Large-scale molecular dynamics simulations are conducted on single crystal copper along eight representative orientations to investigate dislocation-dominated void nucleation during shock loading and spall failure, including mechanisms and anisotropy. Spall strength estimated from free surface velocity decreases in the order of group I ([001]), group IV ([012] and [011]), group III ([122] and [123]) and group II ([114], [112] and [111]), respectively, in good agreement with anisotropy of spall strength in previous experiments and simulations. A lower spall strength is statistically associated with a higher void nucleation rate and a higher density of stable immobile dislocations ($1/6〈110〉$ and $1/3〈100〉$) formed before void nucleation. Stable immobile dislocation plays a key role in void nucleation. The formation of stable immobile dislocations requires three conditions: high resolved shear stress for activating mobile dislocations, two or more main slip planes for dislocation reaction, and high angle between activated slip directions for high stability of immobile dislocations. Based on crystal elastic–plastic theory, resolved shear stress on all slip systems is calculated to analyze orientation effects on the three conditions. The three conditions can be fulfilled by group II orientations, but cannot by group I, III, and IV orientations, leading to anisotropy in void nucleation and spall strength.

沿八个代表性方向对单晶铜进行大规模分子动力学模拟，以研究在冲击载荷和剥落失效期间以位错为主的空洞成核，包括机制和各向异性。根据自由表面速度估计的剥落强度按 I 组（[001]）、IV 组（[012] 和 [011]）、III 组（[122] 和 [123]）和 II 组（[114]）的顺序降低, [112] 和 [111]) 分别与先前实验和模拟中剥落强度的各向异性非常一致。较低的剥落强度在统计上与较高的空洞成核率和较高的稳定固定位错密度相关（$1/6〈110〉$和$1/3〈100〉$) 在空洞成核之前形成。稳定的固定位错在空洞成核中起关键作用。稳定的固定位错的形成需要三个条件：激活移动位错的高分辨剪切应力，位错反应的两个或多个主滑移面，以及固定位错高稳定性的激活滑移方向之间的高角度。基于晶体弹塑性理论，计算了所有滑移系上的解析剪应力，以分析三个条件下的取向效应。这三个条件可以通过 II 族取向来满足，但不能通过 I、III 和 IV 族取向来满足，从而导致空洞形核和剥落强度的各向异性。