Molecular dynamics simulation study on orientation effects on the shock-induced spallation of single-crystal aluminum

Under shock loading, the evolution of spall damage in single crystals exhibits significant orientation effects due to variations in crystal orientation and plastic deformation modes. However, the influence of loading strength on the orientation dependence of spall damage has been largely overlooked. Shock-induced spallation behaviors of single-crystal aluminum (Al) were simulated in eight crystal orientations using molecular dynamics (MD) simulations across a range of loading velocities from 0.5 to 2.1 km/s. Mechanical responses during the process of impact loading were analyzed, including shock wave propagation and microstructural evolution. It was found that spall strength, and plasticity mechanisms exhibit a combined influence of crystal orientation and loading velocity. In the [001] crystal orientation, the single-crystal Al showed the highest spall strength values (8.588-10.137 GPa) across the entire range of loading velocities, with no obvious elastic-plastic double-wave separation observed, while salient features of elastic-plastic waves separation at loading velocities above a critical value are found in the remaining orientation. Notably, the elastic-plastic waves separation phenomenon in the [111] crystal orientation showed significant hysteresis, accompanied by the largest decrease in spall strength (1.733 GPa) and a marked overshoot at the leading edge of the stress wave (Vp = 1.4 km/s). Plastic deformation in the [001] crystal orientation was dominated by stacking faults and lattice transformation. As the loading velocity increased, the spall mechanism transitioned from heterogeneous void nucleation induced by stacking fault intersections to homogeneous void nucleation driven by disordered structures. Disordered structures are more likely to form in crystal orientations such as [012] and [111]. At higher loading velocities (Vp >= 1.4 km/s), the spallation process exhibits a homogeneous void nucleation mechanism due to significant amorphization. This study provides new insights into the modeling of dynamic damage in metals.