Lubricant film thickness in rough surface, mixed elastohydrodynamic contact

A spacer layer imaging method has been employed to map lubricant film thick ness in very thin film, rough surface, rolling elastohydrodynamic (EHD) con tacts. A series of model roughnesses have been produced by depositing tiny ridges and blimps on a steel ball surface and the influence of these featur es on film thickness has been investigated at a range of rolling speeds. It has been shown that all the model surface features studied form speed-depe ndent, micro-EHD lubricating films, but the detailed shape and thickness of these films depends upon the geometry of the feature and the rolling speed All model surface features also produce a net increase in mean film thickn ess, compared to the smooth surface, under operating conditio,ls where the Pbn thickness is less than the out-of-contact height of the surface feature studied. For a real, random, rough surface, however, mean film thickness i s less than the smooth surface case. The film thickness mapping technique h as also been used to measure the effective roughness of surfaces in lubrica ted contact. This shows that surfaces based on 2-D array of tiny circular b limps become rougher as the rolling speed and thus film thickness increases . However, real, rough surfaces appear to show a decrease of in-contact rou ghness with increasing rolling speed.