氧化铝、氮化硅和碳化硅的疲劳特性与寿命预测

分析了几种典型的结构陶瓷在长期载荷下的失效特性和差别。认为长期失效的本质是强度衰减，建立了一个疲劳失效的强度衰减模型和提出了寿命预测方法。分别研究了氧化铝、氮化硅和碳化硅几种常用工程陶瓷在常温和高温下的疲劳特性和差异。采用三点弯曲的受力方式测试了不同载荷水平下的断裂时间。结果表明：碳化硅的疲劳门榄值超过强度的80％，而且受温度影响最小；氧化铝的静疲劳受微小裂纹扩展控制；氮化硅的高温疲劳主要是蠕变机制导致强度衰减，疲劳门槛值不超过强度50％。由实验研究了氮化硅的高温静疲劳、动疲劳和循环疲劳三者在相同温度和相同应力峰值变化下的寿命关系，结果与计算一致。

FAILURE BEHAVIORS AND LIFETIME PREDICTION OF Al2O3, SiC and HP-Si3N4

Fatigue behavior of three ceramics materials Al2O3, SiC, HP-Si3N4 and their differences were investigated. The study confirmes that the long_term failure of ceramics is due to the strength degradation that can be caused by various factors. A model of strength degradation for failure evaluation is presented and the lifetime calculation can be simplified as a motion equation. Static fatigue behaviors of Al2O3, SiC, HP-Si3N4, and their difference at room temperature and high temperature, were investigated experimentally. The lifetimes under different loading levels were measured by means of three_point bending method. The results show that the fatigue threshold of SiC is much higher than that of the other two materials and has no dependence on temperature. The fatigue lifetime of alumina is controlled mainly by subcritical crack growth, and the fatigue failure of silicon nitride at high temperature is due to strength degradation caused by creep. The relations between lifetime and loads measured for alumina and silicon nitride are consistent with the predicted by the model of strength degradation. It is found that the data of lifetime of SiC greatly scatter and fatigue threshold is over 80% of strength. The lifetime relations of Si3N4 under static, cyclic and dynamic fatigue at 1 200 ℃ were tested and the results agree well with calculation results.