The effect of sliding velocity on the friction and wear of UHMWPE for use in total artificial joints

Abstract

The effect of two different sliding velocities on the friction and wear of ultrahigh molecular weight polyethylene (UHMWPE) has been investigated in a tri-pin-on-disc apparatus using bovine serum as the lubricant. UHMWPE pins were slid at velocities of 35 and 240 mm s − 1 on stainless steel counterfaces with the surface roughness R a being varied in the range 0.014–0.078 μm. The coefficient of friction was found to be in the range 0.07–0.2 and was not dependent on the sliding velocity. The highest friction values were found with a counterface roughness R a of 0.042 μm. Sliding velocity had little effect on the wear factor. For smooth counterfaces with a surface roughness of less than 0.05 μm, all the wear factors were less than 1.3 × 10 − 8 mm 3 Nm and there was no significant difference in the wear factors produced for the two different sliding velocities. An increase in the counterface roughness to between 0.07 to 0.08 μm increased the wear factor by over twenty times to a value greater than 3 × 10 − 7 mm 3 N − 1 m − 1. For these rougher counterfaces a statistically significantly higher wear factor was found for the lower sliding velocity. The results show clearly that variation in the sliding velocity has only a small effect on the wear of UHMWPE compared with the changes found when the counterface topography was altered. The results indicate that it is reasonable to accelerate tri-pin-on-disc wear tests by increasing the sliding velocity within the range specified, but it is essential to control the topography of the counterface.