Abstract Fatigue crack growth assessments are typically conducted using the stress intensity factor K, under the assumption of small-scale yielding conditions. Given that the K-calculation is to be repeated for each cycle of loading, simplified K-solutions have been incorporated into the Codes and Standards, such as the JSME Rules on Fitness for Service (FFS) and the ASME Section XI in the US. However, methodologies for fatigue crack growth calculations beyond the small-scale yielding condition have not been established. To address this gap, the FDF-III subcommittee of the Japan Welding Engineering Society is actively preparing a simplified J-integral calculation method tailored for pipes with an axial or a circumferential flaw, as well as for plates with a semi-elliptical surface flaw. This initiative aims to incorporate these methods into existing Codes and Standards for evaluating fatigue crack growth under a large cyclic loading level that exceeds the small-scale yielding condition. The proposed simplified J solutions are based on the reference stress method, as adopted in the JSME Rules on FFS, API 579-1/ASME FFS-1 in the US, R6 in the UK, and RCC-M/RSE-M in France. The authors contributed to prepare a simplified J-solution specifically for pipes with a circumferential semi-elliptical flaw. This effort involved conducting FE analyses across eleven cases, varying the flaw depth-to-thickness ratio a/t and aspect ratio a/c. J values were extracted at both the deepest and surface points of the flaw. To refine the reference stress-based J formulation, two fitting parameters, α and β, were introduced to account for small-scale yielding corrections in relation to the ratio of reference stress to yield stress σref/σy, in accordance with the small-scale yielding correction of R6. These parameters were calibrated to closely align the J values obtained from FE analysis. To validate the applicability of the simplified J solution, the crack growth behaviors during two cyclic loading tests on pipes with a circumferential surface flaw, which were conducted by other researchers in the preparatory committee of FDF-III subcommittee, were predicted. For the fatigue crack growth analysis, ΔJ was computed using the fatigue crack growth rate derived from the ferritic fatigue crack growth rate in air, as specified in the JSME Rules on FFS, converted to ΔJ basis. The predicted fatigue crack growth behaviors were then compared with experimental data. It was revealed that the predicted numbers of cycles at the pipe wall penetration were conservative. Currently, the simplified J solution has been established for the deepest point of the flaw, with plans to investigate the solution for the surface point in the next step.
Hojo et al. (Sun,) studied this question.