Evaluation of equivalent plastic strain and stress triaxiality and ΔJ for proposing a crack growth formula under extremely low cycle fatigue

Abstract

It is important for piping to predict unstable failure in a structure due to excessive cyclic load caused by a huge earthquake. It is necessary to accurately predict the fracture behavior of ductile materials. Damage evaluation is performed by ΔK and ΔJ. The evaluation by wrinkles, ΔK, is only for small-scale yield conditions, and the applicability under the extremely low cyclic load of ΔJ has not been verified yet. And, it is expected that the crack tip state under the extremely low cycle load due to the huge earthquake will be a large deformation elastoplastic state. The objective to propose fracture mechanics parameters for crack propagation in a large deformation elastic-plastic region, and as a basic study for it, we calculate and evaluate ΔJ. In addition, the distribution from the vicinity of the crack tip to the distance with respect to the equivalent plastic strain and stress triaxiality governing the generation limit of the ductile crack will be evaluated in detail under extremely low cycle fatigue.