• Transactions of Materials Processing
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• v.17 no.3
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• pp.161-169
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• 2008

In the present work, the two-back stress model is proposed and continuum damage mechanics (CDM) is incorporated into the plastic constitutive relation in order to describe the plastic deformation localization and the damage evolution in a deforming continuum body. Coupling between damage mechanics and isothermal rate independent plasticity is performed using the kinematic hardening rule, which in turn is formulated by combining the nonlinear Armstrong-Frederick rule and the Phillips rule. The numerical analyses are carried out within h deformation theory. It is noted that the damage evolution within a work piece accelerates the plastic deformation localization such that the material with lower hardening exponent results in a rapid shear band formation. Moreover, the results from the numerical analysis reflected closely with the micro-structures around the fractured regime. The effects of the various hardening parameters on deformation localization are also investigated. As the nonlinear strain rate description in the back stress evolution becomes dominant, the strain localization becomes intensified as well as the damage evolution.

• Multiscale and Multiphysics Mechanics
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• v.1 no.2
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• pp.171-188
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• 2016

Gradient enhanced theories of crystal plasticity enjoy great research interest. The focus of this work is on thermodynamically consistent modeling of grain size dependent hardening effects. In this contribution, we develop a model framework for damage coupled to gradient enhanced crystal thermoplasticity. The damage initiation is directly linked to the accumulated plastic slip. The theoretical setting is that of finite strains. Numerical results on single-crystalline metal showing the development of damage conclude the paper.

• Journal of Welding and Joining
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• v.25 no.1
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• pp.63-69
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• 2007

Once assessment of material failure characteristics is captured precisely in a unified way, it can bedirectly incorporated into the structural failure assessment under various loading environments, based on the theoretical backgrounds so called Local Approach to Fracture. The aim of this study is to develop a numerical fatigue test method by continuum damage mechanics applicable for the assessment of structural integrity throughout crack initiation and structural failure based on the Local Approach to Fracture. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, is developed and employed in the 3-D FEA code in order to numerically evaluate the material and/or structural responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations for each material, are implemented in numerical fatigue test method. The material constants selected from constitutive equations are used directly in the failure assessment of material and/or structures. The performance of the developed system has been evaluated with assessing the S-N diagram of stainless steel materials.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.3
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• pp.58-67
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• 1991

A theory of continuum damage mechanics based on the theory of materials of type N was developed and its nonlinear finite element approximation and numerical simulation was carried out. To solve the finite elastoplasticity problems, reasonable kinematics of large deformed solids was introduced and constitutive relations based on the theory of materials of type-N were derived. These highly nonlinear equations were reduced to the incremental weak formulation and approximated by the theory of nonlinear finite element method. Two types of problems, compression moulding problem and pure bending problem, were solved for aluminum 2024.

• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.70-75
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• 2000

In this paper a new constitutive model for ductile materials was proposed. This model can describe the material degradation due to the evolution of isotropic damage during elasto-platic deformation. The plastic flow rule was derived under the framework of thermodynamic approach of continuum damage mechanics(CDM) in which plastic strain hardening parameters and isotropic damage were taken as thermodynamic state variables. And the process to determine material constants for constitutive model using an experimental data was presented.

• Transactions of Materials Processing
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• v.4 no.2
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• pp.131-140
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• 1995

In this paper damage propagation of a material during forming is investigated with the concept of continuum damage mechanics. An isotropic damage model based on the theory of materials of type N is adopted to describe the damage process of a ductile material with large elasto-viscoplastic deformation. The stiffness degradation of the loaded material is chosen as a damage measure. The highly nonlinear equilibrium equations are reduced to the incremental weak form and approximated by the total Lagrangian finite element method. To simulate contact condition, extended interior penalty method with modified coulomb friction law is adopted. The displacement control method along with the modified Riks' continuation technique is used to solve the incremental iterative equations. As numerical examples, upsetting problem and backward extrusion problem are simulated and the results of damage propagation and $J_2$ stress contours with and without friction are presented.

• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.76-83
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• 2000

this paper was concentrated on the finite element formulation to solve boundary value problems by using the isotropic elasto-plastic damage constitutive model proposed previously(Noh, 2000) The plastic damage of ductile materials is generally accompanied by large plasticdeformation and strain. So nonlinearity problems induced by large deformation large rotation and large strain behaviors were dealt with using the nonlinear kinematics of elasto-plastic deformations based on the continuum mechanics. The elasto-plastic damage constitutive model was applied to the nonlinear finite element formulation process of Shin et al(1997) and an improved analysis model considering the all nonlinearities of structural behaviors is proposed. Finally to investigate the applicability and validity of the numerical model some numerial examples were considered.

• Journal of Ocean Engineering and Technology
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• v.16 no.4
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• pp.32-36
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• 2002

In this paper, a numerical methodology for health monitoring of weldment was proposed using finite element method coupled with continuum damage mechanics. The welding-induced residual stress distribution of T-joint weldment was calculated using a commercial finite element package SYSWELD+. The distribution of latent damage was evaluated from the stress and strain components taken as the output of a finite element calculation. Numerical examples were given to demonstrate the usefulness of this so-called "post-processing approach" in the case of welding-induced damage assessment.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.49-54
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• 2009

In this study, the numerical analysis model for fatigue life prediction of welded structures are presented. In order to evaluate the structural degradation of welded structures due to fatigue loading, continuum damage mechanics approach is applied. Damage evolution equation of welded structures under arbitrary fatigue loading is constructed as a unified plasticity-damage theory. Moreover, by integration of damage evolution equation regarding to stress amplitude and number of cycles, the simplified fatigue life prediction model is derived. The proposed model is compared with fatigue test results of T-joint welded structures to obtain its validation and usefulness. It is confirmed that the predicted fatigue life of T-joint welded structures are coincided well with the fatigue test results.

• Structural Engineering and Mechanics
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• v.25 no.5
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• pp.519-540
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• 2007

In this paper, the energy-based plastic-damage model previously proposed by the authors [International Journal of Solids and Structures, 43(3-4): 583-612] is first simplified with an empirically defined evolution law for the irreversible strains, and then it is extended to its rate-dependent version to account for the strain rate effect. Regarding the energy dissipation by the motion of the structure under dynamic loadings, within the framework of continuum damage mechanics a new damping model is proposed and incorporated into the developed rate-dependent plastic-damage mode, leading to a unified constitutive model which is capable of directly considering the damping on the material scale. Pertinent computational aspects concerning the numerical implementation and the algorithmic consistent modulus for the unified model are also discussed in details, through which the dynamic nonlinear analysis of damping structures can be coped with by the same procedures as those without damping. The proposed unified plastic-damage model is verfied by the simulations of concrete specimens under different quasistatic and high rate straining loading conditions, and is then applied to the Koyna dam under earthquake motions. The numerical predictions agree fairly well with the results obtained from experimental tests and/or reported by other investigators, demonstrating its capability for reproducing most of the typical nonlinear performances of concrete under quasi-static and dynamic loading conditions.