Limit conditions on local failure of nuclear containment steels. Tensile tests for notched plate and notched thick plate specimens

A series of tensile tests were conducted for notched plate specimens whose shapes are similar to the pressure shell to clarify the local failure characteristics for the steel nuclear containment. The specimens included the full or partial-width notched plate specimens of 10 mm thickness, and full-width notched thick plate specimens of 34 mm thickness the same as the actual pressure shell. In the full-width notched plate specimens with a small curvature notch, the cracking occurred on the notch bottom, and the crack propagated and finally ruptured. The plate specimens with a large curvature notch failed in shear suddenly without notch bottom cracking. Those failure modes were very unlike notched round-bar specimens, in which failure always starts at the notch section center. In the case of partial-width notch plate specimens, the notch bottom cracking also occurred for a small curvature notch, and the notch section failure happened before the specimen's rupture for a large curvature notch. The limit strain diagrams were 40% to 50% lower than those of the notched round-bar specimens. The limit failure stress indexes, which correspond to the stress indications for the limit strain diagrams, could be applied to the shear failure of notched plate specimens. The indexes of the notched plate specimens were approximately 10% lower than those of the round-bar specimens. The crack initiation points for small curvature notch specimens were concentrated in the range of stress triaxiality 0.6 and equivalent plastic strain 0.5 to 0.8. In the full-width notched thick plate specimens, notch bottom cracking occurred for all specimens, and the cracking conditions were almost the same as the full and partial notched plate specimens. However, the maximum nominal stress exceeded 2/3 of the design tensile strength, and it was concluded that local failure occurs at more than twice the design pressure. (author)