No 1 (2019)

The paper deals with the description of a new technique of calculations of the heat release processes at the high and ultra-high frequencies associated with the losses in composite materials (CM) what may cause the destruction of radio components. The study of thermal breakdown is necessary to determine the mechanism and nature of change of dielectric properties. Thermal breakdown influences destructively the composite material radio components or even causes their failure. The heating phenomena are rather complex and the calculation of its origination mechanism, as well as the stages of the origination and development of thermal effect and composite material aging, are scientifically and practically attractive.

The goal of the study is the development of a technique for calculation of heat removal and thermal breakdown voltage in the high-frequency structures both for a structure cooled from the one side and for a structure cooled from two sides.

The author got the formulas for calculation of the thermal breakdown voltage of the small-size insulators both in the cases when the electric field is uniform and in the cases when it is non-uniform.

It is experimentally proved that when increasing the temperature of the environment, the value of thermal overload decreases for the composite dielectric materials. When increasing the frequency, the temperature differential increases; at the high frequencies, large temperature differentials occur in the structures made of composite dielectric materials that cause the destruction.

The calculation technique proposed by the author ensures the calculation accuracy sufficiently high for the practical purpose. The study of the breakdown of the discoid components made of a composite containing titanium dioxide shows that in the interval of frequencies f from 0.5 to 1.5 MHz, the temperature and frequency dependencies of thermal breakdown voltage are compliant with the calculations according to the proposed technique.

The authors considered the problems of technological preparation of processing of blank parts of the machine non-rigid elements (FE) and proposed the methodology for specifying the mill modes with regard to the conditions of rigidity implemented through the definition of possible combinations of the cutting mode elements. The factors having the greatest impact on the elastic pressing of the workpiece elements during processing are determined. The authors developed and tested the experimental plant with the thin wall with the height equal to 15 and more of its thicknesses that allows processing the standard blank parts using the ultrasonic field energy in the cutting zone. The experiments on the processing of VT6 titanium alloy with the subsequent assessment of the level of technological residual stresses (TRS) of a surface layer (PS) of the treated surface, as well as the changes in phase composition (PC) were carried out. The authors assessed the influence of the cutting mode elements on the technological residual stresses and phase composition when applying the ultrasonic field energy to the zone of formation of a surface layer of the nonrigid components surfaces and introduced the regression dependences for calculation of the cutting force components and the TRS level depending on the cutting mode elements. The study determined that when developing NC codes of the advanced CNC machines, it is possible to implement the automated specifying of the mill conditions for the blank parts of the machine non-rigid elements considering the conditions of their toughness. The authors proved the efficacy of the technique comparing it with the results of CAE-analysis. The increase of feed per minute when milling VT6 titanium alloy blank parts causes the improvement of its performance characteristics (heat resistance) by means of the increase of β-titanium content; the applying of ultrasonic vibrations to the cutting zone causes the greater growth.

The development and adoption of new titanium-based structural materials combining high heat resistance and low density are a very important task of modern materials science. The existing materials based on the intermetallide alloys of the Ti-Al system have low ductility at room temperatures, which complicates their practical application. One of the ways to increase the plasticity of titanium aluminides is the alloying of an intermetallide alloy. The use of components soluble in titanium aluminides which are in close proximity to aluminum and titanium in the D.I. Mendeleev’s periodic table will allow increasing the ductility of a Ti-Al-based intermetallide alloy.

This paper presents the results of the study of the processes of the argon-arc surfacing of alloys of the Ti-Al system alloyed with nickel using aluminum and nickel filler wires. The authors found out the relationship between the deposition modes and the chemical composition of the deposited metal, as well as determined the effect of nickel on the hardness, wear resistance, heat resistance and crack resistance of the deposited alloys of the Ti-Al system.

The studies showed that alloying with nickel in the amount of 4.5–11.7 % (by weight) with the aluminum content of 10.4–34 % (by weight) increased the hardness and wear resistance of metal deposit. The alloying with nickel within the specified limits with the aluminum content of up to 33 % does not increase the heat resistance of the deposited alloys in comparison with the non-alloyed intermetallide Ti-Al-based alloy. When alloying the deposited alloys with the aluminum content of more than 33 % with nickel the heat resistance of the metal deposit increases.

The alloying with nickel increases the probability of crack formation in the deposited alloys of the Ti-Al system, which is associated with the formation of the Ti2Ni fragile phase inclusions in the metal structure.

The paper presents the technique of the study of the loads on the gyroscopes of the spacecraft motion control system in the flight segment as a part of a space rocket. This problem is a problem of vibration resistance and is solved mainly for the attachments, which is mounted to the body of a vehicle. These attachments can be the mechanisms, antennas, locks, explosive charges, electrical actuators, telemetry transmitters, devices, and assemblies of a spacecraft. In addition to the above mentioned the elements of fastening equipment: fittings, landing planes, brackets, and flanges may be an object of consideration as well.

The goal of the study is the description of the calculation of the loads (dynamic analysis) for the onboard equipment of a spacecraft in the flight segment as a part of a space rocket. The load values are necessary for strength calculations, the results of which are considered when designing the fixtures for the devices and units, as well as when designing and configuring the devices of rocket and space technology.

As an example of calculation, the authors chose the gyroscopes of the motion control system of small spacecraft “AIST-2D”, the load case was “the max-q”. Based on the initial data, the authors constructed a finite element model (FEM) of the plants to determine the loading values. The model is constructed in the FEMAP software program for interactive creation and maintenance. NX NASTRAN is the solver that is used to carry out the dynamic analysis of the structure – the transient analysis.

As a result of the solution, based on the data obtained, the time change of characteristic parameters of loading – acelerations – is shown. Operational overloads influencing the gyroscope assemblies in each direction of the rectangular coordinate system are obtained from the acceleration graphs by dividing by the acceleration of gravity. The authors compared the calculated and experimental data. For the convenience of performance evaluation, the values are shown for one of four gyroscopes mounted in the spacecraft service systems module.

The paper covers the study of special aspects of the application of ionization sensors intended for determining the characteristics of flame propagation (flame propagation velocity and the width of chemical combustion reactions area) in the variable volume combustion chamber. The review of contemporary methods of study of the process of hydrocarbon fuel combustion in piston engines showed the perspectivity of ionization sensors application. On a single-cylinder engine, the authors experimentally obtained and studied the main parameters of fuel combustion using the specially developed ionization sensors designed for identifying the characteristics of flame propagation when changing temperature, pressure, turbulence, and the combustion chamber volume in a wide range within several milliseconds. The variance of ion current, flame propagation turbulent velocity and the width of combustion chemical reactions area are determined depending on the fuel-air mixture composition when changing its physical and chemical properties due to the addition of hydrogen. It is shown that the change in the flame propagation turbulent velocity when adding hydrogen is caused by the increase in its normal component, and the width of turbulent combustion area is linearly related to the ion current value and its variance reflects the intensity of chemical combustion reactions. It is identified that despite the change in the excess air factor, the hydrogen concentration in fuel, and the engine speed rate, the linear dependence of flame width on the flame propagation turbulent velocity in the second combustion phase remains: the velocity increase corresponds to the flame width narrowing.