Stability of critical distance approach to predict fretting fatigue cracking: a “ ℓ opt – b opt ” concept

Fretting fatigue life prediction is a strategic issue for modern industry. Accurate prediction of totallifetime depends on crack nucleation time prediction. However, fretting fatigue is characterized by a high stress gradient which overestimates cracking risk at the hotspot. Hence non-local analyses are required. The present study focused on the critical distance method. However, no defined method is currently established to obtain this value, which has been shown to depend on microstructure or stress gradient. The present study investigated the influence of incipient crack length on critical distance crack nucleation prediction. An optimal ‘opt–bopt condition was introduced enabling accurate prediction of the crack nucleation condition whatever the loading condition. This approach was then applied to fretting endurance experiments, allowing to correlate fretting cracking endurance with shear fatigue data. Finally it was used on fretting fatigue lifetime experiments, showing good endurance prediction.