变温条件下热结构的声疲劳寿命评估

ACOUSTIC FATIGUE LIFE ASSESSMENT OF HOT STRUCTURES UNDER VARIABLE TEMPERATURE CONDITIONS

为提高C/Si C热结构在热-声载荷下的疲劳寿命评估精度,分析了热结构声疲劳寿命的温度依赖性。基于频域疲劳评估方法,从温度变化改变结构动应力响应和温度与材料S-N曲线的对应关系两个方面,分析了变温条件下的结构声疲劳寿命评估。对C/Si C热防护壁板进行的数值仿真研究发现,随着温度的升高,加筋板结构的刚度降低,动应力响应峰值在整体上呈现左移且上移的趋势;在3个典型温度水平1100℃、1300℃和1500℃下,热防护材料C/Si C的疲劳性能随着温度的升高而降低。热-声两方面因素的共同作用,使得C/Si C加筋壁板在1300℃时危险点的寿命降为1100℃时的7.1%,而1500℃时声疲劳寿命降低到1300℃时的3.9%。计及和不计及温度变化的过程,在4000 s内的疲劳损伤的计算结果相差约102倍。

In order to improve the accuracy of acoustic fatigue life assessment for C/SiC hot structures under variable temperature conditions, the temperature-dependence of their acoustic fatigue life was investigated. Effects of variable temperatures on both the structural responses and the S-N curves were considered. A procedure for assessing acoustic fatigue under variable temperature conditions was proposed based on the frequency domain assessment method. A simulation study was conducted for a thermal protection panel. Results show that structural stiffness decreases as the temperature goes up and that the peaks of the stress responses tend to shift left and up. At three typical temperature levels, i.e. 1100~C, 1300~C and 1500~C, the fatigue performance of C/SiC degrades as the temperature increases. These two factors lead to a reduction in acoustic fatigue life of hot structures at elevated temperatures. The analysis shows acoustic fatigue life of the hot spot at 1300℃drops to 7.1% of that at 1100℃, while at 1500℃ the fatigue life is 3.9% of that at 1300℃. With the inclusion of variable temperatures, the acoustic fatigue damage stemming from 4000 seconds of exposure increased roughly 102 times.