Crack Resistance Curve Measurement With Miniaturized CT Specimen

The use of miniature compact tension (mini-CT) specimens for fracture mechanics was experimentally demonstrated to allow the characterization of ferritic steels in the transition regime. In particular, the master curve transition temperature T0 can confidently be determined according to the ASTM E1921 standard using mini-CT specimens. This means that specimen size effect is well taken into account if loss of constraint is limited by restricting the test temperature range to remain below the allowed maximum loading level. In the upper shelf ductile regime, where stable crack growth occurs, a number of challenges should be overcome to use such a geometry to derive the crack resistance curve, or JR-curve, transferrable to a structure. Indeed, despite a large scatter, the experimental data on several materials suggest a size effect that underestimates the crack resistance when reducing specimen size. The crack resistance behavior of several reactor pressure vessel materials was investigated with square-sized ligament compact tension specimens of various size ranging from 1 inch-thickness (B = 25 mm) to the smallest thickness (B = 4.2 mm) of the mini-CT. The main objective of this paper is to estimate the crack resistance behavior of RPV steels that would be obtained with a standard 1T-CT specimen by using mini-CT with the appropriate specimen size correction. After a series of scaling attempts that were not successful, based on a simple dimensional analysis, a simple analytical formulation based on specimen thickness and ligament is suggested to account for specimen size effect for the CT geometry. Reasonable agreement could generally be found on a number of RPV materials between crack resistance measured with mini-CT and standard 1T-CT specimens.