A simplified solution to the combined squeeze-sliding lubrication problem

Abstract

The unfavourable elastohydrodynamic lubrication situation in combined squeeze and sliding motion has been analysed both theoretically and experimentally. In experiments a rotating roller impacted and rebounded on a lubricated surface. It was found that oil film breakdown always occurs at the end of the impact time, when the contact force is low. It has also been found that there exists an upper limit for the sliding velocity. Below this limiting velocity no oil film breakdown occurs. This paper is an initial attempt to explain theoretically why oil film breakdown takes place towards the end of the impact, and why an increasing sliding velocity reduces the capability of the oil film to separate the lubricated surfaces. If the oil film's elastic and damping behaviour are taken into consideration it can be shown that a considerable phase shift between maximum contact force and oil film breakdown will arise. It has been found that the squeeze action dominates the pressure formation in the contact and thus the hydrodynamic effect of sliding motion is moderate. Furthermore, several effects, such as non-newtonian behaviour, surface roughness, temperature rise, starvation and deformations, which are not included in the theoretical model, may decrease the oil film thickness if the sliding velocity increases.