SIGNIFICANCE OF STRENGTH MISMATCH IN FRACTURE PERFORMANCE EVALUATION OF WELDED JOINTS - CHARACTERIZATION OF MISMATCH EFFECT BY THE WEIBULL STRESS CRITERION

摘要

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= δ_(Mismatch)/δ_(Match), is proposed to quantify the mismatch effect, where δ_(Mismatch) and δ_(Match) 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/δ_(WP), is employed to correct the constraint loss in the structural component, where δ and δ_(WP) 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.