This paper investigates the effect of welding residual stress and plastic constraint on brittle fracture of a 780 MPa class high-strength steel (HT780). In order to investigate the effect of welding residual stress, three point bend (3PB) fracture toughness tests were conducted using the parent-material specimens and groove-welded specimens which were prepared to have the same cross-sectional proportion; i.e., a ratio of thickness to width of 0.5. Crack length was determined so that the crack tip was located in the base-metal zone far from the heat-affected zone of the welded specimen to eliminate the effect of any degradation of the parent-material property on fracture resistance. Also, in order to investigate the effect of constraint, tensile loading tests in which the plastic constraint was expected to be less than 3PB were conducted using welded specimens as the same as employed in the 3PB test. Three dimensional finite element (FE) analyses were performed to evaluate the stress state near the crack tip at the point of brittle fracture initiation for each test condition. From the results of experiments and FE analyses, it is confirmed that the fracture test results can be evaluated using J or KJ – Q theory, by considering enhancement or reduction due to residual stress.
SummaryA method for the estimation of the CTOD fracture toughness c from toughness results of bend specimens with a machined notch has been studied. The Weibull stress criterion is adopted as a brittle fracture criterion. The equivalent CTOD ratio β has been defined as the ratio of CTOD of the fatigue crack specimen to CTOD _M of the machined notch specimen (β = / _M) at the same level of the Weibull stress. CTOD tests are conducted for SM490A steel. It has been found that the equivalent CTOD ratio β is useful to convert the critical CTOD of the machined notch specimen to that of the fatigue crack specimens. The CTOD ratio β depends on the yield-to-tensile strength ratio YR; the steel with a high YR leads to a large β value than the steel with a low YR. Such dependence of β on YR has been verified with CTOD toughness data for various steel with different YR in the range YR=0.60-0.95 in FTC committee in Japan Welding Society.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.