A quantitative approach of Ti-6Al-4V fretting damage:: friction, wear and crack nucleation

The fretting behaviour of a Ti-6Al-4V alloy was studied in a plain cylinder/plane contact configuration under ambient conditions. Inspired by a fretting map approach, a global quantitative methodology is introduced. The transition from partial to gross slip condition was defined through an energy discontinuity analysis. Dominated by adhesion phenomena, the friction coefficient behaviour at the sliding transition is formalized through pressure dependence formulations. The crack nucleation risk under stabilized partial slip condition is expressed through a closed form applying the Crossland's high cycle multiaxial fatigue criterion. Comparison with experiments concludes that the size effect must be considered. An averaged stress approach, based on the identification of an intrinsic representative damage volume, was developed and confirmed by comparing various loading conditions. Integrating both debris formation and debris ejection mechanisms, an energy wear approach is adapted to formalize the fretting wear response under gross slip conditions. Extending the classical Archard's formalism by considering the friction coefficient and sliding amplitude impacts, this wear energy model displays a very good stability through a wide range of pressure, sliding amplitude and test duration conditions. It is finally discussed how the introduction of a restricted number of "constitutive fretting damage variables" can be transposed in FEM codes to model more complex industrial contacts. (C) 2004 Published by Elsevier B.V.