Abstract
In order to clarify properties of the surface-originating fracture in high vacuum environments, uniaxial tension fatigue tests were carried out in air and high vacuum using pieces made of Ti-6Al-4V alloy with micro-defects by drilling. As a result, the following were obtained : (1) Compared with in air, fatigue lives in high vacuum strongly depended on stress. (2) Interior-originating fractures in high vacuum occurred from higher stress level than those in air. Therefore, we must pay attention to the effect of the interior-originating fracture in case of using this material in vacuum environment like space. (3) There was the possibility that the effect of the dependence of the &K_<th> on crack size in high vacuum is stronger than that in air.
