Session: MF-01-01 Application of Fracture Mechanics in Failure Assessment

Paper Number: 121407

121407 - Effect of Specimen Rotation on Crack Size Estimation in J-R Curve Testing Using Compact Tension Specimen 

In order 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 particular, in the case of nuclear piping system to which Leak Before Break (LBB) 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 test 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. To explain in more detail, when performing a fracture toughness test of a high-toughness material using a CT specimen, the specimen rotates while applying the load. Therefore, when estimating the crack size during testing using the compliance method, compliance is measured with the test specimen rotated. At this time, in order to obtain reliable J-R curve data, accurate crack size estimation is required from the compliance measured on the rotated test specimen. ASTM E1820 introduces a compliance correction equation to correct for the rotation effect of the test specimen. In a previous paper, the author proposed a new crack size estimation method that additionally considered 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 method (FEM) analysis of specimens deformed by rotation. In the FEM analysis, evaluation has been performed when the specimen rotation was large or small, and crack size to specimen width ratio, a/W, was varied between 0.5 and 0.7. As a result of FEM analysis, the proposed method showed better accuracy than the existing ASTM E1820 method. Thereby, it was verified that the author’s method for estimating crack size according to rotation of CT specimens has better accuracy in both finite element analysis and experimental evaluation compared to the existing ASTM E1820 method.

Presenting Author: Kuk-Cheol Kim Doosan Enerbility

Presenting Author Biography: Upon receiving MS in Mechanical Engineering from Sungkyunkwan University in 1993. Mr.Kim joined DOOSAN as an R&D engineer. His professional interest includes fatigue and fracture toughness evaluation of power plant materials

Authors:

Kuk-Cheol Kim Doosan Enerbility
Jeon-Young Song Doosan Enerbility
Young-Wha Ma Doosan Enerbility