1997 年 46 巻 10 号 p. 1184-1188
In order to investigate the effects of environmental conditions, especially water vapor in the atmosphere and high temperature, on the strength behavior of alumina ceramics, fast fracture tests, static and cyclic fatigue tests were carried out in vacuum and at elevated temperatures. Cyclic fatigue tests were also carried out under three different varying load conditions to clarify the effect of load pattern on fatigue behavior. The results of cyclic fatigue tests at room temperature reveal the following fatigue behavior of alumina ceramics. The cyclic degradation is observed clearly in ordinary atmospheric environment, and the higher is the load repetition frequency the lower becomes the fatigue strength when the fatigue strength is evaluated from the view point of cumulative loading time to failure. Furthermore, the degradation disappears in vacuum. The results of high temperature cyclic fatigue tests indicate that the cyclic degradation also disappears at a certain temperature over 800°C as same as the case in vacuum. The above results indicate that the cyclic degradation in ordinary atmospheric environment results from an interaction of time-dependent degradation and cyclic-dependent one, which is assisted by water vapor in air.