A FEM fretting map modeling: Effect of surface wear on crack nucleation

Much research demonstrated that the fretting sliding condition greatly influences fretting damage. Small displacement amplitudes, inducing partial slip, favor cracking, whereas large dissipative sliding gross slip amplitudes favor wear. Considering a Ti-6Al-4V/Ti-6Al-4V cylinder/plane contact, this typical evolution was quantified by plotting the evolution of maximum crack length versus displacement amplitude. Under partial slip, the crack nucleated above a critical tangential loading, related to a threshold δCN_PS displacement amplitude. Above the sliding transition (δt), although tangential loading remained high, crack length decreased to zero at the gross slip threshold δCN_GS, due to surface wear extension which reduced contact stress and removed incipient nucleated cracks. This fretting damage evolution was simulated using an FEM code, enabling synergic modeling of wear and crack phenomena. The crack nucleation risk was quantified using an SWT parameter combined with a linear cumulative damage law. Surface wear evolution was simulated by a local friction energy density wear approach. The three displacement values, δt, δCN_PS and δCN_GS, were shown to be accurately predicted if, respectively, the FEM simulation takes account of the tangential accommodation of the test system, the damage law is calibrated using reverse analysis of experimental partial slip crack nucleation results, and the energy wear rate is determined from the wear volume analysis in gross slip regions next to the sliding transition. This very good correlation enabled “Material Response Fretting Map” modeling and optimization of palliative coating strategy.