考虑平均应力效应的高温高周疲劳损伤机理与寿命设计研究

For the long-period reliable operation needs of the advanced ultra-supercritical steam turbine key components, the high cycle fatigue property, damage mechanism and life design criteria will be investigated for high pressure blade material under complex loading and high temperature environment. The following issues will be focused in the present project. (1) Series of high cycle fatigue tests are conducted under various alternating stress and mean stress levels at elevated temperature. The mean stress contributes to the cyclic strain evolution and mechanical properties degradation of the material are demonstrated. (2) It is recognized by the microscopic inspection at different life stages that the mean stress effects the changes of microstructures and the crack initiation mechanism. The correlation between microstructures change and macroscopic damage parameter is produced. (3) The 2-D damage assessment diagram by taking into account the mean stress and cyclic strain through the parameter of non-elastic strain energy density is developed. The approach of life prediction and strength design is produced by damage mechanics. This research is expected to provide a scientific basis that leads to innovations of life design on high pressure blade of ultra-supercritical steam turbine.

面向先进超超临界汽轮机关键部件长周期可靠运行的需求，对复杂载荷作用下高压端叶片材料的高周疲劳性能、损伤机理及寿命设计方法开展研究。主要包括：（1）开展不同应力幅值及平均应力条件下高温高周疲劳试验，揭示平均应力对材料疲劳进程中循环应变演化和宏观基本力学性能退化的作用机制；（2）通过不同寿命阶段的微观观察，澄清平均应力对微观结构演化及裂纹萌生机制的影响，实现微观组织演化与宏观损伤参量之间的关联；（3）基于非弹性应变能量密度参量，发展平均应力—循环载荷两维损伤评定图方法，建立基于损伤力学的寿命预测及强度设计方法。本研究有望为先进超超临界汽轮机高压叶片寿命设计方法的革新提供科学依据。

高温高周疲劳研究对解决长寿命服役条件下结构强度设计具有重要意义。项目围绕“考虑平均应力效应的高温高周疲劳强度设计”这一科学问题，开展了循环载荷与平均应力下共同作用下材料的高温高周疲劳性能与损伤机制、高温高周疲劳强度考核方法、考虑蠕变效应的高温高周疲劳强度设计准则等3个方面的研究。研究取得的进展包括：（1）澄清了温度及应力比对疲劳强度的影响机制，阐明了高温高周/超高周疲劳裂纹萌生特征及微观损伤机理；（2）建立了考核汽轮机叶片和转子高温疲劳强度的Haigh图；（3）建立了不同平均应力下，考虑蠕变效应的高温高周/超高周疲劳强度设计准则。研究共申请中国发明专利1项，预计在International Journal of Fatigue等本领域权威期刊上发表学术论文3篇（在审1篇，拟投稿2篇）；培养博士、硕士研究生各1人。