Soap-thickener induced local pressure fluctuations in a grease-lubricated elastohydrodynamic point contact

While passing through a contact such soap-thickener lumps significantly disturb the film thickness by locally increasing the surface deformation. These film-thickness fluctuations must be accompanied by pressure fluctuations. A combined experimental/numerical approach to generate insight into such pressure fluctuations is presented. From a fringe pattern obtained with optical interferometry (ball-on-disc apparatus) a film-thickness map is created employing image analysis. This map serves as input to a numerical algorithm for the calculation of the pressure from force balance and elastic deformation theory. The method was tested on an oil-lubricated contact. This test gave essential insight into the accuracy of the method proposed here and in the magnitude of surface texture induced pressure fluctuations. Subsequently the approach was successfully used to estimate the pressure variations resulting from soap-thickener formations in a grease-lubricated contact (between the same ball and disc). (from Authors)