Statistical Study of Voltage Fluctuations in Power Connectors During Fretting Vibration

It is well known that vibration of contact interfaces is the main cause of contact degradation by the so called fretting corrosion phenomenon. In fact the process of generating particles by mechanical wear produces an increase of contact voltage, frequently manifested by a high contact resistance in low power and signal connectors. In high power connectors, this degradation is expected to be accentuated by thermal effects generated by increasing the contact voltage up to melting and arcing voltages. The main objective of this work is to examine conjointly the electrical behavior and amount of wear of a connector terminal under vibration and higher current stress. In order to reproduce harsh vibration conditions, spring with lamella shape from an automotive connector, made from a copper alloy and coated with 2 mum of tin, are submitted to a high number of oscillations (10³ to 10⁶) where the pin is firmly attached to a fixed support. High frequency oscillations (100 Hz) with an amplitude of 50 mum is used. The contact is inserted into a resistive circuit supplied by 20 V and 3 A. The contact voltage is measured with a fast sampling oscilloscope and the voltage histogram is built up in real time. The losses of mass in the erosion track are evaluated by micro weighing. The main results show that at the low level of wear observed during the earlier stage of fretting, the contact voltage corresponds to pure constriction voltage < 20 mV. However, after this initiation period as the wear is increased, the contact voltage is increased and reaches a few hundred millivolts (melting and fritting voltage). Finally in last stage of degradation, an arcing voltage due to bounce phenomena is detected. These short arcs, observed for the first time in fretting under power, could accentuate the wear and the degradation process by erosion and mass transfer.