J estimation and defect assessment for combined residual stress and mechanical loading

Abstract

Procedures for dealing with residual stresses in fracture assessments are examined in this paper. Two current J estimation methods, the EPRI scheme and the reference stress method, are evaluated using the finite element approach. The treatment of secondary stresses (a category which includes residual stresses) in the R6 defect assessment procedure has also been examined. Two geometries have been analysed, a centre cracked plate with an idealised residual stress distribution and a T-plate welded joint with a measured distribution. Both components are subjected to mechanical load, the former loaded in tension, the latter in three point bend. Results show that both the EPRI and reference stress methods give conservative J-values when the mechanical load is greater than the limit load. However, when the mechanical load is less than the limit load, the conservatism of both methods is dependent on the residual stress distribution along the uncracked ligament. The results also show that the use of Appendix 4 of the current R6 procedure yields a safe assessment except for the case of a small flaw in a region of uniform tensile residual stress.