13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- conditions, on the other hand, only hardening occur independent of applied stress intensity factor rate conditions. Based on these analyses results mentioned above, softening around a crack tip occur at the low hydrogen concentration and the low applied stress intensity factor rate conditions. Therefore, the amount of plastic deformation around a crack tip is supposed to increase and yield in the fracture mechanism of HELP and/or HESIV so far. However, at the high hydrogen concentration or the high applied stress rate conditions, hardening around a crack tip lead the brittle type fracture, HEDE so far. The schematic illustration of these relationships of hydrogen embrittlement mechanisms depending on environmental and mechanical conditions are shown in Figure 7. Figure 7. Hydrogen embrittlement fracture mechanisms for different hydrogen concentration and applied stress intensity factor rate conditions 5. Conclusion In this study, we performed the dislocation dynamics calculation around a crack tip based on the results obtained by atomistic calculations. The results indicate that the hydrogen embrittlement mechanisms possibly change depending on boundary conditions (hydrogen concentration and applied stress intensity rate). Acknowledgements The author would like to acknowledge Prof. A.T. Yokobori,Jr.(Tohoku Univ.) for useful discussions and suggestions. References [1] R.A. Oriani, H.Josephic, Acta Metallurgica, 22 (1974) 1065–1074. [2] C.D. Beachem, Metall. Trans. 3 (1972) 437–451. [3] M. Nagumo, Mater. Sci. Tech. 20 (2004) 940–950. [4] S. Taketomi, R. Matsumoto, N. Miyazaki, J. of Mat. Res., 26, 10 (2011) 1269–1278. [5] S. Taketomi, R. Matsumoto, N.Miyazaki, Proc. of 2012 Hydrogen Conference, (2012) (submitted). [6] A.T. Yokobori, Jr., T. Iwadate, T. Isogai, Acta Metall. Mater., 41 (1993) 1405–1411. [7] A.T. Yokobori, Jr., T. Iwadate, T. Isogai, ASTM STP1207 (1994) 464–477. [8] J.P. Hirth, Metall. Trans. A. 11A (1980) 861–890.
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