Acta Metall Sin  2018, Vol. 54 Issue (9): 1322-1332    DOI: 10.11900/0412.1961.2017.00553
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Investigation of Strain Rate Effect by Three-Dimensional Discrete Dislocation Dynamics for fcc Single Crystal During Compression Process
Xiangru GUO1,2, Chaoyang SUN1,2(), Chunhui WANG1,2, Lingyun QIAN1,2, Fengxian LIU3
1 School of Mechanical and Engineering, University of Science and Technology Beijing, Beijing 100083, China
2 Beijing Key Laboratory of Lightweight Metal Forming, University of Science and Technology Beijing, Beijing 100083, China
3 Applied Mechanics Lab., School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
Abstract

 ZTFLH: TG142.1
Fund: Supported by National Natural Science Foundation of China (No.51575039) and Joint Fund of National Natural Science Foundation of China and Chinese Academy of Engineering Physics (No.U1730121)
 Fig.1  Discretization of dislocation line (The black solid line is the original dislocation line, the blue segments represent the discrete dislocation segments, bi is the Burgers vector of dislocation segment i) Fig.2  Four slip systems are chosen symmetrically in twelve slip systems of single crystal Ni (a) and plastic strain rate evolution during stress relaxation (b) (Inset in Fig.2b shows the corresponding dislocation snapshot after stress relaxation) Fig.3  Comparisons of 3D-DDD simulated and experimental statistical[4] results of stress and dislocation density with strain under constant strain rate 2×102 s-1 compression loading of Ni single crystal micropillar with a diameter of 5 μm Fig.4  SEM image of Ni single crystal micropillar (a)[4] and dislocation snapshot after compression (b) Fig.5  Dislocation snapshots corresponding to strains of 0.03% (a), 0.20% (b), 0.27% (c), 0.43% (d), 0.55% (e) and 0.70% (f) in the compression process of Ni single crystal micropillar Fig.6  3D-DDD simulation results of stress (a) and dislocation density (b) with strain under different strain rates compression of Ni single crystal micropillar with a diameter of 5 μm, and dislocation snapshots corresponding to true strain 0.8% in the compression ($ε˙$—strain rate ) (c) Fig.7  Respective contributions of τ*, τα and τFR to the flow stress during plastic deformation under strains rate of 2×102 s-1 (a), 1×103 s-1 (b), 1×104 s-1 (c) and 5×104 s-1 (d) (τ* is the effective stress on the dislocation, τα is the elastic interaction stress related to dislocation density, τFR is the critical resolved shear stress to activate FR source) Table 1  Dislocation densities corresponding to different strains of Ni single crystal micropillar under different strain rates Fig.8  Simulation results of flow stress and dislocation density with different initial dislocation densities ρ0 under strain rates of 2×102 s-1 (a) and 5×104 s-1 (b) Fig.9  Plastic strains contributed by four slip systems with initial dislocation density of 1.2×1011 m-2 under loading strain rates of 2×102 s-1 (a), 1×103 s-1 (b), 1×104 s-1 (c) and 5×104 s-1 (d) Fig.10  Dislocation snapshots corresponding to strains of 0.11% (a), 0.20% (b), 0.32% (c), 0.45% (d), 0.58% (e) and 0.78% (f) in the compression