The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform
George Z. Voyiadjis - One of the best experts on this subject based on the ideXlab platform.
-
theoretical formulation of a coupled elastic plastic anisotropic damage model for concrete using the strain energy equivalence concept
International Journal of Damage Mechanics, 2009Co-Authors: George Z. Voyiadjis, Ziad N Taqieddin, Peter I. KattanAbstract:An anisotropic damage constitutive model for concrete is developed within the framework of elastoplasticity and continuum damage mechanics. The transformation from the effective (unDamaged) to the Damaged Configuration in the elastic regime is obtained by using the hypothesis of elastic strain energy equivalence. Damage in plasticity is accounted for by developing a new formulation relating the plastic strains rate tensors in the effective and Damaged Configurations. Two anisotropic damage criteria are introduced to account for the different concrete behavior effects under tensile and compressive loadings. The total stress is decomposed into tensile and compressive components in order to satisfy these damage criteria. The plasticity yield criterion presented in this work accounts for the spectral decomposition of the stress tensor and will be used simultaneously with the damage criteria. The transformation of stresses from the effective to the Damaged Configuration is achieved by using a fourth order transformation tensor that is based on second order tensile and compressive damage tensors. Expressions are derived for the elastoplastic tangent operator in the effective and Damaged Configurations. The formulations are derived consistently based on sound thermodynamic principles.
-
Theoretical Formulation of a Coupled Elastic—Plastic Anisotropic Damage Model for Concrete using the Strain Energy Equivalence Concept
International Journal of Damage Mechanics, 2008Co-Authors: George Z. Voyiadjis, Ziad N Taqieddin, Peter I. KattanAbstract:An anisotropic damage constitutive model for concrete is developed within the framework of elastoplasticity and continuum damage mechanics. The transformation from the effective (unDamaged) to the Damaged Configuration in the elastic regime is obtained by using the hypothesis of elastic strain energy equivalence. Damage in plasticity is accounted for by developing a new formulation relating the plastic strains rate tensors in the effective and Damaged Configurations. Two anisotropic damage criteria are introduced to account for the different concrete behavior effects under tensile and compressive loadings. The total stress is decomposed into tensile and compressive components in order to satisfy these damage criteria. The plasticity yield criterion presented in this work accounts for the spectral decomposition of the stress tensor and will be used simultaneously with the damage criteria. The transformation of stresses from the effective to the Damaged Configuration is achieved by using a fourth order transformation tensor that is based on second order tensile and compressive damage tensors. Expressions are derived for the elastoplastic tangent operator in the effective and Damaged Configurations. The formulations are derived consistently based on sound thermodynamic principles.
-
A damage cyclic plasticity model for MMC`s using a micromechanical model
1997Co-Authors: Ganesh Thiagarajan, George Z. VoyiadjisAbstract:A plasticity model is presented for metal-matrix composites which also incorporates the effects of damage in the material. The cyclic plasticity model is the basis of the damage-plasticity model. A six parameter general anisotropic yield surface was previously proposed by Voyiadjis and Thiagarajan (1995) for continuous unidirectionally reinforced MMC`s. The model presented here uses the yield surface proposed earlier to describe the behavior of MMC`s subjected to cyclic, proportional as well as non-proportional loadings and is based on the modifications of the bounding surface model proposed by Dafalias and Popov (1976). Plastic strains have been experimentally observed to develop in a non-associative manner. A non-associative rule based on a proposed potential function is described here. The elasto-plastic stiffness matrix is then developed based on these premises and model curves generated are compared to the experimental curves as shown in the end. The experimental curves obtained by (Dvorak et al., 1988) and (Nigam et al., 1993a) are used for determination of parameters and also for the stress-strain curve comparisons. The cyclic plasticity model is used in a fictitious effective Configuration. This Configuration is then transformed to the actual Damaged Configuration using the damage effect tensor. The constitutive equations in the actualmore » Configuration is outlined along with some experimental comparisons.« less
-
Micro and macro anisotropic cyclic damage-plasticity models for MMCS
International Journal of Engineering Science, 1997Co-Authors: George Z. Voyiadjis, Ganesh ThiagarajanAbstract:Abstract Two approaches to modeling the cyclic damage-plasticity behavior of metal matrix composites are presented in this paper, namely: a micro (micromechanical-damage) and a macro (continuum-damage) based approach. Each of these approaches involves a fictitious unDamaged ‘effective’ Configuration to which the plasticity equations are applied and constitutive equations derived. Using the equations for the transformation of stress from the unDamaged to the Damaged Configuration, the transformation of these equations to the actual Damaged Configuration is performed. Two new concepts are introduced here: (i) the incorporation of a term ϒ, similar to backstress, in the thermodynamic force Y space in the cyclic damage criterion, and (ii) the concept of cyclic damage under cyclic loading situations. This paper outlines the results from the two models in comparison with experimental results and compares and contrasts the effectiveness of the two models.
-
Finite Strain Plasticity and Damage in Constitutive Modeling of Metals With Spin Tensors
Applied Mechanics Reviews, 1992Co-Authors: George Z. Voyiadjis, Peter I. KattanAbstract:The analysis of damage and plastic deformation in metals is very important towards the full understanding of the various damage mechanisms in these materials. A coupled theory of damage mechanics and finite strain plasticity is proposed. The theory is based on a sound mathematical and mechanical background and is thermodynamically consistent. It is formulated using spatial coordinates utilizing a von Mises type yield criterion with both isotropic and kinematic hardening. The derivation is based on the concept of effective stress that was originally proposed by Kachanov [1] for the case of uniaxial tension. The plasticity model is first formulated in a fictitious unDamaged Configuration of the body. Then certain transformation equations are derived to transform this model into a damage-plasticity model in the Damaged Configuration of the body. Certain assumptions are made in order to make this transformation possible. These assumptions include small elastic strains and the hypothesis of elastic energy equivalence of Ref 17. The corotational stress rate equations are also discussed since they are used extensively in the constitutive relations. Therefore, the use of spin tensors is also discussed since they play a major role in the definition of the corotational rates. In addition, a modified spin tensor is proposed to be used in the coupled model. Furthermore, the nature of the fourth-rank damage effect tensor is discussed for a general state of deformation and damage. Also, the explicit matrix representation of this tensor is rigorously derived and can be used in future applications to solve plane stress and plane strain problems involving damage. Finally, the problem of finite simple shear is investigated using the proposed model. The resulting equations are solved using a Runge-Kutta-Verner fifth order and sixth order method. The stress-strain curves are obtained for a certain expression of the modified spin tensor and are compared with other spin tensors. Also, the evolution of the backstress and damage variables is presented. The results obtained compare favorably with previous results.
Peter I. Kattan - One of the best experts on this subject based on the ideXlab platform.
-
theoretical formulation of a coupled elastic plastic anisotropic damage model for concrete using the strain energy equivalence concept
International Journal of Damage Mechanics, 2009Co-Authors: George Z. Voyiadjis, Ziad N Taqieddin, Peter I. KattanAbstract:An anisotropic damage constitutive model for concrete is developed within the framework of elastoplasticity and continuum damage mechanics. The transformation from the effective (unDamaged) to the Damaged Configuration in the elastic regime is obtained by using the hypothesis of elastic strain energy equivalence. Damage in plasticity is accounted for by developing a new formulation relating the plastic strains rate tensors in the effective and Damaged Configurations. Two anisotropic damage criteria are introduced to account for the different concrete behavior effects under tensile and compressive loadings. The total stress is decomposed into tensile and compressive components in order to satisfy these damage criteria. The plasticity yield criterion presented in this work accounts for the spectral decomposition of the stress tensor and will be used simultaneously with the damage criteria. The transformation of stresses from the effective to the Damaged Configuration is achieved by using a fourth order transformation tensor that is based on second order tensile and compressive damage tensors. Expressions are derived for the elastoplastic tangent operator in the effective and Damaged Configurations. The formulations are derived consistently based on sound thermodynamic principles.
-
Theoretical Formulation of a Coupled Elastic—Plastic Anisotropic Damage Model for Concrete using the Strain Energy Equivalence Concept
International Journal of Damage Mechanics, 2008Co-Authors: George Z. Voyiadjis, Ziad N Taqieddin, Peter I. KattanAbstract:An anisotropic damage constitutive model for concrete is developed within the framework of elastoplasticity and continuum damage mechanics. The transformation from the effective (unDamaged) to the Damaged Configuration in the elastic regime is obtained by using the hypothesis of elastic strain energy equivalence. Damage in plasticity is accounted for by developing a new formulation relating the plastic strains rate tensors in the effective and Damaged Configurations. Two anisotropic damage criteria are introduced to account for the different concrete behavior effects under tensile and compressive loadings. The total stress is decomposed into tensile and compressive components in order to satisfy these damage criteria. The plasticity yield criterion presented in this work accounts for the spectral decomposition of the stress tensor and will be used simultaneously with the damage criteria. The transformation of stresses from the effective to the Damaged Configuration is achieved by using a fourth order transformation tensor that is based on second order tensile and compressive damage tensors. Expressions are derived for the elastoplastic tangent operator in the effective and Damaged Configurations. The formulations are derived consistently based on sound thermodynamic principles.
-
Finite Strain Plasticity and Damage in Constitutive Modeling of Metals With Spin Tensors
Applied Mechanics Reviews, 1992Co-Authors: George Z. Voyiadjis, Peter I. KattanAbstract:The analysis of damage and plastic deformation in metals is very important towards the full understanding of the various damage mechanisms in these materials. A coupled theory of damage mechanics and finite strain plasticity is proposed. The theory is based on a sound mathematical and mechanical background and is thermodynamically consistent. It is formulated using spatial coordinates utilizing a von Mises type yield criterion with both isotropic and kinematic hardening. The derivation is based on the concept of effective stress that was originally proposed by Kachanov [1] for the case of uniaxial tension. The plasticity model is first formulated in a fictitious unDamaged Configuration of the body. Then certain transformation equations are derived to transform this model into a damage-plasticity model in the Damaged Configuration of the body. Certain assumptions are made in order to make this transformation possible. These assumptions include small elastic strains and the hypothesis of elastic energy equivalence of Ref 17. The corotational stress rate equations are also discussed since they are used extensively in the constitutive relations. Therefore, the use of spin tensors is also discussed since they play a major role in the definition of the corotational rates. In addition, a modified spin tensor is proposed to be used in the coupled model. Furthermore, the nature of the fourth-rank damage effect tensor is discussed for a general state of deformation and damage. Also, the explicit matrix representation of this tensor is rigorously derived and can be used in future applications to solve plane stress and plane strain problems involving damage. Finally, the problem of finite simple shear is investigated using the proposed model. The resulting equations are solved using a Runge-Kutta-Verner fifth order and sixth order method. The stress-strain curves are obtained for a certain expression of the modified spin tensor and are compared with other spin tensors. Also, the evolution of the backstress and damage variables is presented. The results obtained compare favorably with previous results.
-
Finite Strain Plasticity and Damage in Constitutive Modeling of Metals With Spin Tensors
Applied Mechanics Reviews, 1992Co-Authors: George Z. Voyiadjis, Peter I. KattanAbstract:The analysis of damage and plastic deformation in metals is very important towards the full understanding of the various damage mechanisms in these materials. A coupled theory of damage mechanics and finite strain plasticity is proposed. The theory is based on a sound mathematical and mechanical background and is thermodynamically consistent. It is formulated using spatial coordinates utilizing a von Mises type yield criterion with both isotropic and kinematic hardening. The derivation is based on the concept of effective stress that was originally proposed by Kachanov for the case of uniaxial tension. The plasticity model is first formulated in a fictitious unDamaged Configuration of the body. Then certain transformation equations are derived to transform this model into a damage-plasticity model in the Damaged Configuration of the body. Certain assumptions are made in order to make this transformation possible. These assumptions include small elastic strains and the hypothesis of elastic energy equivalence. 39 refs., 6 figs.
Michael Brunig - One of the best experts on this subject based on the ideXlab platform.
-
an anisotropic ductile damage model based on irreversible thermodynamics
International Journal of Plasticity, 2003Co-Authors: Michael BrunigAbstract:Abstract The paper deals with fundamental constitutive issues in the elastic–plastic-damage rate theory and the numerical modelling of the large strain elastic–plastic deformation behavior of anisotropically Damaged ductile metals. The proposed model is based on a generalized macroscopic theory within the framework of nonlinear continuum damage mechanics taking into account kinematic description of damage. It employs the consideration of Damaged as well as fictitious unDamaged Configurations related via metric transformations which lead to the definition of damage strain tensors. The modular structure of the continuum theory is accomplished by the kinematic decomposition of strain rates into elastic, plastic and damage parts. To be able to address both the plastic flow and the anisotropic damage process, respective Helmholtz free energy functions of the fictitious unDamaged Configuration and of the current Damaged Configuration are introduced separately. A generalized yield condition based on invariants of the effective stress tensor is used to adequately describe the plastic flow properties of ductile metals and the plastic strain rate tensor is determined by a non-associated flow rule. Considering the Damaged Configurations a damage criterion is formulated using stress components referred to the elastically unloaded damage Configuration. The damage strain rate tensor takes into account isotropic as well as anisotropic effects providing a realistic physical representation of ductile material degradation. Identification of material parameters is discussed in some detail. The applicability of the proposed continuum damage theory is demonstrated by numerical simulation of the inelastic deformation process of tension specimens.
-
A framework for large strain elastic–plastic damage mechanics based on metric transformations
International Journal of Engineering Science, 2001Co-Authors: Michael BrunigAbstract:Abstract A continuum elastic–plastic damage model employing irreversible thermodynamics and internal state variables is presented. The approach is based on a kinematic description using multiplicative decomposition of the metric transformation tensor into elastic and damage-plastic parts. Furthermore, unDamaged Configurations are introduced which are related to the Damaged ones via associated metric transformations which allow for the interpretation as damage tensors. Thus, the damage tensor is explicitly characterized in terms of a kinematic measure of damage. This leads to the definition of appropriate logarithmic strain measures. Strain rates are shown to be additively decomposed into elastic, plastic and damage strain rate tensors. Moreover, based on the standard dissipative material approach and a generalized effective stress concept, work-conjugate stress tensors are introduced. Elastic and plastic constitutive equations are formulated in an effective stress space. A generalized macroscopic yield condition is employed and the evolution of the effective plastic part of the strain rate tensor is determined via a non-associated flow rule. Considering the Damaged Configurations a generalized damage criterion is formulated using stress components referred to the elastically unloaded (stress free) Damaged Configuration. The evolution of the damage part of the strain rate tensor is discussed in some detail. It is based on a damage potential function and takes into account isotropic as well as anisotropic effects.
Thomas Michelitsch - One of the best experts on this subject based on the ideXlab platform.
-
Aging in transport processes on networks with stochastic cumulative damage
Physical Review E, 2019Co-Authors: Alejandro Riascos, Jicun Wang-michelitsch, Thomas MichelitschAbstract:In this paper we explore the evolution of transport capacity on networks with stochastic incidence of damage and accumulation of faults in their connections. For each Damaged Configuration of the network, we analyze a Markovian random walker that hops over weighted links that quantify the capacity of transport of each connection. The weights of the links in the network evolve due to randomly occurring damage effects that reduce gradually the transport capacity of the structure. We introduce a global measure to determine the functionality of each Configuration and how the system ages due to the accumulation of damage that cannot be repaired completely. Then, by assuming a minimum value of the functionality required for the system to be "alive", we explore the statistics of the lifetimes for several realizations of this process in different types of networks. Finally, we analyze the characteristic longevity of such a system and its relation with the "complexity" of the network structure. One finding is that systems with greater complexity live longer. Our approach introduces a model of aging processes relating the reduction of functionality with the accumulation of "misrepairs" and the lifetime of a complex system.
Ganesh Thiagarajan - One of the best experts on this subject based on the ideXlab platform.
-
A damage cyclic plasticity model for MMC`s using a micromechanical model
1997Co-Authors: Ganesh Thiagarajan, George Z. VoyiadjisAbstract:A plasticity model is presented for metal-matrix composites which also incorporates the effects of damage in the material. The cyclic plasticity model is the basis of the damage-plasticity model. A six parameter general anisotropic yield surface was previously proposed by Voyiadjis and Thiagarajan (1995) for continuous unidirectionally reinforced MMC`s. The model presented here uses the yield surface proposed earlier to describe the behavior of MMC`s subjected to cyclic, proportional as well as non-proportional loadings and is based on the modifications of the bounding surface model proposed by Dafalias and Popov (1976). Plastic strains have been experimentally observed to develop in a non-associative manner. A non-associative rule based on a proposed potential function is described here. The elasto-plastic stiffness matrix is then developed based on these premises and model curves generated are compared to the experimental curves as shown in the end. The experimental curves obtained by (Dvorak et al., 1988) and (Nigam et al., 1993a) are used for determination of parameters and also for the stress-strain curve comparisons. The cyclic plasticity model is used in a fictitious effective Configuration. This Configuration is then transformed to the actual Damaged Configuration using the damage effect tensor. The constitutive equations in the actualmore » Configuration is outlined along with some experimental comparisons.« less
-
Micro and macro anisotropic cyclic damage-plasticity models for MMCS
International Journal of Engineering Science, 1997Co-Authors: George Z. Voyiadjis, Ganesh ThiagarajanAbstract:Abstract Two approaches to modeling the cyclic damage-plasticity behavior of metal matrix composites are presented in this paper, namely: a micro (micromechanical-damage) and a macro (continuum-damage) based approach. Each of these approaches involves a fictitious unDamaged ‘effective’ Configuration to which the plasticity equations are applied and constitutive equations derived. Using the equations for the transformation of stress from the unDamaged to the Damaged Configuration, the transformation of these equations to the actual Damaged Configuration is performed. Two new concepts are introduced here: (i) the incorporation of a term ϒ, similar to backstress, in the thermodynamic force Y space in the cyclic damage criterion, and (ii) the concept of cyclic damage under cyclic loading situations. This paper outlines the results from the two models in comparison with experimental results and compares and contrasts the effectiveness of the two models.
