An Investigation of the Fatigue Induced Failure Modes

It is proposed to use elastomeric composites as artificial joint bearing surfaces to increase their fluid film lubrication and therefore reduce the number of failures which have been attributed to wear mechanisms. The fluid generated between the surfaces supports part of the load and prevents direct contact of the bearing surfaces. However, permanent deformation and failure of model elastomeric composites has been observed following debonding between fibers and matrix. It is hypothesized that the heat generated at the contact between the elastomeric composite and the reciprocating counter part may contribute significantly to the failure of the elastomer. A polyurethane thermoplastic elastomer was characterized with dynamic and thermal mechanical analyses and a study was conducted to determine the effectiveness of a tribological experimental model to verify this hypothesis. The coefficient of friction between ultra high molecular weight polyethylene and metal and also an unreinforced polyurethane elastomer bearing against metal was measured using reciprocating motion. The next step of this project will consist of using this experimental model to analyze the effect of friction on heat transfer in the elastomeric matrix and on the failure of elastomeric composites composed of the polyurethane matrix and fibers.