本文旨在探讨发动机的热负荷对排气歧管模态的影响。首先，在阐述模态分析理论的基础上，建立了排气歧管有限元模型，分别进行自由状态和承受螺栓预紧力的约束状态下的冷-热模态分析；接着构建模态试验系统，分别在自由状态和约束状态下进行排气歧管冷-热模态试验。最后，有限元模态分析和模态试验的结果对比表明，有限元模态分析的结果与试验结果基本吻合；螺栓预紧力的约束和热负荷都对排气歧管的模态产生影响，螺栓预紧力的约束使其固有频率显著提高，而温度升高则使固有频率稍有降低。%This paper aims at investigating the effects of the thermal load of engine on the vibration modes of exhaust manifold. Firstly after the theory of modal analysis is expounded, a finite element model for exhaust man-ifold is built and modal analyses in both normal and raised temperature conditions are conducted in free state and constraint state of bolt pre-tightening force respectively. Then modal test system is constructed and modal tests in both normal and raised temperature conditions are also performed in free state and bolt pre-tightening constraint state respectively. Finally the comparison between the results of finite element modal analysis and modal tests indicate that the results of finite element modal analysis are well agree with that of modal tests;both the thermal load of en-gine and the constraint of bolt pre-tightening force have obvious effects on the vibration modes of exhaust manifold:the natural frequencies of exhaust manifold significantly rise with the constraint of bolt pre-tightening applied, but they slightly fall with the increase in temperature.
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