Low Cycle Fatigue Behaviour and Its Mechanisms for Zirconium Alloys

The low cycle fatigue life of the zirconium alloys can be expressed as the Coffin-Manson relationship, Nβ_fΔε_p=C_1. Many factors, such as the purity of the alloy, the test condition, can influence the low cycle fatigue life. The fatigue cracks usually stem from the region where incompatible plastic deformations occur, and the crack propagation rate can be described as the Paris formula, dα/dN=C_2(ΔK)n. The flow stress in cyclic deformation can be separated into the friction stress and back stress. During cyclic loading, the alloys exhibit cyclic hardening, cyclic softening or cyclic saturation depended on the test temperature and strain amplitude, while their mechanisms are rather different. Dislocation lines, dislocation bands, cell and labyrinth structures are typical dislocation configurations in the fatigued alloys.