C*estimation for cracks in mismatched welds and finite element validation

Abstract

A C* integral estimation method is proposed for a crack located in the weld with a mismatch in mechanical properties from the surrounding base material. The method involves the definition of an equivalent stress-creep strain rate (ESCSR) relationship based on the mechanical properties of both the weld and base materials and the geometrical dimension of welding seam. The value of creep fracture mechanics parameter C*, for the mismatched weldment, is then estimated using the proposed ESCSR in conjunction with the reference stress (RS) method where the reference stress is defined based on the plastic limit load and the GE/EPRI estimation scheme. Referring to the equivalent stress-plastic strain (ESPS) curve in R6 and SINTAP procedures, an approximate solution for the ESCSR relationship has been obtained. Detailed formulae for the compact tension (CT) specimens have been derived on the basis of limit load solutions. Nonlinear finite element analysis of 48 cases with various degrees of mismatch in creep behaviour and different dimension of welding seam has been performed for CT specimens. Overall good agreement between the ESCSR method and the FE results provides confidence in the use of the proposed method in practice.