13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- 7. Conclusions This paper presents experimental investigations on crack initiation and short crack propagation in Ti6Al4V and shows, how the results are used in a numerical model. Crack growth mainly occurs on single slip systems (basal or prismatic) although in some cases cracks are found on boundaries where no slip system could be assigned. The numerical approach considers these crack growth mechanisms and uses either the range of the crack tip slide displacement or the crack tip opening displacement to describe the crack propagation rate. The modeling results show excellent agreement with propagation data of observed cracks. By means of calculations of the microstructurally controlled short fatigue crack growth in artificially generated “virtual” microstructures the significance and effect of microstructure parameters can be identified and analyzed, providing a mechanism-based foundation for a purposeful material development towards higher fatigue resistance. Moreover, a statistical treatment of the calculation results in terms of the evaluation of the distribution of the number of loading cycles necessary to reach a critical stress intensity factor under given loading conditions forms a sound methodology for fatigue life assessment. Acknowledgement The authors would like to express their gratitude to Böhler Schmiedetechnik GmbH & Co KG for financially supporting the project and supplying the material. References: [1] R.R. Boyer, An overview on the use of titanium in aerospace industry. Mat Sci Eng A, A213 (1996) 103-114. [2] P.C. Paris, M.P. Gomez, W.E. Anderson, A rational analytic theory of fatigue. Trend Eng, 13 (1961) 9-14. [3] O.H. Basquin, The exponential law of endurance tests. Proc Annual Meeting ASTM, 10 (1919) 625-634 [4] L.F. Coffin, Fatigue at high temperatures. ASTM STP, 520 (1973) 744-782. [5] S.S. Manson, Fatigue: A complex subject-some simple approximations. J Exp Mech, 5 (1965) 193-226. [6] B. Künkler, O. Düber, P. Köster, U. Krupp, C.P. Fritzen, H.-J. Christ, Modelling of short crack propagation – transition from stage I to stage II. Eng Frac Mech, 75 (2008) 715-725. [7] G. Lütjering, J.C. Williams, Titanium (2nd Edition), Springe, Berlin-Heidelberg-New York, 2007. [8] S. Taira, K. Tanaka, Y. Nakai, A model of crack-tip slip band blocked by grain boundary. Mechanics Research Communications, 5 (1978) 375-381. [9] A. Navarro, E.R. de los Rios, Short and long fatigue crack growth: A unified model. Phil. Mag. A, 57 (1988) 15-36. [10]O. Düber, B. Künkler, U. Krupp, H.-J. Christ, C.P. Fritzen, Experimental characterization and two-dimensional simulation of short-crack propagation in an austenitic–ferritic duplex steel. Int. J. of Fatigue, 28 (2006) 983-992. [11]A.J. Wilkinson, S.G. Roberts, P.B. Hirsch, Modelling the threshold conditions for propagation of stage I fatigue cracks. Acta Mater, 46 (1998) 379-390.
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