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L A Glenn - One of the best experts on this subject based on the ideXlab platform.

  • mechanical and numerical modeling of a porous Elastic Viscoplastic Material with tensile failure
    International Journal of Solids and Structures, 2000
    Co-Authors: M B Rubin, Yu O Vorobiev, L A Glenn
    Abstract:

    The objective of this paper is to develop simple but comprehensive constitutive equations that model a number of physical phenomena exhibited by dry porous geological Materials and metals. For geological Materials the equations model: porous compaction; porous dilation due to distortional deformation and tensile failure; shear enhanced compaction; pressure hardening of the yield strength; damage of the yield strength due to distortional deformation and porosity changes; and dependence of the yield strength on the Lode angle. For metals the equations model: hardening of the yield strength due to plastic deformation; pressure and temperature dependence of the yield strength, and damage due to nucleation of porosity during tensile failure. The equations are valid for large deformations and the Elastic response is hyperElastic in the sense that the stress is related to a derivative of the Helmholtz free energy. Also, the equations are Viscoplastic with rate dependence occurring in both the evolution equations of porosity and Elastic distortional deformations. Moreover, formulas are presented for robust numerical integration of the evolution equations at the element level that can be easily implemented into standard computer programs for dynamic response of Materials.

  • modeling of porous Elastic Viscoplastic Material with tensile failure
    4th International Conference on Constitutive Laws for Engineering Materials: Experiment Theory Computation and Applications Troy NY (US) 07 27 1999--0, 1998
    Co-Authors: L A Glenn, M B Rubin, O Vorobiev
    Abstract:

    This work describes simple but comprehensive constitutive equations that model a number of physical phenomena exhibited by dry porous geological Materials and metals. Moreover, formulas have been developed for robust numerical integration of the evolution equations at the element level that can be easily implemented into standard computer programs for dynamic response of Materials.

  • Numerical modeling of porous Elastic-Viscoplastic Material with tensile failure
    1998
    Co-Authors: L A Glenn, O Y Vorobiev
    Abstract:

    We report here on the development of a multi-Material hydrocode for simulation of elastoplastic flows with large deformations. Using this hydrocode a new constitutive model for porous Elastic-Viscoplastic Materials has been evaluated and the penetration of an aluminum projectile into porous rock Material has been simulated numerically. The dependence of the penetration depth upon model parameters has been studed.

Xavier Deprince - One of the best experts on this subject based on the ideXlab platform.

  • numerical study of impact penetration shearing employing finite strain Viscoplasticity model incorporating adiabatic shear banding
    Journal of Engineering Materials and Technology-transactions of The Asme, 2009
    Co-Authors: Patrice Longere, Andre Dragon, Xavier Deprince
    Abstract:

    This work brings forward a twofold contribution relevant to the adiabatic shear banding (ASB) process as a part of dynamic plasticity of high-strength metallic Materials. The first contribution is a reassessment of a three-dimensional finite deformation model starting from a specific scale postulate and devoted to cover a wide range of dissipative phenomena, including ASB-related Material instabilities (strong softening prefailure stage). The model, particularly destined to deal with impacted structures was first detailed by (Longere et al. 2003, "Modelling Adiabatic Shear Banding Via Damage Mechanics Approach, " Arch. Mech., 55, pp. 3-38; 2005, "Adiabatic Shear Banding Induced Degradation in a Thermo-Elastic/Viscoplastic Material Under Dynamic Loading," Int. J. Impact Eng., 32, pp. 285-320). The second novel contribution concerns numerical solution of a genuine ballistic penetration problem employing the above model for a target plate Material. The ASB trajectories are shown to follow a multistage history and complex distribution pattern leading finally to plugging failure mechanism. The corresponding analysis and related parametric study are intended to put to the test the pertinency of the model as an advanced predictive tool for complex shock related problems.

  • adiabatic shear banding induced degradation in a thermo Elastic Viscoplastic Material under dynamic loading
    International Journal of Impact Engineering, 2005
    Co-Authors: Patrice Longere, Andre Dragon, Herve Trumel, Xavier Deprince
    Abstract:

    Abstract In the approach presented, adiabatic shear banding (ASB) is considered as a form of anisotropic deterioration. The anisotropic mechanical degradation induced in the structural Material by the bands is dealt with by using a second-order tensor internal variable. The kinematical consequences of the presence of the bands are described by means of the corresponding part (deterioration-induced part in addition to the genuinely plastic part) of the velocity gradient embodying the notion of a “super-dislocation”. The kinematical framework involves finite strain anisotropic Elastic-irreversible formulation based on the multiplicative decomposition of the deformation gradient. Constitutive equations integrating ASB-deterioration-like process are derived from thermodynamic potentials namely the free energy and dissipative potentials in the general framework of the internal state variables formulation. The hypothesis of a single yield function has been put to describe the chronology of the Viscoplastic dissipative mechanisms and to account for the strong coupling between plasticity and band induced deterioration. An auxiliary indicator needed for determining the conditions for shear bands initiation and orientation has been obtained from a simplified analysis based on the linear theory of perturbations. This three-dimensional constitutive model, including anisotropic effects due to the ASB-induced deterioration in the context of finite Elastic–plastic strains, rate sensitivity, strain hardening and thermal softening, has been implemented as ‘user Material’ in the finite element code LS-DYNA. Three-dimensional numerical simulations of adiabatic shear banding-induced degradation have been performed considering the hat shape structure under dynamic shearing employing a direct Hopkinson pressure bar device. Depending on the impact velocity and on the loading duration, deterioration bands propagate or arrest inside the hat shape structure. Numerical results show the evolution of the band tip velocity during the deterioration process. Numerical deterioration maps inside the hat shape structure and the load transmitted to the output bar are in good agreement with experimental evidence including band orientation. Because of the modelling scale we use herein, mesh refining in the areas crossed by the bands—which usually supposes the a priori knowledge of the band trajectory—is not necessary. Thanks to the regularising effects of viscosity (in the model viscosity is double, concerning plasticity but also deterioration) and a further adaptive time procedure, a weak mesh dependency of the numerical results has been observed.

Jonas Faleskog - One of the best experts on this subject based on the ideXlab platform.

  • influence of crack deflection into the carbide ferrite interface on cleavage fracture initiation in ferritic steels
    Mechanics of Materials, 2008
    Co-Authors: Martin Kroon, Jonas Faleskog
    Abstract:

    Abstract In this and a companion study (Kroon, M., Faleskog, J., 2005. Micromechanics of cleavage fracture initiation in ferritic steels by carbide cracking. J. Mech. Phys. Solids 53, 171–196), the initiation of cleavage fracture in ferritic steels is studied. The initiation is modelled explicitly in the form of a microcrack, which nucleates in a brittle carbide and propagates into the surrounding ferrite. The carbide is modelled as an Elastic cylinder and the ferrite as an Elastic Viscoplastic Material. The crack growth is modelled using a cohesive surface, in which the tractions are governed by a modified exponential cohesive law. The advancing microcrack, which has nucleated in the carbide, may either continue into the ferrite or deflect into the interface between the carbide and the ferrite. Special attention is given to the influence of the mode mixity factor β , which is defined as the ratio between the shear and tensile strength of the interface between the carbide and the ferrite. Crack growth in the interface occurs in shear mode and is driven by a fibre loading mechanism. For mode mixity values β ⩽ 0.2 , the crack deflects into the interface. The results indicate that crack growth in the interface can have a profound influence on the macroscopic fracture toughness of ferritic steels.

Patrice Longere - One of the best experts on this subject based on the ideXlab platform.

  • numerical study of impact penetration shearing employing finite strain Viscoplasticity model incorporating adiabatic shear banding
    Journal of Engineering Materials and Technology-transactions of The Asme, 2009
    Co-Authors: Patrice Longere, Andre Dragon, Xavier Deprince
    Abstract:

    This work brings forward a twofold contribution relevant to the adiabatic shear banding (ASB) process as a part of dynamic plasticity of high-strength metallic Materials. The first contribution is a reassessment of a three-dimensional finite deformation model starting from a specific scale postulate and devoted to cover a wide range of dissipative phenomena, including ASB-related Material instabilities (strong softening prefailure stage). The model, particularly destined to deal with impacted structures was first detailed by (Longere et al. 2003, "Modelling Adiabatic Shear Banding Via Damage Mechanics Approach, " Arch. Mech., 55, pp. 3-38; 2005, "Adiabatic Shear Banding Induced Degradation in a Thermo-Elastic/Viscoplastic Material Under Dynamic Loading," Int. J. Impact Eng., 32, pp. 285-320). The second novel contribution concerns numerical solution of a genuine ballistic penetration problem employing the above model for a target plate Material. The ASB trajectories are shown to follow a multistage history and complex distribution pattern leading finally to plugging failure mechanism. The corresponding analysis and related parametric study are intended to put to the test the pertinency of the model as an advanced predictive tool for complex shock related problems.

  • adiabatic shear banding induced degradation in a thermo Elastic Viscoplastic Material under dynamic loading
    International Journal of Impact Engineering, 2005
    Co-Authors: Patrice Longere, Andre Dragon, Herve Trumel, Xavier Deprince
    Abstract:

    Abstract In the approach presented, adiabatic shear banding (ASB) is considered as a form of anisotropic deterioration. The anisotropic mechanical degradation induced in the structural Material by the bands is dealt with by using a second-order tensor internal variable. The kinematical consequences of the presence of the bands are described by means of the corresponding part (deterioration-induced part in addition to the genuinely plastic part) of the velocity gradient embodying the notion of a “super-dislocation”. The kinematical framework involves finite strain anisotropic Elastic-irreversible formulation based on the multiplicative decomposition of the deformation gradient. Constitutive equations integrating ASB-deterioration-like process are derived from thermodynamic potentials namely the free energy and dissipative potentials in the general framework of the internal state variables formulation. The hypothesis of a single yield function has been put to describe the chronology of the Viscoplastic dissipative mechanisms and to account for the strong coupling between plasticity and band induced deterioration. An auxiliary indicator needed for determining the conditions for shear bands initiation and orientation has been obtained from a simplified analysis based on the linear theory of perturbations. This three-dimensional constitutive model, including anisotropic effects due to the ASB-induced deterioration in the context of finite Elastic–plastic strains, rate sensitivity, strain hardening and thermal softening, has been implemented as ‘user Material’ in the finite element code LS-DYNA. Three-dimensional numerical simulations of adiabatic shear banding-induced degradation have been performed considering the hat shape structure under dynamic shearing employing a direct Hopkinson pressure bar device. Depending on the impact velocity and on the loading duration, deterioration bands propagate or arrest inside the hat shape structure. Numerical results show the evolution of the band tip velocity during the deterioration process. Numerical deterioration maps inside the hat shape structure and the load transmitted to the output bar are in good agreement with experimental evidence including band orientation. Because of the modelling scale we use herein, mesh refining in the areas crossed by the bands—which usually supposes the a priori knowledge of the band trajectory—is not necessary. Thanks to the regularising effects of viscosity (in the model viscosity is double, concerning plasticity but also deterioration) and a further adaptive time procedure, a weak mesh dependency of the numerical results has been observed.

Haim Waisman - One of the best experts on this subject based on the ideXlab platform.

  • a unified model for metal failure capturing shear banding and fracture
    International Journal of Plasticity, 2015
    Co-Authors: Colin Mcauliffe, Haim Waisman
    Abstract:

    Dynamic fracture of metals may be brittle or ductile depending on factors such as Material properties, loading rate and specimen geometry. At high strain rates, a thermo plastic instability known as shear banding may occur, which typically precedes fracture. Experiments on notched plate impact show a ductile–brittle failure transition, where lower impact velocities lead to brittle behavior, while higher impact velocities lead to shear banding. For more complex problems such as armor penetration, both brittle fracture and shear banding have been observed in the same specimen, however, current failure models can either account for fracture or shear banding. For predictive numerical simulations of dynamic failure, it is thus crucial to account for both failure modes, since exclusion of either mode neglects important physics observed in experiments. In this work a thermodynamically consistent model which accounts for both shear banding and dynamic fracture and can thus capture both failure bodes at intermediate strain rates, is presented. The model consists of an Elastic–Viscoplastic Material with strain hardening, strain rate hardening, and thermal softening. Fracture is modeled with the phase field method, for which a novel modification is presented here to account for the creation of fracture surfaces by inElastic work. Numerical examples are presented to illustrate the basic behavior of the model, and to compare it to three special cases: a damage free case, an isothermal case, and an isothermal case where the contribution of inElastic work to fracture is excluded.