Impact fracture toughness of a nuclear graphite measured by the one-point-bending method

Abstract

The impact fracture toughness K Id of a nuclear graphite IG-110 was measured by a one-pointbending impact tester. The impact fracture toughness K Id was compared with the static fracture toughness K IC measured by three-point-bending test. A Charpy-type specimen was precracked at the center of the bottom side by the bridge compression method and used for the fracture toughness test. In the one-pointbending impact test, the specimen is freely suspended at both ends with thin ceramic threads, and an impact force is applied at the center of the upper side of the specimen by a dropping cylindrical bar. A series of impact tests was performed for specimens with various precrack lengths ( a W = 0.2 ∼ 0.6 , a: precrack length, W: specimen height). It was found that the K Id and K IC of graphite IG-110 specimen with a w = 0.2 were almost the same, 1.0 MPa √m. However, K Id increased by 0.8 MPa √m with the increase in a W from 0.2 to 0.6, while K IC by 0.3 MPa √m. The crack length dependence of the fracture toughness was explained by the bridging effect of the precracked surface; the bridging ligament length was estimated to be greater in the dynamic tests than in the static tests.