J-dominance and size requirements in strength-mismatched fracture specimens with weld centerline cracks

Abstract

The strong dependence of crack-tip fields on specimen geometry and remote loading, particularly for moderate-to-low hardening materials under LSY conditions underlies the constraint loss phenomenon and invalidates the one-parameter characterization of unstable cracking behavior in terms of the \(J\)-integral. Previous research efforts have enabled establishing size requirements for valid \(J\) fracture toughness testing based on the dominance of the HRR singularity which are essentially applicable to homogeneous materials. Only little effort has been expended in the past years to extend the one-parameter characterization of crack-tip conditions to welded structural components. The present work addresses the coupling effect of specimen geometry and weld strength mismatch on the crack-tip deformation limits for which \(J\)-dominance is valid in weld centerline fracture specimens. Very detailed nonlinear finite element analyses of plane-strain models for common specimen geometries, including deep and shallow crack bend SE(B) and tension SE(T) fracture specimens, with weld centerline cracks enable resolving the required crack-tip stress fields from which the variation of crack-tip constraint with increased values of \(J\) can be assessed. The present study provides further insight into the coupled effects of specimen geometry and weld strength mismatch on the levels of deformation limit defined by \(M=(b\sigma _{0}^{WM})/J\), where \(b\) is the remaining crack ligament and \(\sigma _{0}^{WM}\) denotes a reference (yield) stress for the weld material, at which a one-parameter characterization of crack-tip stress fields still remains valid.