301 アルミナ単繊維の疲労破壊に及ぼす湿潤ガス環境効果(GS-6 疲労(1))  [in Japanese] 301 Effects of wet environment on fatigue fracture behavior of Al_2O_3 single fiber  [in Japanese]

An investigation has been carried out concerning the influence of wet environment on the fracture behavior of γ-alumina single fiber (Altex). Tension-tension fatigue tests were conducted under sinusoidal waveform in dry air, laboratory air and wet air. Sustained load tests (SCC tests) were conducted in dry air and wet air. For fatigue tests in dry air, two types of failure mode were detected; fracture during the first cycle and no failure after 1.0×10^6 cycles. In contrast with this, for fatigue tests in laboratory air and wet air, fiber fractured depending on the cyclic stress. The fatigue strength in laboratory air and wet air was lower than that in dry air, indicating that the strength decreased with the increase of amount of moisture. The same tendency was observed for SCC tests. In dry air, some specimens fracture at the beginning of SCC tests and the others did not fracture after 2.0×10^5s: the strength of SCC tests in wet air was smaller than that in dry air. Time to fracture of fatigue and SCC tests were almost the same. The fracture surfaces were observed with a high-resolution field emission type scanning electron microscope and were quantitatively analyzed to correlate the fracture behavior of the fiber.