PSI - Issue 33

M.P. Tretyakov et al. / Procedia Structural Integrity 33 (2021) 871–877 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The issues of experimental and theoretical study of the laws of postcritical deformation of materials attract the attention of researchers in connection with the use of deformation reserves of materials, increasing the bearing capacity and survivability of structures, as well as the possibility of more accurate prediction of the kinetics of fracture processes.

Nomenclature E

Young's modulus Poisson's ratio tensile strength elongation at break engineering stress yield stress

ν

σ т σ в

δ σ ε

strain

σ i ε i

stress intensity strain intensity

δ max

maximum transverse constriction

Experimental studies of the regularities of the postcritical behavior of metallic materials are accompanied by developed plastic deformations, which leads to the appearance of such an effect as the localization of deformations in the form of a "neck" in the working part of the sample. It is shown that this phenomenon requires taking into account and significantly complicates the methods of interpreting the experimental data recorded in the experiments. By Vildemann et al. (1997, 2008, 2019) is shown that the numerical and experimental study of the processes of localization of deformations in the form of a neck is an urgent problem both from a practical and a fundamental point of view, since they carry information about the physical and mechanical processes occurring in the material, which ultimately lead to complete destruction. During the formation of localization of deformations, the stress state in the sample becomes uniaxial and inhomogeneous. The problem of the formation of localization of deformations is discussed in the works of Shesterikov and Lokoschenko (1996), Tretyakov et al. (2016, 2018) and Vildemann et al. (2014). The moment of the transition from homogeneous to inhomogeneous deformation, as well as the effect of loading conditions on this, is of great interest from the point of understanding of the ongoing physical processes. Experiments on stretching cylindrical specimens and modeling the behavior of a specimen under tension under conditions of the formation of localization of deformations in the form of a neck is an urgent task from the point of view of studying the processes of deformation and fracture of materials and structural elements. The advantage of using video systems for recording displacement and deformation fields based on the method of correlation of digital images in studies of inhomogeneous deformation processes (DIC) is shown by Vildemann et al. (2016), Tretyakova and Wildemann (2019). By Berezhnoi and Paimushin (2011) is shown that the geometry of specimen grips and the methods of applying loads lead to the appearance of stress concentration and the formation of primary zones of plastic deformations, which, in turn, are the main reason for the initiation of secondary zones of localization of plastic deformations and necking even in qualitatively manufactured specimens from various plastic materials. It is possible to significantly reduce the influence of this factor on the necking process with the help of a stronger perturbation in solving the problem, for example, a decrease in the diameter in the center of the working part of the sample. The processes of crack growth in materials, and especially their equilibrium stage and transition to dynamic fracture, deserve special attention in assessing the strength and survivability of structural elements. In the study of such processes, it is promising to use the approaches of the mechanics of postcritical deformation, which is shown by