Fretting wear of low current electrical contacts: Quantification of electrical endurance

In many industrial applications like automotive, aeronautics, train but also nuclear energy connectors need to maintain low stable electrical contact resistance. However, they are subject to vibrations that cause severe fretting wear damage which increases the electrical contact resistance and degrades information transmission. Fretting wear damages can induce dramatic increase of the direct current Electrical Contact Resistance (ECR) inducing the connector failure. The purpose of this paper is to expose a synthesis describing how fretting loadings but also material properties of coatings can influence the fretting DC-ECR behavior. The analysis first focuses on "laboratory" fretting test specifications that must be as possible representative of the pin-clip interface and sufficiently instrumented to measure fretting loading parameters such as sliding amplitude, normal loading friction energy, and ambient condition. To compare noble (Au, Ag) and non noble (Sn) coatings, an ECR endurance variable is introduced so that N(fretting cycle) = Nc when ΔR> ΔRc = 4mΩ. This synthesis exposed how the sliding condition from small partial slip to large gross slip sliding influences from infinite to finite Nc endurances. Then focusing on the gross slip finite endurances, different formulations are introduced to quantify the effect of fretting sliding amplitude, normal force, material properties but also coating thickness. Focusing on Ag/Ag interface, this research demonstrates that the ECR endurance is controlled by the fretting wear rate of the contact. This investigation also underlines how the application of sequential large reciprocatings can increase the fretting ECR endurance through a refilling process of fretting scar with silver transferred from the outer part of the lateral reciprocating track.