A unified theory of wear for ultra-high molecular weight polyethylene in multi-directional sliding

A theoretical wear model based on the effective frictional work concept was developed for ultra-high molecular weight polyethylene in lubricated multi-directional sliding. The model assumes the occurrence of preferential molecular alignment in the principal direction of sliding and rupture or splitting of the oriented molecules in the perpendicular direction associated with secondary sliding. The model unifies the effects of interfacial friction, crosslink density and cross-shear angle in a simple equation and provides a theoretical explanation for the effects of crosslinking and multi-directional motion on the wear of UHMWPE in total hip and total knee replacements. Experimental results correlating each of the three variables to the wear rate of UHMWPE in a hip joint simulator and a multi-directional motion wear test machine verified the general validity of the model.