抄録
Fatigue crack consists of crack initiation region of Stage I, Stage II a and crack propagation region after Stage II b. Crack propagation region is effected by mechanics factor greatly and can evaluate quantitatively. But quantitative evaluation in crack initiation region is difficult, because of two rule factors coexist of a mechanics and metallurgical. This study described fatigue crack in three dimensions and examined fatigue crack growth behavior in fatigue crack initiation region. The material investigated was the low carbon steel S10C. As a result, as number of cycle is increased, crack depth is increased. When crack depth reach certain degree of depth, angle between crack growth direction scatter near 45°, 90°. This means that crack transit Stage I, Stage II b at each degree.
