PSI - Issue 30

Kirill Kurgan et al. / Procedia Structural Integrity 30 (2020) 53–58 Kirill Kurgan et al. / Structural Integrity Procedia 00 (2020) 000–000

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According to Klimenov et al. (2017), Lia et al. (2019), Hensel et al. (2018), welds were a stress concentrator, and as a result, significant dynamics of the development of the local spots of the plastic strains in them under the tensile loads was found. However, the local plastic strains in the studied weld (the central part of the welded sample) at the stage of parabolic hardening ( II ) and pre-fracture ( III ) stages (Fig. 4, patterns 5 and 6) were comparable with that at the welded sample edges. It follows from the analysis of the  (  ) curve of the welded sample that its tensile strength was 360 MPa and failure occurred at a strain of 49% (Fig. 2, b). The transition to the fracture stage ( IV ) was accompanied by the formation of a plastic strain region in the weld. The strain values inside this region exceeded 1.5 times than the average for the entire welded specimen (Fig. 4, patterns 7 and 8). Comparison of the stress-strain curves in Fig. 2 enabled to conclude that tensile strength of the welded sample was less than that of the steel one, but the stress at which the welded sample had failure was greater. This was due to the fact that the strains of the steel and welded samples at the pre-fracture stage were caused by different mechanisms. The steel sample thinning was formed under uniaxial tension, while the strain process was more uniform along the entire length of the welded one (Fig. 3 and 4). The presence of the weld, in which the  strain-induced phase transformations had occurred, contributed to the accumulation and the dissipation of mechanical energy due to the rearrangement of the crystal lattice in the studied case. This contributed to the redistribution of stresses in the metal and, consequently, to its more uniform strains (Fig. 4, patterns 6–8). 4. Conclusions In this paper, the dynamics of the strain fields both in plate made of austenitic stainless steel the 0.12%C-18%Cr 10%Ni-1%Ti and in its butt-welded joint under the tensile loads was studied in situ by the digital image correlation methods. The stages of the stress-strain curves were determined, which correlated with the change in the distribution of the stain fields on the sample surfaces. Based on their analysis, it was found that the presence of a weld in the sample center perpendicular to the applied uniaxial tensile load prevented the formation of the thinning. It was shown that the  strain-induced phase transformations, that had occurred in the heat-affected zone and in the weld metal, contributed to the existence of the yield point on the stress-strain curve, as well as the accumulation and dissipation of mechanical energy due to the rearrangement of the crystal lattice. Acknowledgements The work has been conducted with the financial support of the Government Assignment of the Ministry of Education and Science of the Russian Federation (project No. FEMN-2020-0004). References Fu Y., Li W.Y., Yang X.W., 2015. Microstructure analysis of linear friction welded AISI 321 stainless steel joint. Journal of engineering science and technology review 8, 37–39. Gorbatenko V. V., Danilov V. I., Zuev L. B., 2018. Plastic flow instability: Chernov–Luders bands and the Portevin-le Chatelier effect. Technical physics. The Russian journal of applied physics 62, 395–400. Hensel J., Nitschke-Pagel T., Ngoula D. T., Beier H.-Th., Tchuindjang D., Zerbst U., 2018. Welding residual stresses as needed for the prediction of fatigue crack propagation and fatigue strength. Engineering Fracture Mechanics 198, 123–141. Klimenov V. A., Gnyusov S. F., Potekaev A. I., Klopotov A. A. and et. al., 2017. The structure and properties of microcrystalline and submicrocrystalline titanium alloy VT1-0 in the area of the electron beam welding seam. Russian Physics Journal 60, 990–1000. Lia Y., Wanga X., , Wang J., Chenb A., 2019. Stress-relief cracking mechanism in simulated coarse-grained heat-affected zone of T23 steel. Journal of Materials Processing Tech. 266, 73–81. Macherauch E, Wohlfahrt H., 1977. Different sources of residual stress as a result of welding. In: Conference on residual stresses in welded constructions and their effects, London. Sutton M. A., Orteu Jean-Jose, Schreier H. W., 2009. Image Correlation for Shape, Motion and Deformation Measurements. Basic Concepts, Theory and Applications. Springer Science, Business Media 332. Tretyakova T., Wildemann V., 2019. Experimental study of the influence of strain-stress state on the jerky flow in metals and alloys. Procedia Structural Integrity 17, 906–913. Tretyakova T, Zubova E., 2018. Influence of additional vibration impact on kinetics of strain bands due to the Chernov-Luders deformation and Portevin-Le Chatelier effect in metals. Procedia Structural Integrity 13, 1739–1744.