Why Nanoprojectiles Work Differently than Macroimpactors: The Role of Plastic Flow

Atomistic simulation data on crater formation due to the hypervelocity impact of nanoprojectiles of up to 55 nm diameter and with targets containing up to 1.1 x 10(10) atoms are compared to available experimental data on mu m(-), mm(-), and cm-sized projectiles. We show that previous scaling laws do not hold in the nanoregime and outline the reasons: within our simulations we observe that the cratering mechanism changes, going from the smallest to the largest simulated scales, from an evaporative regime to a regime where melt and plastic flow dominate, as is expected in larger microscale experiments. The importance of the strain-rate dependence of strength and of dislocation production and motion are discussed.