Strong plastic deformation and softening of fast colliding Lennard-Jones nanoparticles by Molecular Dynamics simulations

We present a Molecular Dynamics study of the coefficient of restitution $e$ for colliding two equal sized nanoparticles. Nanoparticles often show distinctly different mechanical and dynamical properties than bulk materials. We investigate the collision velocity $v_{\mathrm{coll}}$ and the nanoparticle size dependence of coefficient of restitution. We find that the size dependent yield velocity $v_{Y}$, a sharp crossover point between elastic collision and plastic collision, appears to approach the theoretical constant value for macroscopic spheres as the nanoparticle size grows. We also find that above $v_{Y}$, the coefficient of restitution $e \propto v_{\mathrm{coll}}^{-\alpha}$, where $\alpha \sim 1$, which is distinct from the inelastic macroscopic sphere collision case, $\alpha = 1/4$. It indicates that nanoparticles colliding at high collision velocity are softened. We discuss possible insights of the size dependent yield velocity and the soft nanoparticles above $v_{Y}$.