A critical evaluation of film thickness-derived pressure-viscosity coefficients

A single parameter, the pressure-viscosity coefficient, , quantifies the pressure dependence of the viscosity of the liquid in elastohydrodynamic lubrication (EHL). Most published values of have not been obtained from measurements of viscosity as a function of pressure. Rather, these effective pressure-viscosity coefficients have been derived from the measurement of the EHL film thickness, a more difficult procedure. In this article, five well-characterized liquids that should be Newtonian in the EHL inlet are identified for which film-derived coefficients have been reported. These coefficients are compared with coefficients derived from published viscosity correlations and new viscosity measurements. The film-derived coefficients are found to not be an accurate representation of the piezoviscous response. The procedure of deriving a pressure-viscosity coefficient from a film thickness measurement does not offer an alternative to the simpler and easier viscometer measurement. Copyright (c) 2014 John Wiley & Sons, Ltd.