基于微观单细胞模型的镍基单晶合金低周疲劳寿命灰色预测-机械设计及理论专业论文.docxVIP

II II Abstract The nickel-based single crystal superalloy has been widely used to make blade of aircraft gas turbines in China and US industry. The low cycle fatigue damage of blades occurs under frequently start-stop cyclic loadings. The study of low cycle fatigue damage mechanism and lifetime prediction models are always the hot and difficult problems at home and abroad. In this paper, theoretical models, numerical simulation analysis and experimental tests were used to study the low cycle fatigue characters of DD3 nickel-based single crystal superalloy. A micro unit cell finite element model was firstly established, after deep investigation of the method of the elastic-plastic mechanical behavior and low cycle fatigue properties of nickel-based single crystal superalloy at high temperature. Grey Relationship analyses were then used to find the major factor of affecting the fatigue lifetime. A GM (1, N) model was built to predict the low cycle fatigue lifetime and to improve the accuracy of fatigue lifetime prediction. The main content of the paper is as follows, 1, From a micro-structure view of point, a micro unit cell finite element model of single crystal superalloy was established. The model was then analyzed under the single axial loadings. The results showed that the matrix and precipitated phase interface are in complex stress condition, and the yield intensity of the precipitated phase is much higher than the matrix phase. The fatigue damage starts from the matrix phase and the precipitated phase improves the macro single crystal alloy material strength. The average stress deduced by the law of composite material mixture calculation formula is consistent with the uniaxial tension test stress value, which verifying accuracy of the single cell finite element model. 2, For DD3 single crystal nickel-based alloy thin-walled cylindrical specimens multiaxial low cycle fatigue test respectively at 680℃ high temperature, the macro/micro finite element model (Tensi