On the origin of sliding friction: Role of lattice trapping

TL;DR

This study uses molecular dynamics to explore how lattice trapping influences sliding friction, revealing that atomic snap-in/out events at crack tips dominate friction force, which is mostly velocity-independent except near the sound velocity.

Contribution

It demonstrates that lattice trapping causes velocity-independent friction due to atomic events at crack tips, clarifying the microscopic origin of friction force.

Findings

Friction force is nearly velocity independent due to phonon emission.

Atomic snap-in/out events at crack tips dominate friction.

Friction increases near the transverse sound velocity.

Abstract

Using molecular dynamics we study the dependence of the friction force on the sliding speed when an elastic slab (block) is sliding on a rigid substrate with a ${\rm sin} (q_0 x)$ surface height profile. The friction force is nearly velocity independent due to phonon emission at the closing and opening crack tips, where rapid atomic snap-in and -out events occur during sliding. The rapid events result from lattice trapping and are closely related to the velocity gap and hysteresis effects observed in model studies of crack propagation in solids. This indicates that the friction force is dominated by processes occurring at the edges of the contact area, which is confirmed by calculations showing that the friction force is independent of the normal force. The friction force increases drastically when the sliding velocity approaches the solid transverse sound velocity, as expected from the theory of cracks.