Degradation of electrical contacts under low frequency fretting conditions

Experimental and theoretical analyses have been conducted upon electrical connector contacts under low frequency fretting conditions. The phenomena of "fretting" -relative micromovements in the components parts of an electrical contact - is known to take a major role in the degeneration of electrical contacts. Low frequency fretting is of particular interest and is typically caused by thermal differential expansion of the component parts due to temperature changes in the environment or the device itself. This thesis begins with a survey of possible failure mechanisms of the contact system. These are analysed and classified into three groups of chemical, physical, and mechanical degradation mechanisms. Fretting has been classified under the mechanical mechanism of degradation but is reported to exacerbate other degradation mechanisms resulting in the phenomena of "fretting corrosion". Developments in contact technology are then surveyed with the emphasis of this study on lubrication of the contact system. A novel fretting simulation apparatus has been developed to study the degradation mechanisms upon the contact system resulting from low frequency micromovements. The study includes investigations on the simulation apparatus of the contact system under different conditions. Particular! y emphasis is given to contacts under the conditions of electrical load and lubrication. Novel trends in the contact performance are reported with respect to electrical contact resistance, corrosion and wear of the contact interface. It is shown that electrically loading or lubricating the contact system has dramatic effects upon the contact performance. Chemical, physical and mechanical mechanisms at the contact interface are presented to explain the contact behaviour under several conditions of low frequency fretting. A "Two Process Model" is proposed which summarises the interaction of these different mechanisms. This model consists of two processes in balance - contact cleaning and contact degradation processes - which either increases or reduces the electrical area of contact. A theoretical computer simulation model is proposed for evaluating contact resistance behaviour of a fretting contact system under several conditions, particularly conditions of electrically loaded and lubricated conditions. Chemical, physical and mechanical mechanisms and their interact are simulated in the model using the Monte Carlo technique.