Sphere and cylinder contact mechanics during slip

Using molecular dynamics (MD) we study the dependency of the contact mechanics on the sliding speed when an elastically soft slab (block) is sliding on a rigid substrate with a sin(q₀x) surface height profile. The atoms on the block interact with the substrate atoms by Lennard-Jones potentials. We consider contacts with and without adhesion. The contact area and the friction force are nearly velocity independent for small velocities (v < 0.25 m/s) in spite of the fact that the shear stress in the contact area is rather non-uniform. For the case of no adhesion the friction coefficient is very small. For the case of adhesion the friction coefficient is higher, and is mainly due to energy dissipation at the opening crack tip, where rapid atomic snap-off events occur during sliding. We comment on the role of elastic non-linearity on the change in the contact area with increasing tangential force.