The effect of the viscosity-pressure behaviour of lubricants on the film thickness in elastohydrodynamically lubricated line contacts

In this paper the influence of the viscosity-pressure relationship on the film thickness for the line contact situation is presented. The viscosity-pressure behaviour of many lubricants differs significantly from the behaviour according to Barus which is commonly used in EHL. This topic is of interest due to the fact that, for instance, water based lubricants, like emulsions, or biodegradable lubricants are frequently used. Also the “liquid to solid” behaviour of lubricants results in viscosity-pressure relations differing from the Barus relation. It will be shown that, if the viscosity-pressure behaviour differs significant from the Barus relation, the presented film thickness formulas in literature are not accurate. The effect on the minimum film thickness of the viscosity-pressure relations according to Roelands and to Bair & Winer, in the different EHL-regimes, will be shown in this paper. On the bases of this investigation a modified film thickness formula will be proposed.