Interferometric Studies of Effects of Striated Roughness on Lubricant Film Thickness Under Elastohydrodynamic Conditions

Experimental results for striated roughness, obtained from an interferometric EHD test rig, are presented. The roughnesses are straight-edged grooves etched in a flat sapphire surface, yielding fringes over the flat lands. A new feature is the method of recording: Visual inspection, serial photography and digital analysis of the photographs, gives the relative light intensity in the central region of the contact zone. This permits the construction of curves relating light intensity and thence film thickness to speed. We find: transversely oriented grooves produce a higher central film thickness than do longitudinal ones, and films generated by smooth surfaces are thicker still. The slopes of the curves, on log-log paper, all tend to the value 0.67. The curves for rough surfaces are very different at low speeds, due to the escape of lubricant along the grooves.