STUDY ON FRETTING CORROSION OF TIN-COATED ELECTRICAL CONTACTS

The examination of the failure of electric connectors of electric powered vehicles is at the forefront of current vehicle developments, because the connector's operating time increases significantly in comparison with internal combustion engine vehicles. It was observed that the low amplitude fretting corrosion plays the most important role in failure, so the lifetime of the failure process is decisive in the life span of the connector. Typically, the failure of an electrical connector in terms of product is an increase in electrical resistance that can even cause malfunction of the drive within the product expected lifetime because of the generated Joule heat that causes temperature rise. The aim of our work is to study the fretting corrosion process in a given geometry and material quality of electrical connection by experiment and numerical model. In the experimental test, an experimental construction was set which simulated contact properties of the built-in connectors. Tests for failure-life were performed as a function of the clamping force of the mating members and the amplitude of the relative displacement of the contact surfaces, of which magnitude can be typically for fretting. The change in resistance at the contact surface was measured and examined when this value reached the limit value for failure, thus determining the life span for fretting corrosion. The experimental set-up was then modelled by finite element method. The purely elastic FE model made it possible to model the gradual removal of the material for given force-amplitude-frequency values by using the Archard's theory. The valid wear coefficient was searched that creates the same wear crater in the calculation as in the measurements. Then, using the measured data, the FE analysis revealed the mechanical stress conditions, the electrical current flow conditions, and the resulting thermal conditions during the wear process both on and below the contact surface, which provides additional information on the details of the fretting corrosion process.