Abstract
Mechanical properties of ultra high molecular weight polyethylene (UHMWPE) used as a bearing material in total joint replacement system have been investigated under impact compressive load. Ten cylindrical specimens, 8mm in both diameter and length, were machined from compression molded UHMWPE rods. Half of these specimens were gamma-irradiated in air at a dose of 2.9 Mrad without post irradiation treatment. Impact compression tests were performed using the split-Hopkinson pressure-bar technique to evaluate dynamic stress-strain relation up to 8% strain at a strain rate of about 400s-1. For both gamma-irradiated and unirradiated specimens, stress-strain relations exhibited relatively linear portions up to 2% strains and the gradients eventually decreased with increasing strain. Young's modulus determined from the linear portion and 0.5% yield stress were significantly higher for gamma-irradiated specimens than for unirradiated specimens. Two-dimensional elasto-plastic stress and strain analysis of hip prosthesis was performed under impact loading using a finite element method. Results indicated that the increase in mechanical properties induced by gamma irradiation reduced plastic strain within the UHMWPE cup.
