Effect of Specimen Rotation on Crack Size Estimation in <i>J</i> – <i>R</i> Curve Testing Using Compact Tension Specimen

Abstract To verify the structural integrity of power generation facilities, many fracture toughness tests are being performed on high-toughness materials, and efforts are being made to obtain reliable J–R curve. In the case of nuclear piping system to which leak before break design is applied, high-toughness materials are used, and fracture toughness testing is also required to be conducted until sufficiently long crack extension is possible. However, when performing a J–R curve testing of a high-toughness material using a compact tension (CT) specimen to a crack extension size as long as possible, it is difficult to obtain reliable test results due to the phenomenon of rotation of the specimen. In our previous paper, the author proposed a new crack size estimation method considering the effect of load line changes due to specimen rotation and proved its validity through testing. In this study, the mechanical mechanism for crack size estimation from rotated specimens has been investigated. In addition, the crack size prediction accuracy of the ASTM E1820 method and the proposed method has been compared and evaluated through finite element (FE) analysis of specimens deformed by rotation. In the FE analysis, the proposed method showed better accuracy than the ASTM E1820 method. Thereby, it was verified that the author's method for estimating crack size considering rotation of CT specimens has better accuracy in both FE analysis and experimental evaluation compared to the ASTM E1820 method.