Effects of Notch Sharpness and Size of Specimen on the Fracture Toughness of Nuclear Graphites

The target of this research is to find the conditions for obtaining the valid fracture toughness value of nuclear graphite. The effects of the notch sharpness and size of specimen on the elastic-plastic fracture toughness values are examined. (1) The maximum notch root radius of curvature required for obtaining nearly constant fracture toughness values depends upon the kind of graphite, ca. 0.25mm for the fine-grained isotropic graphite; IG-110 and ca. 1.2mm for the coarse-grained near isotropic graphite, PGX. (2) The minimum specimen thickness for obtaining nearly constant fracture toughness values depends upon the kind of graphite, ca. 10mm for IG-110 and ca. 20mm for PGX. (3) The conditions that the specimen should satisfy for obtaining the valid fracture toughness values vary with the kind of graphite. (4) The linear elastic-plastic fracture toughness is applicable to IG-110 graphite, and evaluation by the elastic-plastic fracture mechanics is not always necessary for IG-110, but it is considered that for PGX the correct fracture toughness values are not obtained unless the elastic-plastic fracture mechanics approach is applied.