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

摘要

在实验室中，通常在对称循环载荷（应力比，R = -1）下测试用于工程应用（特别是用于疲劳）的材料，但是由于使用过程中的非对称循环载荷，许多结构部件的疲劳寿命比对称载荷所预测的要短。这与锆锡合金-2和礼物平均应力的效果（σ的疲劳行为研究涉及_米），应力振幅（σ_一个），应力速率（\（\点{\西格玛} \） ）对疲劳寿命，变形和断裂非对称循环载荷下300°C时的行为。一系列的疲劳试验，在300℃下非对称应力控制装载用的σ不同组合执行_米（60-80兆帕），σ_一个（115-135 MPa）和\（\ dot {\ sigma} \）（30-750 MPa / s）。变形行为和的上述参数的影响下微观结构的变化（σ_米，σ_一个和\（\点{\西格玛} \） ）通过透射电子显微镜检查。据观察，与上升σ塑性应变增加_米以及σ_一个和循环寿命缩短; 另一方面，随着\（\ dot {\ sigma} \）的增加，塑性应变的累积减少，疲劳寿命增加。结果与在不同测试条件下材料的微观结构变化和断裂行为相关。

图形摘要