John Howard Tripp

Influence of surface topography on friction, film breakdown and running-in in the mixed lubrication regime

Abstract The influence of surface topography on the lubricant film build-up ability and the friction characteristics of potential rolling bearing surfaces has been investigated by experiments on two-disc rigs. Traction-friction torque measurements were made for a variety of surface combinations, together with measurement of the electrical resistance between the discs as an indication of surface separation. For all disc combinations, running-in of the surfaces under load at any slide-roll ratio led eventually to full film separation. Contrary to results reported in the literature, film breakdown did not always increase with slip but depended on certain aspects of the surface structure. Friction torque measurements in the mixed lubrication regime also confirmed that friction is not determined simply by an Ra value. By suitable modification of the surface topography, keeping Ra constant, friction can be varied by as much as 10 per cent.

Amplitude reduction of waviness in elastohydrodynamic lubrication using an Eyring fluid model

Abstract This paper presents a first extension of the amplitude reduction approach, where the deformation of harmonic components of the roughness is considered, to non-Newtonian elastohydrodynamic lubrication (EHL) line contact. The amplitude reduction of one-sided waviness is computed as a function of the slide-roll ratio. Non-Newtonian effects result in an increase in the deformation for positive slide-roll ratios. This contrasts with published results using a Newtonian fluid where the deformation decreased for such conditions. Moreover, the amplitude reduction varies significantly throughout the contact, requiring an additional parameter for the characterization of the amplitude reduction. An explanation of these differences based on the velocity profile of the lubricant inside the contact concludes the paper.