Influence of anisotropic surface roughness on lubricated rubber friction: Extended theory and an application to hydraulic seals

Machine elements and mechanical components have often surfaces with anisotropic roughness, which may result from the machining processes, e.g. grinding, or from wear. Hence, it is important to understand how surface roughness anisotropy affects the contact mechanics properties, such as friction and the interface separation, which is important for lubricated contacts. Here we extend a multiscale mean-field model to the lubricated contact between a soft (e.g. rubber) elastic solid and a rigid countersurface. We consider surfaces with anisotropic surface roughness, and discuss how the fluid flow factors and friction factors depend on the roughness power spectral density, as well as on the location of roughness on the interacting solids. Finally, we present an experimental study of the lubricated sliding contact between a nitrile butadiene rubber O-ring and steel surfaces with different kinds of isotropic and anisotropic surface roughness. The good quantitative comparison between the experimental results and the theory predictions suggests that the multiscale lubrication mechanisms are accurately captured by the theory.