円周き裂付き丸棒から得られるR曲線と臨界J値に関する考察

抄録

A round bar with a deep circumferential crack is proposed as one of specimens of fracture toughness test. A bar specimen has larger strain constraint for its size than a CT specimen. However a ligament of a bar specimen is so narrow that the specimen is easily fractured without enough stable crack growth area. The specimens in this research are annealed or quenched steel with 0.45 % carbon. These specimens with b/R = 0.3-0.4 (ligament/radius) and R = 5 mm showed pre-crack blunt and the following growth crack blunt, and total stretch zone size were 0.6mm of quenched one and 0.9 mm of annealed one. The corresponding J integral are 17 kJ/m² and 31 kJ/m², respectively. Although J-R curves of a CT and a bar show not big difference each other, the corresponding J of a bar as mentioned above is much different scale from critical J of CT specimen. On the other hand, the relative comparison of the annealed and the quenched steel, the ratio 1.8, is near with that obtained by CT specimen, 1.5.