13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- for the reasons mentioned above. In the present study, we have not yet obtained the full understanding on the mechanisms by which the fatigue properties are influenced by the test conditions such as RB, US and frequencies. It is believed that such effects involve some rate-controlled processes like the diffusion and trapping of H atoms in different microstructures. (a) <100> grain. (b) <111> grain. (c) {100} fracture in <111> grain. Fig. 14 Crytallographic geometries. Thompson tetrahedron is used in (a) and (b). 5. Summary The present study shows that extruded 7075 T6 Al alloy exhibits the deterioration of fatigue strength in high humidity environment. However the fracture mode strongly depends not only on the history of the metalworking and heat treatment, but also on the test conditions. The results of EBSD and XRD analyses indicate that these differences may arise from the grain size, texture structure and dislocation density. In particular, the shear mode cracking with the angle of 35o from loading axis can be correlated with the crytallographic geometry of slips which are selected in the texture strongly aligned in <111> direction. In order to interpret the whole phenomena including the test conditions, more analyses taking into the characteristics of microstructures will be needed. References [1] I.J. Polmear, Light Alloys, Second Edition, Edwald Arnold, London, 1989. [2] N.E. Frost, K.J. Marsh, L.P. Pook, Metal Fatigue, Dover, New York, 1999. [3] N. Kawagoshi, T. Fukudome, Y. Nakamura, Y. Ozono, M. Goto, J JSME A, 76 (2010) 938-946. [4] K. Kariya, N. Kawagoishi, T. Fukudome, Y. Nakamura, E. Kondo, J-JSMS, 60 (2011) 339-344. [5] N. Kawagoishi, K. Kariya, Q. Chen, M. Goto, Y. Nakamura, J-JSMS, 60 (2011) 890-897. [6] K. Kariya, N. Kawagoishi, S. Furumoto, Y. Nakamura, E. Kondo, J-JSMS, 60 (2011) 1015-1022. [7] K. Kariya, H. Maeda, N. Kawagoishi, Q. Chen, Y. Nakamura, K. Morino, J-JSMS, 61 (2012) 712-718. [8] A. Guinier, X ray Diffraction in Crystals, Imperfect Crystals, and Amorphous Bodies, Dover, New York, 1994. [9] C.D. Beacham, Met Trans, 3 (1972) 437-451. [10]H.K. Birnbaum, P. Sofronis, Mater Sci Eng, A176 (1994) 191-202. [11] P.J. Ferreira, I.M. Robertson, H.K. Birnbaum, Acta Mater, 47 (1999) 2991-2998. [12]G.M. Bond, I. M. Robertson and H. K. Birnbaum, Acta Metall, 35 (1987) 2289-2296. [13]K. Kariya, Doctoral Thesis, Kagoshima University, Japan (2012). [100] [111] [111] [011] [011] x y z ° 35.3 ° 35.3 [111] z [11 1] ° 35.3 ° 35.3 [111] [111] y [211] ° 35.3 x[011] ° 35.3 [100] [111] [11 1] [111] [011] b b
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