Empirical relationship between interfacial shear stress and contact pressure in micro- and macro-scale friction

Abstract

This study examines the empirical relationship between frictional shear stress and pressure in macro- and micro-scale contact and sliding. Two types of friction tests are reported; the macro-scale tests deal with kinetic friction between stainless steel surfaces in a vapor phase lubrication condition, and the micro-scale tests measure kinetic friction at interfaces formed between MoS2 basal planes and surfaces of alumina or stainless steel specimens, using a quartz crystal microbalance microtribometer. A numerical model is used to calculate the contact areas in the macro-scale tests. The results from both friction tests confirmed that the interfacial shear stress in the contact area due to kinetic friction is proportional to the average contact pressure, and the constant of proportionality is close to the coefficient of friction (COF). These observations add to the validation of the Amontons’ law.