〈111〉晶向冲击加载下单晶铜中纳米孔洞增长的早期动力学行为

利用分子动力学方法模拟计算了单晶铜中纳米孔洞在沿〈111〉晶向冲击加载下增长的早期过程.测量发现不同加载强度下等效孔洞半径随时间近似成线性变化.观测到单孔洞增长的两种位错生长机理：加载强度较低时，只在沿着冲击加载方向的孔洞顶点附近区域有位错的成核和运动；而随着加载强度超过一定阈值，在沿冲击加载和其垂直方向的孔洞顶点区域都观察到位错的成核和运动.在前一种机理作用下，孔洞只沿加载方向增长；在后一种机理作用下，孔洞同时沿加载和垂直于加载方向增长.分析孔洞表面原子的位移历史，发现沿加载及与其垂直方向的孔洞顶点沿径向的速度基本恒定，由此提出了一个孔洞生长模型，可以解释孔洞增长的线性生长规律. 关键词： 纳米孔洞 分子动力学 冲击加载 位错

Initial dynamic behavior of nano-void growth in single-crystal copper under shock loading along <111> direction

Initial stage of nano-void growth in single crystal copper under shock loading along <111> direction has been investigated by using molecular dynamics (MD) simulation. The results show the void growth rate, represented by iucrease of equivalent radius of void vs time, keeps constant under certain shock strength. Two kinds of dislocation mechanisms of single void growth have been observed. When shock strength is lower than a critical value, dislocations nucleate and move outward only in the area around two vertices of the void along the shock direction and the void only grows along shock direction. When shock strength exceeds the critical value, dislocations nucleate and move outward not just in the above area but also in the equator perpendicular to the shock direction, and the void grows both along the shock direction and its normal. By examining the displacement history of atoms around the void surface, we find that the radial velocities of the vertices along and perpendicular to the shock direction almost keep constant during the tensile process. Based on constant radial velocities of vertices, we have derived a model of void growth which explains the constant void growth rate well.