Experimental study and modeling of the anisotropic viscoplastic behaviour of zircaloy 4 in two metallurgical states

The aim of this work is the study and the modelization of the anisotropic viscoplastic behaviour of zircaloy 4 in two metallurgical states: recrystallized and cold-worked stress-relieved. The results of experiments performed in the intermediate temperature domain (20 - 450 deg C) are presented. In order to characterize the anisotropy, especially at 350 deg C, the tests were made under both monotonic and cyclic uni- and bidirectional loadings, i.e. tension-compression, tension-torsion and tension-internal pressure tests. The results would seem to indicate that the set of anisotropy coefficients do not depend or temperature. An important feature of the behaviour of this alloy in the neighbourhood of 300 deg C is attributed to the dynamic strain aging frequently observed in solid insertion solutions. This material also presents a slight supplementary hardening during out-of-phase cyclic loading (tension-torsion with a 90 deg C phase lag). In the last part, we propose to extend the formulation of a unified viscoplastic model, developed and identified elsewhere for other isotropic materials, to the case of zircaloy 4. From a general point of view, the introduction of anisotropy in the model is performed by the introduction cf four tensors of rank 4 affecting the flow directions, the linear parts of the kinematical hardening variables, the dynamic and static recoveries of these hardening variables. The identification of this model is performed at 350 deg C. (author)