Fatigue Crack Propagation under Large Cyclic Plastic Strain Conditions

Outside the application limit of the stress intensity factor based fatigue life calculation, a substitute procedure has to be defined. Various proposals for a crack driving force parameter in elastic-plastic fracture mechanics are discussed. A preference in favor of the cyclic ΔJ-integral is elaborated, keeping its theoretical limitations in mind. Crack closure is also an important issue under large-scale yielding conditions. Experience cannot be transferred from the small-scale to the large-scale cyclic yielding regime or vice versa. The consequences for the fatigue lives under variable amplitude and multiaxial loading are shown.