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The paper studies the large-scale convective flow of viscous incompressible fluid in the equatorial zone, taking into account two components of the Coriolis force. Temperature gradients are set at the flow boundaries. The Marangoni effect works on the free boundary. The existence and position of stagnation points is analyzed. The parameter values at which stagnation points can appear are determined. The possibility of a double stagnation point is shown. [ABSTRACT FROM AUTHOR]

The deformation mechanisms of hardened amorphous alloys and graphene-reinforced nanolayer composites are studied by molecular dynamics modeling (MD). It has been established (using CuZrAl as an example) that in amorphous alloys, under the influence of intense deformations accompanied by heat release, a dendritic nanophase is formed, which contributes to their strengthening. The dendritic nanophase hardens the alloys by tensile strength up to 20% at loads of 2300 MPa; the yield strength exceeds 1550 MPa. In graphene-reinforced nanolayer composites (Me/graphene, where Me = Ni, Al, Ti), a deformation mechanism of the transfer type is realized. The transfer-type mechanism is the appearance of uniformly distributed microscopic cracks ("strain transfer") on the surface of the sample (along its entire length). In composites subjected to such deformation, the strength characteristics are significantly increased. The simulation results show good agreement (10 to 15%) with experimental literature data. [ABSTRACT FROM AUTHOR]

In this paper, the limits of applicability of the signal processing algorithm obtained when sounding metal objects for the purposes of acoustic tensometry are investigated. The object of the study is an algorithm for interpolating intermediate points, which is based on the use of an algorithm for finding the maximum of the correlation function. The purpose of this study is to evaluate the results obtained by varying the width of the analysis window and its position relative to the measured pulses. During the research, program studies of signals obtained on a massive sample in 6 sections and 2 positions were carried out. As part of this research, a program was developed in the MathCAD environment, which allows us to read automatically an echogram from a file with data recorded by the Prince-VIII software, select time periods from that echogram corresponding to several reflections, and calculate the correlation function for the selected signal fragments. The optimal coordinates and dimensions of the window for signal analysis are determined, and the numbers of reflections suitable for processing are highlighted. It is proposed to use the value of the pulse delay increment during the transition from the 1st to the 2nd reflection of the signal as the measured parameter. [ABSTRACT FROM AUTHOR]

The effect of applying combined fillers containing carbon and basalt fibers on the mechanical and tribological properties of ultrafine polytetrafluoroethylene (UPTFE) is studied. It is shown that the introduction of combined fillers in PTFE improves compressive strength by 52-76% relative to the original polymer. The results of tribological studies have shown that polymer composite materials (PCMs) containing mechanically activated basalt fibers have high wear resistance compared to samples without mechanical activation. Scanning electron microscopy (SEM) shows that secondary protective structures formed on the worn surface contribute to an increase in the wear resistance of polymer composites material with mechanically activated basalt fiber, which is not observed in other composites. The developed materials can be used as materials for sealing devices and parts of friction units due to the low friction coefficient and high wear resistance. [ABSTRACT FROM AUTHOR]

The northern regions characterized by harsh climatic conditions should be developed using modern technology employing polymeric materials suitable for use at temperatures down to -60 °C. The creation of polymer composite materials based on polytetrafluoroethylene (PTFE) with highly perfected service characteristics is one of the priority tasks of modern materials science. The paper discusses the physical-mechanical, tribological, and thermodynamic properties of composites based on PTFE and various types of fillers. The results of the study show that complex filling in a certain combination provides a high degree of interaction between the polymer and the filler, thereby significantly improving the properties of PTFE-based composites. [ABSTRACT FROM AUTHOR]

The process of producing permeable highly porous nickel-based powder materials is described. The porous structure of the materials is formed due to the partial sintering of pressed metal powder, as well as due to the addition of a temporary pore filler. The system of interconnected macropores, formed due to large particles of porogen, ensures the permeability of the material based on nickel nanopowder to a level of 2.5 x 10−12 m2. The average limiting diameter in the system of through channels, formed by interpenetrating macropores, depending on the number and size of the particles of the pore-forming agent, reaches 20 to 95 µm. [ABSTRACT FROM AUTHOR]

The paper is devoted to solving the problem of excluding areas of irregularities in material surface images. To solve this problem, we propose an algorithm for automatic mask construction with identifying the areas with material, areas without material, and crack areas; this combines image processing methods (pattern search, threshold flood filling, boundary search) with crack detection algorithms. It is demonstrated that this algorithm is applicable to experimental images with a large number of frames in a series. [ABSTRACT FROM AUTHOR]

A new exact solution of the Navier-Stokes equation for the convective flow of an infinite horizontal layer of a viscous incompressible fluid is obtained. Parabolic heating is specified at one of the layer boundaries. The other boundary of the fluid layer is permeable. The obtained exact solution generalizes the isothermal Couette flow and the Ostroumov-Birikh convective analogues. The proposed class of exact solutions takes into account the horizontal change in hydrodynamic fields. The obtained solution analysis for the velocity and temperature fields is presented. The possibility of the existence of stagnation points and counterflow areas in a moving layer of a non-isothermal viscous incompressible fluid is demonstrated. [ABSTRACT FROM AUTHOR]

A new method of transversal strengthening of a laminated fabric-reinforced composite is proposed. The fabric pack is punched with needles for felting, which partly pull out and damage the warp/weft threads by barbs, pulling some fibers in the direction of thickness (Z-direction). By increasing the density of needle punches per unit area in the felting zone, it is possible to increase the ability of a layered composite to resist transversal tension or shear stresses. In this case, the strength of the composite in the XY plane decreases slightly. By the example of the single-lap joint of composites (plain weave fabric with a thermoplastic binder), it was shown that felting with a punching density of 30...60 cm−2 about doubles the shear strength in comparison with typical glued samples without felting. [ABSTRACT FROM AUTHOR]

Powder compositions based on vanadium-containing iron powder with alloying microadditives Zn, Cu, and C, obtained as a result of mechanical mixing, have been investigated. The strength of green briquettes from powders based on iron with different contents of alloying additions was investigated according to the results of tests for uniaxial and diametral compression depending on the density of the samples. The features of the formation of the strength properties of each of the powder compositions are revealed. [ABSTRACT FROM AUTHOR]

In the framework of the current mathematical theory of growing solids, a nonclassical mechanical model is developed to trace the evolution of elastic technological stresses in cylindrical composite pieces during the additive processes of their manufacturing by the method of multi-layer power thread winding, taking into account the structure of the material being formed and an arbitrary law of changing the thread pre-tension. Based on the proposed model, the closed analytical dependencies are constructed. [ABSTRACT FROM AUTHOR]

The paper investigates the physical-mechanical, tribotechnical characteristics and structure of the friction surface of polymer-silicate composites based on polytetrafluoroethylene (PTFE) and vermiculite with the addition of FORUM®. It is established that the combined influence of the fillers used improves the operational properties of the developed composites. [ABSTRACT FROM AUTHOR]

This paper presents a physical and mathematical model that has been developed in the framework of the approach used in the computational mechanics of materials. The model is designed to enable the study of the patterns of deformation and fracture of ceramic composites with a transformation-hardened matrix at the mesoscopic and macroscopic levels under intense dynamic loading. The influence of the loading rate on the formation of the fracture and energy dissipation fronts for composite materials based on the Al2O3-20%ZrO2 system is shown. Nonlinear effects in the considered composites under intense dynamic loading are associated with the processes of the self-organization of structural fragments at the mesoscopic level, as well as with the occurrence of martensitic phase transformations in the volumes of the strengthening particles. In this paper, specific destruction work is used as the main parameter that determines the contribution of each composite component to the destruction work. [ABSTRACT FROM AUTHOR]

The article is focused on the study of segmental dynamics in electrospun PHB fibers and the same fibers subjected to cold rolling based on the analysis of a spin probe characteristics obtained by ESR technique. It was found that the presence of two TEMPO probe populations with different correlation times indicates the heterogeneous structure of intercrystalline areas in the fibrous materials and in cold-rolled fibrous materials. The ESR data shows a model of the amorphous state in semicrystalline polymers. The study uses the ESR technique data for the analysis of water impacts on probe mobility. It is shown that the electrospun fibers, and especially the fibers after cold rolling, lead to denser field formation in the intercrystalline area of PHB, thus favoring fiber stabilization against the exterior water. [ABSTRACT FROM AUTHOR]

Heterogeneous nanocoatings obtained by argon-acetylene plasma treatment of the elastic polyurethane surface are studied. The structural and mechanical properties of the coatings are determined by atomic force microscopy and finite element modeling. During nanoindentation of the treated surface, the probe presses the coating into the soft substrate and eventually pierces it. Measuring the depth of the imprint allowed determining the thickness of the coatings (1.6 nm). Comparison of the initial part of the indentation curve (prior to piercing) with the model calculations (stiff paraboloid indents the layer of known thickness on an elastic substrate) allows us to estimate the elastic modulus of the coating (several GPa). The obtained materials can be used in the manufacture of flexible biomedical products with improved properties. [ABSTRACT FROM AUTHOR]

Regularities in thickness and roughness growth of calcium phosphate coating during the micro-arc oxidation process under external ultrasound field are studied. The relationship of the electrophysical parameters of the ultrasound-assisted microarc oxidation (current density and time) to the physicochemical properties of the coatings (thickness, roughness, thickness growth rate, and roughness growth rate) is established. It is found that the increase in the thickness and roughness of the coatings with the deposition time occurs according to the logarithmic law and that the decrease in the current density and the growth rate of the coating thickness and roughness follow the hyperbolic law. It is shown that the coatings deposited under external ultrasound have a more intensive increase in the thickness and roughness with the deposition time, compared to the control micro-arc oxidation coating. This leads to a more intensive decrease in the coating thickness growth rate during micro-arc oxidation processing under the applied ultrasound, while the change in the coating roughness growth rate are independent of such external factor as the ultrasound field. [ABSTRACT FROM AUTHOR]

The paper presents a mathematical modeling of nonstationary laminar Bénard-Marangoni convection of a viscous incompressible fluid moving in an infinite band. The main attention is paid to the study of the position and displacement of the stagnation point of the solution with time, the appearance and disappearance of counterflows. It is shown that the overdetermined initial boundary value problem within the here presented class of exact solutions of the Oberbeck-Boussinesq equations is reducible to the Sturm-Liouville problem. The hydrodynamic fields indicating the presence of counterflows in the fluid and their change during fluid acceleration are analyzed with the use of a computational experiment. [ABSTRACT FROM AUTHOR]

The aim of the paper is to study the effect of various types of mechanical loads on the state of carbonized layers on the surface of polyurethane samples using atomic force microscopy. We study the ability of the carbon layer to maintain its structural integrity as a result of large deformations, as well as the possibility of cracking and delamination in the case of insufficient elasticity and weak adhesion of this layer to the substrate of the raw material. Particular attention is paid to the study of the ability (or inability) of the carbon layer to maintain the listed operational properties in the temperature range relevant to the human body. The results of the study are actual in the search for optimal parameters for the manufacture and ion-plasma processing of samples capable of maintaining the integrity of the surface layer without destruction and the appearance of defects. [ABSTRACT FROM AUTHOR]

In the huge and still poorly mastered gap between the macrolevel and the atomic level, obeying the laws of quantum mechanics, there is an extensive meso-hierarchical level of the structure of matter. At the macrolevel, continuum theories of continuous media and engineering methods of calculation and construction are well developed. The meso-hierarchical level of the structure of matter is known as the level with unprecedented products and technologies, which can be created artificially. Nanotechnology is a qualitatively new strategy in technology: it creates objects in the totally opposite way, i.e. large objects are created from small ones. We have developed a new method for the analysis of acoustic monitoring of an elastic medium with layered blocks with several hierarchical inclusions of various physical and mechanical hierarchical structures and various sizes. [ABSTRACT FROM AUTHOR]

Electron probe microanalysis and X-ray diffraction analysis show that the maximum abrasive wear resistance of the 260Kh16M2 and 250Kh25MFT chromium cast irons with different types of carbides, Cr7C3 and Cr23C6, is provided by a metal base consisting of metastable retained austenite and martensite. This microstructure of the cast iron matrix before testing is created by high-temperature quenching with heating to temperatures of 1125-1170 °C and cooling in oil or in air. During operation, austenite on the working surface turns into dispersed martensite as a result of exposure to abrasive particles. Martensite, together with carbides, gives a high level of hardening and operability of the secondary microstructure of cast irons. An additional reserve of increasing the abrasive wear resistance of chromium cast irons by 20% consists in cold treatment after high-temperature quenching. The latter increases the content of cooling-induced carbon martensite before wear resistance testing and forms new portions of strain-induced martensite during testing. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying the effect of diphenylguanidine (DPG) on the physical and mechanical properties, adhesive interaction, and structure of ultra-high molecular weight polyethylene (UHMWPE) and elastomers based on isoprene rubber. The introduction of DPG into UHMWPE and the rubber mixture significantly increases the physical and mechanical properties and adhesion between UHMWPE and the elastomer. Structural studies by scanning electron microscopy show that the modification of UHMWPE leads to the transformation of the supramolecular structure. On the IR-spectra of UHMWPE modified with DPG, new oxygen-containing functional groups have been revealed. The presence of such groups indicates the participation of DPG in the structuring processes, which causes an increase in interfacial interaction with an elastomer based on isoprene rubber. [ABSTRACT FROM AUTHOR]

An inhomogeneous solution describing the laminar large-scale isothermal Poiseuille-Ekman flow of the viscous incompressible fluid in the equatorial zone is constructed. At the free boundary, tangent stresses are set to simulate the effect of wind. The slip conditions for the Navier fluid are set on the solid surface. The condition of compatibility of the redefined system of equations describing the laminar flow is obtained. The compatibility condition imposes restrictions on the boundary conditions. The solution is constructed in the form of polynomials. [ABSTRACT FROM AUTHOR]

An analytical solution describing the stationary isobaric flow of a viscous incompressible slowly rotating fluid in an infinitely extended layer is obtained, with inhomogeneous velocity distribution. The fluid flow is considered at constant pressure, in accordance with the generalization of the classical Ekman flow. The allowance made for velocity gradients can both increase and decrease the number of stagnation points in the fluid layer as compared to the homogeneous Ekman flow. It is shown that the new exact solution allows us to construct new classes of exact solutions of the Navier-Stokes equations describing fluid flow in an inertial coordinate system and in a rotating one. [ABSTRACT FROM AUTHOR]

Studies of the mechanical properties of elastomeric nanocomposites depending on the shape of the filler particles are carried out. Graphene nanoplates, detonation nanodiamonds, and single-walled graphene nanotubes are used as fillers. Samples are tested for uniaxial tension at a constant speed. The viscoelastic behavior of these composites is studied using a special technique based on the cyclic loading of the sample with increasing strain amplitude at each subsequent step and stops for relaxation after load direction reverse. Experimental tests have shown that the greatest effect of changing the mechanical behavior of the elastomer is observed when graphene nanotubes are used. These composites show well-defined viscoelastic properties and a softening effect, as well as the strongest hardening. It has been hypothesized that all these differences are related to the geometry of the filler and that all these differences are related to filler particle geometry. Graphene nanotubes can be considered as long and flexible fibers that can form a spatial network in the elastomeric matrix even at sufficiently low fillings. When the composite is loaded, this network can be destroyed, and this is accompanied by reorientation and mutual slipping of the nanofibers. These processes require significantly higher energy costs than those for moving and turning granular or lamellar particles. [ABSTRACT FROM AUTHOR]

Anisogrid structures made of high-modulus carbon fiber reinforced plastics have become widely employed as structural elements of spacecrafts. The unique mechanical behavior of anisogrid cylindrical shells determines the use of these structures in the development of new types of space technology. An example is a space telescope, whose main load-bearing component consists of a thin-walled lattice cylinder with massive equipment attached to its edges. The buckling of a telescope structure under thermal loading is an important issue to be addressed in design. The computational model for this problem is an anisogrid lattice cylindrical shell formed by composite helical and circumferential ribs experiencing a sudden temperature rise. This paper aims to numerically determine the temperature at which the two edges clamped lattice cylinder buckles. To simulate the anisogrid shell as a spatial frame, a beam-type finite element is used. A parametric study is performed to evaluate the influence of the number of helical ribs and their orientation angle on the critical buckling temperature. [ABSTRACT FROM AUTHOR]

The influence of thermal conditions and some technological methods (intermediate inserts of monolithic metal, nanomodifying additives) on the quality of the permanent joint of porous titanium obtained by laser welding is studied experimentally. It has been established that, to obtain a high-quality defect-free weld, it is necessary to use an intermediate insert made of compact metal placed butt-to-butt between the ends of the butt-welded plates. The position of the focal spot should be set at a depth equal to the thickness of the plate, i.e. on its bottom surface. The use of modifying additives based on titanium nitride increases the dispersion and uniformity of the weld structure and the heat-affected zone, and this positively affects the mechanical characteristics of the metal. [ABSTRACT FROM AUTHOR]

To manufacture extended elements for steam pipelines, steam superheater pipes, gas turbines, and collectors operated under high pressure, one uses the 12Kh1MF heat-resistant structural pearlitic steel or the 12Kh18N12T corrosion- and heat-resistant austenitic steel. During operation even after first 10 thousand hours, mainly as a result of temperature fluctuations causing changes in the metal structure, the internal surfaces of the product corrode with the formation and growth of a more than 0.1 mm thick oxide film. The structure of such formation consists of an internal dense magnetite layer and an external porous one. The increase in the total thickness of the oxide layer slows down over time due to the inhibition of the diffusion processes of iron transition through the magnetite layer. To a certain extent, the oxide layer can be considered as a protective one, and its deformation-free destruction resulting from thermal cycling is an extremely undesirable phenomenon, which leads to the failure of the entire unit. In this regard, the timely and accurate diagnosis of the deformability of the oxide layer seems to be an urgent task. The deformability of the oxide layer is evaluated on samples cut out from a pipe, which are subjected to a flattening test. During testing at room temperature, the stages of destruction of the oxide layer are observed and, according to the nomographic chart of the experimental dependence of the deformation in the compression zone on the increase in the diameter of the pope, its operability is estimated. However, this approach does not take into account the actual operating temperature of the product and does not ensure the accuracy of determining the time of defect occurrence in the oxide layer, and this decreases the quality of predicting the residual life of the structure. To solve the above-mentioned problems, an improved technique is proposed. According to this technique, the flattening test of the superheater pipe samples is carried out at operating temperatures, and flattening is recorded synchronously with the video recording of the internal surface of the samples until a continuous oxide-free metal strip is formed. [ABSTRACT FROM AUTHOR]

This paper proposes to use the method of statistical modeling, i.e. the Monte Carlo method, to predict the probability of the survival of torsion bars in the Blagonravov continuously variable mechanical transmission. To solve this problem it is proposed to use Rzhanitsyn's indestructibility function. The two-parametric representation of cyclic torsional strain ranges is presented. Data on the survival probability of torsion bars in specific motor vehicle operating modes, predicted using the MathCAD processor, are presented. The possibility of applying the developed procedures to estimating the survival probability of torsion bars when using the Blagonravov transmission for motor vehicles of various designations is shown. [ABSTRACT FROM AUTHOR]

The regular state monitoring of industrial facilities, gas pipelines, in particular, represents one of the key factors ensuring their further reliable operation. Besides corrosion, the growth of manufacturing flaws and assembly defects remains a significant issue influencing fractures and deterioration of bearing capacity in structures. Nonmetallic inclusions, liquation or delamination are common engineering and manufacturing defects detected during operation. Delamination and internal defects in a metal can be disclosed timely by means of thickness measuring. The reported paper proposes a visualization method of monitoring results to identify defects in the internal material structure with a high degree of probability. [ABSTRACT FROM AUTHOR]

The paper discusses the enhancement of the energy efficiency of motor vehicles with conventional engines when using a continuously variable mechanical transmission with internal force function control. Such a transmission has torsion shafts working in torsion under conditions of random cyclic loading at a frequency corresponding to the ICE shaft rotation speed. The fatigue strength of torsion shafts can be a limitation on the operating life of the entire transmission. Technological measures increasing the fatigue limit of the torsion shaft material are analyzed. Developing the elastic strains of torsion bars is theoretically considered. The theoretical strain cycle fluctuates with the asymmetry ratio R = 0. The amplitude of the elastic strain is determined by the external load. The test procedure for a prototype vehicle with an engineering specimen of a transmission in specific motor vehicle operating modes is presented. The need for the ongoing monitoring to limit torsional strain by the control system is shown. According to the field test results, the nature of torsion bar loading cycles in operating conditions is estimated in detail. In most operating modes, the experimental character of torsion bar loading has a reversed strain cycle with the negative strain ratio R = −0.04 ... −0.79. The inexpediency of torsion bar hardening is shown. Fragments of oscillograms demonstrating elastic strains of the torsion bars and distribution of the mean and amplitude values of the strain cycles for typical operating conditions are given. [ABSTRACT FROM AUTHOR]

The article covers a method for calculating the failure probability of torsion bars of new-type infinitely variable transmissions. The solution to the problem is obtained using the mathematical apparatus of nonparametric statistics, which provides calculation of failure probability regardless of the complexity of the effective and allowable stresses that occur during the torsion bar twisting. Calculations of the probability of the torsion bar failure during the heaviest-duty transmission operation are presented. The implementation of the method in the MathCad mathematical processor allowed defining the failure probability of the torsion bar under study, which is 3.82%. [ABSTRACT FROM AUTHOR]

Despite the results already achieved in this field of research, interest in the transformation phase of the 15Kh2MFA steels remains high, which is due, in the first place, to the long-term operation of important products manufactured from this steel and the need for evaluation of their service life. The stability of the carbide phases in steels of this type, alloyed with niobium, after undergoing various modes of basic and post-welding heat treatments, is reviewed. It is shown that an increase in the duration and temperature of post-welding tempering stabilizes the phase composition and, therefore, increases the stability of the structure during operation. [ABSTRACT FROM AUTHOR]

The possibility of synthesizing Fe-Cr-Co powder magnetic materials with low and medium cobalt content (8 to 16%) at a low sintering temperature of 1100 °C is shown. The relative density of the sintered specimens after sintering is about 94%. When the cobalt content in the material is 8%, the alloy is single-phase (α-phase). With an increase in the cobalt content to 16%, faint traces of the γ-phase (about 1%) appear. The magnetic hysteresis characteristics of the synthesized specimens are measured, and they have values that are acceptable for practical use according to GOST 24897-81. The functional properties of the obtained materials at a low sintering temperature of 1100 °C are compared with the properties of materials sintered at temperatures of up to 1400 °C. [ABSTRACT FROM AUTHOR]

Alloys of the Au-Co system characterized by restricted solubility of the constituents were produced by shear deformation under high quasi-hydrostatic pressure. Resistance to shear strain was recorded during mechanical fusion. The forming pressure dependence of shear stress during deformation has been revealed, with the form of the curve remaining qualitatively unchanged. The form of the curve for the joint deformation of the Au-Co constituents differs from the curve recorded during the deformation of one constituent, namely gold. In the former case there are stages of sharp increase, retardation, and attainment of saturation, whereas in the latter case there is a sharp increase followed by attainment of saturation. This indicates the appearance of the deformation interaction of the constituents, which manifests itself in a prolonged increase in shear stress with an increase in strain, as distinct from the case of a single element, where there occur only structural changes caused by torsion under pressure. After the samples had been made, their Vickers hardness was measured, which demonstrates practically equal values of the hardness of the Au-Co alloys produced under different pressures. [ABSTRACT FROM AUTHOR]

The use of the statistical analysis approach based on the application of finite mixture models and using an expectation-maximization algorithm to describe the experimental grain size distributions of HPT-nanostructured Cu-7.4Sn bronze allows us to decompose them into a set of groups of grains with sufficient accuracy. It is shown that the saturation stage after one revolution of HPT has not been reached in comparison with the sample after five revolutions. At the same time, grain structure evolution during heating depends on the initial strain state. However, the character of the evolution of both samples is similar. It is demonstrated that grains which form one of the groups are characterized by higher density of defects and enhanced energy; this decreases the volume fraction of the group during heating, with hardly changing other features. The other groups of grains seem to be formed under the influence of relaxation processes during subsequent annealing. Moreover, each subsequently formed group of grains demonstrates more intensive growth during heating, while the volume fraction of existing groups slows down until they disappear completely. [ABSTRACT FROM AUTHOR]

Virtually, all the reference literature presents mechanical characteristics of fibrous composites along fibers, but these characteristics are most difficult to determine. The test methods of composites along the fibers are standardized (GOST 32656-2014, ISO 527-4:1997, ASTM D638-08), and there is a warning in the standards saying: "Excessive pressure created by the grip can lead to specimen fragmentation due to the low strength of the test materials in the transverse direction. Hydraulic grips that can set constant pressure are recommended". However, even for testing in constant force grips there are difficulties in specimen fastening, and a unidirectional composite specimen very rarely (almost never) breaks within the gauge length. Therefore, during tensile tests of unidirectional composites, not quite correct data are obtained, i.e., if the specimen breaks, it happens beyond the gauge length. This study proposes to use another specimen shape; namely, the specimen exterior resembles a dumbbell test specimen, but with the following feature: the cross-sectional area of the specimen remains constant along its length (constarea) - there are no cut fibers in it. [ABSTRACT FROM AUTHOR]

Mixed mode I+II fracture of triangular shape specimens is studied experimentally and numerically. The investigated fracture results have been obtained for a brittle polycarbonate by testing an inclined edge crack triangular shape specimen subjected to symmetrical three-point bend loading in the entire range of mode mixities from pure mode I to pure mode II. Stress intensity factors, T-stresses and higher-order terms have been found by the digital photoelasticity and finite element methods. It is shown that the experimental and numerical results are in good agreement. [ABSTRACT FROM AUTHOR]

The paper considers an algorithm for determining the unknown function of random variable distribution density presented in the form of a finite trigonometric series. The random variable is given by a sample of values. To calculate the coefficients of the series, we use a set of quantile values of a random variable, obtained on the basis of the function of random value distribution density, recovered from the sample by means of Parzen-Rosenblatt estimates. The problem is reduced to solving a system of equations that are linear towards the desired coefficients. The developed algorithm is exemplified by experimental data processing. [ABSTRACT FROM AUTHOR]

There are various processes used to produce long metalware pieces, and each has advantages over others. The Institute of Machinery and Metallurgy, Far Eastern Branch of the Russian Academy of Sciences, has designed and made a device for the continuous production of metal shapes. It allows several process stages to be combined in one unit, but under the condition that the process temperature parameters are exactly maintained. Mathematical simulation of processes is an integral part of production and thus allows one to find temperature conditions that would be most optimal for forming long metal products. The conducted physical experiment has allowed us to find temperature distribution in the mold of a metal casting and deformation unit. The obtained temperature field is used to adjust the boundary conditions in the mathematical model of the process of forming a product in the unit. The mathematical model with adjusted temperatures enables us to control parameters for the mathematical and physical simulation of forming long forgings in a metal casting and deforming unit. [ABSTRACT FROM AUTHOR]

Layer-by-layer phase analysis of hard alloys produced by the method of spark plasma sintering of the WC + 10% Co powder is carried out. The through-the-depth phase composition heterogeneity of a hard alloy workpiece is revealed. This heterogeneity is due to the diffusion of carbon from the graphite punches into hard alloy samples during the sintering process. The brittle η-phase (Co3W3C) is detected in the hard alloy samples at a depth of no more than 100 µm. [ABSTRACT FROM AUTHOR]

The paper models the mechanical behavior of the human cornea affected by intraocular pressure and external effects. It reviews publications on the development of mathematical models of the cornea and some approaches to studying its mechanical behavior. A finite element model of the cornea is proposed, which allows the stress-strain state in the cornea to be determined from solving the boundary value problem of the theory of elasticity. Test calculations are shown. The model can be used, particularly, for studying the strain of the cornea resulting from surgery. [ABSTRACT FROM AUTHOR]

The plastic properties of commercially pure copper are considered. Using the strain diagrams (for strain rates of 0.002, 0.016, 150.0, 2000.0, and 13300.0 s−1) and the hardening curve for copper under static compression, the analytical dependence of copper yield stress on strain (in the range from 0 to 0.45) and strain rate (in the range from 0.002 to 13300.0 s−1) is found. [ABSTRACT FROM AUTHOR]

The paper presents the result of an experimental study of the strain state of a large-scale reinforced concrete structure. The spatial-temporal distribution of the deformation response of structural elements to an applied localized self-balanced load and pulsed force action is obtained. The tests conducted in the elastic deformation mode allowed us to obtain a vibrational picture of the structure, which provided basic information for the future experiments aimed at studying inelastic deformation of a structure until its ultimate failure. The study is aimed at identifying the patterns of damage of the structure under quasistatic loads, searching for precursors of failure, as well as developing criteria to record the forthcoming critical state of the structure. [ABSTRACT FROM AUTHOR]

The increasing complexity of the design of rotor systems necessitates the use of more complex mathematical models, the identification of which by the results of bench tests alone is often difficult. A method for element-by-element identification of rotor systems is proposed, which consists in dividing the model into substructures with their subsequent identification by modal characteristics. The proposed methodology is demonstrated by the example of a model rotor system with a flexible disk having non-axisymmetric vibration modes in the operating frequency range. Based on the results of determining modal characteristics, a technique is proposed for refining the mathematical model of a flexible disk by changing its elastic modulus. [ABSTRACT FROM AUTHOR]

The paper discusses an approach to the maintenance diagnostics and predictive evaluation of the operational health of electromechanical systems (EMS). It presents a mathematical model of an EMS, which is intended for problems of diagnosing an individual EMS and an EMS operation mode group, offers information on the EMS vector spaces, and describes the general methodology for vector space testing. To solve problems of the maintenance diagnostics and predictive evaluation of EMS health, it is proposed to use hybrid models based on a combination of the fuzzy cognitive approach and the fuzzy logic one. [ABSTRACT FROM AUTHOR]

The paper proposes a possible approach to estimating the residual life of welded joints, based on a phenomenological model of damage accumulation and fracture. The adequacy of the developed approach is confirmed by comparison with experimental data on the cyclic loading of specimens with a natural concentrator in the form of a weld. [ABSTRACT FROM AUTHOR]

The nonlinear fourth-order differential eigenvalue problem governing eigenvibrations of a cantilever beam with elastically attached load is investigated. This problem has an increasing sequence of positive simple eigenvalues with a limit point at infinity. To the sequence of eigenvalues there corresponds a system of normalized eigenfunctions. The original nonlinear differential eigenvalue problem is approximated by the finite difference method on a uniform grid. The existence and error estimates for approximate eigenvalues and eigenfunctions are established. Theoretical results are illustrated by numerical experiments for a model problem. The studies reported in this paper can be extended to the cases of more complicated and important problems on eigenvibrations of plates and shells with elastically attached loads. [ABSTRACT FROM AUTHOR]

The article presents the results of a study conducted in patients with connective tissue dysplasia and heart rate variability. The most important signs for making a diagnosis of undifferentiated connective tissue dysplasia are flat feet, Walker-Murdoch wrist sign, alar chest, hypermobility of thumbs, elbows and fingers, and Steinberg thumb sign. Vagal predominance in the heart rate regulation was higher in patients with multiple signs of undifferentiated connective tissue dysplasia. Rhythmocardiography was more useful in identifying the characteristics of heart rate regulation in UCTD patients compared to other noninvasive diagnostic methods. [ABSTRACT FROM AUTHOR]

The paper shoes the possibility of estimating surface stresses (active, residual, initial) based on mathematical treatment of the fields of residual displacements caused by dynamic indentation and recorded by optical-digital methods (method of electronic digital speckle interferometry). The basis of this methodology is a search for the minimum of the objective function representing the discrepancy of the considerable arrays of experimental data (fields of surface displacements for the object under study) from the results of calculation assemblies for test problems under various values of required parameters (required stresses). [ABSTRACT FROM AUTHOR]

This article discusses the methodology for determining residual stresses in case-hardened material layers. It includes the joint use of the slitting method and the method of electronic pattern speckle interferometry. In the final part, experimental data are obtained from studies of samples with and without force strengthening effect. [ABSTRACT FROM AUTHOR]