Cyclic hardening and softening behavior of a fully annealed zircaloy-4

Abstract

Polycrystalline metals with a hexagonal close-packed (HCP) crystalline structure show a unique deformation behavior and fracture characteristics under cyclic loading conditions. As the HCP materials have limited slip systems and a tendency to develop a preferred orientation (texture), they show deformation anisotropy resulting from the texture during plastic deformation. Therefore, this anisotropy of the materials will affect not only the fatigue crack initiation/growth process but also the stress responses due to the increase in the slip irreversibility. It is well known that the fully annealed metals usually cyclically harden not soften. However, the initial cyclic hardening followed by softening in the higher strain ranges and the only cyclic softening to fracture in the lower strain ranges were observed in the fully annealed Zircaloy-4. This paper is proposing a new model to explain such cyclic behavior in Zircaloy-4 in terms of texture change during fatigue.