Fracture toughness Jc of the material in ductile to brittle transition temperature region is known to have two specimen size effects; the planar size effect and the test specimen thickness effect. It was presented that these size effects can be solved by applying modified Richie-Knott-Rice failure criterion in previous research. As a next step, in this study, engineering method to predict the minimum Jc for a specimen type and thickness from only tensile test results is proposed. The method focused on our finding the crack-opening stress σ22, measured at a distance from the crack tip equal to four times the crack-tip opening displacement (CTOD) δt, denoted as σ22d, saturated with increasing load, and the J corresponding to the load first reaching this saturated σ22d, denoted as Js, seemed to predict the minimum toughness for a given specimen and material at a specific temperature. The method was validated for 0.5T SE(B) and 1TCT specimen. The material was 0.55% carbon steel JIS 0.55C, which was tested at master curve reference temperature.

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