13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- 5. Conclusions Simulation of cyclic loading to model fatigue is possible in MD. Already after very few cycles, essential changes in the system behavior were observed. Contrary to the first cycles, where reversible changes were dominant, not dissolving restructuring occurs in the sense of dislocations and remaining lattice defects or in other words, plasticity. Numerical simulations of the fatigue crack initiation and growth of martensitic steel, based on modified Tanaka-Mura, was presented. A simulation model related to the micro-crack nucleation along slip bands was presented. Results obtained by using the proposed simulation model were compared to high cycle fatigue tests and showed reasonably good agreement. Crack propagation simulation based on numerical integration of a power law equation, taking account of welding residual stresses, was implemented to welded stiffened panel specimens. The FE analysis of the stiffened panel specimens showed that high tensile residual stresses in the vicinity of a stiffener significantly increase Kres and Ktot. The simulated crack growth rate was higher in this region, which is in good agreement with experimental results. Compressive welding residual stresses decreased the total SIF value Ktot, and the crack growth rate between the two stiffeners. Residual stresses should thus be taken into account for a proper evaluation of SIFs and fatigue crack growth rates in welded stiffened panels. Acknowledgements This work was supported by the Deutsche Forschungsgemeinschaft (DFG) under Grant No. Schm 746/132-1. The support is gratefully acknowledged. References [1] J. Stadler, R. Mikulla, H.-R. Trebin, IMD: A software package for molecular dynamics studies on parallel computers, Int. J. Mod. Phys., 8 (1997) 1131. [2] G. Bonny, R.C. Pasianot, N. Castin, L. Malerba, Ternary Fe-Cu-Ni many-body potential to model reactor pressure vessel steels: First validation by simulated thermal annealing, Phil. Mag., 89 (2009) 3531–3546. [3] S. Grottel, G. Reina, C. Dachsbacher, T. Ertl, Coherent Culling and Shading for Large Molecular Dynamics Visualization, Computer Graphics Forum (Proceedings of EUROVIS 2010), 29(3) (2010) 953 – 962. [4] A. Stukowski, V.V. Bulatov, A. Arsenlis, Automated identification and indexing of dislocations in crystal interfaces, Modelling Simul. Mater. Sci. Eng., 20 (2012) 085007. [5] A. Stukowski, DXA user manual Version 1.3.4, (2010), http://dxa.ovito.org/README.txt [6] S. Glodez, N. Jezernik, J. Kramberger and T. Lassen, Numerical modelling of fatigue crack initiation of martensitic steel, Advances in Engineering Software, 41(5) (2010) 823-829. [7] WA. Wood, Fatigue in aircraft structures, Academic Press, New York, 1956. [8] M.E. Fine, R.O. Ritchie, Fatigue-crack initiation and near-threshold crack growth. In: M. Meshii (Eds.), Fatigue and microstructure, Metals Park (OH): ASM, 1978, pp. 245–278. [9] C. Laird, Mechanisms and theories of fatigue. In: M. Meshii (Eds.), Fatigue and microstructure. Metals Park (OH): ASM, 1978, pp. 149–203. [10]M. Klesnil, P. Lukas, Fatigue of metallic materials, Elsevier, New York, 1980, pp. 57–80. [11] H. Mughrabi, Rev Phys Appl, 23 (1988) 367–379. [12]H. Mughrabi, In: K.S. Chan, P.K. Liaw, R.S. Bellows, T. Zogas, W.O. Soboyejo (Eds.), Fatigue: David L. Davidson symposium, Warrendale (PA): TMS, 2002, pp. 3–15. [13]D.L. Davidson, K.S. Chan, Crystallography of fatigue crack initiation in Astrology at ambient
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