward H. Glaessgen
    Abstract:

    A traction-displacement relationship that may be embedded into a Cohesive Zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics simulations. A molecular-dynamics model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element an atomistic analog to a continuum Cohesive Zone model element - the results from the molecular-dynamics simulation are recast to obtain an average continuum traction-displacement relationship to represent Cohesive Zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion. Keywords: Crack-tip plasticity; Cohesive Zone model; Grain boundary decohesion; Intergranular fracture; Molecular-dynamics simulation