A load-separation technique to evaluate crack growth and fracture resistance behaviour of thin-walled axially cracked tubular specimens

摘要

Integrity assessment of thin-walled tubular components such as nuclear reactor fuel pins during postulated and beyond-design-basis accident scenarios is an important issue for limiting the release of radioactivity into the surrounding fluid. The fracture resistance behaviour of these tubes cannot be evaluated using standard ASTM techniques. It is because of the inability of these axially cracked specimens to meet the stringent plane strain requirement due to their geometry and the high ductility of the zirconium alloy used for their fabrication. Moreover, the measurement of crack growth during the testing by conventional methods is a cumbersome process and sometimes it is not possible to use them due to the small size of these specimens. Alternative methods such as load-normalization and load-separation techniques are suitable for these types of situations. In this article, the crack growth data during loading of the axially cracked tubular specimens have been evaluated using a load-separation method. Several specimens have been tested in order to evaluate their fracture resistance behaviour. These specimens have different values of initial crack lengths. A modified procedure for the estimation of the material constant 'm' has been developed in this study so that data from multiple specimens can be used. This will lead to a more reliable estimation of crack growth during the loading process. The J-R curves, obtained using the current method, have also been compared with those obtained using load-normalization technique. It was observed that this modified method of load separation is a convenient and reliable technique for the evaluation of fracture resistance behaviour of nonstandard specimens.