Elastohydrodynamic Film Thicknesses at Extreme Pressures

Abstract

There has recently been disagreement on the effect of load on elastohydrodynamic film thicknesses at pressures beyond 7 × 108 Nm−2, which was the approximate limit of earlier experiments. This disagreement which concerns a departure from established theory has been heightened by the fact that it is based on results from rather novel techniques. This paper describes an extension of well-characterized optical interferometric measurements on rolling-point contacts to pressures of over 2 × 109 Nm−2. The central film thickness is found to fall off with load at a rate which agrees well with theory. In view of this, the results from other techniques are considered and in one case reproduced. It is concluded that the theory is essentially correct as far as it goes and possible causes of the disagreements are advanced in terms of thermal and surface roughness effects.