PSI - Issue 2_A

Mikhail V. Bannikov et al. / Procedia Structural Integrity 2 (2016) 1071–1076 Author name / StructuralIntegrity Procedia 00 (2016) 000–000

1076

6

the spectra of electrons reflected from the fracture in the scanning electron microscope allowed us to determine that the liquid metal penetrates into the material to a depth of about 200 microns and resides exclusively in the center of crack initiation. While crack grows further into the material it is not affected by the surfactant. In one of the samples we also observed two centers of crack initiation at one site, which is common to fatigue failure by corrosion by Palin-Luc (2010), and is also observed in the case when crack formation occurs at a distance from the region of maximum stresses. Thus, we can say that the effect of liquid metal embrittlement is observed only at the stage of fatigue crack initiation, and its propagation deep into the sample is governed by the classical Paris law. This fact can also be supported by the results obtained by Shevelya (1967) for low and high cycle fatigue loading, when a decrease of fatigue strength was takes place only a few times because the stage of fatigue crack initiation in such regimes is significantly shorter. 4. Conclusion It can be concluded that the effect of liquid-metal embrittlement occurs mainly at the stage of fatigue crack initiation and the process of the crack growth is governed by the classical Paris law. This fact can also be substantiated by the results obtained by Naimark (2014) under low- and high-cycle fatigue loading regimes, when a decrease in durability (several times) was observed despite the fact that the stage of fatigue crack initiation under low-cycle fatigue loading is significantly shorter. Taking into account the peculiarities of the Rehbinder effect, which consist in qualitative changes of the multi-scale kinetics of dislocation ensemble in the surface layer making contact with a surfactant, the effect of surface-active media (molten metal) on the fatigue life of Armco iron in the gigacycle regime can be associated with a qualitative change in the role of the surface. The property of the surface, as the high power "drain" for defects is significantly reduced in the case when the proximity of the chemical potentials of the solid and surfactant provides "adiabatic" scenario for the process of damage accumulation in the bulk of material. Acknowledgement This work was supported by grants from RFBR № 15-08-08921, 16-41-590892, 16-48-590534 . References Bathias, C., 2006. Piezoelectric fatigue testing machines and devices. International Journal of Fatigue 28, 1438-445. Naimark, O.B., Silberschmidt ,V.V., 1991. On fracture of solids with microcracks. Eur.J. of Mechanics 6, 607-619. Naimark, O.B., Plekhov, O.A., Betekhtin, V.I., Kadomtsev, A.G., Narykova, M.V., 2014. Kinetics of defect accumulation and duality of the weller curve in gigacycle fatigue of metals. Technical Physics 59(3), 398-401. Shevelya, V.V., Kosteckiy, B.I., 1967. The influence of surfactant on dislocation formation in fatigue of metals. Doklady Physics 175(6), 1270 1272. (In Russian) Bathias, C., Paris, P.C., 2005. Gigacycle Fatigue in Mechanical Practice, Marcel Dekker Publisher Co., New York USA. Vshivkov, A.N., Prokhorov, A.E., Uvarov, S.V., Plekhov, O.A., 2013. PNRPU Mechanics Bulletin 4,18-32. Bathias, C., Paris, P.C., 2005. Gigacycle Fatigue in Mechanical Practice(Marcel Dekker Publisher Co. New York. Mughrabi, H., 2013. Microstructural fatigue mechanisms: Cyclic slip irreversibility, crack initiation, non-linear elastic damage analysis. Int J Fatigue 57, 2–8. Palin-Luc, T., Perez Mora, R., Bathias, C., Dominguez, G., Paris, P. C., Arana, J. L., 2010. Engineering Fracture Mechanics 77, 1953-1962. P.A., Rehbinder, E.D., Shchukin, 1972. Physics-Uspekhi108, 1. E.D., Shchukin, 2006. Coll. Interf. Sci.,33,123–126. Frenkel, Ya.I., 1975. Kinetic theory of liquids, Leningrad: Nauka, P.592 (in Russian)