Inelastic Collisions and Hypervelocity Impacts at Nanoscopic Level: A Molecular Dynamics Study

In this chapter we present an atomic level study of nano-particle impact using molecular dynamics simulation. Two cases have been considered. First, we simulate the bouncing of a ball over a surface due to a constant force (which mimic the gravity force), modeling the inter-atomic interaction by a modified Lennard-Jones potential, where the ball-surface atom interaction is represented by a purely repulsive term. The analysis of the results makes it possible, among other aspects, to determine the restitution coefficient in each bounce as well as to understand the processes of energy loss in inelastic collisions, which are actually not a loss, but a transfer to thermal and vibrational energy. The second simulation describes the impact mechanisms of a solid projectile hitting a target at high velocity. Both the projectile and the target are made of copper, which is modeled by a realistic many-body tight-binding potential. The projectile velocity is kept constant during all the simulation, representing an extreme condition, where the momentum and hardness of the projectile is much higher than the momentum and hardness of the target. In this regime, we identify two different behavior in dependence of the projectile velocity: at low velocities (less than 4 km/s) the target basically recover its structure after the passage of the projectile, but at higher velocities, the projectile left a permanent hole in the target.