Lubrication Generated Between Two Sliding Parallel Plane Surfaces by Micro Asperities: Part II-Results

Abstract

The present paper is the subsequent research of the first part. It presents the results of the performance of the contact formed between two sliding parallel plane surfaces lubricated by micro asperities calculated from the analysis demonstrated in the first part, for an exemplary operating condition. It is shown that the load carried by the whole contact between the two surfaces is nearly linearly increased with the reductions of both the nominal distance between the two surfaces and the statistical average film thickness at the asperity contact center. It is found that the physical adsorbed layer boundary lubrication occurring in asperity contacts can not considerablely influence the load-carrying capacity, the contact stiffness and the stiffness of the lubrication film of the whole contact between the two surfaces, although it increases the load-carrying capacity of the whole contact. The reason is that the stiffness of the boundary lubrication film in an asperity contact is much larger than that of the asperity in compression. However, the boundary lubrication occurring in the contact significantly influences the local film thickness of the contact i.e., the lubrication film thickness in asperity contacts which is on the nanometer scale, the boundary lubrication which has more pronounced effects gives considerablely higher local film thicknesses of the contact. The boundary lubrication may be intimately relevant to the local lubrication film and contact failures. It is also found that the reduction of the asperity surface hardness increases the friction coefficient of an asperity contact when the asperity is in elastoplastic or fully plastic deformations; When the asperity is in fully plastic deformation, the friction coefficient of an asperity contact remains constant independent of the carried load by the asperity contact. The occurrence of the plastic deformation in an asperity helps to reduce the maximum temperature rise in an asperity contact, as compared to the calculation result based on the elastic asperity assumption.