PREDICTION ON NOTCHED FATIGUE LIMITS FOR CRACK INITIATION AND PROPAGATION

The fracture processes of micro or small cracks may behave differently as suggested by continuum medium mechanics. A minimum fracture unit should exist for a real polycrystalline material; for any part smaller than this unit fracture mechanics cannot be applied. Based on this idea, the elastic stress and stress intensity factor range are expressed in terms of an equivalent fracture unit which is conducted with a through-thickness crack. Theoretical predictions on notched fatigue limits of crack initiation and crack propagation are derived and discussed. Good agreement between predicted values and experimental results has been achieved.