For assessing the safety of welded structural components, it is necessary to investigate the effects of multiple factors, which include the component geometry, load level, weld width, and weld strength mismatch, etc., on the crack tip constraint in weld joints, especially at high level of loading. Based on the J-A2 two-parameter fracture theory, a welding constraint parameter, A2w, is introduced such that the total constraint A2 is the sum of A2w and a geometry constraint A2g. The parameter A2w is developed to quantify the effects of material strength mismatch ratio and weld width, and is used to establish a dual constraint-parameters method (J-A2g-A2w) for characterizing the crack tip stress field in a welded joint. This method is validated by the finite element method (FEM), and the effects of material mismatch and weld width are analyzed. Using a critical crack opening stress as the fracture criterion, the fracture toughness of a welded joint can be predicted from the known fracture toughness value of another welded joint. The procedure and examples are given in this paper.

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