Evaluation of Crack Growth Retardation Effect Due to Nano-scale Voids Based on Molecular Dynamics Method
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Evaluation of Crack Growth Retardation Effect Due to Nano-scale Voids Based on Molecular Dynamics Method Shin Taniguchi1 and Toshihiro Kameda2 1 Graduate Student, University of Tsukuba, Tennodai1-1-1, Tsukuba, Ibaraki, Japan, 305-8573 2 University of Tsukuba, Tennodai1-1-1, Tsukuba, Ibaraki, Japan, 305-8573 ABSTRACT This study has investigated the crack growth retardation effect due to plural nano-scale voids in Cu single crystals using a molecular dynamics (MD) method. Focusing on an interaction between nano-scale voids and dislocations, we have evaluated the optimum placement for crack growth retardation. MD simulations showed that the dislocation activity was further enhanced due to plural nano-scale voids continuously placed on the primary slip direction. The significant ductility enhancement and slight yield stress increase due to the crack shielding effect of nanoscale voids were observed. INTRODUCTION In metallic materials under nuclear plants or outer space environments, there exist various types of nano-scale lattice defects as a consequence of irradiation or crystal deformation. These lattice defects generally degrade the mechanical properties of the metallic materials except the yield stress. In particular, due to these defects, material life span is quiet limited [1], and several irradiation experiments have shown the increased yield stress but ductility loss [2,3]. According to their electron microscopy observations, these lattice defects typically consist of stacking fault tetrahedra (SFT), Frank partial or perfect dislocation loops, and a mixture of nano-scale bubbles and voids. Furthermore, several atomistic simulations have shown that these lattice defects impede the dislocation movement and increase the yield stress [4,5]. From the view point of the ductility of the metal with lattice defects, in general, crack growth behavior depends on the distribution of the lattice defects around cracks. Several numerical simulations have shown that residual dislocations around the crack tip suppress new dislocation emission [6,7]. Other atomistic simulations have shown that nano-scale voids act as dislocation absorption and formation sites during the plastic deformation [8,9]. These studies suggest that nano-scale voids improve the ductility due to the enhancement of the dislocation activity and the smoother plastic deformation around the crack tip and voids. In other words, nano-scale voids may have the capability to retard the crack growth, sustaining the higher yield strength at the same time. In a previous study, we have investigated the crack growth with a nano-scale void on the primary slip direction [10]. However, due to the interactions between nano-scale voids, the further enhanced dislocation activity could improve the ductility tremendously. In this study, we have investigated the crack growth retardation effect due to plural nano-scale voids using a large scale parallel molecular dynamics (MD) method.
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MD SIMULATION METHOD The computations in this study, we carried out using the Large-scale At
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