A mathematical, geometrical wear model for continuous wear measurements based on the normal approach between a spherical and a flat specimen subject to fretting

Fretting wear occurs when normally loaded surfaces are subject to oscillatory relative tangential movements with small amplitude. As a result, the fretting wear volumes are much smaller than macroscopic wear volumes and by consequence are much more difficult to measure. Usually, qualitative or semi-quantitative but discontinuous techniques are used to measure fretting wear (SEM, scar size measurements, 3D topography). This means that the wear can be measured only at the end of the experiment and that many experiments are required in order to obtain a wear curve (wear as a function of number of cycles). In this work it will be shown that continuous measurement of the normal approach between the specimens can be used to obtain wear curves of both test specimens separately. Apart from measuring the normal approach during the test, correct measurement of the wear volumes of both specimens at the end of the experiment is needed. Thin layer activation (TLA) is used for this measurement. A suitable, geometrical wear model is used to obtain continuous wear curves based on the above data. This paper describes the geometrical wear model used and the procedure to convert normal approach measurements into wear volume curves. Some experimental data are used to illustrate the application of the wear model. (C) 1997 Elsevier Science S.A.