Fracture toughness evaluation by the Master Curve method using 4-mm-thick miniature compact tension (mini-C(T)) specimens taken from the broken halves of surveillance Charpy specimens has been proposed. In the present study, we performed finite element analysis (FEA) to examine the difference in the constraint effect of the crack tip for differently sized C(T) and precracked Charpy v-notch specimens. The constraint effect of the mini-C(T) specimens in terms of the T-stress and Q-parameter was similar to that of the larger C(T) specimens. In addition, to optimize the fatigue precracking conditions for the mini-C(T) specimen, plastic zone distribution analysis was performed by FEA. Using plastic zone distribution analysis, we demonstrated that a wider machined notch and shorter fatigue precrack length than that in conventional configurations can be applied for narrow and straight notches. We also obtained the fracture toughness data for two kinds of SA533B-1 steels and one weld metal with different sizes in addition to the data obtained in our previous study. It was shown that the reference temperature To obtained from the mini-C(T) specimens was in good agreement with those from other specimens. We compared the fracture toughness data, including the plane strain fracture toughness value obtained by 4T-C(T) specimens, with T41J-based fracture toughness curves proposed in a recent study. Most of the data, including the 4T-C(T) and irradiated specimens, were enveloped by the proposed lower-bound curve.

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