Electrical and physical modeling of contact defects due to fretting

When the two members of an electrical contact are driven in low-amplitude alternating motion relative to each other, the resulting tribological phenomena may cause an interface to become poorly conductive. If the contact carries low-level signals such as a pulse train, and reaches this stage of degradation, it may deform the signals enough to make them unusable. The present article first describes an experiment in which a signal transmitted through a vibrating contact is compared with an undistorted reference. It is then shown, using theory supported by experiment, that a faulty contact can be modeled by an equivalent resistor and capacitor in parallel. We then attempt to develop a physical model of a contact interface as a third body of variable thickness and find analytical expressions for the contact resistance and capacitance, providing a basis for analyzing the experimental results. This analysis shows that, for the faults observed, the contact interface probably consists of an insulating layer with or without a metallic bridge of very small lateral dimensions passing through it