A NON-NEWTONIAN EFFECT OF SLIDING IN MICRO-EHL

In the 'mixed' regime of elastohydrodynamic lubrication, where the surface roughness is comparable with the elastohydrodynamic film thickness, it is commonly observed that asperity contact is significantly increased with increased sliding speed, even though Newtonian theory predicts the film thickness to be independent of sliding speed. Quantitative disc machine experiments of this effect are reported, using a disc with an artificial regular circumferential roughness. It is proposed that the effect is a consequence of the non-Newtonian properties of the lubricant. A simple theory based upon a viscous-plastic model of the lubricant indicates that the hypothesis is plausible.