Axial Fracture Toughness Testing of Zr-2.5Nb Pressure Tube Material

A complete flaw evaluation of a longitudinal defect in a CANDU (CANada Deuterium Uranium) reactor pressure tube requires knowledge of the axial fracture toughness of the material. This paper addresses the problem of measuring fracture toughness of thin pressure tube material. Compact tension specimens (∼4 mm thickness) are prepared from flattened and stress-relieved Zr-2.5Nb pressure tube material. Axial crack growth resistance curves (J-Δa) and crack opening displacement (COD) are determined at room temperature and 150°C using the unloading compliance method. The latter is shown to give excellent estimates of crack extension for side-grooved specimens (≤2% variation) and for plane specimens at room temperature (≤7% variation for Δa > 1.5 mm). However, for plane specimens at 150°C and short crack extensions (Δa < 1.5 mm), the compliance calculated crack length underestimates the true crack extension by approximately 20%. The J-Δa curves and COD are shown to be in good agreement with previous results of Simpson.