Abstract
In order to investigate the effects of water vapor in air and high temperature on the strength behavior of alumina ceramics, fracture tests, static and cyclic fatigue tests were carried out under four-point bending condition at high temperature and in vacuum. Simple probabilistic evaluation on the fracture strengths in air and in vacuum indicates that though the scatters of the fracture strengths under both conditions are almost the same the strength in vacuum is higher than that in air by about 20%. This suggests that, in air, increment of defect size by water vapor must be taken into account. Results of static and cyclic fatigue tests at room temperature in air indicate that cyclic fatigue degradation is a superposition of time-dependent degradation and cycle-dependent one and both types of degradations are promoted by water vapor, because they are not observed in vacuum. The results of high temperature cyclic fatigue tests indicate that the cyclic fatigue degradation also disappears at high temperature over 800°C similar to the case in vacuum.
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