Investigating UHMWPE wear mechanisms by decomposing wear debris distributions

The precise mechanisms involved in the wear of UHMWPE are poorly understood. Wear debris image analysis has proven useful in characterizing the mechanisms and performance of metal wear, but applying these techniques to UHMWPE may not be appropriate. In this study, debris was collected after UHMWPE pins were worn against counterfaces of three different roughnesses, then imaged in a scanning electron microscope. The debris was characterized using standard analysis techniques: equivalent circle diameter (ECD), roundness factor, and Richardson fractal dimension. Rough counterfaces produced a greater quantity of large, irregular shaped debris, and the image analysis of these particles revealed they were comparable to known abrasive wear values, suggesting that these analysis techniques are valid for UHMWPE, at least over a certain range. Smaller, rough particles appeared to be caused by fatigue processes, both in terms of analysis and visual inspection. Small, smooth particles were not easily classified, and may be particles that were plastically deformed as third bodies in the wear interface.