原子炉格納容器鋼材の局部破損条件に関する検討

<p>Tensile tests for notched round-bar specimens and full-width notched plate specimens were performed to acquire the local failure characteristics of carbon steel used in liner plates of nuclear containment vessels. The limit strains and stresses of the specimens were determined from the measured deformation parameters using Bridgman's solution and an elastoplastic finite element method. The notched round-bar specimens caused tensile ductile fracture, and the critical strain diagram showed conservative results in comparison with the ASME VIII-2 design diagram. The author's proposed limit stress index, defined as the sum of equivalent and mean stresses, was regarded as almost constant and independent of the stress triaxiality. The full-width notched plate specimens caused shear-types ductile fracture. In the case of small notch curvature specimens, the crack initiation occured on the surface of the notch bottom and propagated into the depth of the material, until the specimen finally fractured. The stress triaxiality of the notch bottom was significantly low, and the limit strain was relatively small. Such characteristics appear to match a shear-type ductile fracture at low-stress triaxiality. In the case of large notch curvature specimens, the crack initiation did not occur, and the specimens suddenly fractured in shear after a slight thickness shrinking. The limit strain diagram and stress index were lower than those of the notched round-bar specimens.</p>