불균일 피로균열을 갖는 CCT 시험편의 파괴인성실험의 유효성에 관한 실험적 고찰

The aim of this study is to demonstrate the validity of the fracture toughness of Zr-2.5Nb pressure tube obtained from the CCT (Curved Compact Tension) specimen with a non-uniformed pre-fatigue crack. This study covers the comparison of the J-R values of the CCT specimen taken from the unirradiated Zr-2.5Nb tubes with low and high fracture toughness and the irradiated Zr-2.5Nb tube with low fracture toughness, respectively. The fracture toughness tests were carried out at RT, 250 and 300℃. At high temperatures such as 250 or 300℃, it was found that the CCT specimen with the non-uniformed pre-fatigue crack has fracture toughness, dJ/da comparable to that of the CCT specimen with the uniform pre-fatigue irrespective of fracture toughness of Zr-2.5Nb pressure tube. In contrast, at RT, the CCT specimen with the non-uniformed pre-fatigue crack had different fracture toughness from that of the CCT specimen with the uniform pre-fatigue crack, which becomes non-conservative. Especially, the CCT specimens with the non-uniform pre-fatigue crack taken from both unirradiated and irradiated Zr-2.5Nb pressure tube of low fracture toughness yield lower fracture toughness than that of the CCT specimen with the uniform pre-fatigue crack, leading to a conservatism. Finally, using both yield strength correction constant, C₁, and fracture toughness growth ratio correction constant, C₂, it is possible to predict the fracture toughness of CCT specimen with the uniform pre-fatigue crack from the result of non-uniform pre-fatigue crack.