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 character istics in the ultra high molecular weight polyethylene (UHMWPE), tension-te nsion fatigue tests of notched specimens were carried out in the present st udy. The effects of frequency and stress ratio on the fatigue characteristi cs were also investigated and fractography was discussed. The fatigue strength does not increase with increasing molecular weight. Th e fatigue strength might be influenced by the high degree of crystallinity in spite of the decreased tie molecule density in this study. Almost no eff ect of frequency on the number of cycles to failure can be observed. Howeve r, the higher the frequency, the higher the crack tip temperature. The effe cts of heat and strain rate on the fatigue strength must be considered in p olymer materials. At a high stress ratio, the stress-number of cycles to fa ilure (S-N) curves shift to high number cycles to failure side. Both stress amplitude and mean stress influence the fatigue life of UHMWPE. (C) 2001 K luwer Academic Publishers.