Shock wave propagation and spall failure in single crystal Mg at atomic scales

Large scale molecular dynamics (MD) simulations are carried out to investigate the wave propagation and failure behavior of single crystal Mg under shock loading conditions. The embedded atom method interatomic potential, used to model the Mg systems, is first validated by comparing the predicted Hugoniot behavior with that observed using experiments. The first simulations are carried out to investigate the effect of loading orientation on the wave propagation and failure behavior by shock loading the system along the [0001] direction (c-axis) and the [10 (1) over bar0] direction using a piston velocity of 1500 m/s. The spall strength (peak tensile pressure prior to failure) is predicted to be higher for loading along the [10 (1) over bar0] direction than that predicted for loading along the [0001] direction. To investigate the effect of shock pressure on the failure behavior and spall strength of the metal, the MD simulations are carried out using piston velocities of 500 m/s, 1000 m/s, 1500 m/s, and 2000 m/s for loading along the c-axis. The results indicate that the higher piston velocities result in higher shock pressures, and the predicted values for the spall strength decrease with an increase in the shock pressure. In addition, the simulations reveal that the various piston velocities result in variations in the interactions between the reflected waves and the tail of the pressure waves and, hence, variations in the failure behavior. In addition, MD simulations are also carried out to investigate the effect of temperature on the wave propagation behavior and spall strength by equilibrating the initial system at temperatures of 300 K, 600 K, and 800 K prior to shock loading simulations using a piston velocity of 1000 m/s. The results suggest a decrease in spall strength of the single crystal metal with an increase in the initial temperature of the system. The strain rates generated, the evolution of temperature, the variations in the wave interactions, and the spall strength computed using MD simulations are discussed and compared to experimental results in the literature. (C) 2016 AIP Publishing LLC.