PSI - Issue 33

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

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Lomakin and Tretyakov (2016), Tretyakov and Wildemann (2017). In the work of Goldstein and Perelmuter (2001) the expediency of using models of softening media in describing processes at the crack tip is shown. Thus, the development of models of the mechanics of a deformable solid, describing the postcritical stage and the corresponding conditions of destruction, are important for improving the methods of refined strength analysis of critical structures, predicting their behavior in emergency situations, assessing survivability and safety. The aim of this work is to study the processes of localization of strains in the form of a neck at the postcritical stage of deformation in the numerical simulation of the processes of inelastic deformation of structural steels. 2. Procedure and materials The specified mechanical characteristics of structural alloy steel 40Cr (GOST 4543-71) were obtained experimentally earlier on solid cylindrical samples. Steel 40Cr is widely used in construction and mechanical engineering in the manufacture of critical parts and structural elements. The chemical composition of the steel is shown in Table 1. The content of components not listed in the table is less than 0.0025 % each. The main mechanical characteristics of steel, which characterize the elastoplastic behavior, are given in Table 2. The transition of the deformation process to the postcritical stage corresponded to the achievement of the limiting stress σ B = 865 MPa and deformation ε = 0.09. The mechanical characteristics given in Table 4 are defined as basic for further specification of material properties in numerical calculations.

Table 1. Chemical composition of steel 40Cr. Fe C Cr Mn Si W 97,3% 0,362% 0,996% 0,619% 0,240% 0,204% 0,166% 0,030% Cu Ni

Table 2. Mechanical properties of steel 40Cr. Mechanical properties Units

Value

E

GPa

215

ν

-

0,3

σ т σ в

MPa MPa

515 865

δ

-

36

The scheme for setting material properties with areas of hardening and softening is shown in Figure 1. A piecewise linear dependence was used that characterizes elastic deformation (in the range from zero stresses to σ Т ), elastoplastic behavior of 40Cr steel with a nonlinear hardening area (in the range from σ Т to σ В ) and postcritical deformation (in the range from σ В to maximum deformation). The numerical values of stress intensity σi and strain intensity ε i used in the calculation, which characterize the elastoplastic and postcritical behavior of the material, are given in Table 3.

Table 3. Numerical values describing elastic and postcritical deformation of the material. Point 1 2 3 4 5 6 7 8 9 σ i 515 621 720 821 865 850 822 782 715 ε i 0,003 0,012 0,023 0,043 0,085 0,13 0,17 0,22 0,28