An experimental study of film thickness between rough surfaces in EHD contacts

A spacer layer imaging method has been employed to map lubricant film thickness in a very thin film, rough surface, rolling elastohydrodynamic (EHD) contact. A model roughness has been studied, produced by depositing a 160-nm high asperity ridge on one surface. The results show that elastic deformation at the asperity is reduced as the rolling speed increases, indicating that the fluid film contributes to a lowering of asperity pressure. When oriented both transverse and at 60° to the rolling direction, the asperity has the effect of increasing mean EHD film thickness. At slow speeds, negligible EHD film thickness at the asperity tip is produced, but as rolling speed is raised, a micro-EHD film develops whose thickness increases with speed in a classical elastohydrodynamic fashion. A simple model has been developed to predict the micro-EHD film thickness, based on the curvature of the out-of-contact asperity shape.