Mechanical modeling of fretting cycles of electrical contacts

Fretting-corrosion of electrical contacts is one of the main causes of failure of the electrical systems used in automobiles. The micro-motion involved in fretting is induced by the vibrations of the vehicle as well as by thermal cycling. Tin is mainly used as a low-cost plating for the contact elements which are made of copper alloys. Using gold coatings is restricted to vital functions. For a better understanding of the wear processes during a fretting cycle, fretting-corrosion tests have been carried-out and curves giving the evolution of the tangential force versus the displacement have been recorded. The particular shape of these curves as well as their evolution during the test lead us to propose a mechanical model which takes into account the profile of the wear track along the male surface, the dynamic friction coefficient and the stiffness of the set up. From the analysis of the curves, we conclude that friction does not occur during the whole cycle: for a given pair of contacts, this friction duration depends on the normal force, on the wear track profile and on the stiffness of the set up.