PSI - Issue 40

Aleksandr Zalazinskiy et al. / Procedia Structural Integrity 40 (2022) 461–469 Aleksandr Zalazinskiy at al. / Structural Integrity Procedia 00 (2022) 000 – 000

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minimum value of the quality criterion of the technological process

1. Introduction The work aims to improve the technology of industrial production of wires made of metal matrix composite materials (Nb-Ti)+Cu alloy fibers evenly distributed in a copper matrix) with low-temperature superconductivity; they are widely used for windings of powerful electromagnets (Metallurgy, 1979). The requirements for wires include the specified dimensional accuracy, surface cleanliness, and minimal damage to the fibers of the composite wire. The technology of industrial production of this type of product is energy-intensive and requires significant material and labor costs. Ensuring the necessary technological properties of products requires solving rather complex scientific and technical problems. Such tasks include reducing the energy intensity of production; increasing the overall degree of deformation of workpieces with a simultaneous increase in the plasticity of the deformable material and a decrease in the heterogeneity of the material of workpieces and products. Improving the technology of pressing composite blanks will increase the accuracy of product dimensions and minimize damage to composite material components (Johnson, 1962). To study the extrusion of the Nb-Ti+Cu metal matrix composite, hydromechanical pressing (HMP) was implemented (Avitzur, 1965). This method preserves the positive aspects of hydrostatic extrusion and has a number of significant advantages: the workpiece is rigidly fixed in the container and the possibility of its misalignment is excluded; the stick-sleep effect (extrusion by jerks) is absent; the process is controlled; the uniformity of metal outflow increases due to the peculiarities of pressure distribution at the end of the ingot; the lateral pressure of the liquid is 10 – 20% less than the end pressure, as a result of which the stresses on the container walls are also reduced by 10 – 20% compared to hydrostatic extrusion. Experimental and analytical methods are used to study the HMP process. The main theoretical methods are the energy method, the upper-bound method, the slip-line method, the moire-fringe method, and the experimental analytical visioplasticity method. In order to avoid significant costs for conducting physical and field experimental studies, simulation modeling using the finite element method, supported by modern CAE systems, is currently used to analyze HMP (Byon, 1997, Hongbo, 2005, Hwang, 2002, Kang , 2002). To calculate the damage of the workpiece material, the foundations of the phenomenological theory of metal destruction under large plastic deformations were used (Kolmogorov, 1970). The purpose of the work is to implement mathematical modeling of HMP using the example of the extrusion of a metal matrix composite Nb-Ti+Cu; using multicriteria optimization methods, to determine the rational parameters of the technological process according to the quality criteria of the extruded blanks: minimum extrusion stress, minimum damage to the deformable material, minimum heterogeneity of the extruded blanks. To achieve this goal, it is necessary: - to investigate the effect of pressure on the surface of the workpiece and boundary friction, as well as the extrusion ratio, on the specific extrusion stress; - set the minimum pressure of the working medium for the implementation of the extrusion process; - to study the influence of technological parameters on the accumulation of damage during deformation; - to perform a computational experiment, regression analysis of its results, as well as a multi-criteria selection of optimal technological parameters of HMP for the improvement of composite materials for electrical purposes. 2. Description of the problem and the solution method The Nb-Ti alloy ( 50%Nb, 50%Ti  ) was considered as the material for the fibers (conductive cores) of the composite; copper was used as the matrix material, in which the conductive cores were evenly distributed. The composite wire design implements an efficient heat sink during operation. The data (Kolmogorov, 1991, Savitskiy, 1981, Zalazinskiy, 2000) were used to determine the mechanical properties of the composite components. The analysis of the results of an experimental study of the mechanical properties of composite components (Figure 1) made it possible to introduce approximating expressions for the dependencies of the yield strength of the materials of Nb-Ti alloy fibers f s  and the MB Cu matrix m s  , as well as for the effective yield strength of the