New J and COD estimates for thin-walled pipes with axial through-wall cracks and high strain hardening exponents

In this study, the approximate estimates of elastic-plastic J and COD for thin-walled pipes with axial through-wall cracks (TWCs) and high strain hardening exponents under internal pressure are developed based on the GE/EPRI and enhanced reference stress (ERS) methods. For the estimations based on the GE/EPRI method, the proposed tabulated plastic influence functions for fully plastic J and COD are derived from three-dimensional finite element (FE) analyses. On the basis of these plastic influence functions, an optimized reference load (which plays an important role in the ERS method) is newly suggested. Finally, the present elastic-plastic J and COD estimations are verified by comparing the predicted results with the FE results using actual tensile behavior of SA312 type 304 SAW stainless steel. The estimations based on both GE/EPRI and ERS methods provide better approximations for thin-walled pipes with axial TWC and high strain hardening exponent, than do the existing estimations. The importance of the elastic-plastic fracture mechanics assessment, using the present solutions for thin-walled pipe with axial TWC and high strain hardening exponent, are also discussed.