Origin for Static Friction at Atomic Level Studied with Molecular Dynamics Simulations

Static friction has been always an interesting topic because of its ubiquitous presence in the sliding. With Molecular Dynamics simulations, we studied the static friction behavior for commensurate and incommensurate Al$_{2}$O$_{3}$/Al$_{2}$O$_{3}$ interfaces, and flat and rough Al/Al interfaces. It is found that incommensurate Al$_{2}$O$_{3}$/Al$_{2}$O$_{3}$ interface has lower static friction than commensurate Al$_{2}$O$_{3}$/Al$_{2}$O$_{3}$ interface and roughness on the surface increases the static friction drastically. The relation between interfacial adhesion and friction has been investigated. Simulation results reveal that the origin of static friction is to overcome the potential barriers at the interface along the sliding distance. Static friction is determined by the amplitude of potential barrier of interfacial interaction rather than the absolute value of interfacial adhesion. The relation of static friction and kinetic friction are also discussed.