抄録
In our previous studies, crack growth tests have been conducted in a high vacuum to simulate interior-originating cracks of Ti-6Al-4V in very high cycle fatigue. As a result, granular region which is very similar to fracture surface of interior-originating fracture was observed. In addition, we inferred that repeating compressive stress on fracture surface is involved in the formation of granular region. So, crack growth tests under R=-1, 0.1 using MT specimens were conducted in air to reveal effects of repeating compressive stress on the formation of granular region and on fatigue crack growth behavior. As a result, repeating compressive stress in air had no significant effect on fatigue crack growth behavior, and did not cause the formation of granular region. The existence of both repeating compressive stress and vacuum environment can be the main reason of granular region.
