Polycrystalline modeling of the behavior of neutron-irradiated recrystallized zirconium alloys during strain path change tests

Abstract

During normal operating conditions, zirconium alloy nuclear fuel cladding tubes experience various biaxial loadings with complex strain path histories. Experiments have been conducted on neutron-irradiated thin cladding tubes in order to study the response to changes in the loading path. These tests consist of alternate internal pressure tests and axial tensile tests. During the internal pressure test steps, the flow stress exhibits significant cyclic strain softening, while axial tensile tests exhibit a smaller degree of cyclic strain softening. TEM analyses of the tested samples have revealed that the observed mechanical behavior can be attributed to clearing of irradiation-induced defect by gliding dislocations. The cyclic strain softening observed for internal pressure tests is due to clearing of defects by dislocations gliding in the basal planes. The smaller degree of cyclic strain softening in tensile tests is due to clearing of defects by dislocations gliding in the prismatic and pyramidal planes. A polycrystalline model has been developed to simulate these tests. This model is able to reproduce many features of the complex behavior of the material and provides a better understanding of the role of the clearing of defects and the contribution of kinematic hardening on the behavior of neutron-irradiated recrystallized zirconium alloys.