Residual compression, UHMWPE

The wear rate of YPSZ on UHMWPE can be five times less than the wear rate of alumina on UHMWPE, depending on experimental conditions (Kumar et al., 1991 Davidson, 1993 Derbyshire et al., 1994). Wear resistance is a function of grain size, surface roughness, and residual compressive stresses induced by the phase transformation. The increased mechanical properties may allow for smaller-diameter femoral heads to be used in comparison with alumina. 

Methods have been proposed by Griffith et al. (1978) and Deavane et al (1995) to radiographically measure linear wear in UHMWPE acetabular cups of total hip replacements. The overall penetration of a femoral head (Tables 7.8 and 7.9) into a UHMWPE acetabular cup is a consequence of both creep and wear, where creep is predominantly observed for the first million loading cycles (Dowson, 1995). Atkinson et al (1980) estimated that the total UHMWPE residual compression due to creep in total hip replacements after x can be estimated by ... 

As described in Chapter 2 of this Handbook, the mechanical properties of compression molded and direct compression molded UHMWPE depend on the molding conditions (time, temperature, pressure) used to consolidate the part. Incomplete consolidation, as evidenced by residual UHMWPE powder particle boundaries in microtome shces of the consolidated product, can result in inferior mechanical properties. 

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