PSI - Issue 7

Dalila Dimaggio et al. / Procedia Structural Integrity 7 (2017) 198–205 D. Dimaggio et al. / Structural Integrity Procedia 00 (2017) 000–000

205

8

Figure 6 HSV 90% calculation at dovetail-refined mesh

7. Conclusions This study investigated the fatigue behaviour of a rotor blade precipitation-hardening steel at different stress ratios (0 ≤ R ≤ 0.7) under constant and near -service loading by using different load types (axial, bending) to investigate the mean stress sensitivity of the material and the influence of local stress distribution on the fatigue strength. This approach was used to evaluate the fatigue behaviour for real components with typical geometry and operating loads of the dovetails of last stage turbine blades. An ad-hoc MATLAB® software has been developed which is able to evaluate the HSV 90% on a real component basing on FE elastic analysis results. The HSV 90% has been used to evaluate the local stress influence on a real case study leading to a component life estimation, in agreement with the life of the steam turbine. The reliability of the notch support effect is guaranteed as long as the notched specimens’ geometry is conceived in order to be representative of the target critical region, especially from the point of view of the stress concentration factor and stress gradient. The HSV approach represents the experimental results for the investigated material with high accuracy. In cases where no refined mesh is available the HSV approach should be replaced by a stress gradient approach. Acknowledgements The authors express their gratitude to Luca Bordo, Andrea Cavicchi, Mauro Macciò, Roland Muecke, Eleonora Poggio, Alessio Tomasella, Laura Traversone, Paolo Villari and David Day for the fruitful technical discussion. Carla Penno and Ansaldo Energia management are acknowledged for their support to the activity. References [1] Mishra, R. K., Thomas, J., Srinivasan, K., Nandi, V., Bhatt, R. R.: “Failure analysis of an un-cooled turbine blade in an aero gas turbine engine”, Engineering Failure Analysis 79, (2017): pp. 836-844. [2] Neuber H., Kerbspannungslehre, 2nd ed., Berlin, Göttingen, Heidelberg, Springer, 1958. [3] Rainer G., Errechnen von Spannungen in Schweißverbindungen mit der Methode der Finiten Elemente. PhD-Thesis, TH Darmstadt, 1978. [4] Sonsino, C.M., Course of S-N-curves especially in the high-cycle fatigue regime with regard to component design and safety, International Journal of Fatigue 29, (2007): pp. 2246-2258. [5] Haibach, E., Betriebsfestigkeit: Verfahren und Daten zur Bauteilberechnung. Berlin, Heidelberg, New York, Springer, 2006. [6] Radaj, D., Vormwald, M., “Ermüdungsfestigkeit”. Berlin, Heidelberg, New York, Springer, 2007. [7] Kuguel R., “A Relation between Theoretical Stress Concentration Factor and Fatigue Notch Factor Deduced From the Concept of Highly Stressed Volume”, Proc. ASTM vol. 61, (1961): pp. 732-744. [8] Sonsino, C.M., Kaufmann, H., Grubisic, V, Transferability of Material Data for the Example of a Randomly Loaded Forged Truck Stub Axle, SAE Technical Paper 970708, (1997). [9] FKM Richtlinie: English language version of “Rechnerischer FestigkeitS-Nachweis für Maschinenbauteile aus Stahl, Eisenguss- und Aluminiumwerkstoffen” VDMA, 6th edition, (2012), ISBN: 978-3-8163-0649-8. [10] Edelsbrunner H., Mücke E.P., Three dimension alpha shapes. Manuscript UIUCDCS-R-92-1734 Dept. Comput.Sci. Univ. Illinois, Urbana Champaign,IL,1992