Introduction. Selective transfer is a typical example of the self-organization processes in tribosystems. In this case, joint surfaces of the servovite film are formed in the contact area, which changes fundamentally the friction and wear conditions. To form selective transfer in the area of mating surfaces, some power of the irreversible transformations of the input energy is needed, which depends on the elastic-dissipative properties of the contact surfaces.

Materials and Methods. The mathematical model of the dynamic system considering the evolutionary changing servovite film is given. Its formation depends on the phase path of the irreversible transformations power in the area of surface matching, and it is represented by the Volterra integral operator of the second kind.

Research Results. The outcome analysis including dependences of the servovite film formation on the dynamic parameters of interacting subsystems is provided. The mathematical simulation of the evolution of the friction unit properties with the formation or destruction of the servovite film is first considered.

Discussion and Conclusions. During the evolutionary process of the servovite film formation, the dynamic coupling parameters generated in the friction unit, change. Consequently, the dynamic properties of the system also change. The tribosystem dynamics is first considered under the process of forming the selective transfer.

Introduction. Functional properties of diamond powders are determined by a large-scale structural factor since it affects the formation of structurally sensitive mechanical properties — stress limit and yield value. Considering the qualitative correlation between yield value and hardness, it is possible to predict an increase in hardness including highly rigid materials.

Materials and Methods. Physical characteristics of the basic types of fillers that make up the reinforcers are considered, systematized and tabulated. M2-01 tin bronze (20 wt. % tin, 80% copper) was used as a bond. Ultradisperse natural diamond (UDND, 0.5-4 wt. %) was added to it, as well as powders of natural diamond (3/2 pm fraction, 7/5 pm, -40 pm) obtained through processing diamonds at the enterprise of “Sakha Daimond” JSC. The above materials were made on the crushing and screening equipment and shaking tables. The stages of obtaining powders were recorded using the raster electron microscopy. Vibroscreens were applied for the grain-size classification of diamond powders. Physical and mechanical characteristics of the produced samples were tested by standard methods. VLTE-500 electronic fourth-class laboratory balance was used for weighing. Density was determined by MK 0-25 mm micrometer according to GOST 6507-78.

Research Results. Porosity was calculated through the actual and theoretical density. It was found that with a decrease in the filler size, an improvement in the physicomechanical properties of the binder modified with a diamond powder is observed. The best performance was observed in the samples with the UDND filler.

Discussion and Conclusions. As a result of the study, it was recorded that the calculated data differ from the experimental data since they show an increase in the material hardening pro rata to the amount of the diamond particles introduced into the volume. An assumption has been made that the considered hardening model (Orowan model) does not take into account the formation of carbon and the agglomeration of diamonds into larger objects in the matrix volume under an increase in the number of input diamonds. If the UDND particle volume reaches 3%, the carbon con tent in the material increases. As a result, the filler particles are not fully oxidized, thus increasing the number of pores in the material.

Introduction. The development of computational-and-experimental methods for evaluating the force distribution pattern across the width of the toothed rim and in the circumferential direction of the toothing of a large wave gear is considered. The study is based on the results of the test tooth tensometry using scale modeling of prototype units. The work objective is to create a reliable experimental-theoretical model of the teeth force interaction in a large wave gearing. Such a solution involves the transformation of model sample deformations into a distributed load between teeth which will eliminate the basic uncontrollable nonlinear errors and improve the accuracy of estimation of force

Materials and Methods. An improved power analysis procedure of a large wave gearing, optimized by accuracy criteria, is developed. The accuracy of the research results is enhanced through improving physical and computational models. This approach enables to obtain reasonable dependences of the power factors distribution in a large wave gearing.

Research Results. The design shape of the control tooth is simplified; an invariant profile is introduced over the full width of the ring gear. Thus, non-linear distortions of the experimental results introduced by a variable tooth shape across the width of the ring gear are excluded. In this case, the installation of tensoresistors across the full width of the test tooth is possible. In addition, the proposed solution can establish the dependence of the teeth deformation across the full width of the ring gear, and not only in the extreme areas as suggested by the well-known techniques. The development of perfect physical and mathematical models enables to increase accuracy of the results of theoretical and experimental studies on power processes in the large wave gearing. The scientific-based two-parameter dependences of the force distribution in gearing are obtained.

Discussion and Conclusions. Approximation of the involute-tooth profile in the trapezoidal profile has simplified evidence of identity of the elasticity equations and the boundary conditions of mathematical models. The results obtained are applicable in the mathematical simulation of the planar stress state of teeth with nonlinear profiles. Comparative evaluation of errors introduced by deviations of geometry and dimensions of physical models and mathematical analogues supports the experiment correctness and the validity of the quantitative data obtained. The research results can be used in the improved calculation of the design parameters of the gear components in the engineering process of large heavily loaded wave reducers.

Introduction. Two factors of metal turning are compared: the dissipated temperature and the power of irreversible transformations in the material of the product and the tool. The paper is devoted to the issues of mathematical modeling of their link.

Materials and Methods. The mathematical apparatus is based on the modification of the Volterra equation which involves the use of double integral. It shows how the thermal energy released earlier during cutting affects the current state of temperature in the tool-to-work contact zone. In addition to the proposed new basic mathematical model, the processing effect of the observed data on the power of irreversible transformations and the measured temperature in the tool-to-work contact zone under metal turning are used. The experiments were carried out on 1K625 machine and STD.201-1 stand. A specialized software tool for processing information arrays describing the processes occurring during cutting (reaction forces, tool vibrations and power of irreversible transformations) was created in the Matlab package. The same tool has performed the temperature calculation in the tool-to-work contact zone.

Research Results. The procedure of parametric identification of the proposed basic mathematical model is carried out. The resulting model showed a high degree of proximity of the experimental data on the temperature in the cutting zone and the simulated level of thermal energy; but in the initial section of the measurable temperature dependence, the results of these two approaches are in rather poor agreement. This can be explained by an error of the experimental temperature measurement based on the estimate of the thermoelectromotive force (thermal EMF) output which is generated as a result of the dynamic thermocouple formation in the tool-to-work contact zone.

Discussion and Conclusions. The proposed mathematical model enables to adequately describe the conversion of the mechanical component of the cutting energy into the thermal component through the indicator of the total output power of the mechanical interaction in the cutting zone for all the processing time.

Introduction. Microhardness and wear resistance of the aluminum alloy (AK5M7) after its surface treatment through electrospark doping (ESD) using A (Cu) and P (Cu+P) electrodes with different applied energy is considered. The work objective is to study the relationship of the physicomechanical and strength properties of the surface of AK5M7 alloy obtained after ESD with copper and copper-phosphorus electrodes.

Materials and Methods. X-ray diffraction and X-ray fluorescence analysis methods were used to determine the phase composition, coherent-scattering regions (CSR), and the surface microstrain.

Research Results. It is established that with increasing energy, the values of microhardness and wear resistance increase when using both electrodes. The sample was modified by P electrode with the energy of 0.79 J. In this case, the maximum value of microhardness increased 5.3 times, wear resistance -1.6 times. It is found that with ESD, new intermetallic phases of Al₂Cu and Cu₃P are formed on the surface of the alloy under study. If the value of the energy used is maximum (0.79 J), the concentration of the Al₂Cu phase increases 5 and 9 times with A and P electrodes, respectively, and the concentration of the Cu₃P phase increases more than 4 times when using P electrode. The experimental data obtained suggest size reduction of the CSR and an increase in the microstrain values for all the Al, Al₂Cu, and Cu₃P phases on the surface.

Discussion and Conclusions. An increase in energy with the ESD involves an increase in the defective factors and a change in the phase composition of the newly obtained surfaces. This may explain the increase in wear resistance of the surface.

Introduction. It is acknowledged that electroelastic modules do not depend on the amplitude and frequency of oscillations. This approach is reflected in the Russian and foreign standards for determining the complete set of electro-elastic piezoceramics modules. For example, to determine d₃₁ piezomodule of a disc-shaped sample, it is required to take measurements in three frequency domains: in the first and second resonances, in the antiresonance region, and at frequencies much below 1 kHz. Accordingly, it is assumed that when determining d₃₁, the modules of the ceramic under study in the frequency range from 1 KHz to the second resonance are independent of frequency. The work objective is to study the frequency dependence of electro-elastic ceramic modules. In this case, a disc-shaped sample from LZT (lead zirconate titanate) is used.

Materials and Methods. Techniques of setting and solving problems of the stationary electroelasticity and sections of the electrical engineering basics are applied. To implement the finite element method, the perturbation technique and the ANSYS application package are used. The experimental results are processed in the MATLAB environment.

Research Results. For the LZT piezoelectric ceramics, the frequency dependences of various modules (piezoelectric d₃₁, dielectric ε₃₃^???????? and elastic modules of compliance ????????₁₁, ????????₁₂, ????????₁₃) were investigated. Radial oscillations of a discshaped sample with electrodes on the ends were considered. The sample thickness was 1 mm, the diameter was 40 mm, and the oscillation range was up to 700 KHz. First, the frequency dependence was studied for the elastic ceramic modules from the determination of ten resonance frequencies. Then, the frequency dependence of d₃₁and ε₃₃^???????? modules was determined from the measured values of the sample conductivity. For this purpose, we used the expression for the electrical conductivity obtained from the solution of the radial oscillations of the disc considering its thickness.

Discussion and Conclusions. A technique is developed for determining the frequency dependence of LZT piezoelectric ceramic modules. The disc-shaped sample was studied in 15650 KHz frequency range. It is shown that in the range up to 650 KHz, ????????₁₁, ????????₁₂, ????????₁₃ elastic modules with E superscript (it is omitted) or measured at dc field are practically independent of frequency. In the specified range, ε₃₃^????????, d₃₁, kp constants have an insignificant frequency dependence for the considered radial oscillations.

Introduction. Polymeric materials (PM) are increasingly used in various industries and agriculture. Under the action of UV light, PM are destroyed. UV stabilizers are used to protect PM from photodegradation. Their action is based on the absorption of the photoactive sunlight component or on the deactivation of excited molecules that have already absorbed a light quantum, as well as on the inhibition of dark light-induced reactions. The work objective is to provide a comparative analysis of compounds of the sterically hindered phenols (SHP) series and nitroxide radicals (NR) as the PM photodegradation inhibitors.

Materials and Methods. Reagents of the “purum” grade, LDPE premium grade 15803-020 polyethylene film were used for the investigations. The stabilizer was applied to the film by dipping. Carbonyl groups in polyethylene were determined by IR spectroscopy. IR spectra were recorded on Varian-640 instrument.

Research Results. 2,4,6-tri-tert-amylphenol (1), 2-methyl-4,6-di-tert-butylphenol         (2),         4-acetylamino-2,2,6,6-tetramethylpiperidin-1-oxyl (3), 3-carboxamido-2,2,5,5-tetramethylpyrrolin-1-oxyl (4) were tested as stabilizers for photo-oxidative degradation of polyethylene. It is known that the accumulation of carbonyl and hydroxyl groups is recorded in PM samples under irradiation in the process of photodegradation through the IR spectroscopy. The absorption band of the carbonyl group at 1720 cm^{- 1} appears in the IR spectra of oxidized polyethylene. The IR spectra analysis shows that the content of carbonyl groups in the check samples is significantly higher than in the samples treated by stabilizer solutions.

Discussion and Conclusions. The experiments show that ni-troxide radicals of 3-carboxamido-2,2,5,5-tetramethylpyrrolin-1-oxyl series and 4-acetylamino-2,2,6,6-tetramethylpiperidin-1-oxyl are the best photostabilizers of polyethylene. Moreover, there is no significant difference between the radicals of the 2,2,6,6-tetramethylpiperidine and 2,2,5,5-tetramethylpyrroline series. Sterically hindered phenols, under photodegradation, have a far smaller stabilizing effect, falling short of nitroxide radicals.

Introduction. The synthesized basic diagram of the frictional contact of solids in forging-and-stamping machines is considered. The possibility of obtaining the maximum load characteristics of the frictional contact within the variation interval of the friction factor is determined. The following two possibilities of frictional contact forces are indicated: they will be equal at the boundaries of the specified interval if there is maximum balance; they achieve the greatest stability under these conditions.

Materials and Methods. When the angle value changes, the position of the maximum point changes. This causes violation of the friction forces balance at the boundaries of the variation interval of the friction factor. In this case, the accuracy coefficient should be determined by the ratio of the maximum of function to the least boundary value. Doing this requires establishing trends of changing the boundary function values associated with the angle variation. To solve this problem, a new value of the pressure angle tangent was presented as a product of the coefficient of variation by the base value of the angle tangent.

Research Results. The results show high stability of the friction force under slipping of the frictional contact (FC) bodies. However, at large values of the pressure angle of sensing elements of the transducer, the maximum friction force can be for a short moment proportional to the current value of the friction factor.

Discussion and Conclusions. The upgraded FC basic diagram enables to theoretically obtain very high stability of the friction force. The FC should not vanish within the variation interval of the friction factor of the output parameter of the basic friction group (BFG) and at the maximum of function of the FC load capacity. A necessary condition for that is the transfer of full capacity of the additional friction group (AFG) by the sensing elements.

Introduction. The heating efficiency or regulation of the operating temperature of the fluid located in the gauge tank of a mobile pumping unit (PU) using the exhaust system of the internal combustion engine (ICE) is studied. The paper objective is to improve the design process and to reduce costs of field experiments.

Materials and Methods. To solve this problem, numerical analysis methods were used when calculating the heating systems of the gauge tank with the external location of the pipeline from the ICE exhaust system by the example of the widely used installations (TsA-320, UNB, AChF, etc.). Siemens STAR-CCM+, a non-stationary non-linear solver of gas-dynamic processes, was used, which evaluates the correctness of the problem statement and reduces significantly the costs of full-scale field tests.

Research Results. The study was conducted for the operating conditions of the cementing unit on the Kamaz-43118 chassis with the SIN-32 pump and a drive from the power take-off attachment on the gearbox of the chassis engine. In the calculation model, a convection-type heat transfer was applied between the body of the gauge tank and the surrounding air; between the body of the gauge tank and the liquid; between the chassis exhaust system duct and ambient air; between the exhaust system duct and exhaust gases. The following study results were obtained: characteristic curves of the temperature variation of the gauge tank liquid at the watch points; the distribution of the temperature field of the liquid in the gauge tank; the distribution of the ambient air temperature field; lines of flows and ambient air speed field and of the ICE exhaust gases.

Discussion and Conclusions. The study has revealed poor effectiveness of the considered structure. The data analysis allows us to offer an improved design of the gauge tank heating. The results obtained in the work can be used in the calculations of such devices used in the hydraulic fracturing units and grout machines.

Introduction. Some theoretical and engineering aspects of sealing joints through magnetostriction, as well as the polarization of the sealed medium under the external induction are considered. Control of surface roughness of joined parts to increase the joint density when induced by an external magnetic field is studied. The creation of electromagnetic barriers for the migration of molecules of the sealed medium through a sealer is considered. The work objective is to validate the technological conditions for sealing movable joints in the cases described above.

Materials and Methods. The conditions for ensuring the joint density are shown as a result of the contact problem solution and as a factor determined by the molecular-mechanical friction theory. Geometric, operational and tribological conditions of joint tightness are accepted. Damping properties of the fixed friction contact are determined by the molecular component. The theoretical and calculated analysis of the factors affecting the joint density is presented. Decrease in the smoothing depth, reduction of the ratio of transverse and longitudinal roughness steps, and increase in the contact area are indicated as the target results of the process preparation of the surfaces of the joint parts. Loss of tightness is defined as a specific transfer of molecules. They are transferred to the area of the joined surfaces or migrate freely through the sealer at the stages of sorption, diffusion and desorption. The predominance of any stage occurs when the entropy changes, and it is due to temperature and pressure. The schemes of sealing joints in the controlled magnetic field and of the dependence of magnetostriction and magnetostrictive stresses on the magnetic field strength are visualized.

Research Results. The stability of sealers in highly volatile and gaseous media during their polarization and magnetization in an external field is experimentally investigated. In the former case, the magnetic induction vector was first oriented perpendicular to the longitudinal axis of the joint. A drop in the magnitude of the magnetic flux was observed when the compound was under the on-load operation for 268 hours. The total operating time of the joint was 1070 hours. If the magnetic induction vector was oriented longitudinally to the shaft axis, the operating time to the correction of the field strength was 87 hours. In the gas environment, the operating time of the connection to the adjustment of the tension was 187 hours with a total operating time of 935 hours.

Discussion and Conclusions. The penetrating ability of pressurized media decreases in the “gas - vapor - liquid” series. It depends on the temperature at the joint contact. Depressurization can be traced through changes in the magnetic flux determined by the intrinsic magnetic permeability of the molecules of the sealed medium as they penetrate the interface surface.

To increase tightness, it is required to suppress the activity of molecules. For this purpose, ionization and induction in the constant and alternating magnetic field with the intensity of <60 kA/m are used.

Introduction. The problem of adequate modeling of physical processes and objects is an urgent task of modern science. Automation of work in this area increases the accuracy of modeling and saves money on full-scale modeling of objects under study. The research objective was to create a computer program that would automatically form dimensionless similarity criteria based on the initial set of parameters.

Materials and Methods. The calculation algorithm is based on к-theorem of similarity theory and the basic provisions of the dimensional theory.

Research Results. The computer program is developed. It enables to get all the theoretically possible similarity criteria for the simulation of the physical process or object of interest. Discussion and Conclusions. The results obtained can be used in the industrial and scientific modeling of physical objects of research, calculation of new similarity criteria, solving problems of describing complex processes, etc.

Introduction. The NTRUEncrypt cryptographic system, the calculation of the algorithmic complexity of the development of the NTRUEncrypt cryptosystem and its modifications are considered. The study objectives are to develop NTRUEncrypt, an efficient post-quantum cryptographic algorithm, which has high cryptographic resistance to quantum computer attacks, to work out a modification of the proposed algorithm, to analyze and experimentally validate its advantages.

Materials and Methods. A description of the NTRUEncrypt encryption system is proposed. The modification of the considered algorithm is studied; the block diagram of the implementation of the software based on it is presented. An example of the software operation and its characteristic is given. The reliability of the results is proved using the Mann-Whitney U test. During the experiment, the third-party software implementation of the RSA cryptosystem was used. A Stopwatch class element was introduced in the source code of all three programs of NTRUEncrypt, RSA, and NTRUEncrypt modifications. This class provides a set of methods and properties that can be used for the precise measurement of the execution time. Thus, it became possible to record the results of the time spent on all three basic stages: key creation, encryption and decryption of the message.

Research Results. The advantages of the developed cryptosystems in terms of the performance characteristics are proved. An experimental comparison of the implemented NTRUEncrypt algorithm and its modification is performed. All advantages of the latter are indicated.

Discussion and Conclusions. The advantage of using the NTRUEncrypt algorithm modification is experimentally validated. The new application is 25% faster to perform general work on key generation, encryption and decryption. In addition, the internal memory usage is optimized through reducing the weight of the source program file and the size of the secret key. When attempting to crack a ciphertext, cryptographic robustness and complexity of using quantum algorithms are shown.

Introduction. The solution to the problem of optimal control of the biogas process under its conversion in two digesters is considered. The work objectives are to propose a mathematical model of this process and to develop an optimal control algorithm.

Materials and Methods. The developed mathematical model describes the biomethanation from animal waste through the downstream processing of the substrate in two digesters. Cases of the same and different temperature media (mesophilic and thermophilic) are considered. An optimal control problem is defined as a Lagrange problem for this model. Its modifiers are the rates of substrate entry into the digesters. The algorithm for solving this problem is proposed; it is based on the numerical implementation of the Pontryagin maximum principle. When optimizing, a hybrid genetic algorithm was used with an additional search in the neighborhood of the best solution through the conjugate gradient method.

Research Results. A new mathematical model is developed. It describes the biomethanation during the downstream processing of the substrate in two digesters. A numerical algorithm for solving an optimal control problem is proposed and software-implemented. The numerical studies have shown that the biogas production rate is nearly twice as high for a thermophilic medium as for a mesophilic one. It is established that the downstream processing of the substrate in two digesters with the same temperature medium allows the biogas production rate to be doubled. If the temperature media in the digesters are different, then in the first of them, the mesophilic medium should be used, and in the second - the thermophilic medium. At this, the biogas formation rate is somewhat lower compared to the case when there is a mesophilic medium in each of the digesters; however, the degree of the substrate processing is by 10-15% higher.

Discussion and Conclusions. The results obtained can be used for the calculation and design of biogas plants, as well as in the development of appropriate software.