Lubrication Modelling of Artificial Hip Joints: From Fluid Film to Boundary Lubrication Regimes

A full numerical methodology was developed for the mixed lubrication analysis of hip implants, covering a continuous spectrum from full fluid film to boundary (dry contact) lubrication regimes. The methodology was applied to a typical hip implant employing an ultra high molecular weight polyethylene (UHMWPE) acetabular cup in articulation with a metallic femoral head. It was shown that as the viscosity decreased, direct contact was initiated at the exit regions both in the entraining and side-leakage directions where the minimum film thickness occurred. As the viscosity decreased further, the direct contact area increased and until eventually became similar to the dry contact area.