A mixed EHL model of grease lubrication considering surface roughness and the study of friction behavior

Grease lubrication is widely used in rolling element bearing because of its special rheological characteristics. Available studies are mainly based on experiments, while the relevant numerical studies of grease are quite limited. The purpose of this article is to establish a mixed elastohydrodynamic lubrication (EHL) model in point contact based on the rheological model of grease, which can calculate film thickness distribution applied to smooth and roughness surface. The obtained result is compared with that of it operated only in base oil. Besides, the impacts of load, surface roughness and rheological parameters on the grease film thickness have been investigated. In addition, the Stribeck curves of four greases covering different base oil viscosity and thickener types were measured on a ball-on-disc device, which can ensure that the contact area was in full film lubrication. From the study, it is concluded that the obtained grease friction behavior agrees well with the variation of grease film thickness calculated by the present mixed EHL model.