MATERIALS SCIENCES AND ENGINEERING, METALLURGY
The correlation between the synthesis modes, chemical composition, crystal structure, surface microstructure, and also the mechanical properties of thin nanostructured Ni – Fe films has been studied. Thin Ni–Fe films on the Si with Au sublayer were obtained using electrolyte deposition with different current modes: direct current and three pulsed modes with pulse duration of 1 s, 10–3 and 10–5 s. It is shown that a decrease in the pulse duration to 10–5 s leads to an increase in the film elastic modulus and the hardness due to the small grain size and a large number of grain boundaries with increased resistance to plastic deformation. The effect of heat treatment at 100, 200, 300, and 400 °C on the surface microstructure and micromechanical properties of the films was investigated. An increase in grain size from 6 to 200 nm was found after heat treatment at 400 °C which, in combination with interfusion processes of the half-layer material, led to a significant decrease in hardness and elastic modulus. Ni–Fe films with improved mechanical properties can be used as coatings for microelectronic body for their electromagnetic protection.
The layered multiferroics Co/PZT were obtained by ion-beam sputtering-deposition method, where PZT is a ferroelectric ceramic based on lead titanate zirconate of the composition PbZr0.45Ti0.55O3 with a thermostable plane-parallel ferroelectric/ferromagnet interface. Using cross-sectional scanning electron microscopy (SEM), we studied the interface of a cobalt layer up to several micrometers thick with a thick ceramic substrate of lead zirconate titanate. It has been shown that the use of a titanium dioxide barrier layer of TiO2 instead of PZT allows quality improvement of the interface by reducing the duration of ion-beam planarization of the ferroelectric substrate, and also to eliminate the formation of intermediate chemical compounds. Based on the data of X-ray phase analysis (XRD), it was concluded that the TiO2 layer is amorphous. Magnetoelectric measurements have shown that the use of titanium dioxide instead of PZT under appropriate planarization modes can increase the low-frequency magnetoelectric effect to 5 mV/(cm∙Ое), compared with structures with a sputtering planarizing layer of PZT, where the magnitude of the low-frequency magnetoelectric effect is 2 mV/(cm∙Оe). These results allow us to improve the characteristics of these structures when used as sensitive elements in devices for formation – processing of information and magnetic field sensors based on the magnetoelectric effect.
The results of an experimental determination of the characteristics of cyclic crack growth resistance of specimens made of stainless steel 08Kh18N12T are given. Compact samples 20 mm thick cut from Du 550–30 pipes of the primary circuit of the main circulation pipeline (MCР) were studied under eccentric tension in the initial state and after 100 thousand hours of operation in the conditions of the Novo-Voronezh NPP. Using a new engineering approach based on measuring the specimen tightening and constructing a cyclic elastoplastic fracture diagram for a specimen with a crack in the coordinates “tightening – the stress intensity factor, calculated taking into account the plasticity correction”, a calculated life estimation is given for the pipe of Du 550–30 MCР NPP, made of 08Kh18N12T steel, according to the criterion of cyclic crack growth resistance, taking into account operational degradation of properties caused by the running time of 100 thousand hours. The life (survivability), expressed in a number of cycles of change in internal pressure, for a pipe with the most dangerous defects (surface semi-elliptical crack and combined defect “pitting + crack”) is determined. An analysis of the influence of the level of initial damage and the type of hazardous defect on the survivability of the pipes is made. The results can be used to analyze damage and predict the life of pipes made of ductile metals and alloys, in cooling systems of reactors, as well as main pipelines of hydrocarbon transport.
The physico-mechanical and technological characteristics of mixed waste of thermoplastic polymers, including that from the recyclable electronic and electrical equipment based on ABS plastic, were investigated. Target modifying additives were introduced into the composite system to improve the compatibility of polymer components of mixtures and the stable rheological properties of composition during processing. It is established that the secondary polymers behavior in their mixtures is caused by combination of their rheological characteristics and other parameters of mutual compatibility, that has significant impact on phase composition and microphases mutual order. Dispersed additives make a significant contribution to these processes, affecting the structuring of the associated polymer microvolumes. Target regulation of the rheological properties of components will ensure the achievement of acceptable and reproducible physico-mechanical characteristics and technological parameters of process, which will create prerequisites for the production of competitive products with a high guaranteed service life without use of scarce raw materials. Composite materials have been developed that are adapted to stable processing by extrusion, injection molding, and formation molding into technical products with acceptable performance characteristics.
The stress-migration phenomenon in films of alloy Al–Si which is observed at a current of high density (an order 105 А/mm2) is investigated. By results of researches the technical decision which allows quality raise of obtained film structures is offered. Its essence consists in formation in films the traps for migrating atoms of aluminium at course of a current of high density at the expense of formation the passive layer of TiN on the metal layer surface, for example, Al–1,5 %Si. In the presence of advanced relief of a surface of modern integrated circuits, for example with sub-micron sizes of the topology elements, the thickness and structure of metal current-carrying films on relief steps differs from what are located on planar sites. It leads to occurrence of essential gradients of mechanical pressure which are stress-migration motive power. As it is known, that temperature factor of linear expansion of aluminium is approximately 20 times, than SiO2, that causes active generation of dot defects in a layer of the alloy on the base of aluminium which is much more plastic than SiO2. Under the influence of a gradient of residual pressure, dot defects, existed in films, for example vacancies, come to movement mainly on border of metal - dielectric and in due course under the influence of a current of high density lead to formation of group defects in an alloy film, in particular emptiness, hills etc. Since stress-migration processes on these sites occur most intensively, as a result there is a rupture of films mainly on steps of a topological relief. Results of the research have passed approbation and can be used at manufacturing of silicon semi-conductor devices and integrated microcircuits.
The dependences of the structure and properties of polyamide 6 (PA6) with a functionalized polyolefin (FPO) mixtures on the dispersing method of organically modified clay Cloisite 30В (Cl30В) were studied. The concentration of Cl30B organoclay in PA6/fPO mixtures was constant and amounted to 3.0 wt.%, and the content of fPO varied from 10 to 50 wt.%. Compounding of the mixtures was carried out in the melt using a twin-screw extrusion reactor-mixer. Organoclay was introduced into the composition of the mixtures in two ways: simultaneously with all polymer components (one-stage process) and from the previously obtained Cl30B concentrate into fPO (two-stage process). It is established that the introduction of Cl30B organoclay into the composition of the PA6/fPO mixture using the two-stage technology makes it possible to obtain nanocomposites with increased yield strengths (5–6 %), tensile strength (9–15 %), and elongation at break (1.2–4 times) compared with nanocomposites prepared according to a single-stage technology. At the same time, nanocomposites obtained by a single-stage technology in which PA6 forms a dispersion medium, regardless of the type of incision and the test method, have higher impact resistance (up to 1.2 times) than materials prepared by the two-stage method. This is explained by differences in the degree of dispersion of the nanofiller and the level of interphase interactions between the polymer components and nanoparticles, as a result of which the crystallinity of the components in the mixtures changes, as well as the complex of their rheological and mechanical characteristics. It was also shown that Cl30B organoclay additives, irrespective to the method of its introduction, increase the thermal stability of PA 6/fPO mixtures in comparison with the initial PA6. The results can be used in the development of real technical nanocomposites with improved properties based on PA6 and fPO.
MECHANICAL ENGINEERING AND MECHANICS
The development tasks of OJSC “BELAZ” – Management Company of Holding “BELAZ-HOLDING”, are defined, which consist in using and introducing the latest achievements in the field of technical sciences and innovative technologies created on their basis into the design and production processes of mining equipment; development of new competitive products and promising sales markets, diversification of exports. Together with scientific organizations, studies have been carried out that have allowed us to develop new and improve existing methodological approaches to solving urgent problems in all problematic areas of creating modern mining dump trucks especially and in excess of extra heavy lifting capacity. OJSC “BELAZ” is the only manufacturer and supplier of dump trucks with a carrying capacity of 450–500 tons. As a result of research on the creation of such machines, the model of a short-base maneuverable dump truck with a rigid frame of a special design was first recommended, which reduces the center of gravity and loading height of a mining dump truck, designed according to the 4 × 4 scheme (two drive axles) with double axle busbar and the use of existing tires with a maximum carrying capacity of 104 tons. The proposed and comprehensively tested new layout solutions give reason to believe that the development of dump trucks with a carrying capacity of up to 600 tons is a reality when mastering the production of tires with a carrying capacity of more than 110 tons. А new generation of dump trucks with hydromechanical transmissions is designed; work is underway to create robotic complexes for the mining industry. Particular attention is paid to computerization, digitalization and environmental friendliness of mining equipment, ensuring the reliability of technology by creating and applying new structural materials and technologies for large parts and systems.
A method for processing high-precision conical surfaces under conditions of free grinding on a lever machine is proposed, which allows adjusting the process parameters taking into account the technological heredity of the workpiece from the point of view of the distribution pattern of the allowance to be removed from its surface. The scheme of implementation of the method in which the main links are a tool in the form of a faceplate and a separator for maintaining the required accuracy of its flatness. In order to develop a method of targeted control of the actuation of the working surface of the tool to maintain the required accuracy of its flatness, mathematical modeling of the motion patterns of the links of the actuator of the base machine, on which the proposed device for processing conical parts is installed, was performed. In the process of mathematical simulation structural analysis of the executive mechanism of the lever machine is carried out, connection between the generalized coordinate and provisions of links of the executive mechanism of the lever machine is established, position of the lever and the upper link in the vertical plane is probed, geometrical parameters of reflexive rotational motion of the upper link are considered, the ratio for calculation of length of a crank of the executive mechanism of the machine depending on amplitude of figurative movement of its output link is obtained. An analytical relationship has been established between the input and output links of the machine actuator, which makes it possible to calculate the length of the first of the marked links depending on the required amplitude of the oscillatory motion of the second of them and creates the prerequisites for the development of engineering methods for controlling the process of forming high-precision conical surfaces under conditions of free grinding.
The work is devoted to solving the axisymmetric problem of the theory of pressing porous bodies with practical application in the form of force calculation of metallurgical processes of briquetting small fractional bulk materials: powder, chip, granulated and other metalworking wastes. For such materials, the shape of the particles (structural elements) is not geometrically correct or generally definable. This was the basis for the decision to be based on the continual model of a porous body. As a result of bringing this model to a two-dimensional spatial model, a closed analytical solution was obtained by the method of jointly solving differential equilibrium equations and the Guber–Mises energy condition of plasticity. The following assumptions were adopted as working hypotheses: the normal radial stress is equal to the tangential one, the lateral pressure coefficient is equal to the relative density of the compact. Due to the fact that the problem is solved in a general form and in a general formulation, the solution itself should be considered as methodological for any axisymmetric loading scheme. The transcendental equations of the deformation compaction of a porous body are obtained both for an ideal pressing process and taking into account contact friction forces. As a result of the development of a method for solving these equations, the formulas for calculating the local characteristics of the stressed state of the pressing, as well as the integral parameters of the pressing process are derived: pressure, stress, and deformation work.
POWER ENGINEERING, HEAT AND MASS TRANSFER
The objective of the present work was to study heat and hydraulic parameters of an air cooling apparatus of oil (ACAO), whose geometry of its flow-through part is changed to decrease hydraulic losses in its air conduit and to increase the cooling efficiency of oil. Using numerical simulation methods of heat transfer, we have developed and tested the computational techniques applied in a wide class of heat exchange apparatuses, including those consisting of the sections of finned flat tubes manufactured by extrusion with subsequent deforming cutting. We have proposed to make a finned part of a heat-exchange surface in the form of porous inserts. This has allowed us to reduce numerical simulation equipment requirements and to decrease computational time. Predicted results well agree with experimental data; their analysis shows that the calculated value of thermal performance of the oil cooler due to the revealed construction drawbacks of the air conduit is by 19 % less than that of the designed one. Based on the results of the numerical simulation studies, a number of recommendations have been made how to improve the layout inside the air cooling apparatus for oil in order to enhance its thermal performance and aerodynamic quality. In particular, we have proposed to mount new fan blades to enhance its performance; to change the construction of the air outlet valve by taking away a baffle that partially overshadows the exit area of the bottom fan; to modify the shape of the bottom collector of the oil cooler in order to make a uniform velocity profile at the entrance of cooling sections. Connecting in series heat exchange sections may be a perspective engineering decision. The outcomes of all proposed engineering decisions can be assessed by numerical simulation methods that will allow us not to design expensive equipment.
DIAGNOSTICS AND SAFETY OF TECHNICAL AND ENVIRONMENT SYSTEMS
The article presents the results of computational modeling of the development of accidents in the containment of NPP with water-water energy reactor (WWER) using the COCOSYS software. The containment of the Balakovo NPP with WWER-1000/V-320 was selected as the object of study. The results of the calculation of environmental parameters in the containment during a beyond design basis accident with a “large” leak from the primary circuit at the following initial events: break of the main circulation pipeline DN850 with a full cross section at the reactor inlet, with simultaneous failure of all AC sources including diesel generators for a long period, without operating personnel intervention. A comparison of the results of calculations with the results obtained using the ANGAR software certified by Rostekhnadzor is performed. The calculation results are in good agreement: emergency scenarios are similar; the maximum deviation from absolute pressure values is less than 10 %. Thus, it was concluded that the analysis of processes occurring in the NPP containment during an accident can be performed using the COCOSYS code. This software can be used to independent safety assessment of NPP required by the IAEA standards.
To study the kinetics of subcritical systems and determine the optimal conditions for the transmutation of longlived radioactive waste in the neutron spectrum of ADS-systems the “Yalina” research nuclear facility was created at Joint Institute for Power and Nuclear Research – Sosny (Minsk, Belarus). The main safety indicator of a subcritical system (active zone reactivity) was measured for a “Yalina-Thermal” assembly via three independent methods: inverse multiplication, probabilistic and impulse ones. For the inverse multiplication method, the neutron flux density was monitored during assembly loading. For a fuel load of 285 EK-10 rods the neutron multiplication was M = 22.3±0.6, and the effective neutron multiplication coefficient was keff = 0.9551± 0.0016. The probabilistic method (Feynman-alpha method), based on measuring fluctuations in the neutron density level within a system with a fission chain reaction, gave the ratio of the variance to the average counting rate value D/n = 1.779±0.005, which corresponds to keff = 0.9597 ±0.0003. The pulse method is aimed at studying the neutron flux behavior of after the neutron pulse injection into the breeding system. Measurements were held with the same setup, used in the Feynman-alpha method. The measured decay constant of instantaneous neutrons is α = –670±0.7 1/s, which corresponds to keff = 0.9560±0.0001. The effective multiplication factor keff of the subcritical assembly “Yalina-Thermal”, obtained via three different independent methods, is around average value of keff = 0.9569 ± 0.0018. The methods considered can be used for subcritical level monitoring for ADS-systems and research nuclear facilities.
The purpose of the study is calculation research of the radiation characteristics of fission products and actinides at different phases of spent nuclear fuel (SNF) management of the Belarusian Nuclear Power Plant (NPP). The study is aimed at the scientific support of the government decision as determined by the “On approval of the spent nuclear fuel management Strategy of the Belarusian nuclear power plant”. А probabilistic forecasting model and an effective code CUB for the spent nuclear fuel radioactivity inventory assessment were developed by the authors. Radionuclides activities as function of nuclear fuel burnup for nuclear fuel with the initial enrichment on the 235U equals to 4.81 % on the base of approximation relations of Regulation RB-093-14 (Moskow, 2014) have been calculated. Basic relations between specific activities of the main hazardous fission products and actinide, the SNF burnup and initial degree of fuel enrichment were analyzed. The rates of decrease of individual and total fission products and actinides activities of the Units №1 and 2 of the Belarusian NPP were obtained depending on the specific phase of spent SNF management. The results are of value for decision-making on ecology acceptable SNF management option introduced by Spent Nuclear Fuel Management Strategy of the Belarusian NPP.
SCIENTISTS OF BELARUS
ISSN 2524-244X (Online)