Evaluation of anisotropic elastic and plastic parameters of zircaloy-4 fuel cladding from biaxial stress test data and their application to a fracture mechanics analysis

The mechanical properties of fuel cladding near the elastic limit are essential in considering its failure limit during a pellet-cladding mechanical interaction phase under reactivity-initiated accident (RIA) conditions. The mechanical properties of a Zircaloy-4 cladding tube, such as orthotropic elasticity and anisotropic constants for Hill's plasticity law, were evaluated based on the biaxial stress test data, focusing on the equivalent plastic strain up to similar to 2.5%. Samples with various fabrication conditions, such as cold-worked, recrystallized, and stress relieved after cold-work with Q-factors of 2, 3, and 4 were investigated. The evaluation revealed noticeable difference in the elastic and plastic properties between cold-worked, recrystallized and stress relieved samples, including their anisotropic feature, while the impact of Q-factors was minor. The derived mechanical properties were applied to calculation of the fracture mechanics parameter, J-integral, which was found sensitive to the mechanical property differences. Critical J-integral values were then estimated by comparing the calculation and failure limit data from biaxial-expansion-due-to-compression tests on precracked tubes. This produced systematically lower J-integral values of the stress relieved tube than those previously evaluated based on the failure limit data from in-pile RIA-simulated tests.