Issue 19

L. Kunz et alii, Frattura ed Integrità Strutturale, 19 (2012) 61-75; DOI: 10.3221/IGF-ESIS.19.06 74 The fatigue cracks in UFG structure initiate at cyclic slip bands, which are observed under all types of loading and from the LCF to gigacycle region. With decreasing severity of cyclic loading their density decreases and their appearance slightly changes. However, the details of the fatigue crack initiation mechanism are not sufficiently known; particularly, no specific dislocations structures were found beneath the slip bands. The up-to now state of knowledge favours the role of the grain boundary sliding in the crack initiation process. The available data on fatigue crack propagation resistance are somewhat contradictory. Both a higher and lower sensitivity to the crack growth in the threshold region (when compared to CG Cu) was found. The mechanism of the crack propagation and its relation to the microstructure and its changes should be the topic of further goal-directed investigations. A CKNOWLEDGMENT he Czech Science Foundation under contract 108/10/2001 financially supported this work. This support is gratefully acknowledged. R EFERENCES [1] M.C. Murphy, Fatigue of Engng. Mater and Struct., 4 (1981) 199. [2] G. Saada, Mat. Sci. Eng. A.,400-401 (2005) 146. [3] V. M. Segal, Mat. Sci. Eng. A., 197 (1995) 157. [4] R. Z.Valiev, T.G. Langdon, Prog Mater Sci., 51 (2006) 881. [5] J.T. Wang, et al. (Eds.), Nanomaterials by severe plastic deformation: NanoSPD5. TTP Publications LTD, Switzerland, (2011). [6] A. Vinogradov, Y. Kaneko, K. Kitagawa, S. Hashimoto, V. Stolyarov, R. Valiev, Scripta Mater., 36 (1997) 1345. [7] S. R. Agnew, A. Yu. Vinogradov, , S. Hashimoto, J. R. Weertman, J. Electronic Mater., 28 (1999) 1038. [8] R.Z.Valiev, R.K. Islamgaliev, I.V. Alexandrov, Prog. Mater. Sci., 45 (2000) 103. [9] Y. T. Zhu, T. G. Langdon, JOM, (2004) 58. [10] B. Mingler, H.P. Karnthaler, M. Zehetbauer, R.Z. Valiev, Mat. Sci. Eng. A, 319-321 (2001) 242. [11] A. Vinogradov, S.Hashimoto, Mater. Trans.,42 (2001) 74. [12] A. J. Wilkinson, P. B. Hirch, Micron, 28 (1997) 279. [13] M. Besterci, T. Kvackaj, L. Kovác, K. Sulleiová, Kovove Mater., 44 (2006) 101. [14] M. Goto, S. Z. Han, S. S. Kim, Y. Ando, N. Kwagoishi, Scripta Mat., 60 (2009) 729. [15] A. Vinogradov, S. Hashimoto, V. Patlan, K. Kitagawa, Mat. Sci. Eng. A., 319 (2001) 862. [16] P. Lukáš, L. Kunz, Mat. Sci. Eng., 85 (1987) 67. [17] A. W. Thompson, W. A. Backofen, Acta Met., 19 (1971) 597. [18] P. Lukáš, M.Klesnil, Mat. Sci. Eng., 11 (1973) 345. [19] J. Polák, M.Klesnil, Mat. Sci. Eng., 63 (1984) 189. [20] V. T. Kuokkala, P. Kettunen, Fat. Fract. Eng. Mater. and Struct., 8 (1985) 277. [21] P. Lukáš, L. Kunz, Mat. Sci. Eng. A., 103 (1988) 233. [22] M. Klesnil, P. Lukáš, Fatigue of metallic materials, Academia/Elsevier, Prague, Czech Republic (1992). [23] H. W. Höppel, R. Z. Valiev, Z. Metallkd., 93 (2002) 641. [24] L. Kunz, P. Lukáš, M. Svoboda, Mat. Sci. Eng. A., 424 (2006) 97. [25] H. W. Höppel, H. Mughrabi, A. Vinogradov, In: Bulk Nanostructured materials, Zehetbauer, M. et al. (Eds.), Wiley- VCH Verlag, Weinheim (2009) 481. [26] H. Mughrabi, H. W. Höppel, Int. J. Fatigue, 32 (2010) 1413. [27] S. Z. Han, M. Goto, Ch. Lim, S.H. Kim, S. Kim, J of Alloys and Comp., 434-435 (2007) 304. [28] S. Z. Han, M. Goto, Ch. Lim, S.H. Kim, S. Kim, J of Alloys and Comp., 483 (2009) 159. [29] M. Goto, S. Z. Han, T. Yakushiji, S. S. Kim, C. Y. Lim, Int. J. Fatigue, 30 (2008) 1333. [30] S. R. Agnew, J. R. Weertman, Mat. Sci. Eng. A., 244 (1988) 145. [31] H. W. Höppel, M. Kautz, C. Xu, M. Murashkin, T. G. Langdon, R. Z. Valiev, H. Mughrabi, Int. J. Fatigue, 28 (2006) 1001. T