On the interrelationship between fracture toughness and material mismatch for cracks located at the fusion line of weldments

The effect of strength mismatch on brittle fracture initiated from cracks l ocated at the fusion line of weldments are investigated. The scope of this research has been to derive expressions for the crack tip constraint and th ereby open for transferability schemes from one geometry/mismatch condition to another. The procedure has been termed the J-Q-M approach, where Q quan tifies the geometry effect and M the material mismatch effects. In the pape r the approach is applied to specific weldments and the influence of fractu re toughness on the effect of mismatch is discussed. The fracture toughness testing included series with up to 50 parallel test specimens and the theo retical calculations agreed well with the test results. The weld metal yiel d strength overmatch with respect to HAZ was detrimental for the fracture t oughness of the HAZ at CTOD levels lower than about 0.25 mm, at higher toug hness levels evenmatch resulted in the lowest toughness. (C) 1999 Elsevier Science Ltd. All rights reserved.