On the state and severity of frictional sliding contacts between nominally flat metallic surfaces

This paper develops and uses an analytically traceable model to study the state and severity of frictional contacts between nominally flat surfaces of elastic-perfectly-plastic materials. The state and severity of the contact is characterized by four area-of-contact variables. They include the real area of contact, the portion of the real area of contact in full plastic deformation, the portion of the real area of contact with high interfacial shear stresses, and the percentage increase of the real area of contact due to the friction-induced junction growth. Problems are studied ranging from very elastic to very plastic contacts under good-to-poor boundary-lubrication conditions. Dimensionless results are presented in a two-dimensional parameter space of the surface plasticity index and a system friction coefficient. Judged by these dimensionless results, the state and severity of the frictional contact is primarily governed by two model parameters: the plasticity index and the coefficient of friction. It is fairly insensitive to other system parameters such as the applied normal load and height distribution of surface asperities. The results may shed some lights on surface run-in, system operations, and possible friction instability of the tribo-system.