Generalized effects in confined fluids: New friction map for boundary lubrication

Abstract

Recent advances in measuring the rheology and tribology of thin liquid films between shearing surfaces have enabled previously-inaccessible parameters to be measured accurately during frictional sliding. These include the real area of contact, the local asperity load and pressure, and the sheared film thickness. The results show striking non-continuum, non-bulk like effects when the thicknesses of sheared films approach molecular dimensions as occurs under most tribological conditions. Based on these new results, we assess the validity of current presentations of friction processes, such as the Stribeck curve, and propose new constitutive relations and a dynamic friction map, including an alternative Stribeck type curve representation, which are also formulated in terms of more accessible parameters.