Browsing by Author "Koleva E.G."

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    Evaporation processes of alloying components duringwire-arcdeposition of aluminum alloy 5056
    (2020-02-28) Salomatova E.S.; Kartashev M.F.; Trushnikov D.N.; Permykov G.L.; Olshanskaya T.V.; Abashev I.R.; Fedoseeva E.M.; Koleva E.G.
    Additive manufacturing technologies are developing fast world wide. Never the less, in the machine-building industry, manufacturing of especially large products is required, and common processes, for example, selective laser melting, are not able to satisfy this requirement. Multilayer wire-arc deposition, allows to make high-quality large-scale products. In addition, the productivity of wire-arc deposition is many times higher than the productivity of powder additive manufacturing. Never the less, the metal obtained by this method is likely to lose easily evaporated alloying elements, which is mainly due to excessive heat and high deposition rates. This process leads to reduced mechanical properties of the deposited metal. The paper presents the results of chemical analysis of the sample obtained by CMT deposition of aluminum alloy 5056.It was revealed that during wire-arc deposition there is evaporation of some alloy components, for example magnesium. A nonlinear theoretical model of nonequilibrium processes in the liquid phase of the deposited metal and the processes of evaporation of chemical easily evaporated elements in the zone of influence of the heating source of wire-arc deposition is presented. Verification of the model was carried out by studying the chemical composition of the samples. During X-ray fluorescence analysis, reduced magnesium content of the first deposited layer was revealed. Increase in the magnesium content was in the upper deposited layers.
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    Graphical user interface for investigation and optimization of electron beam induced grafting of starch
    (2018-10-19) Braşoveanu M.; Koleva L.S.; Nemţanu M.R.; Koleva E.G.; Paneva T.P.
    The challenge of this paper consisted in optimization application in the case of starch grafting with a vinyl monomer under accelerated electron field. Thus, the robust engineering approach and multi-criteria optimization were considered. Methods based on graphical optimization as well as on overall optimization were implemented. Moreover, a graphical user interface previously developed was uplifted and its usage mode is detailed in the present work. To uplift the graphical interface both previously reported experimental data and new one were used. This graphical user interface is useful for investigation, optimization and education in the field of material processing by using ionizing radiation. Furthermore, other new functions can be implemented in the future.
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    Numerical model of a hollow cathode arc discharge formation in vacuum
    (2020-02-01) Permyakov G.L.; Trushnikov D.N.; Mindibaev M.K.; Koleva E.G.
    Industrial application of hollow cathode arc (HCA) discharge necessitates understanding the processes of interaction between the plasma and the cathode and the anode, as well as related processes. The first step is to study the formation process of HCA discharge in vacuum with the micro-flow of plasma-forming gas through the hollow cathode. In this work presents a two-dimensional model describing the related processes of transfer of charged particles and the movement of plasma-forming gas flows. Electron density and mean electron energy are calculated by solving the drift-diffusion equations. The mass transfer equation for a multicomponent mixture is used to describe the mass transfer of heavy plasma particles. To calculate the electric field strength the Poisson equation is used. The emission of secondary electrons from the inner surface of the cathode is taken into account. The boundary conditions take into account the loss of charge as a result of chaotic motion and its occurrence due to thermal emission effects. The gas flow is determined by collisions and diffuse re-reflection from all surfaces assumed in accordance with Knudsen's law. Calculations of plasma formation and the movement of plasma-forming gas flows were performed using the simulation package COMSOL Multiphysics.