Constraint effects in testing different curved geometries of Zr-2.5Nb pressure tube material have been studied with the aim of understanding discrepancies between toughness (critical crack length) values obtained from small specimens and burst tests. Crack growth resistance or deformation J-R curves were obtained on unirradiated pressure tube material at room temperature using small 17 and 34 mm wide curved compact specimens, 60 mm wide curved centre cracked specimens and burst test specimens.
The J-R curves from the burst tests were in excellent agreement with those from the curved compact specimens at short crack extensions (up to 2 mm per crack tip). However, at larger crack extensions the burst test J-R curves deviated from the small specimen results, being higher than those from the 17 mm specimen but only slightly lower (about 10%) than those from the 34 mm specimen up to 6 mm crack growth; i.e. the onset of instability at maximum pressure. In comparison, the J-R curves from the centre cracked specimens were well above those of the curved compact and burst test specimens at all crack extensions. The results suggest that the crack tip constraint of the burst test is most similar to that of a compact specimen, the centre cracked specimen having a much lower crack tip constraint. Fractographic studies confirmed the experimental results.