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High-performance engineering polymers are a potential frictional material candidate for mechanical systems with moving parts, especially at high load and speed conditions. In this study, reciprocating friction and wear of aramid fibers/polyimide composites filled with graphite, MoS 2  or Polytetrafluoroethylene, respectively, were systematically investigated on a Pin-on-Flat test rig. The experimental setup was simplified into friction materials reciprocating against a phosphor bronze pin to simulate the rotor/stator contact state in ultrasonic motors. A comparative study on friction reduction and wear resistance of polyimide composites indicated that graphite showed the best lubricity with low friction coefficient and wear rate. Experimental results of pressure time average velocity measurements showed that frequencies ranging from 3 to 11 Hz played a significant role on the friction coefficient variations of these porous polyimide composites, whereas increasing pressure from 4 to 6 MPa had little effect on friction reduction. Then, the microstructure of the worn surface of the three different materials was observed by scanning electron microscope to reveal the wear mechanisms. This study is expected to provide a good guidance for porous polyimide composites application in ultrasonic motors.

Reciprocating friction and wear of polyimide composites filled with solid lubricants