Evaluation of Cleavage Fracture Toughness for Steel by Chevron-Notched Specimen

Fracture toughness tests were conducted for an A533B-1 steel by using chevron-notched compact specimens in the temperature range from the lower shelf regime up to the transition temperature in order to assess the R-curve for cleavage fracture. The applicability of these specimens to the simple fracture toughness test without introducing fatigue pre-cracks was examind. The following are the summary of the results obtained. (1) The fracture toughness test by using the chevron-notched specimen gave an overestimated value due to the absence of stable crack growth by cleavage from the notch tip. The difficulty of introducing pre-cracks by cleavage suggests that the fracture resistance for crack initiation by cleavage is considerably higher than that for crack growth by the same fracture mechanism. (2) By introducing fatigue pre-cracks to the chevron-notched specimen, the fracture toughness value can be evaluated accurately at the lower shelf regime. At the transition temperature, however, it is overestimated, the reason of which should be attributed to the thinner effective thickness along the pre-crack front of the chevron-notched specimen compared with that of the conventional throughthickness cracked specimen. キー ・ワー ド:破 壊 じん性,シ ェブロン切欠 き試験 片,へ き開破壊,合 金鋼