Allowance for Residual Stresses and Material Interfaces When Calculating J in and Close to Welded Joints

The J-integral is used widely as a measure of crack driving force within structural integrity assessments of engineering structures. The calculation of J in and close to welds using the Equivalent Domain Integral (EDI) found in some finite element (FE) codes can give unreliable, domain-dependent, results. This arises because FE codes typically use simplified, “default” implementations of the EDI which do not allow for the non-uniform strain field, material interface and/or material inhomogeneity which are present as a result of the welding process. This paper provides guidance on the corrections that must be made to restore the domain-independence of the EDI, allowing J to be determined from the far stress field for cracks in and close to welds. Example calculations are presented to illustrate the effect of the modifications. The results are compared with those obtained using the default J post-processor built into a commercial FE code. Calculations are presented for cases where there is a material interface, where there are initial non-uniform strains, and where both of these phenomena occur together. It is shown that the default post-processor results are highly domain dependent, but that independence is restored using the corrected EDI formulation.