Improved Method for Fracture Toughness Testing Using Compliance Method for High Toughness Materials

In order to ensure the integrity of structures such as gas turbines and nuclear power plants, the materials used should have excellent toughness. Especially in the case of nuclear piping materials applied to leak before break (LBB) design, high toughness materials are used to meet the stringent fracture toughness criteria and integrity must be verified through static J-R curve testing using the compliance method, one of the measurement techniques for fracture toughness. The measured and estimated values for the crack extension length during the test should also match, within a certain tolerance. However, in the case of materials with high toughness, rotation of the specimen becomes significant, because the test is performed until the crack open displacement (COD) is relatively large to ensure sufficient crack extension. In this case, it is not easy to satisfy these conditions due to the rotational effect on the specimen. Even though ASTM E1820 suggests a method for correcting the crack length for the rotational effect on these specimens, it has been found that there are substantial differences for high toughness materials. To solve this problem, a new crack length correction formula considering the rotation effect is proposed. Through analysis of the data from J-R curve testing with this proposed method, it was confirmed that the accuracy of crack extension length estimation is improved compared to the existing method. The proposed method well explains the variation of crack extension length due to rotation and is suitable as a correction equation for rotation of compact tension specimens.

Numerical Simulation of Modified Compact Tension Test Depicting of Experimental Measurement by ARAMIS

The paper is focused on the determination of mechanical fracture parameters from the modified compact tension test applied to the cement-based composites. The experimental measurement was carried out by means of the ARAMIS equipment. The numerical study is performed by ATENA 2D software (based on a cohesive law for crack propagation) taking the material parameters for numerical study from the standard compression test. The experimental and numerical results are discussed and compared with the help of basic fracture parameters and Load – COD (crack open displacement) diagrams.

A Prediction of the Leakage Through Cracks for Leak Before Break

A code was developed in this study to predict the leakage of the leak before break (LBB). Various stagnation conditions were considered, including the subcooled water, the two-phase fluid and the overheated steam. Moreover, both the critical and noncritical flow was studied. The Henry-Fauske critical flow model was revised by a new phase transition point and the pressure drop due to friction and turns were modified. The code was verified by the comparison with the experimental data on the leakage of conventional pipes, artificial cracks and naturally occurring cracks, which shows a good agreement and this code has a higher precision than the existing codes. The influence of crack morphologies on LBB leakage was discussed, including the local roughness, the global roughness, the crack open displacement (COD) and the number of the corners. Besides, the dependence of the LBB leakage on stagnation enthalpy and back pressure was also investigated.

Exploration of Constants Independent of Material and Layup in Transverse Matrix Cracking of Cross-ply Laminate

Stiffness reduction caused by matrix crack in cross–ply laminates of CFRP, GFRP, KFRP can be predicted well by a shear–lag model assuming a constant of the crack open displacement index. Due to the existence of the saturation crack state (CDS), stiffness reduction has a low boundary, the minimum normalized longitudinal stiffness of the cracked plies is 0.3 instead of 0 used in current lamination theory on the behaviour prediction after FPF.