Ratcheting Fatigue Behaviour of Zircaloy-2 at 300 °C

Abstract

In laboratory, materials designed for engineering applications, specifically for fatigue, are generally tested under symmetrical cyclic loading (stress ratio, R = −1), but many structural components exhibit less fatigue life than predicted from symmetric loading due to asymmetric cyclic loading during service. This study deals with fatigue behaviour of Zircaloy-2 and presents the effect of mean stress (σ_m), stress amplitude (σ_a), stress rate ($\dot{\sigma }$) on fatigue life, deformation and fracture behaviour at 300 °C under asymmetric cyclic loading. A series of fatigue tests are performed at 300 °C under asymmetric stress-controlled loading with different combinations of σ_m (60–80 MPa), σ_a (115–135 MPa) and $\dot{\sigma }$ (30–750 MPa/s). Deformation behaviour and microstructural changes under the influence of above parameters (σ_m, σ_a and $\dot{\sigma }$) are examined by transmission electron microscope. It is observed that plastic strain increases with rise in σ_m as well as σ_a and cyclic life is reduced; on the other hand, with increase in $\dot{\sigma }$ accumulation of plastic strain decreases and fatigue life is enhanced. The results are correlated with microstructural changes and fracture behaviour of the material under different test conditions.

Graphic Abstract