Shock Waves Propagation and Phase Transition in Single Crystal Iron under Ramp Compression: Large Scale Parallel NEMD Simulations

Abstract

The influences of micro-structures of materials on shock wave have long been recognized, but a few are reported. The evolution of micro- structure during shock waves pass through materials is essential to many practical applications, such as the field of blast and ballistic protection. Traditional continuum theory cannot involve any atomic information of materials when shock waves pass through. Non- equilibrium molecular dynamics (NEMD) simulation is thought to be a promising way to bridge microscopic atomic processes with macroscopic continuum behaviors. The α→ɛ transition of iron at about 13GPa has been recognized for more than half a century, but no essential progress have been make until the recent decades. Experiments still have difficulties to reach temporal and spatial scales and NEMD can make an essential complements. Unfortunately, the former atomic interaction potentials of iron are more or less not appropriate to the high pressure area. We have performed large-scale parallel NEMD simulations with recently developed modified analytic embedded-atom-model (MAEAM) potential on the ramp compression of single crystal iron with different orientations at different ramp time. Our results reveal the relations of profile structures and microstructures. And the phase transition mechanisms of iron are examined to be no difference with the case of shock. Different ramp time have no obvious effects on the Hugoniot states a shock could reach after phase transition though it may reach a higher stress state when compared with the situation of shock compression. However, the grains formed after transition incline to contain fewer defects or grow bigger with the increasing ramp time.