The crack-tip stress field and fracture mechanics assessment parameters, such as the elastic stress intensity factor and the elastic-plastic J-integral, for a surface crack can be significantly affected by the loading condition and crack geometry. Current guidance considers that the ductile-to-brittle transition is defined using uniaxially loaded specimens with a deep crack even when the reactor pressure vessel is under biaxial loading and the existence of deep crack is not probable through periodic in-service-inspection. Thus, such a constraint effect caused by differences between standard specimens and a real structure can overestimate the fracture toughness and affects the results of the structural integrity assessment.

The present paper investigates the constraint effect by evaluating the Mater Curve T0 reference temperature of PCVN (Pre-cracked Charpy V-Notch) and small scale cruciform specimens of SA508 Gr. 3 low alloy steel through the fracture toughness tests of theses specimens and 3-dimensional elastic-plastic finite element analyses. Based on the finite element results, the fracture toughness values of a small-scale cruciform specimen were estimated, and the geometry-dependent factors of the cruciform specimen considered in the present study were determined and then the transferability of the test results of these specimens were discussed.

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