7 - Fretting wear analysis through a mechanical friction energy approach: Impact of contact loadings and ambient conditions

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The objective of this chapter is to describe how using the friction energy wear approach (i.e., the friction work dissipated in the interface) it is possible to formalize both wear volume and maximum wear depth extension under gross slip fretting sliding. First, various sliding criteria are shown to clarify the transition between partial and gross slip conditions inducing respectively cracking or wear phenomena. The fretting regime approach formalizing the time evolution of the sliding condition is then detailed allowing the introduction of the fretting map concept. This latter expresses the evolution of the fretting sliding regimes and the surface damage evolutions (cracking and/or surface wear) as a function of the applied normal load and displacement amplitude. Focusing on the gross slip regime condition and the surface wear phenomena it is shown that the friction energy (∑Ed) wear approach provides a more reliable prediction of the wear volume (V) extension than the Archard description as it considers the coefficient of friction in its formulation (i.e., V=α×∑Ed). However, this synthesis also demonstrates that the energy wear coefficient (α) is not constant but depends on the wear process activated within the interface (i.e., adhesive or abrasive wear) in addition to the debris ejection process. To interpret such fluctuations, both third-body theory (TBT) and contact oxygenation concept (COC) are considered. Hence, an extended friction energy wear approach expressing the fretting wear rate coefficient as a power-law function of the loading parameters is considered to achieve pertinent wear volume predictions. Finally, a local approach where the wear profile is expressed as a function of the friction energy density is detailed. These contact simulations underline that obtaining reliable estimations of the maximum wear depth necessitates considering the dynamical evolution of the third-body layer. Using this local friction energy density-wear depth approach, the coating durability can be formalized through the so-called friction energy capacity concept.