Derivation of constraint-dependent J–R curves based on modified \(T\)-stress parameter and GTN model for a low-alloy steel

In this paper, a modified load-independent \(T\)-stress constraint parameter \(\tau ^{*}\) was defined. The \(\tau ^{*}\) of specimens with different crack-tip constraint levels at different \(J\)-integrals was calculated, and its load-independence has been validated. Based on the modified constraint parameter \(\tau ^{*}\) and the numerically calculated J–R curves by using the Gurson–Tvergaard–Needleman (GTN) model for the SENB specimens with different \(a/W\), the equations of constraint-dependent J–R curves for the A508 steel were obtained. The predicted J–R curves using the equations essentially agree with the experimental and calculated J–R curves. The transferability of the constraint-dependent J–R curves to the CT, SENT and CCT specimens was validated. The results show that the modified constraint parameter \(\tau ^{*}\) and the GTN model can be effectively used to derive the constraint-dependent J–R curves for ductile materials.