高温部件蠕变-疲劳寿命预测方法

Prediction of creep-fatigue life for components served at high temperature

近10年来,火电、燃机等发电机组面临调峰运行,机组的运行模式将逐步从恒定载荷状态向间歇载荷状态发生转变。间歇载荷模式下机组结构件不仅要承受高温蠕变损伤,同时还会承受由温度、应力波动产生的高温疲劳损伤。因此,研究蠕变-疲劳载荷条件下材料的交互损伤规律,开发准确的蠕变-疲劳寿命预测模型,探索不同控制模式下的蠕变-疲劳试验方法是该领域研究的热点问题之一。考虑机组部件的实际工况,应变控制模式下的蠕变-疲劳试验被广泛采用。同时,介绍了一种新型应变-应力混合控制模式下的蠕变-疲劳试验方法。该方法通过控制保载阶段的应力以及时间,可以更好的研究蠕变损伤在蠕变-疲劳交互作用中的影响。时间分数法、延性耗散法、应变能密度耗散法以及基于上述三种方法的修正模型已经被广泛用于蠕变-疲劳寿命预测领域。在这些寿命预测方法中,材料在保载阶段产生的应力松弛行为也是研究的重点内容。通过对预测结果进行对比,讨论了不同应力松弛模型的优势与不足。

For the aim of carbon neutrality and emission peak in China,the loading mode of power plants is gradually in transition from base-load-mode to intermittent-mode.The change of temperature and pressure under intermittent-mode leads to both creep damage and fatigue damage.In such a case,it is necessary to study the creep-fatigue interaction,establish an accurate model for life prediction,and develop a novel creep-fatigue loading mode.In general,considering the actual operated condition,strain-controlled creep-fatigue test is adopted.In addition,a hybrid strain-stress controlled creep-fatigue test is introduced.It can describe creep damage more flexible by changing the stress and hold time during the hold period.Moreover,time fraction method,ductility exhaustion method,strain energy density exhaustion method,and the modified methods based on the former three method have been widely used in this field.Besides,the stress relaxation behavior is an important issue.The capabilities of four relaxation models are discussed.