A study of fatigue wear of the ultra-high molecular weight polythylene in terms of frictional heat

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Lubricant temperature of artificial joint increased up to 10^。C due to frictional heat according to the lubricant volume and contact pressure. Temperature increment of lubricant is strongly affected by the thermal properties of the moving part. About 90% of the frictional heat is transferred to the mating part of UHMWPE. The softening of UHMWPE was confirmed with an increment of temperature. The coefficient of friction decreased gradually with an increment of time or sliding distance to about a half of an initial value in a simple reciprocal sliding condition. It is sensitive to the loading conditions rather than temperature changes. The contact temperature between UHMWPE disk and the sapphire glass plate was measured by the infrared radiometric microscope. Lubricant temperature was measured simultaneously and compared with the contact temperature. Temperature rise up to 12^。C was observed in 30 minutes under a condition of the mean contact pressure P__-=12.7 MPa and sliding speed 50nm/s. There was a linear relation between contact temperature and lubricant temperature in the vicinity of the contact band. From this experimental study, it was clarified that an increment of contact temperature with time was about two times higher than that of lubricant temperature near the contact band. The behavior of contact temperature increment in this experimental condition could be explained by a mathematical model of a uniform band heat source model. The Young's modulus of UHMWPE was estimated as 0.4 GPa by using Hertzian contact theory through the measurement of real contact area. The coefficient of friction is strongly influenced by the contact pressure distribution. This finding could be used to improve the lubricating condition of the hip joints by changing the profile of the femoral head to make an optimum contact pressure distribution.