On the relevance of analytical film thickness EHD equations for isothermal point contacts: Qualitative or quantitative predictions?

Thin film and elastohydrodynamic lubrication regimes are rather young domains of tribology and they are still facing unresolved issues. As they rely upon a full separation of the moving surfaces by a thin (or very thin) fluid film, the knowledge of its thickness is of paramount importance, as for instance to developing lubricated mechanisms with long lasting and efficient designs. As a consequence, a large collection of formulae for point contacts have been proposed in the last 40 years. However, their accuracy and validity have rarely been investigated. The purpose of this paper is to offer an evaluation of the most widespread analytical formulae and to define whether they can be used as qualitative or quantitative predictions. The methodology is based on comparisons with a numerical model for two configurations, circular and elliptical, considering both central and minimum film thicknesses.