Ratcheting Fatigue Behaviour of Zircaloy-2 at 300 degrees C

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 (sigma(m)), stress amplitude (sigma(a)), stress rate ((sigma) over dot) on fatigue life, deformation and fracture behaviour at 300 degrees C under asymmetric cyclic loading. A series of fatigue tests are performed at 300 degrees C under asymmetric stress-controlled loading with different combinations of sigma(m) (60-80 MPa), sigma(a) (115-135 MPa) and (sigma) over dot (30-750 MPa/s). Deformation behaviour and microstructural changes under the influence of above parameters (sigma(m), sigma(a) and (sigma) over dot) are examined by transmission electron microscope. It is observed that plastic strain increases with rise in sigma(m) as well as sigma(a) and cyclic life is reduced; on the other hand, with increase in (sigma) over dot 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.