The fatigue test has been carried out on polycrystalline aluminum under plane bending in order to investigate the effect of atmosphere on the fatigue strength of aluminum. The experiments were conducted in the pressure range from ambient pressure to 6×10-5 Torr to know the pressure dependence of the fatigue life of aluminum, and the fatigue failure process of a specimen was examined by stress cycling using the surface profilometer and the micro-Vickers hardness tester to understand its failure mechanism more. Furthermore, the effect of test temperature on the fatigue fracture of aluminum was investigated and discussed from the chemomechanical view points.
The main results obtained were as follows:
(1) The fatigue strength of aluminum in vacuum was higher than that in air. The fatigue resistance of a specimen decreased with increasing temperature both in vacuum and in air.
(2) The increase of fatigue life of aluminum depends upon the degree of vacuum. The transition exists in the pressure range of 10-2∼10-3 Torr, independently of either the applied strain or the test temperature.
(3) The effect of a two-stage environmental fatigue test on the fatigue life of aluminum was notable in the experiments performed at the low stress level but it was not so at the high stress level.
(4) The surface roughness and Vickers hardness of a specimen subjected to fatigue stressing in vacuum were higher than those in air. This tendency became more pronounced at the high stress level.