Evaluation of HAZ Fracture Toughness of Welded Joints with Strength Mis-Matching by the Local

Abstract

In this study, the local approach was applied to evaluate the cleavage fracture resistance ofHAZ-notched specimens with strength mis-matching between the base and weld metals. The main purpose of this study is to demonstrate that the critical Weibull stress at fracture initiation of HAZ-notched specimens can be material property independent of strength mis-matching.For the fundamental study to discuss the effect of strength mis-matching near the notch on the fracture resistance by the local approach, homogeneous specimens and model specimens with only strength mismatching near the notch were used. By using the critical Weibull stress obtained for the homogeneous specimen, strength overmatch effect and undermatch effect on the critical CTOD value were predicted. Close agreement was observed between the critical CTOD value predicted and that obtained by the experiment. As a result, independence of strength mis-matching on the critical Weibull stress was verified.The Weibull stress for the HAZ-notched specimens with strength mis-matching (match and overmatch specimens) was evaluated in consideration of that almost all specimens have fracture initiation points in the CGHAZ (LBZ : Local Brittle Zone). It was demonstrated that the cleavage fracture resistance for the HAZ-notched specimens controlled by the CGHAZ can be uniformly treated by using the Weibull stress irrespective of the existence of strength mis-matching.