13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Vacancy concentration C x, mm 0 hr (Initial) 100 hr 0 2 4 6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 Vacancy concentration C x, mm 0 hr (Initial) 100 hr 0 2 4 6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 Vacancy concentration C z, mm 0 hr (Initial) 100 hr 0 2 4 6 8 0.8 1 1.2 1.4 1.6 1.8 2 2.2 (a) Line segment oa (center) (b) Line segment bc (side) (c) Line segment ob (notch) Figure 12. Distributions of vacancy concentration along each line segment 5. Conclusions Interrupted CCG tests were conducted using C(T) specimens with side-grooves of P92 steel. Then, the creep crack growth path of each interrupted specimen was observed and the creep crack growth behavior of P92 steel was investigated. Furthermore, the three-dimensional vacancy diffusion analysis was conducted to clarify the three-dimensional diffusion behavior of vacancies which related to the void formation and crack growth. Following results were obtained: (1) The creep crack growth forms were different between the center of the thickness direction and near the side-groove. For the center of the thickness direction, the creep crack growth behavior showed the periodic convexo-concave manner. On the other hand, the creep crack grew in a linear manner near the side-groove. (2) The creep crack of C(T) specimen with side-grooves of 25% of specimen thickness preferentially grew near the side-groove. (3) Vacancies remarkably accumulated at the corner of the bottoms of notch and side-groove. 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 near the side-groove. (4) The three-dimensional vacancy diffusion analysis is useful to predict the behavior of creep damage such as creep voids and cracks. Acknowledgements This work was partly supported by the Japan Society for the Promotion of Science Research Fellow 24.2235. References [1] A.T. Yokobori, Jr., R. Sugiura, M. Tabuchi, A. Fuji, T. Adachi, T. Yokobori, The effect of multi-axial stress component on creep crack growth rate concerning structural brittleness, Proc ICF 11 (2005) CD-ROM. [2] R. Sugiura, A.T. Yokobori, Jr., M. Tabuchi, A. Fuji, T. Adachi, Characterization of structural embrittlement of creep crack growth for W-added 12%Cr ferritic heat-resistant steel related to the multi axial stress, Trans of ASME, J Eng Mater Technol, 131 (2009) 011004 1-9. [3] K. Kimura, K. Fujiyama, R. Ishi, K. Saito, Estimation of Creep Damage for the Components of Mod. 9Cr-1Mo Steel: (2nd Report, Creep Damage Assessment for Welded Joint by Means of Void Observation), Trans Jpn Soc Mech Eng, A 66(647) (2000) 1411-1418 (in Japanese). [4] T. Watanabe, M. Yamazaki, H. Hongo, M. Tabuchi, T. Tanabe, Relationship between Type IV
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