PSI - Issue 75

Jan Papuga et al. / Procedia Structural Integrity 75 (2025) 289–298 Author name / Structural Integrity Procedia (2025)

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• The relative stress gradient (RSG) approach remains the optimum solution. Some its versions outperform other variants. Both the original and new proposals of its use defined in FKM-Guideline v. 6 [1] can be recommended. • The use of the theory of critical distances (TCD) in any analysed variant did not provide results which would prove its usability across the whole data set if the critical distance is derived from the push-pull load cases. It is apparent that the concept of a single critical distance valid for all notch configurations with so broad span of notch acuity cannot provide results of acceptable quality. The use of the critical distance derived from the bending load cases diminishes the problems to some extent, but the quality of fatigue estimation remains worse if compared to other concepts analysed here. • The new concept of the critical volume approach yields results slightly worse than the best performing RSG approach but better than its worst representatives. The documented results show that using only the critical volume in its absolute value need not be sufficient to describe both notch and size effect. • Considering the low maturity of the proposed critical volume solution and its results not far away from the best performing standard solutions, the only conclusion can be that there is a vast space for improving the quality of the computational solution describing the notch and size effects. • Any conclusions drawn here are tentative due to the fact how small is the validation data set derived for a single material. To reach more general conclusions, the number of data items in the data set used for evaluation should increase in multiples. Acknowledgements The authors from FME CTU in Prague acknowledge support from the Czech Science Foundation within project 23-06130K and from the Grant Agency of the Czech Technical University in Prague within project SGS23/156/OHK2/3T/12. The team from VŠB - TU Ostrava was supported by Specific Research „Computational and Experimental Modeling in Applied Mechanics and Biomechanics“ (SP2025/048). References [1] R. Rennert, E. Kullig, M. Vormwald, A. Esderts, D. Siegele, FKM Richtlinie - Rechnerischer Festigkeitsnachweis für Maschinenbauteile aus Stahl, Eisenguss- und Aluminiumwerkstoffen, 6th, überarbeitete Ausgabe ed., Forschungskuratorium Maschinenbau, Frankfurt / Main, 2012. [2] M. Nesládek, F. Fojtík, M. Mžourek, J. Papuga, Notched structural steel specimens assessed by selected fatigue analysis metho ds, Journal of Constructional Steel Research 219 (2024) 108789. https://doi.org/10.1016/j.jcsr.2024.108789. [3] R. Kuguel, Highly stressed volume of material as fundamental parameter in fatigue strength of metal members, (1960). http://hdl.handle.net/2142/111879. [4] Y. Ai, S.-P. Zhu, D. Liao, J.A.F.O. Correia, A.M.P. De Jesus, B. Keshtegar, Probabilistic modelling of notch fatigue and size effect of components using highly stressed volume approach, International Journal of Fatigue 127 (2019) 110 – 119. https://doi.org/10.1016/j.ijfatigue.2019.06.002. [5] J.E. Shigley, C.R. Mischke, R.G. Budynas, Mechanical Engineering Design, McGraw-Hill, 2004. https://books.google.cz/books?id=A2mjQR6Nwn4C. [6] Anon., FEMFAT 4.4 Basic Theory Manual, Magna Steyr Engineering, 2006. [7] J.-C. He, S.-P. Zhu, D. Liao, X.-P. Niu, J.-W. Gao, H.-Z. Huang, Combined TCD and HSV approach for probabilistic assessment of notch fatigue considering size effect, Engineering Failure Analysis 120 (2021) 105093. https://doi.org/10.1016/j.engfailanal.2020.105093. [8] L. Serri, Critical volume approach in multiaxial fatigue assessment of notched specimens, Master thesis, University of Padova, 2024. https://hdl.handle.net/20.500.12608/80344. [9] J. Papuga, F. Fojtík, Multiaxial fatigue strength of common structural steel and the response of some estimation methods, International Journal of Fatigue 104 (2017) 27 – 42. https://doi.org/10.1016/j.ijfatigue.2017.07.001. [10] J. Kohout, S. Věchet, A new function for fatigue curves characterization and its multiple merits, International Journal of Fa tigue 23 (2001) 175 – 183. https://doi.org/10.1016/S0142-1123(00)00082-7.