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