Fatigue characteristics of ultra high molecular weight polyethylene with different molecular weight for implant material.

In order to investigate the effect of molecular weight on fatigue characteristics in the ultra high molecular weight polyethylene (UHMWPE), tension-tension fatigue tests of notched specimens were carried out in the present study. The effects of frequency and stress ratio on the fatigue characteristics were also investigated and fractography was discussed. The fatigue strength does not increase with increasing molecular weight. The fatigue strength might be influenced by the high degree of crystallinity in spite of the decreased tie molecule density in this study. Almost no effect of frequency on the number of cycles to failure can be observed. However, the higher the frequency, the higher the crack tip temperature. The effects of heat and strain rate on the fatigue strength must be considered in polymer materials. At a high stress ratio, the stress-number of cycles to failure (S-N) curves shift to high number cycles to failure side. Both stress amplitude and mean stress influence the fatigue life of UHMWPE. Copyright 2001 Kluwer Academic Publishers