热声激励下高温合金薄壁结构振动响应试验验证与疲劳寿命预测

Vibration Responses Experimental Verification and Fatigue Life Prediction of Superalloy Thin-Walled Structures under Thermal-Acoustic Excitations

关键词:  热声激励  薄壁结构  振动响应  疲劳寿命  残余应力  试验验证

Key words:  Thermal-acoustic excitations  Thin-walled structures  Vibration responses  Fatigue life  Residual stress  Experimental verification

摘要:

为了研究金属薄壁结构在热声循环激励下形成的内部残余应力(Residual Stress)对模态频率、响应规律及疲劳性能的影响，采用耦合的有限元/边界元法(FEM/BEM)对薄壁结构进行振动响应计算，重点研究带残余应力结构的动力学响应特性，并与试验结果进行对比分析。结果表明，不同温度下基频的计算值与试验值获得很好的一致性，计算的应变响应结果与试验测试结果量值相当，验证了热声响应计算方法与模型的有效性。最终结合改进雨流计数法(Improved Rain-flow Counting)、Morrow平均应力模型、Miner线性损伤累积理论计算随机疲劳寿命。结果表明，带残余应力结构在屈曲前后温度为50℃，150℃，250℃所对应的损伤量级分别为10-7，10-4，10-7，疲劳寿命也表现出先减小后增大趋势，且硬化现象使疲劳寿命整体降低，寿命谷值随温度变化发生偏移。

Abstract:

To research effects of metallic thin-walled structures internal residual stress caused by repeated thermal-acoustic excitations on modal frequencies，response ways and fatigue performances，coupled FEM/BEM method was used to calculate vibration responses of engines thin-walled structures. Researches were mainly focused on characteristics analysis of structures dynamic responses results with residual stress，which were compared with experimental results. Results show that the fundamental frequencies of calculation value keep a preferable consistency with experiment value，and strain responses of calculation and experiment results have a good alignment，validating the effectiveness of calculation method and model for thermal-acoustic responses. Finally，the Miner linear accumulative damage theory was employed in conjunction with improved rain-flow counting method，Morrow mean stress model to calculate random fatigue life of structures，showing that damage level values of structure with internal residual stress are 10-7，10-4，10-7，respectively corresponding to 50℃，150℃，250℃，which are pre-buckling and post-buckling. And fatigue life shows a trend of increase at first then decrease，hardening phenomenon leads to a lower fatigue life and the skewing of valley value with the change of temperatures.