Frictional traction and lubricant rheology in elastohydrodynamic lubrication

Abstract

Much experimental information on frictional traction in elastohydrodynamic lubrication has been published, but there is no adequate theory to explain the many puzzling features of the results. In this paper, some of the friction results are interpreted in terms of a recently published model of a viscoelastic liquid. This model refers to behaviour in oscillatory shear, and in this work the implications for the behaviour in continuous shear have been examined. The experimental curves of frictional traction against sliding speed have been analysed into three regions; the linear region, the nonlinear (ascending) region, and the thermal (descending) region. In the linear region there is a necessary and close connexion between the friction and the behaviour in oscillatory shear, and many of the experimental features observed have been explained in terms of the new viscoelastic model, which is considerably superior to the more conventional Maxwell model. Some of the experimental results are still unexplained. In the nonlinear (ascending) region, the relation between results in oscillatory shear and those in continuous shear is far less clear-cut, but it is possible to show some measure of agreement between the two fields. In the thermal (descending) region, some of the precision is regained, and an empirical relation proposed in the analysis of the nonlinear (ascending) region is found to give a good quantitative agreement with published results.