The evaluation of fracture under extremely low-cycle fatigue (ELCF) caused by natural disasters such as earthquakes remains a challenge due to the presence of large plastic deformation and the lack of established fracture criteria. As a result, overdesign is often employed, leading to increased manufacturing and maintenance costs in power plant components subjected to severe loading conditions. In a previous study, crack propagation behavior was analyzed using a 1T-CT specimen, and a criterion was proposed based on the equivalent plastic strain increment at mid-thickness and the stress triaxiality. However, this approach failed to reproduce surface crack growth behavior observed in experiments. To address this issue, the present study introduces cumulative equivalent plastic strain as a parameter to account for large deformation under cyclic loading conditions. A new crack propagation criterion was proposed and validated by comparing numerical predictions with experimental results. The improved criterion successfully reproduced the crack front propagation behavior. The applicability and validity of the proposed criterion are discussed in detail.
Kamei et al. (Wed,) studied this question.