In situ observations of the real-time wear of PMMA flat against steel ball under torsional fretting

Detailed fretting wear phenomena are usually hidden between the two compact contact interfaces. Direct or in situ observation of fretting wear is supposed to obtain time-dependent damage information. In this paper, the torsional fretting wear tests of plymethyl methacrylate (PMMA) flat against AISI 52100 steel spheres had been investigated on an improved test rig, which provides the real-time in situ observation, friction vibration and noise measurements. The running behaviours (frictional kinetics characteristics), wear mechanisms, oxidative behaviours and debris behaviours of the torsional fretting contact interfaces in combination with the friction vibration analyses were analyzed in detail. The results of observation suggested that a slight damage could be found in the partial slip regime. And the spindle-like detachment occurred in the mixed fretting regime, which presented a radial pattern distribution in the wear scar. The friction lateral vibration decreased accompanied with the accumulation of the debris, and the appearance of third-bodies helped to reduce the friction vibration. In the mixed fretting regime and slip regime, the wear mechanisms mainly were fatigue wear and oxidative wear.