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Validity of cauchy-born hypothesis in multi-scale modeling of plastic deformations
, Article International Journal of Solids and Structures ; 2017 ; 00207683 (ISSN) ; Jahanshahi, M ; Toloui, G ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
The Cauchy-Born (CB) hypothesis has been widely used in multi-scale modeling of crystalline nano-structures. The violation of CB hypothesis in stress space and the transition to plasticity, which is equivalent to the violation of CB hypothesis in strain space, are generally confused and it becomes crucial to differentiate between the two distinct phenomena; the violation of the former usually occurs at high values of stress and at regions where the surface effects are manifest while the violation of the latter occurs at low stresses when the material loses its strength to tolerate the applied loading. In this paper, a novel technique is developed to investigate the validity of CB hypothesis...
Validity of cauchy–born hypothesis in multi-scale modeling of plastic deformations
, Article International Journal of Solids and Structures ; Volume 115-116 , 2017 , Pages 224-247 ; 00207683 (ISSN) ; Jahanshahi, M ; Toloui, G ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
The Cauchy–Born (CB) hypothesis has been widely used in multi-scale modeling of crystalline nano-structures. The violation of CB hypothesis in stress space and the transition to plasticity, which is equivalent to the violation of CB hypothesis in strain space, are generally confused and it becomes crucial to differentiate between the two distinct phenomena; the violation of the former usually occurs at high values of stress and at regions where the surface effects are manifest while the violation of the latter occurs at low stresses when the material loses its strength to tolerate the applied loading. In this paper, a novel technique is developed to investigate the validity of CB hypothesis...
A plasticity model for metals with dependency on all the stress invariants
, Article Journal of Engineering Materials and Technology, Transactions of the ASME ; Volume 135, Issue 1 , 2013 ; 00944289 (ISSN) ; Hoseini, S. H ; Farrahi, G. H ; Sharif University of Technology
2013
Abstract
Recent experiments on metals have shown that all of the stress invariants should be involved in the constitutive description of the material in plasticity. In this paper, a plasticity model for metals is defined for isotropic materials, which is a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. For this purpose, the Drucker-Prager yield criterion is extended by addition of a new term containing the second and the third deviatoric stress invariants. Furthermore for estimating the cyclic behavior, new terms are incorporated into the Chaboche's hardening evolution equation. These modifications are applied by adding new...
Effects of stress invariants and reverse loading on ductile fracture initiation
, Article International Journal of Solids and Structures ; Volume 49, Issue 13 , 2012 , Pages 1541-1556 ; 00207683 (ISSN) ; Hoseini, S. H ; Farrahi, G. H ; Sharif University of Technology
2012
Abstract
Recent research studies on ductile fracture of metals have shown that the ductile fracture initiation is significantly affected by the stress state. In this study, the effects of the stress invariants as well as the effect of the reverse loading on ductile fracture are considered. To estimate the reduction of load carrying capacity and ductile fracture initiation, a scalar damage expression is proposed. This scalar damage is a function of the accumulated plastic strain, the first stress invariant and the Lode angle. To incorporate the effect of the reverse loading, the accumulated plastic strain is divided into the tension and compression components and each component has a different weight...
An augmented Lagrangian contact formulation for frictional discontinuities with the extended finite element method
, Article Finite Elements in Analysis and Design ; Volume 107 , December , 2015 , Pages 28-43 ; 0168874X (ISSN) ; Vahab, M ; Khoei, A. R ; Sharif University of Technology
Elsevier
2015
Abstract
In this paper, an Uzawa-type augmented Lagrangian contact formulation is presented for modeling frictional discontinuities in the framework of the X-FEM technique. The kinematically nonlinear contact problem is resolved based on an active set strategy to fulfill the Kuhn-Tucker inequalities in the normal direction of contact. The Coulomb's friction rule is employed to address the stick-slip behavior on the contact interface through a return mapping algorithm in conjunction with a symmetrized (nested) augmented Lagrangian approach. A stabilization algorithm is proposed for the robust imposition of the frictional contact constraints within the proposed augmented Lagrangian framework. Several...
3D finite element modeling of shear band localization via the micro-polar Cosserat continuum theory
, Article Computational Materials Science ; Volume 49, Issue 4 , 2010 , Pages 720-733 ; 09270256 (ISSN) ; Yadegari, S ; Biabanaki, S. O. R ; Sharif University of Technology
Abstract
In this paper, a micro-polar continuum model is presented based on the Cosserat theory for 3D modeling of localization phenomena. Since the classical continuum model suffers from the pathological mesh-dependence in strain localization problem, the governing equations are regularized by adding the rotational degrees-of-freedom to conventional degrees-of-freedom. The fundamental relations in three-dimensional Cosserat continuum are presented and the internal length parameters are introduced in the elasto-plastic constitutive matrix to control the shear bandwidth. The mesh independency of Cosserat model in strain-softening problem is verified and the effect of internal parameters is...