13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- 4.3. Analytical Results Figure 10 (a) and (b) represent the distributions of vacancy concentration at 0h (initial) and 100h in a shaded area shown in Fig. 11, respectively. From these figures, vacancies remarkably accumulated at the corner of the bottoms of notch and side-groove. And vacancies also accumulated at the bottom of side-groove near the notch tip. These results are in good agreement with the experimental result of the preferential CCG at the side. Figure 12 (a)-(c) show the distributions of vacancy concentration along line segment oa, bc and ob shown in Fig. 11, respectively. From Fig. 12 (b), the vacancy concentration at the bottom of side-groove increased within about 3 mm from the notch tip and this length correspond to the creep crack length of 226h and 301h at the side. These results indicate that the creep crack preferentially grows in the region of high vacancy concentration. Therefore, it seems that the three-dimensional vacancy diffusion analysis is useful to predict the behavior of creep damage such as creep voids and cracks. From the experimental results, it was clarified that the creep crack of C(T) specimen with side-grooves of 25% of specimen thickness preferentially grew near the side-groove. On the other hand, the creep crack of C(T) specimen without side-grooves preferentially grows at the center and this is crack tunneling. Three-dimensional vacancy diffusion analysis enables us to predict the most appropriate depth of side-grooves which cause the uniform creep crack growth in the thickness direction. side groove notch 1mm 0.8 2.0 ο center x z a b c side groove notch 1mm 0.8 2.0 ο center x z a b c (a) 0h (initial) (b) 100h Figure 10. Distributions of vacancy concentration at a shaded area shown in Fig. 10 z x y ο center a b c Figure 11. A Schematic illustration of 1/4 C(T) specimen
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