Search

Using the created experimental equipment for testing metals by the method of instrumented indentation, a procedure for determining Brinell hardness during the nondestructive testing of structural elements has been developed. In contrast to the conventional method, the hardness is determined by the proposed procedure using the proportionality parameter of plastic indentation, a, which is equal to the slope of the instrumented indentation diagram in the coordinates maximum force of cycle Fmax – residual indentation depth hp after removing the test load of this cycle. Based on the results of a series of tests by the method of instrumented indentation of hardness standards, a linear correlation dependence was obtained between the Brinell hardness value and the proportionality parameter of plastic indentation in a wide range of measured hardness values of 110–650 HBW. The peculiarities of using this procedure and its limitations are analyzed on a number of structural carbon, heat-resistant, and high-strength steels. It is shown that the Brinell hardness measurement results, obtained by the improved procedure, agree within the permissible error with the results of the conventional DSTU ISO 6506-1:2019 method. The difference between their values does not exceed 3.9%. The presented improved procedure can be used in the laboratories of research and educational institutes, central factory laboratories and specialized divisions of various subordination, and other organizations involved in monitoring the condition of the operating critical equipment and setting its further service life both in the laboratory and in the field. [ABSTRACT FROM AUTHOR]

This study conducted modernization of the VK-350 instrumented drop weight impact testing machine (DWITM) developed at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine, equipped with a high-speed strain and force recording system that allows recording a load diagram with a sampling rate of up to 20 MHz, and heating and cooling systems for testing specimens in a wide temperature range. Modernization was carried out to expand the functionality of the DWITM, namely, a new dynamometer and specimen fixing units for impact shear, compression and dynamic pushing tests were installed. The new dynamometer was calibrated for two ranges of amplification and test specimens of various types were tested. The DWITM was also equipped with a video recording system, which includes a high-speed PHOTRON FASTCAM NOVA S9 camera that allows recording the deformation and fracture process at a speed of up to 200,000 frames per second. The camera is equipped with a 12x zoom lens and stroboscopic high-frequency lamps for illumination with the GSVITEC MultiLED G8 control system. Based on the results of the impact bending and shear tests, video signals of the deformation and fracture of the specimens were obtained, which made it possible to determine the time of onset of plastic deformation and formation of adiabatic shear zones in the impact shear specimens, as well as the moment of crack appearance on the side surface of the Charpy specimen and to estimate the rate of its propagation. [ABSTRACT FROM AUTHOR]

The instrumented indentation method, based on the digital recording of the parameters of the entire process of continuous local deformation of the material by an indenter, provides more complete and accurate information about the material's behavior under load. Obtaining such information without compromising the integrity of a critical structure during operation increases its value. Therefore, more and more attention has recently been paid to portable installations and devices that use the instrumented indentation method. To date, no such equipment is manufactured in Ukraine. Therefore, there is a need to develop portable equipment for conducting such tests in the field under various modes of static and cyclic loading in the macro range of forces. The paper describes an updated portable installation PIIT-02M for determining the strength characteristics of structural elements in service by instrumented indentation, which was developed following the requirements of ISO 14577 and is intended for testing at the macro level. The system of fastening the portable installation on the test object was updated from mechanical (hooks and chains) to electromagnetic. This made it possible to conduct tests on pipes and flat surfaces, including sheet materials and structures made of them, significantly increasing the test efficiency and expanding the range of applications. Comparative tests on a 12 mm thick structural carbon 20 steel plate using the previous mechanical fastening system and the new electromagnetic one showed that the indentation diagrams obtained overlap well. Based on the results of tests of high-strength steels, the portable installation PIIT-02M allows one under both laboratory and operating conditions to record the process of indentation of the indenter into specimens of structural materials with high accuracy and, accordingly, to determine their mechanical characteristics by instrumented indentation. [ABSTRACT FROM AUTHOR]

Reliable operation of products made of high-strength alloy steels is ensured by the availability of effective methods and equipment for studying their mechanical properties during manufacturing and operation. One of the most important properties of such products is resistance to impact damage. The implementation of such tests is limited by the high financial costs of manufacturing specimens and impactors (ammunition), the complexity of conducting them, recording the results, and the lack of initial data. Recently, alternative methods have been developed, such as static and dynamic pressing of plate specimens. In this case, the shape of the impactors (punches) is similar to the shape of the impactors used in punching due to similar material behavior. The pressing tests make it possible to confirm the parameters of the models of material deformation and fracture, which are necessary for numerical calculations of complex structures under various types of loads. The equipment and methodology for studying the behavior of high-strength materials under static pressing are presented. It is established that recording the punch movement using a strain gauge can significantly reduce the elastic deformation component of the power chain of the test machine and fixture loading. A series of tests were performed on specimens cut from Armox 500T steel sheets with thicknesses of 3, 5, and 10 mm for static pressing by different punches (conical, flat, and hemispherical). It was shown that the plastic properties of the material decrease with increasing thickness of rolled steel, regardless of the type of punch. The obtained results confirmed the operability of the presented equipment and methodology and can be used in numerical modeling of deformation and fracture processes of high-strength steels. [ABSTRACT FROM AUTHOR]

The paper presents the results of a computational assessment of the shape change of the WWER-1000 reactor core baffle using modern approaches to modeling the processes of radiation swelling, radiation creep, and subcritical damage of irradiated metal by the mechanism of ductile fracture. To simulate radiation effects, mathematical models are used that consider the influence of the stress state and accumulated irreversible deformation on the swelling and creep of austenitic steels exposed to neutron irradiation and elevated temperature. The increased volume concentration of ductile fracture pores in the irradiated metal is considered using the modified Huang equation and the proposed equation derived from Kachanov's solution for a spherical cavity in an unbounded elastic-plastic medium. The determination of the stress-strain state of the WWER-1000 reactor cavity and the inner vessel shaft is based on solving a nonlinear boundary value problem of thermomechanics, which allows describing the kinetics of the coupled processes of elastic-plastic deformation, radiation swelling, radiation creep, contact interaction, and subcritical damage of irradiated metal depending on the accumulated dose of neutron irradiation. The computational analysis is based on a mixed finite element method scheme that provides a continuous approximation for both displacements and stresses and strains, which makes it possible to determine the shape change of the shielding with a high degree of accuracy. The calculation was performed in a two-dimensional formulation for the cross-section of the shielding with the maximum height of the damaging dose and irradiation temperature under the condition of generalized plane deformation. The calculation results were obtained using the median parameters of the temperature-dose dependence of free swelling of austenitic steel 08Kh18N10T. Based on the calculated data, the influence of radiation effects and metal damage according to the ductile fracture models on determining the shape change of the WWER-1000 reactor baffle under conditions of long-term operation was analyzed. [ABSTRACT FROM AUTHOR]

High-strength and armored steels are used in different structural elements and in the development of new military equipment operating under extreme conditions, including high-velocity impact interaction and explosive loading. Under such conditions, the fracture is induced by the combination of different mechanisms that depend on the mechanical properties of materials, strain rate, stress state, temperature, etc. Experimental and computational research methods combine to gain additional information on the behavior of high-strength materials essential for modern military equipment in operation. The test results for the penetration of ARMOX 500T steel target 10 mm thick at different loading rates using a ballistic pendulum are presented. The results of a set of piercing tests with the strikers of three types became the basis for evaluating the integral energy characteristics of material deformation and fracture induced by impact interaction; the target penetration pulse against loading rate was constructed and used in the numerical simulation of impact interaction and validation of model material parameters. The finite element method was employed to numerically simulate the processes of dynamic target penetration with the Johnson-Cook material deformation model. The loading and strain rate effects on the results are estimated. The calculation results are compared with experimental data. [ABSTRACT FROM AUTHOR]

Recently, much attention has been paid to the study of the deformation and failure features of high-strength steels under extreme loads, under which they are mainly operated. One of the topical issues is the correct determination of the parameters of deformation models of materials. The use of tests for barrier penetration at high speeds of 100–1000 m/s is quite complicated and expensive, and also does not allow to obtain enough information. Therefore, alternative experimental methods have been developed recently, which include static and dynamic punching tests of thin sheet specimens at speeds of up to 10 m/s. Such tests are simpler and allow to obtain more information about the behavior of high-strength materials in conditions that simulate operational ones. This paper presents the results of static and dynamic punching tests on thin sheet specimens of 50×50 mm size and 1 mm thickness made of Armox 500T armor steel. The static punching tests were carried out on an Instron 8802 servohydraulic machine, for which special equipment was manufactured. The dynamic punching of thin-sheet specimens was carried out on an instrumented vertical impact tester equipped with a high-speed strain and force recording system. To conduct such tests, the experimental equipment was updated, and a design of special supports for the rigid fixing of thin-sheet specimens was developed. The loading speed was varied from 0.5 to 10 mm/min for static punching and from 3 to 5 m/s for dynamic punching. The tests were conducted using three types of punches: conical, flat and hemispherical. According to the test results, new data on the influence of strain rate on the features of deformation and failure of Armox 500T armor steel were obtained. The influence of the type of punches on the nature and mechanisms of failure of thin-sheet specimens under static and dynamic punching was investigated. It was found that an increase in loading speed leads to an increase in specimen failure force. Thus, the resistance to deformation increases by approximately 20% with an increase in the loading speed from 0.5 mm/min to 5 m/s. [ABSTRACT FROM AUTHOR]

The processes of impact loading have been studied for a long time, but there are still many questions, the solution of which is vital for various industries, especially for the military. This paper presents the results of comprehensive experimental studies to determine the energy characteristics of fracture during crack initiation and propagation in Charpy specimens of high-strength steel Hardox 450 and armored steel Armox 500T, cut from sheets in two different directions, during impact bending tests. The tests were carried out on an instrumented vertical tester equipped with a high-speed data recording system in the temperature range from –196 to 300 °C. According to the test results, the load diagrams in the force-time coordinates were obtained. The total deformation and fracture energy and its components, nucleation energy, ductile growth, brittle crack slip, and ductile fracture energy of the specimen were calculated. Using quantitative fractography methods, the specimens' fracture surfaces were studied, and the specific deformation and fracture energies and their components were determined. It is shown that the direction of cutting of specimens significantly affects the energy characteristics of fracture. On the upper shelf in the specimens cut in the longitudinal direction, the energy value is higher than for the transverse direction for both steels. This difference is approximately 38% for Hardox 450 and almost 118% for Armox 500T. Using a high-speed recording system allows us to determine the average crack propagation velocity and crack velocities in separate areas by comparing the corresponding zones on the load diagram and on the fracture surface of the specimens. The results showed that the average crack propagation velocity for specimens cut in the transverse direction was 10–15% higher than for specimens cut in the longitudinal direction for both steels. [ABSTRACT FROM AUTHOR]

The shortage of metal, which can be used to assess the degree of its degradation, makes it necessary to look for ways to increase the information content of tests to justify the extension of the service life of critical equipment and structural elements of various industries. Today, impact bending tests of various types of specimens are one of the most common types of experimental determination of the energy and mechanical characteristics of structural materials. Different types of impact testers are used to perform them. Conventional pendulum impact testers do not allow us to obtain detailed information about the nature of specimen failure and features of crack propagation in the material, so recently, much attention has been given to the instrumentation of experimental equipment using modern recording systems. In this work, the instrumentation of an MK-30 pendulum impact tester was carried out using a multichannel high-speed strain and force recording system, which allows obtaining results with a sampling rate of up to 20 MHz. A procedure for the calibration of the strain gauges located on the pendulum blade and calibration of the recording system and amplifier blockt for three different signal levels is described. Test trials of specimens of different sizes made of different types of steels were carried out, and loading diagrams in the force–time coordinates were obtained. It is shown that the obtained loading diagrams can be used to calculate the values of the total energy of both deformation and fracture and its components: crack nucleation energy, ductile crack growth energy, brittle crack breakthrough energy and final ductile fracture energy. Using fractographic analysis, the characteristic portions of loading diagrams were compared with the corresponding zones of the fracture surfaces of specimens. The high sensitivity of the recording system allowed us to calculate with high accuracy the values of the crack at brittle fracture and its average velocity in test specimens. [ABSTRACT FROM AUTHOR]

The methodology for determining more reliable values of hardness of high-strength steels has been improved, which contains, in addition to the requirements of DSTU ISO 6506 standards, requirements for the preparation of the outer (front) and back sides of the sheet in the plane of rolling by removing the decarburized metal layer, requirements for surface cleanliness and the choice of indenter load. The influence on the measured hardness values of the surface decarburized metal layer that occurs on the front surfaces of the sheet as a result of "burnout" of oxygen on the surfaces of the sheets during the manufacturing process is determined. This decarburized metal layer distorts the hardness values obtained during indentation. By layer-by-layer metal removal, the size of the decarburized layer was determined. The obtained results made it possible to determine the nature of the hardness distribution over the thickness of the sample, to establish the thickness of the decarburized layer and to determine the level of surface cleanliness of the base metal sufficient to obtain reliable hardness values. The results of experimental studies on determining the Brinell hardness values of high-strength steels are presented. The experimental data show that the existing regulatory documents do not fully provide reliable information about the properties of materials. The requirements for instruments for testing high-strength steels for hardness by the Brinell method are considered. The analysis on the choice of load on the indenter is made. The load is selected such that the ratio of the diameter of the imprint to the diameter of the ball is in the range from 0.3 to 0.4. [ABSTRACT FROM AUTHOR]

The issue of composing a layout of a photovoltaic system is associated with solving the issue of optimizing the tilt angle of the module relative to the horizon and cardinal points in order to maximize the solar radiation flux at its receiving surface. The efficiency of the photovoltaic module functioning is inherently related to the conditions of its illumination, which are determined by their spatial orientation and mutual placement (technological interval between the rows of modules). Partial shading is one of the main reasons for the decrease in the photovoltaic system efficiency. A lot of research in the field of photovoltaic module shading is aimed at studying its electrical characteristics and practically does not consider the joint solution of the issues of their geometric and spatial placement. The purpose of the study is to analyze the impact of the technological interval between the rows of photovoltaic modules in the limited area on the efficiency of their functioning, taking into account the spatial orientation of their receiving surfaces and the size of the area allocated for their installation. The formulation and solution of the issue of determining the layout of the photovoltaic system modules, which ensures the maximum total efficiency of the functioning of the modules, makes it possible to obtain the highest level of electrical energy generation per 1 m2 of modules with the optimal area occupied by them. The analysis of the options for filling modules (for various cases of their spatial orientation) of the photovoltaic system located in the limited area (constant area and shape of the area for their placement) showed that an increase in the number of rows does not always give an increase in electric power generation proportional to the area of modules put into operation due to deterioration of their illumination conditions and it can even lead to a decrease in the utilized solar energy resource below the similar value obtained on the receiving surface that is horizontal to Earth's surface. [ABSTRACT FROM AUTHOR]

A nonstationary numerical procedure and program for determining the heating temperature through flat "transparent screens" (TSs) of solar power plants have been developed. The developed procedure makes possible to consider volume absorption of incident and self-radiation of TSs. The program is verified according to mean equilibrium heating temperatures for the glass under a stationary mode of operation. We obtained that under a TS thickness up to 10 mm, the difference between mean equilibrium temperatures is lower than 0.1%. We reveal that a temperature drop in TSs of solar power plants even for glass with a thickness up to 5 mm and if the receiver is heated up to 60°С is not higher than 0.5–0.7°С. We obtain the same gradients in the numerical models for TSs with surface absorptance and heat spectrum emission, but the difference between absolute temperatures can run up to 6°C. The procedure and the program with volume absorption and emission in TSs can be used in nonstationary heat models for solar collectors and energy efficient windows and under heating 1D semi-transparent bodies by solar or laser radiation. [ABSTRACT FROM AUTHOR]

The paper presents the results of the application of the refined calculation guidelines to the analysis of the stress-strain state and fracture resistance of the equipment elements of the NPP primary circuit system with WWER reactor, in particular, the cylindrical part and the zone of the reactor pressure vessel inlet nozzle, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft under the operating and emergency modes of thermomechanical loading. The calculation methodology is based on the use of the modern models and methods of solution to the nonlinear boundary tasks of non-isothermal thermal viscoplasticity and tasks of fracture mechanics using the refined mixed schemes of the finite element method with increased accuracy. They allow one to obtain reliable solutions to the tasks considering the deformation history of thermomechanical loading, modern concepts of fracture mechanics and approaches to the modeling of brittle-viscous fracture defects, irradiation swelling and creep of metal, as well as as the structural elements, under the conditions of elevated temperature, intensive neutron irradiation and nonstationary modes of thermomechanical loading. The authors obtained and analyzed the calculation results for the cylindrical part and zone of the inlet nozzle of the WWER-1000 reactor pressure vessel, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft using the proposed guidelines. The results imply the possibilities of the proposed recommendations and make it possible to analyze some general tendencies and features of the application of the refined calculation models to justify the strength and life extension of the NPP structural elements under investigation. [ABSTRACT FROM AUTHOR]

The peculiarities of the calculated assessment of the stress-strain state and the shape change of the WWER-1000 reactor core baffle under the design and long-term operation conditions are considered. The computational analysis results of the baffle and internals using modern approaches to modeling the processes of radiation swelling and radiation creep of austenitic steels, which are under the effect of neutron irradiation and elevated temperature, are presented. Basic principles of stress-strain calculations of baffle and shaft concerning conditions of their contact interaction are formulated. Calculations are performed in the two-dimensional formulation for a cross section of the baffle with the maximum over-height damaging dose and irradiation temperature under the condition of generalized plane deformation. The data concerning the change in shape of the baffle are obtained from the solution of a coupled contact problem of heat transfer and radiation creep in dependence of the accumulated damaging radiation dose. Calculations of the temperature field and the stress-strain state are performed, taking into account temperature redistribution through the violation of design conditions of coolant flow in the area of the baffle-shaft contact. It is found that taking into account radiation creep contributes to a decrease in the stress level but increases swelling and displacement, which adds conservatism to the predicted estimate of the change in shape of the baffle in comparison with data without taking into account creep. Results of calculations are received using median and conservative parameters of the temperature dependence of free swelling of 08Kh18N10T austenite steel. Obtained results allow one to analyze some general tendencies and peculiarities of applying modern models of radiation swelling and radiation creep to determine stress-deformed mill and change in shape of baffle, taking into account contact interaction with shaft depending on accumulated irradiation dose. [ABSTRACT FROM AUTHOR]

Based on the experimental studies and the corresponding analysis of regulatory documents governing the hardness measurements by the Brinell method, the methodology for determining the hardness of high-strength sheet steels was developed. It allows one to obtain more accurate values of some characteristic cases that led in practice to issues of the inconsistency of metal quality with the stated characteristics. In addition to compliance with the requirements of DSTU ISO 6506, the methodology contains additional requirements to take into account several factors specific to this class of materials, the choice of ball indentation, the load level, the friction force during ball indentation, heterogeneity of structures, surface preparation purity, etc. In developing the methodology, a cycle of studies was carried out to determine reliable Brinell hardness measurements according to DSTU ISO EN 6506 on the example of Armox 500T and Hardox 450 sheet steel, which made it possible to determine the hardness distribution pattern over the sample thickness, to establish the thickness of the decarburized layer, to determine the purity of the base metal surface sufficient to obtain reliable hardness measurements, that is without decarburized layer and to decide the indenter choice and the load level on it. It is recommended that the direction of the line along which the measured hardness is measured be placed along the sheet rolling axis with subsequent determination of the average hardness value. Increasing the number of prints significantly reduces measurement errors due to the ambiguity of the contour of the print caused by the metal sliding. [ABSTRACT FROM AUTHOR]

Results of complex experimental investigations on the determination of energy characteristics of fracture propagation in Charpy specimens cut in three different directions during impact bending tests for heat-resistant 15Kh2NMFA steel are presented. Tests were conducted over a wide temperature range on an instrumented vertical coping equipped with a high-rate data logging system. According to the test results, load diagrams were obtained. Total strain and fracture energy and its components were determined: crack nucleation energy, ductile crack growth energy, brittle crack propagation energy, and ductile final rupture energy. The use of quantitative fractography methods made it possible to determine both the specific strain and fracture energies, their components, and the average propagation rates of brittle and ductile cracks in the specimens' material. Critical brittle fracture temperatures were determined by two methods. The cutting direction of specimens significantly influenced the fracture energy characteristics and crack propagation rates in the material, which might affect the accuracy of strength and resource estimation of the NPP first contour components. [ABSTRACT FROM AUTHOR]

The information on the various parameters of solar radiation should be sufficient, relevant, accessible from the point of view of design, optimization, and justification of the parameters of photovoltaic installations in the place of its proposed location. However, in spite of the large number of sources of actinometrical information, certain difficulties arise when conducting solar engineering calculations associated with database limitations, the large distance from the considered geographical point, or the laboriousness of the research that are needed to be carried out. The purpose of the study is to analyze the available data on the solar energy resource for a set geographic point (46.8° N, 40.6 E), obtained by the indirect method for assessing the parameters of solar radiation using data from ground-based metrological stations; indirect method for assessing the parameters of solar radiation using satellite measurements; calculated method for determining the intensity of solar radiation; and experimental study of the characteristics of solar radiation. The analysis showed that not all approaches provide data on the direct and diffused components of solar radiation. In addition, the availability of hourly values of solar radiation is very important, because only they make it possible to predict the mode of operation of a photovoltaic installation and coordinate its mode of operation with the load schedule of the consumer. The deviation between the data of various sources of actinometrical information can reach 53.0% for hourly values, 58.1% for daily values, 43.1% for monthly values, and 39.1% for annual values, and can significantly affect solar engineer calculations for the choice of parameters of the photovoltaic installation equipment or make great adjustments to the issues of justifying the economic efficiency and feasibility of photovoltaic installation application. [ABSTRACT FROM AUTHOR]

The problem of deposition of dust particles with sizes of large wavelengths of the photoactive part of solar radiation on solar batteries (SBs) is considered. Under the assumption that dust particles in the air do not collide and are deposited on the SB in one layer, formulas are obtained to determine the area of shading of the SB by dust particles in time. These dependences also take into account the size of dust particles, their concentration in air, the angle of incidence of sunlight and the angle of inclination of the SB to the horizon. It is shown that the shading area changes in time mainly linearly, but also has a nonlinear daytime component, which depends on the angle of incidence of sunlight on the SB. The influence of the angle of incidence of the rays on the shading is already noticeable at angles of more than 200. The formulas obtained make it possible to estimate the dynamics of shading of the SB by solid particles of dust and to estimate the frequency of its cleaning from dust (at a given power loss). So, even with standard levels of concentration of dust particles with dimensions of 2.5 and 10 microns and an admissible drop in power of the SB by 5%, the frequency of the SBs cleaning is only about 30 days. The results of the study show that when determining the optimal angle of inclination of the SB, it is necessary to take into account the dust factor. The obtained dependences can also be used to assess the dustiness of flat transparent enclosures of solar installations. [ABSTRACT FROM AUTHOR]

A new method for approximate numerical calculation of the temperature field and heat losses by convection and radiation (Q) of a two-layer cylindrical heat accumulator (HA) with symmetrical boundary conditions is presented and its software implementation is given. We estimate the accuracy of an approximate solution with a known analytical solution for the case with convective heat losses only and with a constant heat transfer coefficient and we reveal that the error of the approximate method starts to exceed 1% when Fo > 2 or when the HA temperature is already less than a half of the HA initial temperature (90°C). It is shown that under permissible heat loss of 10% for 10 h for a HA with R = 0.2 m, the thermal insulation thickness should be about of 5 cm, and the relative heat loss depends greatly on the HA volume. It is important to investigate the effect of thermal insulation emissivity under a small insulation thickness: if thermal insulation thickness is higher than 2 cm, its influence is only of about 5–6%. [ABSTRACT FROM AUTHOR]

The tribological properties of matrix and skeletal titanium carbonitride composites were studied in dry friction conditions in air. Experiments on wetting of the TiCN–Cr3C2 composite by nickel–chromium alloys and copper using the sessile drop method were performed to choose matrix composition and ascertain whether the samples could be produced by impregnation of the porous skeleton. The sessile drop experiments showed that nickel and its alloys formed a low contact angle on the TiCN–Cr3C2 composite (θ ≈ 8°). In particular, Ni3Al intermetallic had θ < 5°, allowing it to be used as a metal matrix. The same situation was observed for copper. A technique was developed for producing TiN–Cr3C2 composites by impregnation of the porous skeleton with Ni3Al and copper melts, and the tribological behavior of the cermets was tested in dry friction conditions. When the starting composite was impregnated with Ni3Al intermetallic, the friction coefficient decreased (μ = = 0.25). Structural studies were conducted with a MIM-10 metallographic microscope and X-ray diffraction with a DRON-2 diffractometer. The hardness and contact area thickness were measured employing a Falcon 9 hardness tester (manufactured in the Netherlands). Thin cross sections were made to examine the structure and phase composition of the contact area. The structure was analyzed using X-ray diffraction and scanning electron microscopy. The effect exerted by hardness of the counterface (steel 45, 40Kh, ShKh15) on the tribological properties of the TiCN–Cr3C2 composite was established. When steel hardness was 60 HRC, the friction coefficient increased with friction distance. These results were, however, obtained at low speeds and loads. Friction losses decreased with loading increasing from 2 to 6 MPa at 12 m/sec: friction coefficient reduced to 0.23. The TiCN–20% Cr3C2 cermets impregnated with Ni3Al may be recommended as antifriction materials for use in high-speed and high-load friction units. [ABSTRACT FROM AUTHOR]

The paper presents the results of the calculated estimate of the critical pressure level in the oxidant tank of the launch vehicle using generalized diagrams of elastic-plastic deformation of the aluminum alloy AMg6. These diagrams consider the anisotropy of the physical and mechanical properties of the material. The calculation of the stress-strain state is performed using the simplified calculation scheme for the specified structural element of the tank depending on the internal pressure in the axisymmetric statement considering the elastic-plastic deformations. The calculation analysis is based on the mixed scheme of the finite element method, which provides the continuous approximation of displacements and stresses. It allows one to determine the stress-strain state of the tank element with high accuracy. It is implied that the maximum values of stresses and strains occur in the area of the fillet region connecting the ring with the cylindrical shell of the tank. Complying with the obtained data, the calculation of the stress-strain state of the tank element using generalized deformation diagrams, taking into account the anisotropy of physical and mechanical properties and the nature of the load of aluminum alloy AMg6, leads to a more conservative estimate of the critical pressure level as compared with the standard calculation based on the uniaxial tensile diagram. [ABSTRACT FROM AUTHOR]

The paper presents the indentation method for strength assessment of the welded joints in high-strength alloy steels, including base metal, heat-affected zone, and welded joint, in production after application of selected flaw detection methods as a final stage of non-destructive testing methods. Non-destructive testing methods are mainly used to detect defects, their location, size, and nature. The indentation method allows one to determine both the joint strength and the strength and dimensions of the heat-affected zone during the production process. The authors performed the comparative analysis on the hardness and strength limit of welded joints of 30Kh2CN2MFA and 28GRA alloy steels as delivered of sheet metal of 6 mm in thickness (for the production of special structures) to corroborate the method efficiency. It is shown that the Brinell hardness values obtained by the TSH-2 stationary hardness tester, ERNST Computest SC portable hardness tester, and instrumented indentation imply the same nature of the hardness distribution along the length of the specimen cut across the axis of the welded joint. The distribution nature of the strength limit values determined by the indentation method is similar to that of the Brinell HBW hardness distribution. It is established that the deviation of strength limit values determined by the indentation method did not exceed 3.7%. [ABSTRACT FROM AUTHOR]

Special features of computational assessment of dimensional change of WWER-1000 reactor core baffle during the reactor operation are discussed. The paper gives results of computational analysis of a change in shape of core baffle, which was performed by applying up-to-date approaches of modeling the irradiation-induced swelling of constrained austenitic steels under the action of neutron irradiation and elevated temperatures. The results have been obtained by using median and conservative values of parameters of the temperature and dose dependence of free swelling of austenitic steel Kh18N10T. The authors have set out the fundamental principles of elastic-plastic stress-strain analysis of the reactor core baffle and core barrel, taking into account the irradiationinduced swelling deformation and contact interaction conditions. The finite-element analysis is based on a FEM mixed scheme that ensures a continuous approximation both for displacements as well as stresses and strains, thus providing a high-accuracy determination of the stress-strain state. The calculations were carried out in the two-dimensional definition for the baffle cross-section with the maximum damaging dose and irradiation temperature in the baffle height, assuming a generalized plane-strain deformation. The calculated results are given for the reactor full-power operation and scheduled shutdown for re-fueling at the end of the charge life. According to the calculation data, disregarding the irradiation-induced swelling deformation leads to an incorrect assessment of the change in shape of the core baffle during its operation, while the use of the accepted free swelling model gives too conservative results on the shape change, even within the designed lifetime. The influence of the mean normal stress on the irradiation-induced swelling of metal makes the principal contribution to the change in shape of the core baffle. During the reactor operation beyond the designed lifetime there occurs a local contact between the core baffle and the core barrel in the zone of the largest-diameter circular opening of the longitudinal cooling channel and the port channel for coolant flow between the baffle and the barrel. The paper gives results of the analysis of the change in shape of the baffle in modeling of the contact conditions taking into consideration the temperature re-distribution due to deviation from the design coolant passage conditions in the zone where the baffle is in contact with the barrel. In the case of using the median dependence of the free swelling, no loss of the nominal gap between the core baffle and the core barrel is observed within the designed lifetime. The computational assessment using the conservative parameters of the irradiation-induced swelling leads to a distinct decrease of the gap between the core baffle and the core barrel and a local contact between them at the end of the designed lifetime. The residual gap between the spacer grids of edge fuel assemblies and the baffle faces is ensured in the case of the median and conservative dependence of the irradiation-induced swelling. [ABSTRACT FROM AUTHOR]

The purpose of the study is to substantiate the parameters and operation mode of the photovoltaic installation as part of the power supply system of real agricultural enterprise in order to reduce the cost of paying for electric energy. The object of research is the system of intra-workshop lighting of two departments of the baking mill in the Rostov oblast. Placing photovoltaic modules on the inclined part of the industrial building's roof of the mill compartments, having an inclination angle of 10° relative to the horizon measuring 39 × 10 m and oriented by the wide side strictly to the South. Three options for the layout of the solar power installation with photovoltaic panels were considered: option 1– maximum power supply to the consumer from the solar power plant in the summer (30 modules); option 2–generation mode without the use of electric energy storage devices; option 3–14 modules and the presence of an electric energy storage system. Specific capital investments in the third option increased by 40% in comparison with the second option, although the installed capacity of the installation increased only by 27.2%. The increase in the power of solar installation to 5.4 kW requires specific costs 2.5 times greater than for the second option. The calculation results allow us to highlight the lowest value of the prime cost of generated electric energy, obtained for the second option, which is 4.33 rubles/(kW h). Thus, the use of photovoltaic installations on industrial building roofs of agricultural facilities makes it possible to reduce the payment for each kW h of consumed electrical energy almost by 2.5 times. [ABSTRACT FROM AUTHOR]

Low-potential solar plants, including flat-plate water-heating collectors (FSWHC), are complex systems in terms of heat engineering. A problem in the development of both stationary and non-stationary heat engineering FSWHC models is to specify convective heat exchange in SWHC channels. This paper considers the features and conditions of convective heat transfer in SWHC channels to water. It is shown that the water flow hydrodynamic and thermal stabilization sections in FSWHCs and at potential speeds of their heat carriers reach only 10 to 13 cm in length and the convective heat exchange in SWHCs can be calculated at a constant value of Nu. It is found that the differences in temperature between the walls of a SWHC channel and between the wall and the liquid will not exceed 10 and 5°C, respectively. These conditions make mixed free and forced convection in SWHC channels possible. Since the heat mainly comes from the upper walls of the channel, this determines the need for pilot studies to determine the distribution of temperature on the walls and in the liquid along the channel length and the difference in temperature between them. The heat exchange in SWHC channels can be heavily affected by free convection. An important issue when elaborating design models of heat exchange in SWHCs is the possibility of applying the convective heat exchange formulas used for plates to the walls of SWHC channels. [ABSTRACT FROM AUTHOR]

The main normative documents for the nuclear power industry of Ukraine, which regulate the determination of mechanical characteristics from hardness measurement data, are considered and analyzed. It has been shown that the use of these documents for monitoring the technical condition of the equipment of nuclear power stations, in particular of the metals of the bypass pipeline of the high-pressure pump SAOZ of the core emergency cooling system (08Kh18N10T steel), coil from the welded joint zone of the Du 600 inlet branch pipe of the IRA30S02 non-return valve (16GS steel), and the body shell of the dismounted PV2500-97-10A (09G2S steel) high-pressure heater calls for their more detailed justification. To determine the mechanical characteristics of metals and to increase the reliability of their evaluation in nondestructive monitoring, a standard developed by the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine is used. According to this standard, the evaluation is made not only on the basis of hardness measurement data, but also by the method of instrumented indentation. It has been shown that this method is more efficient for the determination of the strength characteristics of steels. The difference between the ultimate strength and yield strength values according to this standard and those obtained in tensile tests is not over 8.6% and not over 6.6%, respectively. When diagnosing the technical condition of the metal of pipelines, indentation tests allow one to determine strength characteristics not only in the axial and tangential directions, but also in the radial direction. [ABSTRACT FROM AUTHOR]

The complex experimental equipment has been developed and manufactured in compliance with the existing standards for measuring hardness and strength characteristics via the method of instrumented indentation, as well as for short-term static uniaxial tensile tests of structural materials and small punch testing of miniature disk specimens in the macrorange of loads of 2–10,000 N. This allows one to obtain the necessary characteristics of hardness and strength in relation to the current state of materials of the main equipment at NPP and thereby minimize the volume of material used for the production of specimens on the same setup employing various normative techniques of both destructive and non-destructive inspections. The equipment is designed in the form of replaceable units: indentation, tension, and punching of miniature disk specimens, which are installed depending on the test method. As a result, there is a unified assembly that makes it possible to reduce the effect of instrument errors in the validity of the data obtained using different test methods and facilitate its modification according to the other tests. The developed experimental equipment has been tested using the segment of metal of the double ball pipe wall ∅990 × 70 mm (the basic metal is 10GN2MFA steel and the deposited material is 08Kh19N10G2B steel) of the Du850 main circulation pipeline of NPP from WWER-1000 reactor pressure vessel. The mechanical characteristics obtained by the methods of indirect control were compared with those obtained from standard tensile tests. At the same time, the deviation of the values of yield strength and ultimate strength obtained employing the indirect control methods from the values obtained in the standard tensile testing is within the limits recommended by the normative documents. [ABSTRACT FROM AUTHOR]

To evaluate the possibility of obtaining the maximum of electric power generation at a preset point of time by varying the spatial orientation of photovoltaic modules, its effect on the amount of utilized solar radiation was studied. The experiment was conducted by the example of Zernograd, Rostov oblast, Russia, with specially designed research equipment. The analysis of input of solar radiation to surfaces with different spatial orientation revealed that, owing to different combinations of spatial placement of the receiving site with respect to cardinal directions and the horizon line, it is possible to shift the maximum of power takeoff with photovoltaic modules relative to midday to the morning and evening time about by 4.5 h. [ABSTRACT FROM AUTHOR]

The main methodological principles and the procedure of the refined calculation of the stress-strain state and fracture strength of the branch pipe zone of the reactor vessel under thermal shock have been formulated. A mixed scheme of the finite element method was taken as a basis of finite element analysis; it ensures continuous approximation both for displacements and for stresses and strains, which allows the fracture mechanics parameters to be determined with a high degree of accuracy. The paper presents the results of an elastic-plastic analysis of the fracture strength of the inlet branch pipe zone with an underpad crack in the simulation of the typical emergency core cooling conditions of a WWER-1000 reactor. The location and orientation of the postulated crack are substantiated to obtain the most conservative estimate of the fracture strength of the branch pipe. The calculations were performed with including the postulated crack in the finite element model of a fragment of the inlet branch pipe zone using the procedure of successive mesh thickening in the crack region. To determine the allowable critical temperature of brittleness of the branch pipe base metal, the tangent point, thermal crimping and descending branch approaches were used. According to the obtained results, the elastoplastic deformation of the metal and stress history affect the calculated estimate of the fracture strength of the branch pipe zone of the reactor vessel. It has been shown that the traditional linear elastic calculation, which is used to evaluate the fracture strength of the branch pipe, does not have sufficient degree of conservatism, which results in an exaggerated estimate of its strength. [ABSTRACT FROM AUTHOR]

This article describes an algorithm that has been developed for optimization of the compound and capacity of diesel generators (DGs) and wind turbines (WTs) functioning in wind-diesel systems (WDSs) taking into account data of grid loads and wind- and air-density variability as dependent on the elevation and time period for each area. The cost of electric energy generated by a WDS, degree of substitution of diesel-fuel consumption (by using wind turbines), payback period, net present value, and internal rate of return of WDS projects were chosen as optimization criteria. We developed software, EAST, based on the described algorithm, and determined the optimal configuration of a WDS for the town of Tiksi (Yakutia). Our findings are given in this paper. Optimization was performed for different ratios of the nominal capacity of diesel generators and wind turbines. We also calculated the energy and economic effect of using WDSs, which reaches a maximum if the ratio is around 1 (according to wind-energy-potential and grid-load data for the town of Tiksi). The degree of substitution of diesel-fuel consumption in this case reaches 35%, and the generated-energy cost drops up to 25%. According to calculations, the most energy- and cost-effective models of wind turbines for the WDS in Tiksi are VestasV-850 (Denmark) and GamesaG-58 (Spain), both with a rated power of 850 kW and a tower height of 55 m. [ABSTRACT FROM AUTHOR]

In designing generating solar-engineering devices, the first priority is the predesign study of the potential of local resources of solar energy at the places where they may be located. Currently, actinometric information is obtained in several ways. They include direct measurement of solar-radiation characteristics at meteorological stations or from satellites and analytical methods for calculating intensity of solar radiation. Despite the significant number of sources of actinometric information, it seems impossible to evaluate the potential of incoming solar energy in the region, to substantiate the composition and parameters of solar-power-plant equipment, and to predict its operation at the initial stage. Using the example of the town of Kamyshin in Volgograd oblast, the sufficiency of required actinometric information is analyzed for further solar-engineering calculations and the data accuracy and limits of their applicability are estimated. [ABSTRACT FROM AUTHOR]

We present the results of numerical evaluation of the possibility of application of additional thermomechanical treatment to the welded joints of the headers with connecting pipes of PGV-1000 steam generators from WWER-1000 reactor units of nuclear power plants with an aim to decrease the level of stresses formed after maintenance and in the process of subsequent operation. It is shown that this type of treatment is quite promising for extending the service life of the unit. [ABSTRACT FROM AUTHOR]

We investigate the structure, hardness, strength, plasticity and fracture character of Cu–Cr microlayer composite material for electric contacts with prescribed microlayered structure and chemical composition in the temperature range from 290 to 1070 K. The correlation relationships between the hardness and strength characteristics have been established. [ABSTRACT FROM AUTHOR]

Additional heating of a thickened portion of the steam generator connector during postrepair thermal treatment of the header-connector weldment leads to a decrease in residual tensile stress levels. It is shown that during hydrostatic tests performed after thermal treatment inelastic strains on the inner connector surface are reduced, which inhances the cycle life of the weldment. [ABSTRACT FROM AUTHOR]

Results of numerical analysis of stress intensity factors KI for semielliptical surface cracks in the WWER-1000 reactor pressure vessel by emergency cooling simulation with known engineering procedures, the equivalent spatial integration and direct methods are presented. Engineering procedures employ the results of numerical solution of axially symmetric boundary value problems of thermoelasticity based on the mixed mesh-projection scheme of the finite element method implemented in the RELAX software. The three-dimensional KI computations were performed with the SPACE software. [ABSTRACT FROM AUTHOR]

The procedure for calculating the life of header - steam generator connector weld joints is proposed. It allows for running out the material plasticity reserve upon static cyclic elastoplastic loading as well as operating conditions, local stress concentrations, and residual stresses after welding. [ABSTRACT FROM AUTHOR]

General methodological approaches to solving the problems of strength and life of NPP equipment and results recently obtained in this field at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine are outlined. The urgency of the strength and life issues for reactor pressure vessels and steam generator shells is demonstrated. Application of a comprehensive calculation and experimental approach to the stress-strain state analysis is illustrated by the example of steam generator joints with defects. [ABSTRACT FROM AUTHOR]

The paper describes a method and main results of a refined stress-strain state evaluation for a welded joint of the hot collector to steam generator nozzle of a nuclear power plant with a WWÉR-1000 reactor, which takes into account a fuller range of the actual loading conditions in operation. In calculations, we considered the stresses induced by uncompensated thermal expansion of the reactor elements. The results of 3D finite element calculations suggest that the level of local stresses in the area of the joint exceeds the metal yield stress. The calculated stresses for the outer nozzle surface agree satisfactorily with the in-situ strain measurement data. [ABSTRACT FROM AUTHOR]

The paper describes a 32-channel system for studying full-scale structures developed with the use of the state-of-the-art components. It provides continuous long-term measurement of strains and temperatures up to $\backslash +\; 350\; deg$C and accumulation and storage of measurement data. The system was used to record the elastic strains and temperatures of a welded joint of the hot collector to the PGV-1000 steam generator nozzle in the period between the preventive maintenances. The measurement results reveal a complex pattern of strain and temperature distribution different from the axisymmetric one. [ABSTRACT FROM AUTHOR]