Application of the Friction Energy Density Approach to Predict Electrical Contact Endurance in a Silver-Plated Coating Subjected to Fretting Wear

Abstract

Electrical contacts such as those involved in connectors are subject to critical fretting wear damage due to vibration. To increase electrical contact resistance (ECR) endurance, noble layer such gold or silver can be applied. However, when these top layers are worn through the introduction of copper and nickel oxides debris extracted from the substrate, fretting wear process drops ECR endurance. The ECR endurance is therefore governed by the wear rate of the protective top noble layer. It is, however, critical to be able to predict the endurance of such an interface. Extensive fretting wear analysis of a homogeneous Ag-Ni / Ag-Ni (2 µm) interface was here investigated for various gross sliding amplitudes (5<δg<15 µm) and various normal forces (1N<P<6N) under controlled ambient conditions at 10% relative humidity. For each condition, ECR endurance (Nc: i.e., ΔR=ΔRc=4 mΩ) was determined. To formalize such complex loading conditions, an original local friction energy density approach was applied. Analysis confirmed Nc could be formalized as a function of the local mean friction energy density dissipated per fretting cycle. Hence, a single endurance master curve was obtained according to a friction energy density parameter (dEd) combining the effects of normal force through a pressure component, the coefficient of friction and the relative sliding imposed. However, analysis found this local wear description to be adapted only if the contact area extension induced by plastic deformation and surface wear processes is taken into account. The very good correlation between experimental and predicted Nc values provided by a simple exponential function of dEd confirmed that, for the noble silver layer under study, ECR endurance was governed by a progressive wear process which could itself be monitored by the friction energy density in the interface. Finally, an alternative Archard description involving normal force work is introduced and compared to the reference friction energy formalism.