Issue 43

M.P. Tretyakov et alii, Frattura ed Integrità Strutturale, 43 (2018) 146-154; DOI: 10.3221/IGF-ESIS.43.11 153 by two schemes were made to evaluate the material behavior in the absence of geometrical nonlinearity determined by the presence of a neck (a turning along the entire length) and to evaluate the state of the material directly in the necking zone. By using the noncontact 3D video system for recording the displacement and strain fields of Vic 3D Correlated Solutions based on the digital images correlation technique, registration of the displacement and strain fields in the gauge length of both the original specimens with the neck and after the groove ones according to the two different schemes was performed. According to the experimental results, the stiffness and strength of structural steel 40Cr were evaluated in a necked specimen at various stages of postcritical deformation. It is noted that the value of the modulus of elasticity does not depend significantly on the level of the previously achieved postcritical deformation and the way in which specimens are grooved. It is also shown that the material in the peripheral areas of the test part of the specimen can be in a strengthened state, which does not change at different degrees of previously achieved postcritical deformation. The strength of the steel 40Cr in the neck formation area is thereby increased and reaches values that can be 30 % higher the strength limit obtained during the stretching the initial specimens. A CKNOWLEDGMENTS he work is carrying out in Perm National Research Polytechnic University with financial support of grant of President of Russian Federation for government support of young Russian scientists (Grant № МК-3293.2017.1.) and with partial financial support of Russian Foundation for Basic Research (Grants № 17-48-590096 and № 17- 48-590158). R EFERENCES [1] Fridman, Y.B., Mechanical Properties of Metals, Мoscow, Oborongiz, (1952). [2] Vildeman, V.E., Sokolkin, Yu.V., Tashkinov, А.А., Mechanics of inelastic deformation and fracture of composite materials, Moscow, Nauka (1997). [3] Bazant, Z.P., Di Luizo, G., Nonlocal microplane model with strain-softening yield limits, Intern. J. of Solids and Struct, 41 (2004) 7209–7240. DOI: 10.1016/j.ijsolstr.2004.05.065. [4] Vildeman, V.E., Mechanics of postcritical deformation and questions of strength analysis methodology, International Journal for Computational Civil and Structural Engineering, 4 (2) (2008) 43. [5] Struganov, V.V., Deformation stability of plastic beam under pure bending, Physical Mesomechanics, 7(S1-1) (2004) 169. [6] Radchenko, V.P., Gorbunov, S.V., The method of solution of the elastic-plastic boundary value problem of tension of strip with stress raisers with allowance for local domains of softening plasticity of material, J. Samara State Tech. Univ., Ser. Phys. & Math. Sci., 4 (37) (2014) 98–110. DOI: 10.14498/vsgtu1366. [7] Davidenkov, N.N., Spiridonova, N.I., Analysis of stress state in the neck of specimen under tension, Industrial laboratory (1945) 583-593. [8] Ahmetzyanov, M.H., Albaut, G.N., Barishnikov, V.N., Investigation of stress-stain state in the neck of plate specimens of steels under tension by the method of photo-elastic coatings, Industrial laboratory. Materials diagnostics, 70(8) (2004) 41–51. [9] Kukudzhanov, V.N., Levitin, A.L., Rheological instability and localization of strains in plane elastoplastic specimens under extension, Mechanics of Solids, 40 (6) (2005) 69-80. [10] Bazhenov, V.G., Zhegalov, D.V., Pavlenkova, E.V., Numerical and experimental study of elastoplastic tension-torsion processes in axisymmetric bodies under large deformations, Mechanics of Solids 46(2) (2011) 204-212. DOI: 10.3103/S0025654411020087. [11] Bai, Y., Teng, X., On the application of stress triaxiality formula for plane strain fracture testing, Journal of Engineering Materials and Technology, 131 (2009). DOI: 10.1115/1.3078390. [12] Xue, Z., Pontin, M.G., Zok, F.W., Hutchinson, J.W., Calibration procedures for a computational model of ductile fracture, Engineering Fracture Mechanics, 77(3) (2010) 492-509. DOI: 10.1016/j.engfracmech.2009.10.007. [13] Aretz, H., Keller, S., Vogt, R., Engler. O., Modelling of ductile failure in aluminum sheet forming simulation, Int J Mater Form 4 (2011) 163–182. T