Voltage saturation in electrical contacts via viscoplastic creep

Electrical contact resistance affects the performance of electrical switches and other current-carrying interfaces. This study investigates the behavior of electrical contact resistance for copper–copper and aluminum–aluminum sphere-on-flat contact as a function of current through the interface. It is observed that the contact resistance may either increase or decrease with increasing current, depending on the current level as well as the current history. At low current levels the voltage drop across the interface increases initially with increasing current until it saturates. The voltage level remains nearly constant even if the current is increased beyond the value corresponding to saturation. Hereafter any subsequent decrease in current yields a corresponding decrease in voltage, so that the associated current cycle shows substantial hysteresis. However, subsequent cycles of current are reversible so long as the voltage remains below the saturation point. Analyses of the results suggest that the mechanism of viscoplastic creep is responsible for the voltage saturation phenomenon.