Nano-Fractography Study of Fatigue Crack Growth under Service Loading in Ceramics

In order to investigate cyclic fatigue crack growth behavior of a gas-pressure-sintered silicon nitride， Si ― D23 ― D2N ― D24 ― D2 and Si ― D23 ― D2N ― D2 /BN compound sintered Ceramics under constant and variable amplitude load sequences， fatigue crack growth tests were carried out using compact type （CT） specimens。Crack length and Macroscopic Crack closure were measured using an unloading弹性合规方法。谷物联锁是在所有疾病测试条件下观察到的裂纹破裂，这种材料的缺陷裂纹增长与通过循环加载的渐进退化有关。Fatigue crack growth rate， da/dn， under constant amplitude loading不仅由maximum stress intensity factor控制，Kyi D2 max yie D2，但也是压力amplitude，而Kyi D2 max yie D2是循环fatigue crack growth中最重要的因素。过载和高级别负载排除产生了脂肪裂纹增长的加速和低级别加载下裂纹闭合点的退化。这一决定是一个想法，以从大量严重的撞车或结构性的谷物联锁和裂缝封闭可以解释加速行为的质量。

In order to investigate cyclic fatigue crack growth behavior of a gas-pressure-sintered silicon nitride, SiィイD23ィエD2NィイD24ィエD2 and SiィイD23ィエD2NィイD24ィエD2 /BN compound sintered ceramics under constant and variable amplitude load sequences, fatigue crack growth tests were carried out using compact type (CT) specimens. Crack length and macroscopic crack closure were measured using an unloading elastic compliance method. The grain interlocking was observed around crack wake in all fatigue test conditions, which implied fatigue crack growth of this material was associated with progressive degradation of the grain interlocking by cyclic loading. Fatigue crack growth rate, da/dn, under constant amplitude loading was controlled not only by maximum stress intensity factor, KィイD2maxィエD2, but also stress amplitude, while KィイD2maxィエD2 was the most important factor in cyclic fatigue crack growth. The overload and high-level load excursion produced the acceleration of fatigue crack growth and the decrease of crack closure point under low-level loading. This decrease was thought to result from much severer crash or frictional wear of grain interlocking and the crack closure could explain the acceleration behavior qualitatively.