Ultra-elastic and inelastic impact of Cu nanoparticles

The degree of elasticity for the impact of a particle with a rigid wall is normally characterized with the restitution parameter, R. We examine such impact behavior of Cu nanoparticles with molecular dynamics simulations, for different particle sizes (1-15 nm in radius) and impact velocities (25-200 m s ^{- 1}). The impact can be ultra-elastic (R > 1) or inelastic (R < 1). Ultra-elastic or inelastic impact may occur for the smallest nanoparticles soly due to fluctuations, and the impact is inelastic but can be highly elastic (R ∼ 0.9-1) for larger sizes. R decreases with increasing size and impact velocity in general. Impact-induced structure transitions (e.g., dislocations) can be reversible and induce irreversible heating regardless of their reversibility. Such heating along with remnant plasticity is the key mechanism for impact inelasticity. Inelastic impact may occur with little remnant plasticity.