An experimental and theoretical analysis has been carried out into normal
force reduction in electronic contact springs. This is a phenomenon whereby the
force produced by the contact spring reduces with time. A series of ten elevated temperature heat age tests were carried out for time periods of up to three
months. Over 6,500 normal force reduction measurements have been made.
Examination of the data revealed a high correlation for the normal force to exhibit a logarithmic relationship with time. Theoretical analysis showed that this could be explained by assuming that the phenomenon of normal force reduction is thermally activated with an activation energy that is variable and related to the amount of stored energy in the contact spring.
A theoretical model for the process has been proposed, and the values of
the parameters calculated for the ten temperatures for which data has been
collected. This model can be used to predict end of life normal forces for
electrical contacts, provided that the model parameters are determined
experimentally at the required temperature. In addition, it is also possible to
obtain confidence levels associated with these predictions.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.