The effect of ‘running-in’ on the tribology and surface morphology of metal-on-metal Birmingham hip resurfacing device in simulator studies

Abstract

It is well documented that hard bearing combinations show a running-in phenomenon in vitro and there is also some evidence of this from retrieval studies. In order to investigate this phenomenon, five Birmingham hip resurfacing devices were tested in a hip wear simulator. One of these (joint 1) was also tested in a friction simulator before, during, and after the wear test and surface analysis was conducted throughout portions of the testing. The wear showed the classical running in with the wear rate falling from 1.84 mm3 per 106 cycles for the first 106 cycles of testing to 0.24 mm3 per 106 cycles over the final 2 × 106 cycles of testing. The friction tests suggested boundary lubrication initially, but at 1 × 106 cycles a mixed lubrication regime was evident. By 2 × 106 cycles the classical Stribeck curve had formed, indicating a considerable contribution from the fluid film at higher viscosities. This continued to be evident at both 3 × 106 and 5 × 106 cycles. The surface study complements these findings.