PSI - Issue 23

A.A. Shanyavskiy et al. / Procedia Structural Integrity 23 (2019) 63–68 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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As the ratio of σ – 1 /σ 0.2 increases, the stress interval for the metal, where the HCF regime can be realized due to damage accumulation processes localized in the surface layer, decreases. When σ – 1 /σ 0.2 = 1, a “degeneration” of the mesoscopic scale level occurs and the transition from VHCF is realized directly to LCF regime. The HCF regime is located inside the bifurcation region and characterized by a multimodal fatigue life distribution as shown by Mughrabi (2002).

4. Conclusions

1. The development of metal fatigue process occurs in the direction of an increase in the stress level, and it is consistently implemented at the micro-, meso- and macroscopic scale levels corresponding to the VHCF, HCF and LCF regimes, respectively. 2. Between scale levels, there are the bifurcation regions with different energy dissipation methods, where the bimodal fatigue life distribution is realized with different probabilities for one of two damage accumulation mechanisms at a specified stress level. 3. The “ fatigue limit ” , as a metal characteristic, does not exist. It is one of the stresses corresponding to the bifurcation region, which can be implemented depending on the ratio of σ – 1 /σ 0.2 when the transition takes place from VHCF to either HCF or LCF. 4. Damage accumulation modeling based on the S - N curve with a one-scale approach is incorrect since under unsteady loading conditions it is necessary to use factors specified for each scale level. 5. Comparing material behavior in the case of crack origination on the surface (HCF and LCF) and subsurface (VHCF) one can be concluded that it is in the VHCF regime that a metal shows its ability to resist cyclic loading, since only the metal state determines its durability without any environmental influence on metal fatigue behavior. Bastenair, F., 1973. Aspect aleatoire du phenomen de fatigue. Description mathematique at traitement statistique, in: “La fatigue dans les materiaux. Aspects physiques et mechaniques” . In: Boiteux, H. - J. (Ed.). Edisciense, Paris, pp. 107–145. Bathias, C., Paris, P.C., 2005. Gigacycle fatigue in mechanical practice. Marcel Dekker, New York, 305 p. Ivanova, V.S., Terentiev, V.F., 1975. The nature of metal fatigue. Metallurgy, Moscow, 455 p. (Russian) Miner, M.A., 1945. Cumulative damage in fatigue. Journal of Applied Mechanics, A159–A164. Mughrabi, H., 2002. On ‘multi - stage’ fatigue life diagrams and the relevant life - controlling mechanisms in ultrahigh - cycle fatigue. Fatigue and Fracture of Engineering Materials and Structures 25(8 - 9), 755–764. Panin, V.E., 2000. Synergetic principles of physical mesomechanics. Physical Mesomechanics 3(6), 5–34. Panin, V.E., 2015. Physical mesomechanics of materials. TGU, Tomsk, vol. 1, 460 p.; vol. 2, 462 p. (Russian) Sakai, T., Ochi, Y., 2004. Proceedings of the Third International Conference on Very High Cycle Fatigue (VHCF - 3), September 16 - 19, 2004, Ritsumeikan University, Kusatsu, Japan. The Society of Materials Science, Japan, 690 p. Shabalin, V.I., 1967. Experimental study of the fatigue curve shape, in: “Metal strength under cyclic loading conditions” . In: Ivanova, V.S. (Ed.). Nauka, Moscow, pp. 162–169. (Russian) Shanyavskiy, A., 2010. Bifurcation diagram for in - service fatigued metals. Procedia Engineering 2, 241–250. Shanyavskiy, A., Zaharova, T., Potapenko, Yu., 2007. The nature of multi - modal distribution of fatigue durability for titanium alloy VT9, 4th International Conference on Very High Cycle Fatigue (VHCF - 4), Ann Arbor, Michigan, USA, 325–330. Shanyavskiy, A.A., 2007. Modelling of metal fatigue fracture. Synergetics in aviation. Monografi, Ufa, 500 p. (Russian) Shanyavskiy, A.A., 2018. Equivalent uniaxial cyclic tensile stress as an energy characteristic of metal fatigue under multiparameter loading. Physical Mesomechanics 21(6), 483–491. Shanyavskiy, A.A., Soldatenkov, A.P., 2019. Scales of the fatigue limit of metals. Physical Mesomechanics 22, 44–53. (Russian). Stulen, F.B., 1951. On the statistical nature of fatigue. ASTM Symposium on Statistical Nature of Fatigue, 1951, STP No. 121, 23–44. Wöhler, A., 1863. Über die Versuche zur Ermittlung der Festigkeit von Achsen, welche in den Werkstätten der Niederschlesisch - märkischen Eisenbahn zu Frankfurt an der Oder angestellt sind. Zeitschrift für Bauwesen 13, 233–258. Zakharova, T.P., 1974. To the question of statistical nature of fatigue damage of steels and alloys. Strength of materials 4, 17–23. (Russian) Zakharova, T.P., 1981. Statistical nature of fatigue, in: “Structural strength of machine and elements for gas - turbine engine” . In: Birger, I.A., Balashov, B.F. (Eds.). Mashinostroenie, Moscow, 23–29. (Russian) Acknowledgements The work was supported by RSF, grant N19-19-00705. References