Enhanced reference stress-based J and crack opening displacement estimation method for leak-before-break analysis and comparison with GE/EPRI method

Three-dimensional, elastic-plastic finite element analyses for circumferential through-wall cracked pipes are performed using actual tensile data of stainless steels, for two purposes. The first one is to validate the recently proposed enhanced reference stress (ERS) method to estimate the J-integral and rack-opening displacement (COD) for circumferential through-wall cracked pipes. The second one is to compare the J and COD results from the ERS method with those based on the GE/EPRI method, together with the finite element results. It is found that the GE/EPRI method generally provides poor estimations of J and COD, and such poor estimation results from the Ramberg-Osgood (R-O) fit. Moreover, the GE/EPRI results can be very sensitive to how the stress-strain data are fitted using the R-O relation. The most appropriate fitting range for the R-O fit depends on the material, and thus no specific guideline can be given. On the contrary, the J and COD estimations based on the ERS method give more accurate and robust results than the GE/EPRI estimation. The present results, together with the experimental validation presented in the previous paper, provide sufficient confidence in using the proposed method in the leak-before-break analysis.