PSI - Issue 2_B

P.-M. Hilgendorff et al. / Procedia Structural Integrity 2 (2016) 1156–1163 Hilgendorff et al./ Structural Integrity Procedia 00 (2016) 000–000

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induced martensitic phase transformation is determined by simulated plastic sliding deformation and each martensite nucleus is directly represented in the modeled microstructure taking into account the transformation-induced volume expansion. Following the kinetic model of Olsen & Cohen (1975) the amount of generated martensite is affected by temperature-dependent parameters describing the influence of the stacking fault energy and chemical driving force. Both parameters were characterized based on investigations applying tensile tests. A first simulation study showed that with increasing temperature the accumulated irreversible plastic deformation in shear bands is enhanced, while martensitic transformation and its positive effect by obstruction of plastic deformation is reduced. Since the irreversible plastic deformation is decisive for crack initiation, the rise of temperature shows a negative impact on the fatigue endurance. This confirms the reduction of VHCF strength at higher temperatures. However, a comparison to the experimentally measured martensite volume fraction revealed that the kinetic model based on tensile tests is not capable to describe the significantly less influence of temperature on the martensitic transformation during VHCF loading (notwithstanding the effect of plastic deformation). After adjusting the temperature dependence of martensitic transformation directly to experimental measurement, it could be recognized that for the cyclic simulations at two different temperatures with stress amplitudes at the corresponding VHCF strengths an approximately same increase of accumulated irreversible sliding deformation was calculated. This result indicated the same progress of irreversible plastic deformation at the VHCF strengths. The calculated curve for the irreversible plastic deformation could be understood as a temperature-independent ‘limit curve’ for the failure of the metastable austenitic stainless steel in the VHCF regime. Acknowledgements The authors gratefully acknowledge financial support of this study by Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority program Life ∞ (SPP 1466). References Bathias, C., 1999, There is no infinite fatigue life in metallic materials, Fatigue Fract. Eng. M., 22(7), 559–565. Bogers, A.; Burgers, W., 1964, Partial dislocations on the {110} planes in the B.C.C. lattice and the transition of the F.C.C. into the B.C.C. lattice, Acta Metall., 12(2), 255–261. Byun, T.; Hashimoto, N.; Farrell, K., 2004, Temperature dependence of strain hardening and plastic instability behaviors in austenitic stainless steels, Acta Mater., 52(13), 3889–3899. 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