Farsighted Considerations of Fatigue Limit, Crack Opening/Closing Phenomena and Plastic Zone around Crack under Variable Amplitude Loading

Abstract

At first, based on the recognition that fatigue limitt is the condition including many stationary cracks with 'cusp' shape at maximum load, crack opening/closing phenomena and stress distribution near the crack tip is considered. Then, it is mentioned that alternate appearance of compressive plastic zone and tensile plastic zone is necessary for crack propagation under cyclic loading. And, because the crack extension timing has not explained yet and influences the crack opening/closing phenomena, we should consider this unresolved problem when we carry out the crack propagation simulation. Finally, it is indicated that, even if under the fatigue limit, we can not ignore the possibility of 'propagation of stationary crack' when a loading amplitude grows up to larger one.