PSI - Issue 38

Alexander Erbe et al. / Procedia Structural Integrity 38 (2022) 192–201 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

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4. Summary The influence of axis ratio and hold times on the biaxial fatigue life was investigated on cast steel cruciform specimens in the temperature range of 400 to 500 °C. In order to reproducibly generate a defined equivalent design strain at the center point of the specimen, a semi-automated parametrization routine was set up. The stress distribution in the gauge area is then post-assessed to find the maximum strain range in each experiment for comparison with other loading scenarios. The results obtained from the test series at 400 °C demonstrate the significant influence of axis ratio on the resulting hysteresis loops, cyclic hardening trends and crack initiation life. While axis ratios of = 0 and -0.5 lead to comparable specimen life as uniaxial tests, an increasing fatigue life benefit is observed for = 1 and -1. The strain hot spots calculated from the post-assessment coincide with the crack initiation sites observed on the specimen surface. The experiments conducted at 500 °C with and without hold time confirm the pattern in the influence of axis ratio. Furthermore, the introduction of 3 min hold times under tension and compression results in a life reduction which shows an identical order of axis ratio. Overall, the high reproducibility and comparability of the results obtained in this experimental campaign will lay the foundation to investigate and relate further service-related loading situations. Future work packages will expand to more complex loading scenarios such as thermomechanical and non-proportional loading. In addition, higher order assessment approaches will be utilized in order to cover the investigated factors implicitly within future assessment approaches. Acknowledgements The research project “ Improved Lifetime Assessment Accuracy under Consideration of Relevant Multiaxial Fatigue Loading Conditions for Gas Turbine Materials ” (IMPLANT No. 0324299) is undertaken by the Research Centre Jülich (FZJ) with the project management agency Jülich. The project is supported by the Federal Ministry for Economic Affairs and Energy (BMWi). Special thanks to the colleagues from Siemens Energy for the fruitful discussions, supplied material and their contribution to the project funding. References Cui, L., P. Wang, H. Hoche, A. Scholz, C. Berger: The influence of temperature transients on the lifetime of modern high-chromium rotor steel under service-type loading, Materials Science and Engineering: A, 560, 2013, pp.767-780 T. Itoh, M. Sakane, M. Ohmani: High temperature multiaxial low cycle fatigue o fcruciform specimen, Journal of Engineering Materials and Technology, 1994, pp 90-98 [KUL15] D. Kulawinski: Biaxial-planare isotherme und thermo-mechanische Ermüdung an polykristallinen Nickelbasis-Superlegierungen, Dissertation TU Freiberg, 2015 [LYS12] Lyschik, M.: Schädigungsbeschreibung an massiven heißgängigen Kraftwerkskomponenten bei Anfahrvorgängen am Beispiel des Werkstoffes 23CrMoNiWV8-8. Zugl.: Darmstadt, Techn. Univ., Diss., 2012. Aachen: Shaker (Berichte aus der Werkstofftechnik, 2012,1). A. Simon, A. Scholz, C. Berger: Validation of creep fatigue lifetime calculation methods for the application to steam turbine rotors, Variable Amplitude Loading, 23 -26 March 2009, Darmstadt, Proceedings Volume I. Editors: C. M. Sonsino and P.C. McKeighan , DVM, pp 505/516, 2009 [SAK13] M. Sakane, S. Zhang, A. Yoshinari, N. Matsuda, N. Isobe: Multiaxial Low Cycle Fatigue for Ni-Base Single Crystal Super Alloy at High Temperature, In: Advanced Material Models for Structures, Springer, 2013, pp. 297-305 [ITO94] [SIM09] [CUI13]