Fracture of Zircaloy-4 cladding tubes with or without hydride blisters in uniaxial to plane strain conditions with standard and optimized expansion due to compression tests

Two optimizations of the Expansion Due to Compression (EDC) test, which induces a near uniaxial loading, were proposed and developed to reach higher biaxiality ratios (ratio between mechanical quantities in axial and in circumferential direction). The first optimization, named HB-EDC for High-Biaxiality EDC, allowed to reach transverse plane strain conditions. The second optimization, named VHB-EDC for Very High Biaxiality EDC, was designed to reach higher loading biaxiality ratios. These optimized EDC tests were performed at 25 °C, 350 °C and 480 °C on unirradiated hydrided Cold Worked Stress Relieved (CWSR) Zircaloy-4 samples. First, samples unhydrided or uniformly hydrided up to 1130 wppm were tested. Second, samples hydrided at 310 wppm with a hydride blister were tested. A large ductility reduction is induced by the increase in biaxiality level in the absence of a hydride blister or with small blisters ( < 50 μ m deep). The fracture strain decreases quickly with the blister depth at 25 °C, but more progressively at higher temperature. An equation that quantifies the fracture strain reduction with the blister depth is proposed. Eventually, one of the tests developed in the present study, the HB-EDC test, was proven to be a good compromise between the test complexity and the stress state reached. It is a good candidate to characterize the mechanical behaviour of irradiated cladding.