Measurement, analysis and prediction of fretting wear damage in a representative aeroengine spline coupling

A methodology to predict fretting wear in complex couplings is described and validated against results obtained from a reduced scale aeroengine-type spline coupling subjected to complex cyclic load cases. The methodology uses three-dimensional finite element analysis, together with coefficient of friction data obtained from stroke controlled round-against-flat fretting tests, to determine spline tooth contact pressure and slip distributions; the latter as a function of number of loading cycles. A modified Archard equation is used to calculate wear depths from the contact pressure and slip distributions using wear coefficients obtained from the round-against-flat fretting tests. The slip distributions, and, concomitantly, the wear distributions, are found to depend strongly on the coefficient of friction, which, in turn, depends on the state of lubrication and number of loading cycles. For constant coefficient of friction, the slip distributions stabilise quickly with increasing numbers of loading cycles. The methodology predicts greater wear under lightly lubricated conditions than without added lubrication for the essentially load-controlled tests on the reduced scale aeroengine-type coupling. The wear depth trends are predicted correctly, both axially along the spline teeth and around the tooth flank, and the predicted wear depths bracket the measured values, dependent on the lubrication conditions considered; the latter attributable to the sensitivity of spline wear to the evolving coefficient of friction during testing. The methodology provides a basis for further development.