PSI - Issue 19

Jan Papuga et al. / Procedia Structural Integrity 19 (2019) 405–414 Author name / Structural Integrity Procedia 00 (2019) 000–000

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6. Conclusion Three different methods for predicting the fatigue strength of notched structures were evaluated – the classic nominal approach represented by the Peterson and Buch solutions, various variants of the critical distance (TCD) point method and of the relative stress gradient approach (RSG). The test set comprising of 5 different notch topologies with notch root radius spanning from 0.4 mm (fillet notch) to 2.0 mm (hole) was used. All configurations relate to 2124-T851 aluminum alloy, a single plate of which was used for manufacturing all evaluated specimens. The outcome of the computational testing can be summarized in the following items:  The Buch solution is providing well-balanced prediction, surprisingly thanks to the fact that it enables to zeroize the effect of the notch root radius.  The TCD approaches show too large potential scatter of critical distances based on various input data. The difference between individual variants of the critical distance derivation are not very pronounced to claim some variant clearly better, though the calibration routine was assumed to provide more realistic values of the critical distance. For the common practical use, the extreme prediction difference if only some partial input (  Kth value or just one notch type) is found, can be viewed as negative aspect.  The RSG approaches result generally in less scattered results than the TCD approaches, and above all the FKM based method seems interesting thanks to its low range of errors, and general conservativeness. Because its mean relative errors are essentially conservative, it cannot be compared directly with the Buch method, where the optimization goal function was set to achieve the prediction well-balanced around zero prediction error.  These outputs were obtained for one material only, which thus features one notch sensitivity. A broader comparison is necessary to see, whether these conclusions can be found universal. Acknowledgements Authors acknowledge support from the ESIF, EU Operational Programme Research, Development and Education, from the Center of Advanced Aerospace Technology (CZ.02.1.01/0.0/0.0/16_019/0000826), Faculty of Mechanical Engineering, Czech Technical University in Prague, and from the Grant Agency of the Czech Technical University in Prague, grant No. SGS17/175/OHK2/3T/12. References Anon. 2006. FEMFAT 4.4 Basic Theory Manual. Magna Steyr Engineering. Buch, A., 1984. Notch-Size Effect in Fatigue of Steel Specimens – Verification of Some Calculation Methods. Z. Werkstofftech. 15, 338-348. Kunz, J.: Aplikovaná lomová mechanika. Praha, Česká technika – nakl. ČVUT 2005. Logsdon, W. A.; Liaw, P. K., 1986. Tensile, fracture toughness and fatigue crack growth rate properties of silicon carbide whisker and particulate reinforced aluminium metal matrix composites. Engineering Fracture Mechanics 24, 5., 737-751. Papuga J. et al.: Summary of Experiments on 2124-T851 Realized Within FADOFF Project. [FAD/14/001]. FME, CTU in Prague and FME, VŠB TU in Ostrava 2014. Peterson, R.E., 1974. Stress Concentration Factors. John Wiley & Sons, New York. Rennert, R. et al.: FKM-Richtlinie – Rechnerischer Festigkeitsnachweis für Maschinenbauteile. [6. revised version], Frankfurt/Main, VDMA Verlag GmbH 2012. Schijve, J., 2009. Fatigue of Structures and Materials. Springer Science+Business Media, B.V. Susmel, L.; Taylor, D.: A novel formulation of the theory of critical distances to estimate lifetime of notched components in the medium-cycle fatigue regime. Fatigue Fract. Engng. Mater. Struct. 30 (2007), pp. 567-581.