Journal articles - Siberian Aerospace Journal
All articles: 400
Scientific article
The paper examines issues related to the influence of laser texturing of the surface of a titanium alloy on the characteristics of the titanium-carbon fiber adhesive joint. Using an ytterbium pulsed fiber laser, textures with a linear structure (0°–0° and 90°–90°) and a mesh structure (0°–90°, ±30°, ±45°, ±60°) were created on the surface of a titanium alloy. The surface roughness values in two perpendicular directions were determined, and microsections were made, which can be used to characterize the surface morphology of the titanium alloy. To determine the adhesive strength of the joint, samples with the same surface texture were glued together. The samples were glued together according to OST 1-90281–86. Bonding was carried out within 24 hours after laser surface treatment. Before gluing, the treated surface was cleaned with isopropyl alcohol. Adhesive joint area S = 300 mm2. Three-component adhesive VK-9 based on epoxy and polyamide resin was used as an adhesive. Laser surface treatment of titanium alloys increases the strength of the adhesive joint by more than 70 % relative to the untreated surface. This may indicate that the main mechanisms for increasing the strength of an adhesive joint are an increase in the contact area between the surface and the adhesive, and chemical modification that activates the surface. The processing texture has a lesser effect on the adhesive strength, provided that the specific surface energy of the laser processing is the same. When laser processing, you should pay great attention to the choice of surface texture, because certain textures can give an increase in strength by 20–30 %. If the type of load in the truss load elements is known, then it is better to use linear textures directed perpendicular to the direction of the load (for shear – texture 0°–0°; for torsion – texture 90°–90°). For mixed loads, it is better to use mesh structures ±30°, ±45°, ±60°, which resist loads in two directions.
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The evolution of the concept of a “small” aircraft and the development of its design
Scientific article
This study analyzes the design features of small, aircraft-type unmanned aerial vehicles. The first stage of the study examined the chronology of the evolution of the concept of “small”. It was shown that this concept should be understood as a combination of two factors: small size and low flight speeds. Because of this, the boundary layer flow occurs in a laminar-turbulent transition regime. Due to boundary layer instability, a “laminar bubble” forms above the wing, reducing the lift properties of the vehicle. Reynolds numbers in the range of Re = 105…106 were proposed as an aerodynamic criterion for smallness. At speeds of 70–150 km/h, the mean aerodynamic chord size is in the range of baverage = 0.1–0.9 m. The second stage analyzed the influence of the “square-cube” law on the energy efficiency of the vehicle during the miniaturization of its design. According to this law, the specific wing loading and the (weight)1.5/power ratio are reduced by the magnitude of the reduction factor for the linear dimensions of the aircraft. This is interpreted in the article as a reduction in the efficiency of the aircraft, which converts the kinetic energy of the airflow into lift. When transporting a unit of weight over a unit of distance, a small aircraft consumes several times more fuel than a full-size aircraft. A potential way to increase energy efficiency is to reduce or eliminate the trim losses of lift. This reduction is achieved by reducing the area of the rear-mounted horizontal tail, and the elimination of this loss is achieved by replacing the standard aerodynamic configuration with alternatives: canard or tailless configurations. These configurations do not use a rear-mounted horizontal tail, which generates negative lift, requiring additional energy to compensate. At the 3rd stage of the study, recommendations were formulated for the developers of the considered class of devices: 1) small-sized devices have a naturally low aerodynamic and energy efficiency, increasing which to the level of full-size devices is practically impossible; 2) improving aerodynamics is possible through the use of special profiles, morphing wing technology and boundary layer control methods; 3) increasing the duration and range of flight is possible due to the reduction of balancing losses of lift, using a beam tail in a normal configuration or using alternative aerodynamic configurations; 4) the article presents a block diagram of the iterative process for determining the wing area, the value of which will satisfy the conditions of the balance of forces and moments for various values of the ratio of the wing and horizontal tail areas.
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The feature of raising the “Express-AMU3” and “Express-AMU7” satellites into geostationary orbit
Scientific article
At present, in order to increase the launch mass, raising satellites into geostationary orbit by their own propulsion subsystem is widely used. Oly the JSC “Academician M. F. Reshetnev “Information Satellite Systems” applied such a scheme for several satellites of their own design - "Express-AM5", "Express-AM6", "Express-80" and "Express-103". Along with this, some diversity of approaches to the implementa-tion of this operation can be noted. In particular, the orbit raising of the above satellites was carried out using the onboard propulsion subsystem based on SPT-100 plasma thrusters. The operation was carried out by one or two thrusters. The use of two thrusters of the "Express-80" and"Express-103" satellites was due to the desire to keep within a reasonable amount of no more than six months with a significant increase in the output mass. Nevertheless, the duration of the orbit raising of about 150 days, which took place dur-ing the raising of satellite data, is also excessively long. It is evidemnt that it can be reduced, other things being equal, only by increasing the available thrust of the thrusters. This can be achieved both by increas-ing the thrust of individual units, and by increasing the number of simultaneously used thrusters. Therefore, for the new Express-AMU3 and Express-AMU7 satellites (with dimensions similar to the Express-80 and Express-103 satellites), for which a paired launch was also assumed, both of these methods were used. For orbit raising, two SPT-100V thrusters and, additionally, an SPT-140D type thruster were used. The total thrust of a cluster of thrusters made it possible to count on a significant reduction in the duration of orbit raising in comparison with the Express-80 and Express-103 satellites. The SPT-140 thruster developed by JSC "Experimental Design Bureau FAKEL" was used in Russia for the first time. For its power supply, the CCS-140D control and conversion device was specially created at the JSC "Design Bureau Polyus". The use of a combination of three thrusters made it possible to significantly reduce the duration of the opera-tion of raising into geostationary orbit.
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Scientific article
This paper examines how precipitation pH affects the phase stability, microstructure, and electrochemical characteristics of solid electrolytes based on zirconia stabilized with 5 mol.% yttria (5 YSZ), which we synthesized by chemical coprecipitation. We obtained precursors under three pH conditions (acidic pH < 2, near-neutral pH = 3–7, and alkaline pH - 10) using nitrate salts and NH4OH as a precipitant. We characterized the products by SEM, X-ray diffraction, Raman, and IR spectroscopy, as well as DC conductivity measurements. The results demonstrate that precipitation pH critically determines the homogeneity of Y3+ ion distribution in the precursor. Acidic conditions hinder yttrium coprecipitation, resulting in pronounced segregation of the elements and a high content of the monoclinic phase after calcination and milling. Alkaline conditions ensure quantitative precipitation but cause partial compositional fluctuations and severe agglomeration, so they necessitate intensive milling, which induces lattice deformations and phase transformations. Near-neutral conditions (pH 5–6) promote homogeneous coprecipitation of Zr4+ and Y3+ ions, forming precursors with a uniform element distribution and weakly agglomerated particles. This homogeneity ensures the complete removal of coordinated hydroxyl groups during heat treatment, maintaining a high concentration of oxygen vacancies and the stability of the tetragonal phase. Ceramics that we sintered from powder obtained under neutral conditions achieve relative density (98.7%) and ionic conductivity (36.4 mS/cm at 850 °C). Solid oxide electrolytes based on stabilized zirconium dioxide function widely as materials for parameter control sensors (oxygen sensors in propulsion systems) and also serve as the basis for the creation of solid oxide fuel cells.
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The influence of prefinishing operations at titanium alloys on the characteristics of MAO coatings
Scientific article
Improving the reliability, service life and operational safety of titanium alloy structures exposed to thermal, chemical and mechanical stresses can be achieved by applying various protective coatings. One of the effective methods of protecting such alloys is the formation on their surface of oxide coatings that are resistant to external factors. Of great interest from this point of view is the method of micro-arc oxidation (MAO), which allows one to obtain multifunctional ceramic-like oxide coatings with unique properties. Such coatings can be used to create a durable heat and electrical insulating layer on parts, protect surfaces from erosion in high-speed gas flows, corrosion in aggressive environments and wear by friction, to increase the surface emissivity, etc. This method is well established for the oxidation of aluminum alloys. Despite the fact that the mechanism of coating formation during MAO is the same for aluminum and titanium alloys, there are certain differences in the structure and characteristics of the resulting coating. For example, it is believed that during the MAO treatment of aluminum alloys, preliminary surface preparation is not required and the adhesive strength is comparable with the strength of the substrate material. However, when processing titanium alloys, we noted cases of a significant decrease in adhesive strength. One of the reasons may be the lack of preliminary surface preparation before coating. Therefore, studies aimed at studying the influence of the method of surface preparation and the resulting roughness on the characteristics of the applied coatings are relevant.
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Scientific article
The burning of fuel in the combustion chamber of a gas turbine engine (GTE) is accompanied by formation of toxic substances. The most dangerous among them are carbon oxides that have a detrimental effect on humans and environment. In this regard the article is solving the urgent problem of determining the optimal method of gaseous fuel supplying in GTE combustion chamber to ensure low carbon-oxide emissions. The paper presents the design features of injectors that work with a separate supply of air and fuel. Natural gas is used as fuel. One of the considered injectors provides jet fuel supply by means of a perforated spray, and another one provides twisted fuel supply by means of a swirler built into the fuel channel. The main geometric parameters of the injectors are given as well, such as the size of the swirler, the number of blades, and the diameter of the output nozzle. In this regard the quality of air-fuel mixture preparation in a swirl jet in the outlet of the burner with two types of injector is defined. It is found that the best quality of mixing is ensured by the injector with jet spray. The design of a heat pipe simulator, in which the tested nozzle is placed, is considered. The design of a stand installation designed for testing injectors in a heat pipe simulator, as well as the modes under which these tests were carried out, are presented. The results were obtained in a heat pipe simulator with installed jet injectors and injectors with a swirling fuel jet. An analysis was conducted, which resulted in conclusions about the effectiveness of using jet injectors. According to the conducted research, the parameters of the injector with a swirling fuel jet are characterized by the presence of high values of CO levels in the combustion products, which is explained by the extremely low quality of mixing fuel with air and, consequently, low efficiency of fuel combustion. Jet fuel injection has low CO values, which indicates good quality of mixing fuel with air and high efficiency of a combustion process. As a result, we have received recommendations on setting the selected type of injectors in a full-size combustion chamber.
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Scientific article
The objective of this work is the computational and experimental assessment of the effect of twisting of an active-reactive type projectile-piercer around its own axis on the parameters of its motion and the depth of penetration into the soil. Research methods: the equations of motion of a rotating active-reactive type projectile-piercer (SPART) are considered. The features of determining the engine thrust, rotating SPART and the resistance force during penetration of SPART into the soil with rotation are ana-lyzed. A comparative analysis of the penetration depths of rotating and non-rotating SPART into loam is carried out. As a result of the studies, a mathematical model of the process of penetration of an active-reactive type projectile-piercer into the soil is developed. The effect of SPART rotation around its own axis of symmetry on the performance of the propulsion system is shown. The effect of contact friction forces be-tween the rotating SPART and the soil on the parameters of its motion and the depth of penetration is as-sessed. Calculations show that by spinning the SPART around its own axis of symmetry, the depth of pene-tration of rotating active-reactive type projectilе-piercers into the soil can be increased by 8–10 %. Con-clusion: the results presented in the article can be useful for researchers, postgraduate students and engi-neers involved in the creation and operation of aviation and rocket and space technology, and can also be useful for students of technical universities studying at the relevant specialties.
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The magnetic anisotropy comparison of polycrystalline and single-crystal Fe3Si films
Scientific article
High-tech devices improvement requires development of technology and search for new materials from science. Currently, the development of the magnetism research field has reached a very broad knowledge, making it possible to create and study a variety of artificial ferromagnetic materials, which are already actively used in science and technology. The latest scientific knowledge shows that the same material in different states can exhibit different electrical and magnetic properties. Thus, thin magnetic films are actively used in modern devices. Physical processes in thin films proceed differently than in bulk materials. As a result, the film elements have characteristics that differ from those of bulk samples and make it possible to observe effects that are not characteristic of bulk samples. A film is a thin layer of a bound condensed substance, the thickness of which is compared with the distance of surface forces action; it is a thermodynamically stable or metastable part of a heterogeneous film-substrate system. Further researsh of film structures led to the creation and study of multilayer magnetic systems. In such structures, the presence of both various ferromagnetic materials layers and non-ferromagnetic interlayers is possible, and the multilayer systems properties can differ significantly from the properties of any system components. These materials also have many practical applications, including radio communications and geological exploration. In our experiment, ferromagnetic thin films of Fe3Si silicide were synthesized by molecular beam epitaxy with co-deposition of Fe and Si. A polycrystalline silicide film was obtained on a SiO2/Si(111) substrate, and a single-crystal film - on Si(111)7×7. The structure was investigated using the diffraction of reflected fast electrons directly during the growth process. The magnetic anisotropy of the obtained samples was studied applying the method of ferromagnetic resonance. It was found that the polycrystalline film is characterized by uniaxial magnetic anisotropy, which is 13.42 Oe and is formed as a result of “oblique” deposition, whereas the magnetic anisotropy for a single-crystal Fe3Si film is formed to a greater extent by internal magnetocrystalline forces.
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Scientific article
In this paper, the issues of ensuring the resistance of the onboard equipment of spacecraft to the effects of ionizing radiation from outer space, which significantly limits the period of active existence of the space-craft, are considered. The paper describes the methodology for ensuring radiation resistance, developed by the specialists of JSC “ISS”. The result of the work done is to ensure the guaranteed performance of the target function by spacecraft with long period of active lifetime of 15 or more years. Among the outer space factors affecting the spacecraft, ionizing radiation of outer space is the main factor limiting the period of active existence. Exposure to energetic particles of ionizing radiation from outer space causes degradation of the electronic component base, which leads to failures and malfunctions of on-board equipment and degradation of its functional surfaces. Ensuring the radiation resistance of a spacecraft (SC) is a complex task, one of the stages of which is to determine the radiation resistance of components that complete the on-board equipment. As a result of accumulated experience in conducting radiation tests and analysis of the results, specialists of JSC “ISS” developed a methodology that allows to guarantee the radiation resistance of the spacecraft under conditions of tight production deadlines and optimized costs.
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Scientific article
The paper proposes the method for the numerical solution of Poisson kinematic equations system determining the evolution of the spacecraft position. The system of Poisson kinematic equations is used to designate the transition matrix from the coordinate system associated with the spacecraft at the selected time t1 to the coordinate system associated with the spacecraft at the current time t2. This matrix is used in the process of solving problems of determining a three-axis orientation of the spacecraft from the readings of the magnetometer using information about its angular velocities. The proposed method is based on replacing the derivatives of the desired functions in the Poisson kinematic equations by partial sums of series in the scaled Haar system. The partial sums of these series are generalized polynomials in the scaled Haar system. Hence, these sums are step (piecewise constant) functions. The estimates of the proposed method error are derived, which reveal that in the case of the coefficients of the equations which are functions matching the Lipschitz condition, the absolute error in calculating each of the elements of the transition matrix from one coordinate system to another is the value O(N–1) at N , where N is the number of partitions of the segment [t1, t2] when constructing a grid of nodes involved in this method. It is proved that the complexity of constructing an algorithm for approximating the system of Poisson kinematic properties insignificantly exceeds the complexity of solving this system by Euler method, which has the first order of accuracy. The research presents the results of numerical experiments, showing that in certain cases the Haar sums method gives an error that is much smaller than the Euler method, and is almost identical to the errors of the Euler – Cauchy and Runge – Kutta methods of the 2nd order, the complexity of which is approximately two times greater than the complexity of the Haar sums method.
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Scientific article
Plates, beams and shells with non-uniform and micro-inhomogeneities regular structure are widely used in aviation and rocket and space technology. At the preliminary design stage, it is initially important to know whether the design safety factor meets the specified strength conditions. To determine the margin factor, it is necessary to solve the elasticity problem for the designed structure by the finite element method (FEM), taking into account its inhomogeneous structure, which requires large computer resources. In this paper, we propose a method of equivalent strength conditions (MESC) for calculating the static strength of elastic structures with a inhomogeneous regular structure. The proposed method is reduced to the calculation of the strength of isotropic homogeneous bodies using equivalent strength conditions. The MESC is based on the following statement. For any composite body V0 , there exists such an isotropic homogeneous body Vb and such a number p (equivalence coefficient) that if the body Vb stock coefficient satisfies 0 nb the equivalent strength conditions 0 pn1 nb pn2 , then the body V0 stock coefficient satisfies n0 the given strength conditions n1 n0 n2 , and Vice versa, n1 , n2 – given, the coefficients 0 nb , n0 , meet the exact solutions of elasticity problems constructed for bodies V0 , Vb . The method under consideration is reduced to FEM strength calculation of isotropic homogeneous bodies, which is the easiest to implement and requires less computer memory than a similar calculation of composite bodies taking into account their inhomogeneous structure. The procedure for determining the equivalence coefficients for a number of composite plates, beams and shells of rotation is described. High-precision multigrid finite elements generating discrete models of small dimension and solutions with small error are used in the construction of elastic solutions according to FEM for isotropic homogeneous bodies. The adjusted equivalent strength conditions are of the form pn1(11) nb pn2 (12 ) , where nb is the body Vb reserve coefficient and the values 1 , 2 correspond to the approximate solution constructed for the body Vb . Implementation of FEM for multigrid discrete models requires several 103-106 times less computer memory than for basic models. The calculation of the strength of a beam with a micro-homogeneous regular structure with the help of MESC is given.
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Scientific article
When the strength of elastic composite structures (plates, beams, shells) widely used in aviation, rocket and space technology is calculated with the finite element method (FEM), it is important to know the solu-tion error. To analyze the solution error, it is necessary to use a sequence of approximate solutions con-structed according to the FEM using the grinding procedure for basic discrete models (BMs), which take into account an inhomogeneous microheterogeneous structure of bodies within the microapproach. Dis-crete models obtained by grinding BMs have a high dimension, which makes it difficult to use the FEM for them. In addition, there are BMs of composite solids (CSs), for example, BMs of bodies with a microhet-erogeneous structure, which have such a high dimension that the implementation of the FEM for such BMs is practically impossible due to limited computer resources. To solve these problems, it is proposed to use fictitious discrete models in the calculations of CSs according to the FEM. In this paper we propose a method of fictitious discrete models (MFDM) for calculating the strength of elastic bodies with an inhomogeneous microheterogeneous regular structure. The MFDM is implemented with the help of the FEM using corrected strength conditions, which take into account the error of ap-proximate solutions. The method is based on the following provision. We believe that BMs of CSs generate solutions that slightly differ from the exact ones. Such BMs always exist for CSs due to the convergence of the FEM. The calculation of CSs according to the MFDM is reduced to the construction and calculation of the strength of fictitious discrete models (FMs), the dimensions of which are smaller than the dimension of the BMs. FMs reflect: the shape, characteristic dimensions, fastening, loading and the type of the inhomogeneous structure of CSs and the distribution of the elastic moduli corresponding to the BM of the CS. The sequence consisting of the FM converges to the BM, i.e., the limiting FM coincides with the BM. The convergence of such a sequence ensures uniform convergence of the FM stresses to the corresponding BM stresses. The implementation of the FEM for FMs with the use of multigrid finite elements leads to a large saving of computer resources, which makes it possible to use the MFDM for strength calculations of bodies with a microheterogeneous regular structure. Calculation of the CS strength according to the MFDM requires times less computer memory volume than a similar calculation using the BM of the CS, and does not contain the procedure for grinding the BM. The given example of calculating the strength of a beam with an inhomogeneous regular fibrous structure according to the MFDM shows its high efficiency. Applying the adjusted strength conditions allows using approximate solutions with larger errors in CS strength calculations, which leads to improving the efficiency of the MFDM.
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Scientific article
A method of synthesizing a digital controller for a solar energy conversion channel in a power supply system of a spacecraft is presented. The method is based on the initial functional diagram of the pulse converter and the method of switching discontinuous functions. In accordance with the technique, which is formally presented in the form of eight consecutively executed items, a block diagram of the shunt converter has been developed in the basis of switching functions, which is taken as an example for testing the technique. The shunt converter is one of the three energy conversion channels in modern power supply systems of a spacecraft. The block diagram showed that all nonlinearity of the system can be reduced to nonlinearities of two multiplication links and nonlinearity of a pulse-width modulator. The possibility and acceptability of joint linearization of each of the specified nonlinear multipliers with a pulse-width modulator at the selected operating point is shown. A linearized block diagram of the control object was obtained, after which the transformation and simplification of the block diagram to a convenient form for calculation was carried out. Using the transfer functions of the linearized block diagram, the logarithmic frequency characteristics were calculated analytically and the results of their comparison with the frequency characteristics obtained experimentally on a simulation model, which confirmed their identity in the working frequency domain, were presented. At the same time, the specified simulation model of a shunt pulse converter, built in the Simulink package of the Matlab design environment, took into account all the mentioned nonlinearities of the real converter. According to the obtained logarithmic characteristics, a classical synthesis of the analogue prototype correcting section was produced. The transition from the analog correcting section of the prototype to the implementation of the digital correcting section is shown. Simulation modeling of a closed-loop power supply system with a synthesized analog controller, in its mode of operation from a solar battery, confirmed the correctness of the methodology and the achievement of the goals. The results of the work are intended to create a new onboard energy conversion equipment for power supply systems of high-potential spacecrafts. The scope of application of the project results is space instrumentation.
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The method of the automation of the plasmotron movement by six-axis robotic manipulator
Scientific article
The article presents a method for automating the creation of trajectories of the plasmotron movement by a six-axis robotic manipulator. The automation system was created on the basis of an industrial robot from KUKA. The automation of the creation of trajectories of the plasmatron over the surface of the part is implemented as follows: the trajectory of the plasmatron is created in a graphic editor in the .dwg format. The created file is loaded into the CAM program for CNC machines. A CAM program converts a vector or an area specified by vectors into a control command in g-code format, which is then converted to KRL by a program written in the Python programming language. The development of the program consisted of two stages: the creation of rectilinear movements and the creation of curvilinear movements. The result of the method is presented.
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The method of the disk friction determining of low mass flow centrifugal pumps
Scientific article
Low mass flow centrifugal pumps are currently widely used in the energy supply system of liquid rocket engines, the engines of correction, docks, consisting of on-Board power sources on-Board sources power supply system of fuel components in the in gas generator systems for inflating fuel tanks, and in temperature control systems of aircraft and spacecraft. When designing low mass flow centrifugal pumps for aerospace purposes, methods for calculating and optimizing the flow rate are often used corresponding to the design methods of full-size centrifugal pumps, which limits the mode and design potential of pumps and affects their energy characteristics and reliability. Reliability requirements often lead to the need to reserve units and fuel-supply systems. Despite the large amount of research works, the issues of reliable design of low mass flow centrifugal pumps with high energy and operational parameters for spacecraft and aircraft remains an urgent task. The article analyses the operational parameters of low mass flow centrifugal pumps used in aircraft and spacecraft power systems. Taking into account working fluid used and the temperature range, it was found that a laminar rotational flow with Reynolds number characteristic Re 103 3105 is realized in the lateral cavity between the impeller and the pump housing. The determination of power losses on disk friction of the impeller technique is developed taking into account design features and the applied schemes. Equations for determining the disk friction coefficients are consistent with the dependencies obtained by other authors. The obtained equations for the laminar rotational flow made it possible to determine the dependences for the resistance moment and the disk friction power of the impeller determining of a low mass flow centrifugal pump.
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The possibility of using methane-hydrogen fuel in converted gas turbine engines for power plants
Scientific article
Taking into account the fact that recently the topic of using methane-hydrogen mixtures as a fuel for gas turbine engines used in power plants has been actively developed, it is necessary to have engineering methods for calculating the fuel system and combustion chamber of engines operating on such fuel. The paper proposes the methodology that allows performing such calculations. A gas turbine unit (GTU) based on a converted aircraft engine NK-16ST was taken for the calculation. The calculation according to this method is carried out in three stages. At the first stage the composition is selected and the thermophysical characteristics of the gas under consideration are determined. At the second stage the fuel system is calculated, the consumption characteristics of the engine fuel system and the combustion chamber system are built. The consumption characteristics built for natural gas and for methane-hydrogen mixture are compared. The analysis makes it possible to develop recommendations for optimizing the design of the fuel supply equipment and fuel nozzles in terms of changing the volume of internal channels. At the third stage the combustion chamber is calculated and recommendations about the need to change the flame tube head or redistribute air along the flame tube length are made. The volumetric heat intensity parameter is used to estimate the sufficiency of the available volume of the flame tube for operation on methane-hydrogen mixture and to determine the gas average temperature in the combustion zone of the combustion chamber. The possibility of operation of the NK-16ST gas turbine unit on a methane-hydrogen mixture was confirmed on the basis of the results of the work performed. It was also concluded that in order to supply large volumes of methane-hydrogen mixture in comparison with natural gas, it is required to increase the size of fuel pipelines, metering and control units and fuel nozzles.
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The process of nanomodifying cast aluminum alloy ingots for components of aerospace vehicles
Scientific article
Currently, increasing attention has been paid to such a class of materials as nanopowders (NP) of chemical compounds, which are ultra-thin formations of not more than 100 nm in size. Such attitude to these materials is explained by the fact that they have unique physical, chemical and mechanical properties significantly different from the properties of materials of the same chemical composition in a massive state, and these properties can be transferred to some extent from them or with their participation to the products. The existing methods of introducing NP into metal melts could not be used due to their special properties in comparison with coarse powders, and therefore a new method of their introduction into the melt was developed, excluding direct contact of NP particles with oxygen and unhindered penetration of particles into the melt through the oxide layer. The essence of the method was as follows. In the aluminum container filled up with aluminum particles or deformable aluminum alloys D1 or D16 and various NP (nitrides, carbides, oxides, etc.), and this composition was pressed into the rod, with its help NP was introduced into the melt during casting of aluminum ingots and deformable aluminum alloys. The results of the study showed that this excludes the appearance of cracks in the ingots, as well as improves their technological and mechanical properties.
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Scientific article
Today, protective coatings are applied to almost all parts and components of engineering products in order to ensure high performance properties of machines, with the lowest economic cost. The method of plasma spraying allows to apply heat-resistant coatings on a different kind of basis, in addition to a wide variety of materials. Therefore, rocket and space engineering is primarily interested in the method. In modern conditions of high rate of mechanical engineering development engineers must develop and put into operation products within the shortest possible period of time. As a rule, engineers select the modes of plasma spraying using the method of selecting the empirical relationship between the properties of the coatings and the values of the specified parameters of plasma spraying, which suggests conducting a huge number of experiments. That is why we see the need to find new methods for selecting the plasma spraying parameters, which are based on mathematical and analytical apparatus. We set the task to study and show the applicability and prospects of the proposed method. In the work we carried out the operations of spraying nichrome coating, at different values of the arc current. We studied the adhesive strength of the coatings obtained and their microstructure. We showed the relationship between the arc current and the adhesion of the coatings using their microstructure. These studies have made it possible to exclude a large number of experiments, which usually establish an empirical relationship between the values of the input parameters of the deposition process and the values of the characteristics of the coatings obtained. In the future, we assume that the database of such relationships will make it possible to fully use this method in engineering industries.
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Scientific article
The most important resource for improving the performance of parts is the reduction of the surface roughness. One of the promising ways to reduce the surface roughness is the abrasive extrusion processing. When developing the AEP technology, it is necessary to know the flow rate (pressure) of the WE, which depends on the viscosity of the latter. In turn, the viscosity of the WE is determined by its temperature. The temperature of the working environment at AEP can be calculated if the coefficients of thermal conductivity and thermal diffusivity of the WE are known. The working environment for AEP consists of two components, therefore, the coefficient of thermal conductivity can be calculated by known formulas. However, the calculation error is significant, therefore, the experimental determination of the abovementioned coefficients is required. The installations for the coefficients research have been presented, the methods of conducting experiments have been developed. After mathematical processing of the experiments results by means of the AdvanceGrapher v. 2.11, the dependences of the thermal conductivity and thermal diffusivity on the abrasive concentration have been obtained. The studies of the thermophysical properties of the working environment have shown that the values of thermal conductivity and thermal diffusivity of the WE are mainly determined by the concentration of abrasive grains in the working environment. The direct dependence of these coefficients on the degree of filling the working environment with abrasive grains has been established.
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Scientific article
Electrical discharge machining and electrochemical machining of metals are used in the production of parts for aircraft and rocket technology, especially electrical discharge machining. A type of electrical discharge machining, electrical contact machining, is used in metallurgy. The paper investigates a combined method of metal machining, including electrical contact and electrochemical methods using vibration of the electrode tool. This method is used for copying and piercing operations in the manufacture of parts from metals that are difficult to machine mechanically. The peculiarity of the above-mentioned method of electrical machining is the formation of surface roughness of the metal being machined due to anodic dissolution and the electrical discharge machining process. The side surface of the workpiece is formed due to electrochemical processes. The end surface is formed due to electrical contact machining. Based on literature data for pulsed electrochemical machining and experiments, expressions for calculating the roughness parameter of the side surface are obtained. The formula takes into account the time of anodic dissolution for one period of oscillation of the cathode tool, the voltage on the electrodes and the concentration of the electrolyte. The calculation of the roughness parameter of the end surface is carried out similarly to the expression for electrical discharge machining, but instead of the duration of the electric pulse, the duration of contact of the electrodes is used. The experiments carried out confirmed the correctness of the expressions used and made it possible to obtain the dependence of the coefficient on the vibration frequency of the cathode-tool.
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