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本研究提出了一种预测承受任意而复杂的温度和循环载荷的高温零件(如涡轮叶片和涡轮盘)热疲劳开裂起始的方法。看来,热疲劳寿命完全可以根据材料的基本力学性能通过计算如下两种性质不同的、独立的失效形式中的每一种寿命来确定:(1)循环蠕变断裂——采用由Robinson提出并经Taira修正的著名的寿命分数法;(2)常规低周疲劳——采用Manson推导的通用斜率法经验方程式计算。为了完整地确定分析程序已详尽地列出了各种方程。用Glenny型热疲劳试验数据说明并评价所推荐的寿命分析方法。在这些试验中,为了得到类似于涡轮叶片和导向叶片在使用后于前、后缘所出现的裂纹,把Nimonic90的锥形盘试样放在流态床内加热和冷却。在本研究中,首先计算锥形盘试样的温度、应变和应力,最后计算寿命。循环是在改变温度和时间的条件下进行的。带有和不带空气内冷。已经发现,28个试样中有24个是以循环蠕变断裂为主要失效形式。计算和观测的寿命一般相当一致。本研究表明,为预测并最终提高高温合金或零件的热疲劳抗努力所作出的种种努力,其重点应放在计算和減少蠕变损伤方面。
This study presents a method to predict the onset of thermal fatigue cracking of hot parts subjected to arbitrary and complex temperature and cyclic loads, such as turbine blades and turbine disks. It seems that the thermal fatigue life can be completely determined by the material’s basic mechanical properties by calculating each of the following two different and independent failure modes: (1) Cyclic creep rupture - The well-known life-time fraction method modified by Taira; (2) Conventional low-cycle fatigue - calculated using the generalized slope empirical equation derived by Manson. Various equations have been exhaustively listed in order to fully determine the analytical procedure. The Glenny-type thermal fatigue test data is used to describe and evaluate the recommended life-cycle analysis method. In these experiments, to obtain cracks similar to the appearance of the turbine blades and guide vanes on the front and rear edges after use, the Nimonic 90 cone disc samples were heated and cooled in a fluidized bed. In this study, the temperature, strain and stress of the conical disc specimen were first calculated and the life time calculated. Circulation is carried out under conditions of varying temperature and time. With and without air cooling. It has been found that 24 out of 28 samples are dominated by cyclic creep rupture. Calculated and observed life expectancy is generally quite consistent. This study shows that efforts to predict and eventually increase the thermal fatigue resistance of superalloys or parts should focus on calculating and reducing creep damage.