Relation of Dry-Friction to Surface Roughness

A formulation of friction force in the interface of a friction pair is developed considering the mechanical components arising from the elastic and plastic deformations of the asperities and the chemical components represented by the adhesive forces between local contact regions. The results relate the normal load and dry-friction force to the relative normal and tangential velocities of a friction pair as a function of asperity deformations and adhesive forces. It is shown that the important parameter in the relationship between normal load and the dry-friction force is the projection of the contact area in normal and tangential directions to the mean planes of contacting surfaces rather than the contact area itself. The two forms of dry-friction force derived from the statements of energy balance at the interface allow alternate approaches to modelling of the friction between interacting rough surfaces.