抄録
Fracture toughness tests were carried out on nuclear graphite, IG-110 and PGX, and the effects of width, ligament ratio of compact tension specimen and cross-head speed on fracture toughness were examined. Crack extension processes in graphite specimen were observed by acoustic emission technique and optical observation method. From the results, it is concluded that:
(1) A knee-point on the electrical potential-load displacement curve indicates macro-cracking in compact tension specimens.
(2) Cracking occurred in the middle part of the notched surface of compact tension specimen and extended from the middle to the surface of specimen.
(3) The value of JIC was constant within the range of ligament ratio from 0.4 to 0.55.
(4) The value of JIC was constant within the range of cross-head speed from 0.005mm/min to 0.05mm/min.
(5) The value of JIC was constant when the specimen width was more than 10mm for PGX graphite and 20mm for IG-110 graphite, respectively. However, JIC decreased as the specimen width decreased below the above-mentioned values. It is considered that this phenomenon is due to the formation of process-zone at the crack front of CT specimen.
