Load separation in 17 mm wide CT specimen of Zr-2.5Nb pressure tube material

Abstract

In PHWR community 17 mm wide curved compact tension (CCT) specimen is most commonly used for fracture toughness testing in axial direction of pressure tube. This specimen geometry is different from Conventional CT specimen (ASTM E 1820–11) in two aspects. First being the curvature of the CCT specimen and second is that it does not meet the alternate thickness criteria of 2≤W/B≤4 for B = 3.6 mm. Despite these differences, the eta and gamma factors used for the fracture toughness measurement of Conventional CT specimen according to ASTM E 1820 –11 are also applied for CCT specimen. In this work, 17 mm wide blunt notched Conventional CT specimens of Zr-2.5Nb pressure tube with different a/W ratios between 0.3 and 0.7 were loaded up to maximum load. The load separabilty was checked and eta factor was calculated using load separation method. The investigation of separation parameter (S) for reference cracks (ai/W) between 0.45 and 0.7 showed that (a) load was separable over whole range of plastic displacement for the CT specimens with ai/W between 0.45 and 0.7, except for small initial inseparable region, and (b) load was not separable over whole range of plastic displacement for the CT specimens with ai/W of 0.35 and 0.40. The small inseparable region in the CT specimens with ai/W between 0.45 and 0.7 is reported in literature to be due to initial blunting of the CT specimen. The eta factor, calculated using load separation method proposed by Sharobeam and Landes, was found to have a constant value of 2.08 for ai/W in range of 0.45 and 0.70. The eta factor was found to be lower than that reported by Sharobeam and Landes as well as in ASTM 1820 – 11. Since load was not separable for CT specimens with a/W of 0.35 and 0.4, eta factor derived for this CT geometry cannot be used for a/W below 0.45.