The effect of boundary slip on elastohydrodynamic lubrication

Abstract

The effect of interfacial slip on the friction and film thickness in an elastohydrodynamic (EHD) contact was directly evaluated. Experiments showed that the film thickness and friction decrease upon the application of an oleophobic coating given a sufficient pressure, as opposed to bare glass. Direct measurements of the slip velocity enabled the determination of a power law relationship between pressure and slip length. This implied the existence of spatial heterogeneity of the flow in the tribological contact due to the pressure distribution, which was confirmed by experiments. The power law relationship could also be used to predict the film thickness and friction based on conservation of mass and by using a rheological model for the lubricant. The film thickness and friction predictions were compared to experimental results. The former matched experimental observations. The latter however, underestimated the reduction in friction due to slip by a factor of two, suggesting the necessity of further work to elucidate the interplay between lubricant flow, rheology and friction.