Thin-Film Lubrication of Dented Surfaces

Abstract

Surface microfeatures introduced to conformal surfaces have been proved in the last decade to provide beneficial tribological performances. They were found to significantly improve load capacity, wear resistance, or friction coefficient in applications that involve mechanical seals, piston rings, thrust bearings, or ultra-high-density magnetic disc drives. Recent studies have suggested that such an approach could be used to improve the lubrication capabilities under thin-film lubrication of highly loaded non-conformal contacts. However, surface micro-features influence the film thickness and pressure distribution within concentrated contacts that could result in surface failures. In this paper, thin-film colorimetric interferometry has been used to study the effects of an artificially produced micro-dent on film thickness distribution within thin-film lubricated contacts. Obtained results have shown that the behavior of dented surfaces significantly depends on the slide-to-roll ratio. An increase in the lubricant film thickness has been observed just upstream of the trailing edge of the micro-dent when the disc is moving slower than the ball with the micro-dent. In the reverse conditions, for a positive slide-to-roll ratio, the presence of the micro-dent within the concentrated contact results in the film thickness reduction located downstream of the leading edge of the micro-dent. This reduction can cause the local film breakdown of very thin films. Nevertheless, it has been observed that highly viscous boundary films can avoid it and rubbing surfaces have been completely separated using the formulated oil even under very thin lubrication conditions.