A Model for Elastohydrodynamic Film Failure in Contacts Between Rough Surfaces Having Transverse Finish

Abstract

The paper describes an elastohydrodynamic lubrication (EHL) model for collapse of the film in a contact of finite width between surfaces which have roughness aligned transverse to that of lubricant entrainment. The failure mechanism proposed is that of sideways leakage of the lubricant in the gaps that are present between the surfaces due to the valley features of the surface roughness. Under typical high temperature conditions with surfaces finished by conventional grinding, it is shown that the gap between the surfaces when lubricated is almost identical to that between the same dry surfaces in contact with the addition of a small land clearance equivalent to the nominal EHL film thickness. Analysis of idealized valley geometries leads to criteria for complete cavitation or significant loss of pressure between asperity contacts, but application of these criteria to a real contact suggests that scuffing occurs under conditions which are less severe than predicted by either of these simple failure models. Detailed analysis of leakage from the valley features in the transverse direction at the edges of a real elliptical contact shows that this can explain the complete loss of the film in a real contact, and this suggests a physical mechanism of scuffing.