Fretting corrosion in power contacts: Electrical and thermal analysis

Fretting corrosion phenomenon is known as the main cause of contact resistance increasing in signal contact. But for power connectors this undesirable phenomenon in embedded systems is more complex because high current induces high voltages and subsequent Joule overheating can be expected during vibration. Our study deals with contact similar power connectors, ones submitted to vibration amplitudes up to 25 micrometres at frequencies of a few 10Hz under a current ramp from 0.1 to 40A under 14VDC. The main measured parameters are the contact voltage during vibration up to a hundred thousand cycles. The average voltage by micro-voltmeter and its fluctuations during one cycle are acquired permanently by oscilloscope. Thermal aspects are also investigated by the use of miniature thermocouples placed as close as possible to the contact zone. It was found that a limiting voltage is reached, similar to the fritting voltage in a tarnished metal film reported by Holm. So contact resistances and the power brought by Joule effect are reduced and the temperature rise is limited. The main factors which playing a role are current, contact materials and its susceptibility to wear and debris oxidation at the interface. This behaviour is confirmed by the SEM-EDX analysis of fretting zone at different steps of fretting.