Critical Distance for Fatigue Life Prediction in Aerospace Materials

This study has investigated a method for estimating the fatigue life of small-notched specimens using the theory of critical distance for aerospace materials of Ti-6Al-4V and In718. Critical distance stress is defined as the average stress within the critical distance from notch root using simple linear-FE results. A good correlation exists between the critical distance stress and fatigue life of small-notched specimens if the critical distance is calibrated by the two notched fatigue failure curves of specimens with different notch root radii. Using these critical distances, the fatigue lives of various small notched specimens can be well predicted for a wide range of fatigue life. Other verification results are shown in a contact edge fatigue problem of the dovetail in aero-engine component. An analogy exists between a flat/rounded contact stress and a small notch stress fields. There have been the possibilities that the predictions using critical distance give the reasonable predicted results for fretting fatigue crack initiation lives.