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 device has been developed, which allows the combination, to various extents, of linear sliding and torsional contact conditions. Using laser profilometry, the amounts of wear debris trapped within the contact or displaced from the 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 torsional to linear sliding, a rapid decrease in the wear volumes was observed, which was associated with the progressive accumulation and compaction of an increased part of the detached PMMA particles within a central roll. These results have been interpreted by considering both the shape and the magnitude of the sliding paths that were generated within the contact under the 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) similar to those of the original PMMA substrate. The achievement of a high level of compaction within the roll formation was explained by considering the effects of third body accumulation on the load carrying capacity of the contact.