Fretting corrosion degradation, threshold behavior and contact instability

This paper addresses the electrical behavior of tin plated contacts as fretting corrosion progresses. Initially, a review of the body of data developed over the last three decades by many authors was conducted to characterize the nature of this degradation mechanism. These results are summarized and used to provide a basis for understanding fretting corrosion phenomena. In addition, an analysis of the present authors previous work on fretting parameters and accelerated environmental tests was conducted to assess various acceleration factors. Subsequently, an empirical model was developed on the basis of accelerated laboratory tests that utilize thermal cycling and vibration as major stress factors. During the course of these studies, a number of characteristics such as oxide film build up and electrical stability were revealed as fretting progressed. Moreover, threshold behavior for the onset of fretting corrosion was observed with respect to fretting amplitude. In addition, a theoretical basis for oxide build up is provided to understand the various results published over the last three decades. It is concluded that consideration of models that include, oxidation rate, stress relaxation, fretting amplitude and fretting cycles are useful in designing accelerated fretting tests. Moreover, it was found that knowledge of amplitude thresholds is needed to relate test parameters to field stresses. It was also shown, from the chaotic behavior of degraded contacts, that stability thresholds occur which help define contact resistance failure criteria. Consequently, the results of these efforts reveal an understanding of the nature of the fretting corrosion degradation mechanism and provide guidelines in developing accelerated tests and performance criteria.