Nano-and Microindentation Testing of UHMWPE

The goal of this chapter is to describe the work that is done to explore the structure, properties, and performance of UHMWPE on the scale of microns or smaller. It focuses on work that has involved the use of mechanical test methods like nanoindentation, microindentation, or, in general, depth sensing indentation (DSI) testing along with techniques that require the atomic force microscope (AFM) and/or other high magnification imaging methods. This study describes indentation testing and scanning electron microscopy (SEM) and AFM characterization of UHMWPE, and reviews various testing approaches and the effects of geometry, processing, degradation, and deformation. Briefly, the geometric relationship between the tip and sample plays a major role in the analysis of indentation data. Depth-sensing indentation testing of UHMWPE has provided important information concerning surface mechanical properties and the effects of processing and oxidation. These techniques, when combined with high-magnification imaging using AFM, SEM, and FTIR, can now provide detailed relationships between structure, properties, and wear performance, as well as the feedback interactions between these. This chapter elaborates new methods for exploring the micro-and nanomechanical processes of wear. Here, a surface deformation mechanics analysis is shown where the surface strains associated with single asperity wear behavior can be determined and related to both polymer structural changes and to changes in mechanical properties of the surface deformed UHMWPE (orientation softening) when these deformations take place on the scale of the particles that are formed. © 2009