Surface roughness in elastohydrodynamically lubricated contacts

The nominal film thickness at which EHL contacts have to operate reliably has decreased to a level where the effects of the surface microgeometry on the film thickness can not be neglected. To predict the effects of the microgeometry on the film thickness one should be able to predict its deformation as a function of the operating conditions. Recent work on the effects of waviness in EHL contacts has shown that the amplitude reduction of harmonic patterns in line and circular contacts under pure rolling could be described as a function of a single nondimensional parameter. In the present paper this work is extended to elliptical contacts. The result is a simple formula that predicts the amplitude reduction of waviness in an EHL contact under pure rolling as a function of its wavelength and the operating conditions of the contact. This formula can be used as a simple tool to obtain a first estimate of the deformed roughness profile inside the contact for any microgeometry. Subsequently, attention is directed to experimental validation of the observed behaviour. Although further experiments are needed the first results are very encouraging.