Significance of Strength Mismatch in Fracture Performance Evaluation of Welded Joints — Characterization of Mismatch Effect by the Weibull Stress Criterion

Abstract

The effect of strength mismatch in welds on the fracture driving force of the heat-affected zone (HAZ) is investigated by 3-dimensional FE-analysis. The Weibull stress is used for the evaluation of the fracture driving force. The CTOD ratio, γ = δMismatch /δMatch, is proposed to quantify the mismatch effect, where δMismatch and δMatch are CTODs of the mismatched joint and the matched joint, respectively, at the same level of the Weibull stress. The CTOD ratio γ is decreased by strength overmatching, which is due to the constraint effect of the overmatch WM on the stress fields in the HAZ. The equivalent CTOD ratio, β = δ/δWP, is employed to correct the constraint loss in the structural component, where δ and δWP are CTODs of the fracture toughness specimen and the wide plate component, respectively, at the same level of the Weibull stress. The analysis using β and γ indicates that strength overmatching leads to a severe requirement of the HAZ toughness, which cannot be directly derived from the CTOD — remote strain relationship for the wide plate joint. By contrast, the toughness requirement of the WM is relaxed by strength overmatching, as a result of the shielding effect of the overmatch WM.