溶接構造用圧延鋼材の安定き裂先端近傍に形成されたボイドの３次元形状の構築

抄録

In this study, construction of 3D shapes of voids near a stable crack tip of welding structural rolled steel (SM490A) and the relation of the void shapes and fracture toughness are described. The voids near the crack tip are formed by inclusions as nuclei and coalesce with each other. Therefore, the void shape is influenced by the distribution of inclusions. For rolled metal materials, the inclusions have directionality due to the influence of the rolling process. For this reason, it is considered that anisotropy occurs in the fracture toughness of the rolled metal material.

The purpose of this study is to make clear the relation of 3D shapes of voids and fracture toughness of rolled metal material. For this purpose, CT specimens of three kinds of orientations were prepared by rolled steel materials for welded structures. Stable cracks were introduced to these specimens, and the surface near the crack tip was polished by about 1 μm at a time. The surfaces involved voids were photographed with a digital microscope each time. The 3D shapes of voids were constructed by image processing from the continuous images. The relation between the shapes and dimension s of voids and the fracture toughness values of the material in each direction was studied. The void size of the specimen which has the lowest fracture toughness value was the largest and had a shape spreading in the crack surface.