Developments of fretting sliding criteria to quantify the local friction coefficient evolution under partial slip condition

Abstract

ABSTRACT The determination of the sliding conditions is of primary importance in describing the loading conditions in a fretting contact. Cracking is mainly observed under partial slip condition [1] whereas gross slip situation with high dissipated energy promotes wear and debris formation. To quantify such sliding conditions, various adimensional criteria have been recently introduced. They allow the quantification of the transition between partial slip to gross slip for sphere/flat contacts through various constants [2]. This study focuses on recent developments, where the sliding criteria are studied, taking into account the time evolution. This permits the formalisation of the concept of fretting regime [3] and more particularly the mixed regime which corresponds to sliding transitions during the test. Moreover the local friction coefficient in the partial slip external annulus can be estimated by combining the sliding ratio with the tangential force evolution. This fundamental study of friction is compared to experiments on a sphere/flat situation with steel contacts. Theoretical local friction coefficient analysis is then compared to local observations in the wear scar obtained under partial slip. The local friction value is related to various distributions of strong metal/metal shear stress interactions and more accommodative debris layers. It is shown that the mixed slip regime is associated with a decrease of the contact dissipated energy which indirectly interacts on the extension of the stick domain and then an increase of the local friction coefficient in the annular sliding zone.