Molecular dynamics study on micro jet in single crystal aluminum

Non-equilibrium molecular dynamics simulations are performed to explore the evolution of one- and two-dimensional micro jets induced by square shock wave in single crystal Al with conical and sinusoidal defects. The particle source of micro jet is obtained using the forward and backward particle tracing techniques, and it is discovered that the structure of particle source in different parts of micro jet closely depends on the defect type, and the formation of micro jet is a layered aggregation process from the defect's surficial layer to its inner layer. The jet head velocity in the conical cases initially experiences a sharp increase, then a rapid decline to be constant, and jet volume in both conical and sinusoidal cases undergoes a nonlinear increase before remaining unaltered. A further analysis on the relationship among particle count, density, velocity, and temperature is performed, where the ejecta velocity along the shock direction fundamentally shows a linear variation and the maximum velocity is in the jet head in the conical cases and sinusoidal case of shock velocity u(p) = 6 km/s, but the jet velocity presents a fluctuant variation and the head velocity lowers than that in the post-head in the sinusoidal case of u(p) = 2 km/s. More importantly, it is revealed that two mechanisms, the necking for the one-dimensional jet and void growth and coalescence for the two-dimensional jet, dominate the jet breakup. In fact, velocity, temperature and pressure perturbations all contribute the jet breakup, with the velocity perturbation having the most important influence. Furthermore, the thickening of void border is due to the velocity gradient, which produces an increase in density in the jet head.