Wavelength dependence of micro-EHL pressure rippling with random surface-roughness profiles

This paper studies line-contact elastohydrodynamic lubrication (EHL) between two rough surfaces of random roughness profiles. A transient micro-EHL model is used to simulate the problems. Numerical results are obtained for a range of practical operating conditions and for relatively small specific film thicknesses (i.e., the Λ-values). The study reveals the wavelength dependence of micro-EHL pressure rippling. For the same Λ-value, the size of the pressure rippling is shown to be significantly smaller than those predicted earlier using more idealized system models. Furthermore, the pressure distribution is essentially unaffected by the short-wavelength components in the random surface-roughness profiles, except under near rolling conditions. It is shown that lubricant non-Newtonian shear-thinning is the mechanism that suppresses the short-wavelength pressure ripples. With a Newtonian lubricant, sharp pressure rippling is generated by the small-scale surface roughness textures. Since EHL lubricants exhibit significant shear-thinning and since the surfaces possess random roughness profiles, the results reported in this paper reflect a main feature that may prevail in realistic EHL conjunctions. Future work will establish a theoretical basis for the numerical analysis conducted in this research.