PSI - Issue 42

Martin Matušů et al. / Procedia Structural Integrity 42 (2022) 102 – 109 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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of heat through the jaws of the testing machine, which is insufficient for the heat generated. Whichever is the truth, and although the linear temperature increase R s could be evaluated to replace T s in some way, the conclusion is that the limiting energy is not constant in these setup conditions. 4. Summary Two methods estimating the experimental fatigue response based on the self-heating effect were analyzed. They are based on observing the temperature evolution during cyclic loading of a specimen with a constant amplitude of stress. The utilized specimens were manufactured from 42CrMo4+QT steel, the thermal response of which was different than anticipated. Contrary to common findings, it presents the second phase of temperature response not with the constant measured temperature, but with behavior closer to steady temperature increase. The recorded parameters of initial rate of the temperature growth R 0 and the rate of the temperature increase in the second phase of the temperature evolution R s were evaluated to determine whether they could be used to estimate the fatigue limit. The method for its detection was based on the proposal made by Huang et al. (2017) on minimizing the radius of curvature of the S-H function, originally in the ∆ T s -  a graph. The method utilizes an unbiased approach to find a breaking point in the expected exponential evolution. If applied here to R 0 -  a or R s -  a graphs, the detected breakpoints cannot be claimed to represent fatigue limits as they are obviously higher. The second method is discussed, based on a parameter called the limiting energy; see Fargione (2001). Fargione assumes that the limiting energy is independent of the load amplitude. In these setup conditions and for this material, this is not the case. The limiting energy is not invariant of the stress amplitude for at least the A01-A03 series, and only A04 could comply to the original expectations. Acknowledgements This work has been supported by 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 Grant Agency of the Czech Technical University in Prague, under grant No. SGS20/158/OHK2/3T/12. References J. Kohout and S. Věchet, 2001. A new function for fatigue curves characterization and its multiple merits. Int. J. Fatigue 23 (2) , 175– 83. Fargione, G., 2001. Rapid determination of the fatigue curve by the thermographic method, Int. J. Fatigue, 24 (1), 11-19. Amiri M. and Khonsari M., 2010. Life prediction of metals undergoing fatigue load based on temperature evolution, Materials Science and Engineering: A, 527(6), 1555-1559. G. Meneghetti, 2007. Analysis of the fatigue strength of a stainless steel based on the energy dissipation. Int. J. Fatigue, 29(1), 81- 94. G. La Rosa and A. Risitano, 2000. Thermographic methodology for rapid determination of the fatigue limit of materials and mechanical components, Int. J. Fatigue, 22 (1), 66 - 73. M. P. Luong, 1998. Fatigue limit evaluation of metals using an infrared thermographic, Mechanics of Materials, 28 (1 - 4), 155- 163. Prochazka, R. and Dzugan J., 2017. Fatigue limit evaluation of structure materials based on thermographic analysis, Procedia Structural Integrity 7 ,315 - 320. Douello, C., Balandraud, X., Duc, E., Verquin, B., Lefebvre, F. and Sar, F., 2019. Fast fatigue characterization by infrared thermography for additive Manufacturing. Procedia Structural Integrity 19, 90 -100. Klesnil, M., Lukáš, P., 1992. Fatigue of metallic materials, 2nd rev. Ed., Elsevier, Amsterdam . Munier, R., Doudard, C., Calloch, S., Weber, B., 2017. Identification of the micro - plasticity mechanisms at the origin of self - heating under cyclic loading with low stress amplitude . Int. J. Fatigue, 103, 122- 135. Fernández - Canteli, A., Castillo, E., Argüelles, A., Fernández, P. and Canales, M., 2012. Checking the fatigue limit from thermographic techniques by means of a probabilistic model of the epsilon – N field, Int. J. Fatigue, 39 109 -115. Huang, J., Pastor, M., Garnier, C. and Gong, X., 2017. Rapid evaluation of fatigue limit on thermographic data analysis, Int. J. Fatigue, 104, 293 301. Khonsari, M. and Amiri, M., 2010. Rapid determination of fatigue failure based on temperature evolution: Fully reversed bending load, Int. J. Fatigue, 32(2), 382 - 389 . Wang, X.G., Crupi, V., Jiang, C., Feng, E.S., Guiglielmino, E. and Wang, C.S., 2017. Energy - based approach for fatigue life prediction of pure copper, Int. J. Fatigue, 104, 243 -250. Pyttel, B., Schwerdt, D. and Beger, C., 2011. Very high cycle fatigue – Is there a fatigue limit?, Int. J. Fatigue, 33, 49 -58.¨