Based on mathematical modeling, a study of the wave fields in molten aluminum formed by the action of a pulse, electric discharge and combined sources was carried out. A comparative analysis of their influence on the wave fields in the melt was performed. An increase in the intensity of the wave fields under the influence of a combined method of loading the melt was registered. The occurrence of cavitation in the melt under the influence of the considered sources of pressure pulses has been determined. The energy features of the action of pressure fields on the melt are noted. The influence of the mass of the melt on the pressure fields arising in it is shown.

Based on mathematical modeling of the process of electrohydraulic sheet stamping, the influence of a pressure plate on the deformation of a workpiece rigidly clamped along its outer contour was studied. The influence of the thickness of the pressure plate and its internal diameter, in relation to the diameter of the cavity of the cylindrical discharge chamber, on the energy of plastic deformation of the workpiece and the shape of its deflection; parameters of the pressure plate on the pressure of hydrodynamic waves on the workpiece; and the shape of its deflection and the efficiency of using the energy stored in the capacitor bank for plastic deformation of the workpiece have been established.

Using the example of stamping a box-shaped part from high-strength sheet steel by a pulsed electro-hydraulic method, the limiting possibilities of its shaping, taking into account the springing of the material, are studied. The influence of the radius of the curvature and the shape of the surface of the corners of the part on the change in the structure of high-strength steel DP780 and the appearance of defects in it is determined. Relations between the radius of the curvature of the surface of the part and the thickness of the workpiece at which there are no defects in the structure of DP780 steel and the limiting possibilities of its deformation are achieved with minimal springing of the material are obtained.

-A comparative analysis of three methods was performed to determine a specific plasma electroconductivity that is formed in the electric discharge in water for the purpose of its being mathematically modeled. The parameters of the empiric function whose mathematical modeling results agree with the experimental data were determined. The necessity of the empirical functions use was substantiated during the specific plasma conductivity calculation. The obtained ratios allowed the authors to significantly increase the adequacy of the earlier developed model to physical processes of the discharge in water and expand the parameter range in which it can be used.

The volume of the discharge chamber has a great influence on the pressure field in the water filling it and on the efficiency of many technological processes; therefore, the study of the relationship between the volume of the chamber and the pressure in it is an urgent task. However, at present, the role of the volume of the discharge chamber in the formation of the pressure field in it has been insufficiently studied. The purpose of this work is to fill the gap. The study was carried out on the basis of a previously developed mathematical model of an electric discharge in water, the adequacy of which was substantiated via a comparison of the simulation results with experimental data. It is determined that the closed volume of the discharge chamber with rigid walls significantly affects the formation of the pressure field in the water filling it. In this case, the interaction of waves reflected from the walls of the discharge chamber with the surface of the discharge channel in water and the vapor-gas cavity is of decisive importance. The reflected waves determine the period and amplitude of the pulsation of the discharge channel and the vapor-gas cavity, thereby influencing the electrical characteristics of the discharge. This influence increases with decreasing the chamber volume.

Mathematical modeling of the electrohydraulic sheet metal stamping process using discharge chambers with a conical cavity was carried out. The influence of the parameters of the conical cavity of the discharge chamber on the plastic deformation energy of the plate and the shape of its deflection was investigated. It was determined that the height of the cone, a small radius of its upper base, and the location of the discharge channel near the upper base increase the plastic deformation energy of the plate to the greatest extent.

The pressure field in the limited-volume discharge chambers with rigid walls very often affects the efficiency of the technological processes, which is an urgent problem. As a result of the electric discharge in the liquid that fills the discharge chamber, a cavity is formed with a compressibility higher than the liquid in the chamber. This cavity is filled at the discharge stage with a nonideal plasma, and, after the discharge, it is filled with a vapor of the liquid and gases dissolved in it (a vapor-gas cavity). Its pulsations form the pressure field in the discharge chamber. A moving boundary of the vapor-gas cavity makes it difficult to calculate the pressure field in the fluid, especially after a great amount of its pulsations. At present, the role of the vaporgas cavity is studied insufficiently in the formation of the pressure field in the discharge chamber. To determine it is the aim of the work. This research is performed based on the mathematical model of the electrical discharge in water developed earlier, which was supplemented in this article by ratios that substantially enhance the calculation precision of the discharge channel resistance and the energy released in it. It was determined that the vapor-gas cavity pulsations ensure the pressure oscillations in it in the antiphase with the pressure in the liquid. The pulsations decay slowly, therefore a static equilibrium cannot be established in the discharge chamber between the cavity and the liquid that surrounds it even after seven pulsations. The effect of change was determined in the plasma's optical transparency on the pressure in the cavity and pressure field in the liquid, which decreases the pressure level.

The complex of methods necessary to experimentally study the effect of the deformation rate on the high strength sheet steels (as exemplified by DP780, DP980, and BH240 steels) on the increase in their plasticity during uniaxial and biaxial stretching is determined. The deformation rates of steels were measured in a wide range from 10 –4 to 17 × 10 3 s –1 . An FP 10/1 HECKERT tensile testing machine, a P6324 hydraulic press with special tools, a Hopkinson–Kolsky machine and a T1226B electro-hydraulic press were used. The deformations of the materials destructed during the biaxial stretching were defined using a control grid on their surfaces. Dependences of the destruction deformations of DP780, DP980, and ВН240 steels vs. the deformation rate and their stress-strain state showing an increase in plasticity of DP780 steel up to 2.9 were determined.

This work formulated and solved the problem of determining the specific electrical conductivity of plasma in the channel of the electrical discharge in water as well as that of the discharge channel resistance taking into account the deviation in its shape from that of a straight circular cylinder. The closing ratios and empirical functions whose parameters agree with the experimental data are obtained. The use of the empirical functions necessary for the calculation of the specific electrical conductivity of plasma is justified in connection with its high nonideality and relatively low degree of ionization. The obtained relations allowed for substantially increasing the adequacy of the mathematical model developed earlier for the physical processes of the discharge in water and expanding the range of parameters in which it can be applied.

The problem of determining initial conditions to ensure the uniqueness of the mathematical modeling of the electric discharge in water was formulated and solved. The method was developed for determining initial values of the discharge characteristics, which ensure their agreement between each other. The method efficiency was exhibited by the example of the electric discharge in water, whose experimental data are known. The effect of the arbitrary parameters of the electric discharge system on the mathematical modeling results was defined. The performed studies made it possible to substantially enhance the adequacy of the mathematical model developed earlier to the processes of the discharge in water at its initial stage.

A mathematical simulation of the electrohydraulic forming using some types of stepped axisymmetric discharge chambers is performed. The mathematical model is tested on the basis of experimental data obtained using the optical method of measuring the deflection of a plate. It is shown that a change in the shape of the discharge chamber can significantly affect the efficiency of electrohydraulic forming with the same parameters of the discharge circuit. It is found that the conical discharge chamber provides the highest forming efficiency.

The influence of orientation of a discharge channel in water and the length of a cylindrical discharge chamber on the kinematic characteristics of the maximum deflection of plates during molding into an open ring matrix have been studied experimentally. The optical method is used to measure the deflection of the plate deformed by pressure waves generated by an electric discharge in water. No significant effect of the discharge channel orientation and relative length of the cylindrical discharge chamber on the plate deflection is detected.

This paper describes an experimental study of the strain rate of DP780, DP980, and VN240 high-strength sheet steels on an increase in their plasticity under uniaxial and biaxial tension. The strain rates of the steels vary in the range from 10−4 to 17 · 103 s−1.

We have experimentally studied the influence of discharge-circuit inductance on the efficiency of conversion of energy stored in a capacitor bank, evolved in the electric-discharge channel in water, and spent for the resulting plastic deformation of plates. It is established for the first time that a growth in inductance of the discharge circuit produces a positive effect on the deformation of plates by increasing the amount of energy spent in this process.

Выполнено экспериментальное исследование влияния индуктивности разрядной цепи на эффективность преобразования энергии, запасаемой в конденсаторной батарее, в канале электрического разряда в воде и в процессе пластического деформирования пластин. Впервые определено положительное влияние увеличения индуктивности разрядной цепи на деформирование пластин, приводящее к увеличению количества используемой для этого энергии. DOI: 10.21883/PJTF.2017.16.44939.16706

The process of the conversion of capacitor bank energy as a result of a high-voltage electrical discharge in water that fills a closed discharge chamber into the plasma, liquid, and solid energy is studied. Mathematical modeling in a coupled geometrically and physically nonlinear statement of electrodynamic, hydrodynamic, and elastic–plastic wave processes in the discharge chamber is used as the main research method. We determine the distribution of the capacitor bank energy transferred into a plasma, liquid, and solid body through their contact boundaries in accordance with the parameters of the dynamic system.

An experimental procedure for measuring the deflection of a plate in the course of its deformation is developed. It is cost-effective and provides immediate consistent results. The measurement error is determined. The method is tested using the deformation of plates by shock waves in water generated by electrical discharges.

Energy consumption of cold plastic deforming the materials determines the efficiency of technological methods and their competitiveness. Specific energy consumption of deforming the materials used often to analyze these processes should be determined for scientific and practical interest. This subject is covered in the articles little. Therefore, the main objective of the present research was to investigate the plastic deformation of metals depending on the density of the energy absorbed during the process of their cold deforming performed in three different stretching ways: quasi-static, shock-impact and pulse electrohydraulic. Specimens of 6111, ВН240 and DP780 alloys were stretched quasi-static at deforming rates in the range 0.1 to 0.3 s -1 . Work of stretching and the density of the energy absorbed within the deformed section of a sample depending on the plastic deformation were obtained from the diagrams. Shock-impact stretching of these same alloys was performed at rates of 200 to 2000 s -1 using the method of Kolskiy and a Hopkinson dissected bar. In this study a scheme of stretching flat samples without stretching a Hopkinson bar was worked out. Pulse electrohydraulic method was used for biaxial deforming the plates. The amount of energy released in a discharge channel, the energy of deforming the specimens and their own deformations equivalent to uniaxial stretching were determined. It was found out as a result of the research that the average deformation on the volume of the plate equivalent to uniaxial stretching the alloys is independent actually on the parameters of pulse electrohydraulic deforming. But the density of the energy absorbed within the alloy during deforming, a deforming rate and a type of the alloys have crucial influence on it. High speed deforming of the high hard steels at rates up to 1000 s -1 requires 25 % as much energy as static deforming. The geometrical characteristics of the discharge chamber and rigging affect the efficiency of the process of deforming the sheet metal alloys significantly.

A mathematical model of the electrodynamic processes in the discharge circuit and the discharge chamber of an electrohydraulic installation as well as the algorithm for solving the resulting system of equations in terms of numerical methods are developed. The discharge channel expansion in water is simulated in a geometrically nonlinear model but on a stationary finite difference grid. Both the mathematical model and algorithm are tested by using the example of a solution of similar problems. The results are compared with experimental data. The influence of the finite diameter of the electrodes on transient processes in the discharge circuit and the dynamics of the discharge channel expansion are analyzed.