PSI - Issue 37

Carl Fällgren et al. / Procedia Structural Integrity 37 (2022) 948–955 Carl Fällgren / Structural Integrity Procedia 00 (2019) 000 – 000

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7. Conclusion Within the scope of the research project described, fundamental data was obtained for the characterisation of ultra high-strength steels. The experimental results obtained from testing of the autofrettaged component-like specimens show that for the thicker specimen geometry studied, an increase in fatigue strength of more than a factor of 2 is possible with the ultra-high-strength steels compared to conventionally used steels. Based on the material modelling where the cyclically stabilised curve, obtained from cyclic material testing, was used as initial unloading curve during the autofrettage simulation, residual stress distributions along the crack propagation paths of the autofrettaged specimens were calculated. The data was used to calculate crack initiation lives with the local strain approach. Reasonable results were achieved compared to the fatigue limits obtained from experiments for non-autofrettaged specimens. The examination of the crack propagation behaviour and the possible occurrence of crack arrest was performed with an approach based on linear-elastic fracture mechanics. The results slightly overestimate the experimentally obtained results. Also the crack propagation lives were calculated with the strip yield model. The results showed good agreement with the experimental data. Still, as all calculation results for autofrettaged specimens are based on the residual stress distribution, the simulation of the autofrettage process and therefore the material modelling is of crucial importance for the derived results. Acknowledgements This work is part of a research project that was carried out in the framework of the industrial collective research programme (IGF No. 19790 N). It was supported by the Federal Ministry for Economic Affairs and Energy (BMWi) through the AiF (German Federation of Industrial Research Associations eV) on the basis of a decision by the German Bundestag References Bauschinger J. (1886) Über die Veränderung der Elastizitätgrenze und der Festigkeit des Eisens und Stahls durch Strecken, Quetschen, Erwärmen, Abkühlen und durch oftmals wiederholte Belastung, Mitteilungen des mechanischen technischen Labors der Technischen Hochschule München 13, 1886. Beier, H. Th., Bergmann, J. W., Diemar, A., Kleemann, A., Kleemann, S., Panic, D., Richter, T., Schlitzer, T., Vormwald, M. (2017). Einfluss der Betriebstemperatur auf die Dauerfestigkeit autofrettierter Bauteile und einsatzgehärteter Bauteil von Dieseleinspritzsystemen: Vorhaben Nr. 1160. Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV), Frankfurt. Besseling, J. F. (1958). A theory of elastic, plastic, and creep deformations of an initially isotropic material showing anisotropic strain-hardening, creep recovery, and secondary creep. Chen, P. C. T. (1986). The Bauschinger and hardening effect on residual stresses in an autofrettaged thick-walled cylinder. Journal of Pressure Vessel Technology, 108(1): 108-112 (5 pages). Fiedler, M., & Vormwald, M. (2016). Considering fatigue load sequence effects by applying the Local Strain Approach and a fracture mechanics based damage parameter. Theoretical and Applied Fracture Mechanics, 83, 31-41. Fiedler, M., & Vormwald, M. (2018). Introduction to the new FKM guideline which considers nonlinear material behaviour. In MATEC Web of Conferences (Vol. 165, p. 10014). EDP Sciences. Herz, E., Thumser, R., Bergmann, J. W., & Vormwald, M. (2006). Endurance limit of autofrettaged Diesel-engine injection tubes with defects. Engineering fracture mechanics, 73(1), 3-21. Herz, E., Hertel, O., & Vormwald, M. (2011). Numerical simulation of plasticity induced fatigue crack opening and closure for autofrettaged intersecting holes. Engineering Fracture Mechanics, 78(3), 559-572. Ramberg, W., & Osgood, W. R. (1943). Description of stress-strain curves by three parameters. Thumser, R., Bergmann, J. W., & Vormwald, M. (2002). Residual stress fields and fatigue analysis of autofrettaged parts. International Journal of Pressure Vessels and Piping, 79(2), 113-117. Thumser, R. (2009). Simulation des Rissfortschritts in autofrettierten und nicht autofrettierten Bohrungsverschneidungen auf der Grundlage der linear-elastischen Bruchmechanik. Vormwald, M., Schlitzer, T., Panic, D., & Beier, H. T. (2018). Fatigue strength of autofrettaged diesel injection system components under elevated temperature. International Journal of Fatigue, 113, 428-437.