On the Pressure Rippling and Roughness Deformation in Elastohydrodynamic Lubrication of Rough Surfaces

The objective of this paper is to conduct a qualitative analysis on the effects of lubricant shear thinning, lubricant shear heating and the roughness-induced transients on the pressure rippling and roughness deformation that occurs under elastohydrodynamic lubrication (EHL) conditions. To facilitate the analysis, the numerical solutions to an example problem of EHL line contact between a perfectly smooth surface and a sinusoidal rough surface are presented. This micro-EHL problem is first solved using the conventional model of a Newtonian lubricant and a stationary rough surface under isothermal conditions. It is then solved by including the non-Newtonian effects, the roughness-induced transients and the thermal effects in sequence, so that the changes in the results brought about by each of these elements can be clearly observed and then analyzed. The analysis, which is not limited to the model problem solved in this paper, suggests that misleading results of large pressure rippling and flattened surface roughness are obtained using the Newtonian lubricant models under steady-state, isothermal conditions. Much less micro-deformation of the surface roughness is actually produced because the magnitude of the pressure ripples is greatly limited by either the lubricant non-Newtonian shear thinning and shear heating or the roughness-induced transients.