VISCOPLASTIC BEHAVIOR AND MODELIZATION OF A RECRYSTALLIZED ZIRCALOY-4 ALLOY UNDER UNIAXIAL AND MULTIAXIAL LOADINGS

The results of experiment performed on a recrystallized zircaloy 4 alloy in the intermediate temperature domain 20 less-than-or-equal-to T less-than-or-equal-to 400-degrees-C are presented. To characterize the anisotropy, especially at 350-degrees-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 different anisotropy coefficients and especially [GRAPHICS] seem to be temperature independent. An important feature of the behavior of this alloy in the neighbourhood of 300-degrees-C is attributed to the dislocations-point defects interactions (dynamic strain aging), phenomena often observed in the solid solutions. For the 2D cyclic non proportional loadings it is shown that a weak supplementary hardening appears, which is a function of the degree of the phase lag. We propose to particularize and to apply a unified viscoplastic model with internal variables to the considered alloy, as the model as already been developed and identified elsewhere for other isotropic materials. From a general point of view the introduction of the anisotropy in the model is made by four tensors of rank 4; [M] is assigned to the flow directions, [N] to the linear parts of the kinematical hardening variables and [Q], [R] respectively to the dynamic and static recoveries of these tensorial variables. This phenomenological formulation leads to a correct representation of the set of the experimental results presented at 350-degrees-C, which provides an a posteriori confirmation of the formalism used.