ACOUSTIC FATIGUE LIFE ASSESSMENT OF HOT STRUCTURES UNDER VARIABLE TEMPERATURE CONDITIONS

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℃, 1300℃ and 1500℃, 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.