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

二軸応力試験データによるジルカロイ-4燃料被覆管の異方性弾-塑性パラメータの評価及びその破壊力学パラメータ計算に係る応用

Li, F.  ; 三原 武  ; 宇田川 豊  

Li, F.; Mihara, Takeshi; Udagawa, Yutaka

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 ~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 cold worked samples and recrystallized samples showed high yield stress and Young's modulus, respectively. The evaluated mechanical properties of the stress relieved samples revealed a limited impact of Q-factors on mechanical behavior, including their anisotropic feature. The derived mechanical properties were applied to evaluate the fracture mechanics parameter, J-integral, based on failure limit data from biaxial-expansion-due-to-compression tests on precracked tubes. This evaluation produced systematically lower J-integral values of the stress relieved tube than previously evaluated based on the failure limit data from in-pile RIA-simulated tests.