Contact damage of poly(methylmethacrylate) during complex microdisplacements

The wear behaviour of a PMMA substrate contacting against a steel ball has been investigated under small amplitude oscillating motions. A friction dev ice has been developed, which allows the combination, to various extents, o f linear sliding and torsional contact conditions. Using laser profilometry , the amounts of wear debris trapped within the contact or displaced from t he contact have been quantified for the various loading configurations. The contact zone kinematics has been found to have a major influence upon the wear resistance of the PMMA. When the contact conditions progressed from to rsional to linear sliding, a rapid decrease in the wear volumes was observe d, which was associated with the progressive accumulation and compaction of an increased part of the detached PMMA particles within a central roll. Th ese results have been interpreted by considering both the shape and the mag nitude of the sliding paths that were generated within the contact under th e various loading configurations. Using nano-indentation tests, it was also observed that the consolidated third body resulting from debris compaction within the rolls exhibits mechanical properties (hardness, modulus) simila r to those of the original PMMA substrate. The achievement of a high level of compaction within the roll formation was explained by considering the ef fects of third body accumulation on the load carrying capacity of the conta ct. (C) 2000 Elsevier Science S.A. All rights reserved.