The contact resistance of rolling silver coated copper contacts

In contrast to most mechanical components electrical contacts require plastic deformation to fulfill their main function. The high contact forces in combination with a large risk for vibrations make gross plastic fretting an important degradation mechanism in the field of electrical contacts [1, 2]. As established in the field of fretting under near elastic conditions, three fretting regimes are distinguished also in gross plastic fretting [3, 4]. All three regimes involve plastic deformation which have distinct effects on the surface damage, the friction and the adhesion to the counter face. The regime prevailing is primarily determined by the combination of fretting amplitude and normal load. In this investigation the influence of rolling on the contact performance has been studied for a crossed cylinders model contact. The contact materials were silver coated (2 or 15 mu m) copper with an intermediate nickel layer (50 mu m) and silver coated (20 mu m) copper both in a clean and in a pre-corroded condition. Also grease lubricated contacts were tested. This paper shows that the surface damage is substantially reduced if one of the cylinders in the crossed cylinders test is free to rotate as compared with a regular fretting contact where both cylinders are fixed.