Effect of fretting slip amplitude on the friction behaviour of electrical contact materials

The effect of slip amplitude on the friction force in the present of electrical current for a ball-on-flat configuration of aluminum-to-aluminum and copper-to-copper joints were studied using a multi-specimen fretting assembly. This unit enables simultaneous measurement of friction and contact resistance of these materials subjected to fretting conditions. The fretting conditions were: frequency 1Hz, slip amplitude 50, 125, 325 and 450 μm, contact load 0.72 N and current 50 mA. Contact resistance and friction force on the oscillating flats were measured continuously. The results indicate that the presence of a 50 mA electrical current in the contact zone is not affecting the wear rate but does have an appreciable effect on the friction force of most materials tested. At higher slip amplitudes, the changes in the contact resistance in both systems investigated correspond to those observed in the friction force. Plausible explanations for the observed differences are discussed.