高温环境下汽油机排气歧管振动特性及疲劳寿命研究

Vibration characteristics and fatigue life of a gasoline engine's exhaust manifold under high temperature environment

为研究热载荷与机械载荷的耦合作用对排气歧管疲劳寿命的影响,对一款汽油机排气歧管进行热机耦合下的振动疲劳寿命分析。通过双向流固耦合的方法得到排气歧管的温度场,进而根据热应力及温度分布建立排气歧管的热机耦合模型,进行热载荷下的频率响应分析。通过计算对比发现,应力刚化效果及温度升高引起的材料力学性能退化使得排气歧管的刚度发生变化,导致频率响应分析得到的应力传递函数发生相应的改变,响应应力幅值及峰值频率均发生了不同程度的变化。振动疲劳寿命预测结果表明,考虑热机耦合的疲劳寿命较不考虑热机耦合的振动疲劳寿命降低了32.7%,热机耦合作用对疲劳寿命影响显著,不可忽视。

In order to study effects of thermo-mechanical coupling on fatigue life of a gasoline engine,s exhaust manifold, a vibration fatigue life analysis was performed for the exhaust manifold under thermo-mechanical coupling. Firstly, the temperature field of the exhaust manifold was calculated based on the two-way FSI method. Then, according to thermal stress and temperature distributions, the thermal-mechanical coupling model of the exhaust manifold was built to perform the frequency response analysis of the exhaust manifold under thermal loads. The results showed that both the response stress amplitude and peak frequency vary when considering temperature and thermal stress, different distributions of temperature and thermal stress lead to different structure stiffness; the fatigue life of the exhaust manifold considering thermo-mechanical coupling is 32. 7% lower than that not considering thermo-mechanical coupling; so the thermal- mechanical coupling has significant effects on the fatigue life of the exhaust manifold and it can , t be ignored.