A unified mixed-lubrication model of rolling-sliding line contacts from elastohydrodynamic lubrication to boundary lubrication

This paper presents a unified mathematical model spanning the entire mixed lubrication for rolling-sliding line contacts. A load-sharing parameter is defined to divide the lubrication spectrum into three regions with increasing proportion of solid load sharing: light-mixed lubrication, significant-mixed lubrication and near-boundary lubrication. The main effort of the work is to develop a model for significant-mixed lubrication and integrate it with two previously developed governing-equation based models for light-mixed and near-boundary lubrication. A preliminary model is first developed by means of smooth, monotonically increasing interpolations of key contact variables obtained by the light-mixed and near-boundary lubrication models. The variables include surface temperature in the contact, friction coefficient, friction power intensity and proportion of solid contact area to the area of the line contact. The model is then refined by factoring in a potential transition of surface tribofilm breakdown which may take place in the second half of the region of significant-mixed lubrication. A basic parametric analysis is presented in the paper to show the sensibility of the model in analyzing the effects of operating conditions on contact stability. The model may be used to perform basic design and analysis calculations for line contacts with various degrees of mixed lubrication. It may also be implemented into a gear-meshing model to study the gear performance under various temperature and lubrication conditions.