Introduction of a new sliding regime criterion to quantify partial, mixed and gross slip fretting regimes: Correlation with wear and cracking processes

Fretting is associated to small displacement amplitudes between two contacting surfaces subjected to vibrations. Depending on the contact loading (normal force, displacement amplitude…), different sliding regimes may arise: partial slip, mixed slip and gross slip. In this paper, the fretting behaviour of Ti-6Al-4V titanium alloy contact has been investigated. Sliding regimes are clearly defined through the analysis of the evolutions of an energy sliding ratio and the tangential force ratio. To accurately determine the sliding regime transition, a new criterion is introduced. It is defined as the proportion of gross slip cycles during the test (%GS). Fretting damage is also investigated though the analysis of crack lengths and wear volumes, compared to the sliding regime. The results show the relevance of this new sliding criterion to quantify the transition between partial, mixed and gross slip regimes. By comparing the values of this criterion and damage mechanisms, three steps have been defined in the competition between cracking and wear in the mixed slip regime. The first relates to a critical increase in cracks lengths, the second to a reduction of crack depths and the formation of a third body in the contact without ejection, and the last to the onset of wear by material removal.