Validation of a non-linear wear model for UHMWPE

Abstract

Since 1960s, Ultra High Molecular Weight Polyethylene (UHMWPE) has been used in orthopedics as a bearing materials, namely for acetabular component of hip prostheses. Despite the success of this material, implants made of this material have limited lifespan due to gradual accumulation of wear debris and loosening of the components. Thus, the prediction of wear plays an important role to predict the life span of the implant materials. It is known that wear dynamics of polymer-metal systems determined by the properties of polymers such as surface energy, modulus of elasticity, specific heat, thermal conductivity, shear strength and other operating variables such as load, speed, sliding duration and sliding length. The hardness and roughness of the counter face also play a role. Though there are different models available for the wear of the polymer, it was not extended to include molecular weight of the polymer, in case of UHMWPE Thus an attempt has been made to develop a non-linear wear model correlating polymer material properties and operating variables which influence the wear behavior of UHMWPE. In this attempt, molecular weight of polymer has been taken into account along with other materials properties. Thus, it can also be extended to HDPE and LDPE. The main aim of this work is to extend a dimensional analysis of wear of polymer to include molecular weight of the polymer. An empirical model in the form of a wear equation is developed based on a non-linear relationship between wear volume and other operating variables. Wear of UHMWPE is tested on pin-on-disk machine. The comparison of results with linear and nonlinear model is also made.