Dislocation Density Based Crystal Plasticity Finite Element Simulation of Alpha-Iron
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Dislocation Density Based Crystal Plasticity Finite Element Simulation of Alpha-Iron Zhe Leng1 and David P. Field1 1 School of Mechanical and Materials Engineering, Washington State University, Pullman, WA, 99164-2920, U.S.A. ABSTRACT Ferritic/martensitic steels such as HT9 steel, is used for structural components in nuclear power plants because of its high strength and good swelling resistance. Understanding the mechanical behavior of these steels is quite important, since it will affect the strength and the life of the component. In this study, a dislocation density based crystal plasticity finite element model is developed in which different types of dislocation evolves on the activated 12 slip systems in alpha-iron. The dislocation evolves in the form of closed loop and the dislocation density is tracked as internal state variable, the generation and annihilation of dislocations are modeled based on the dislocation interaction laws. The plastic flow is calculated based on the dislocation densities and a generalized Taylor equation is used as the hardening law, and the hardening is assumed to be isotropic in this study. The evolution of polycrystal texture of alpha-iron is presented in the form of pole figures, which indicate the orientation spread and agree with the experimental result. The model also indicates the inhomogeneous dislocation distribution and stress concentration at the grain boundaries. INTRODUCTION Currently, more and more focus has been put on the energy generation industry due to the increasing worldwide energy demand. As is known that most energy resources such as coal, oil, and natural gas are not renewable, thus nuclear energy is suggested to be a possible energy source in the future because of its high efficiency. However, the structural components such as pressure vessels [1] in the nuclear energy system are subjected to extreme operational conditions. They must sustain significant thermal and mechanical forces as well as irradiation, and serve for several years without maintenance. Understanding the mechanical behavior of the structure material is essential to predict the elastic-plastic response, the stress concentration and crack initiation and other effects that will result in failure, prevent those effect will, of course, extend the life of the structure component and ensure safety. Recent studies focus on the crystal plasticity using finite element method. The crystal plasticity finite element method is used for studies of heterogeneous structure evolution and explains the plastic behavior, work hardening, texture evolution and dislocation evolution during the plastic deformation. The development of phenomenological crystal plasticity originates from the pioneering work of Taylor [2], and the continuum crystal kinematics framework was first formulated by Mandel [3] and Hill [4]. It is later extended by Rice [5], Asaro [6,7] for finite strain application, the evolution of the plastic flow rule and hardening laws afterward lead to a more sophisticated crystal plasticity formulation [8
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