An asperity based model for friction in mixed lubrication

We propose a model for mixed lubrication between parallel surfaces. We first analyze the microgeometry. We determine a statistical distribution for asperity height and radius. Drawing upon these geometric parameters we identify the main mechanism available on a given asperity where from we deduce the individual normal and friction forces. The five possible mechanisms are iso- or piezo-viscous hydrodynamic, elastohydrodynamic, elastoplastic and full plastic. By association of the results obtained for each asperity, we derive the mechanical behaviour for the entire contact. Several numerical applications are proposed. Theoretical results show the influence of the main contact parameters. They strongly agree with experimental results and theoretically confirm the master curve obtained by plotting the evolution of the friction coefficient versus the _ parameter with respect to a given pair of materials and their microgeometry.