An Asperity-Contact Based Oxidation Model for Fretting Wear with the Presence of Debris

The phenomena of near-surface plastic deformation and the change of microstructure during the fretting process appear to play an important role in fretting damage evolution, including fretting wear and fretting fatigue. However, it is difficult to incorporate such micro-damage mechanisms into conventional macroscopic damage prediction models. In this study an attempt is made to address this issue, with the aim of including the evolution of micro-damage into the modelling of fretting wear with the presence of wear debris, and in particular, to link such phenomena as near-surface plastic deformation and oxidation with macroscopic wear behaviour. Wear debris entrapped within the contact during fretting is here treated as a hardened and oxidised layer structure. As wear proceeds, the debris layer is assumed to continuously penetrate into the substrate by oxidation that is incurred by frictional heating and local plastic deformation; meanwhile the top of the debris layer is assumed to be removed by the abrasive action from the counterbody. A multiscale modelling approach of fretting wear is therefore presented, which integrates a macro-wear simulation tool and a micro-asperity model. The finite element based macro-wear simulation tool predicts local distributions of contact pressure and slip, and determines the material removal from the fretting interface. The former information, together with local thickness of the debris layer, form the inputs to the asperity model, so that cyclic plastic deformation underneath the debris layer can be calculated. By knowing the local plastic deformation, the movement of the debris layer into the substrate within the macro-wear simulation tool can be determined according to a plasticity-enhanced oxidation model. The constants required by the multiscale modelling approach will be identified from fretting tests, and then the simulated results will be validated again testing measurements.