Fatigue Stress Ratio Effect on Fretting-Fatigue Crack Nucleation: Comparison between Multi-Axial and Uni-Axial Predictions
Résumé
This research focuses on high cycle fretting fatigue crack nucleation prediction. A plastic steel/steel cylinder/plane contact was investigated keeping constant the normal force and the maximum fatigue stress ratio but varying the fatigue stress ratio (RF=0.6 to 1). The evolution of the crack length as function of the applied fretting tangential force amplitude at 10^6 cycles allows us to formalize the crack nucleation condition. It shows that the threshold tangential force marking the crack nucleation (i.e. bp_th=0μm) is not affected by the fatigue stress ratio. However an increase of the fatigue stress amplitude sharply increases the crack extension. To model the experiments, a 2D plastic plain strain FEM modeling is performed. As expected the computed stress field description is mesh dependent. However we demonstrate that a representative stress description is obtained at the 3rd node (i.e. 2nd node below the surface). By coupling this mesh condition and non-local critical distance approach, reliable prediction of the crack nucleation risk can be achieved either considering a Crossland multi-axial fatigue analysis or using a basic uni-axial Haighs description.
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