Molecular dynamics of collisions between rough surfaces

Classical molecular-dynamics simulations were carried out to investigate the collisions between two Ni crystals with rough surfaces at relative velocities in the range between 1 and 100 nm ns(-1). The response of the colliding solids was studied by monitoring local kinetic and potential energies as well as local mechanical stresses. A local order parameter was also used to discriminate between solidlike and liquidlike dynamics. Computation results indicate that both temperature and stress increase with the relative collision velocity. Averaged for the atoms within directly interacting surface asperities, the average temperature can reach values as high as 6000 K, the average pressure can be as high as 13 GPa, and the average normal stress as high as 16 GPa. Individual atoms can attain local temperatures as high as 10 000 K and local normal stresses as large as 20 GPa, depending on the surface morphology.