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This paper studies the method for estimating the residual stress effects on brittle fracture of structural steel based on the Weibull stress criterion. First, brittle fracture tests were conducted for four-point bend notched specimens with and without compressive preloading. It is shown that the compressive preloading apparently decreases the critical crack tip opening displacement (CTOD). The critical CTOD of the preloaded specimen can be predicted from monotonically loaded test results based on the Weibull stress criterion. It has been found that the Weibull stress is an effective fracture parameter for brittle fracture initiation under tensile residual stress. Second, using wide plate specimens with and without welding residual stress subjected to uniform tension and three-point bend fracture toughness specimens, welding residual stresses effect on the brittle fracture strength is investigated. Experiments show that the critical CTOD of wide plate with welding residual stress is significantly smaller than that without residual stress. Constraint loss effect on CTOD of wide plate can be assessed by the equivalent CTOD ratio β. β is defined as β=δ3PB∕δWP, where δ3PB and δWP are CTODs of the standard fracture toughness specimen and wide plate, respectively, at the same level of the Weibull stress. Fracture assessment result using β is shown within the context of failure assessment diagram. An excessive conservatism observed in the conventional procedure (β=1) is reasonably reduced by applying the equivalent CTOD ratio β.
brittle fracture, compressive preloading, tensile residual stress, critical CTOD, Weibull stress, constraint loss, failure assessment diagram
IHI Corporation, Yokohama,
Professor, Osaka University, Osaka,