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Mechanical performance of 3d-printed polyamide sandwich beams with different type of the lattice cores is investigated. Four variants of the beams are considered, which differ in the type of connections between the elements in the lattice structure of the core. We consider the pantographic-type lattices formed by the two families of inclined beams placed with small offset and connected by stiff joints (variant 1), by hinges (variant 2) and made without joints (variant 3). The fourth type of the core has the standard plane geometry formed by the intersected beams lying in the same plane (variant 4). Experimental tests were performed for the localized indentation loading according to the three-point bending scheme with small span-to-thickness ratio. From the experiments we found that the plane geometry of variant 4 has the highest rigidity and the highest load bearing capacity in the static tests. However, other three variants of the pantographic-type cores (1–3) demonstrate the better performance under the impact loading. The impact strength of such structures are in 3.5–5 times higher than those one of variant 4 with almost the same mass per unit length. This result is validated by using numerical simulations and explained by the decrease of the stress concentration and the stress state triaxiality and also by the delocalization effects that arise in the pantographic-type cores.

The variation in the magnetoresistance of a spin-valve sensor during its linear movement in an inhomogeneous field of a magnetic label at different orientations of the magnetic moment of the spin-valve structure is considered. It is shown that the shape of the sensor signal and its value critically depend on the initial orientation of the magnetic moment and the trajectory of the sensor in the field of the magnetic label.

Aluminum-fiber-reinforced plastics (GLARE) are promising aviation materials with increased characteristics of specific stiffness and strength, fatigue strength, impact resistance, and residual strength after impact. Nowadays, GLARE are used for making elements of the fuselage of the long-haul passenger aircraft Airbus A380, as well as some other elements of aircraft structures. The results of experimental studies of eigenfrequencies and damping coefficients of three-layer beams made with face sheets of five-layer GLARE and with a core made of polyimide foam are presented. The tests were performed using the method of free bending vibrations of cantilever samples. The dynamic parameters of the three-layer beams were calculated based on the analysis of amplitude-frequency characteristics obtained by the fast Fourier transform method. Mechanical characteristics of GLARE and filler samples are preliminary determined in static and dynamic tests. The damping factor of the core is determined by the dynamic mechanical analysis method. The core shear modulus is determined by measuring the flexural rigidity of manufactured three-layer beams in a quasi-static three-point bending test. Based on a comparison of the design data and the results of the experiments, it is shown that in dynamic tests, the flexural rigidity of three-layer specimens is reduced in comparison with the estimated values, which may be due to the peculiarities of changing the characteristics of the foam core under dynamic loading. The value of the damping factor of GLARE samples was ~0.02, the foamed core was ~0.08 and three-layer beams were ~0.067 in the range of vibration frequency up to 60 Hz.

The relevance of the article is due to the stable growth of the composite industry. Due to its high physical and mechanical characteristics, composite materials (CM) play a vital role in many areas of technology, such as aerospace, aviation, automotive, engineering and instrumentation, and the medical industry. When creating materials with the required mechanical and thermal characteristics, various additives and fillers are often used that affect the strength and elasticity of the samples obtained. In this paper, we study the influence of spherical inclusions in epoxy on the mechanical properties of the material. A composite structure of ED-20 epoxy with inclusions in the form of spherical particles of PBS-50 glass was considered. The characteristic particle size was about 50 μm. Within the framework of this study, batches of samples with a specific volumetric inclusion content of 5%, 10%, 15%, and 20% were produced. Each batch consisted of 6 samples of the same type. To check the distribution of particle volume and inclusion studies, the microstructure of the thin section of the sample and separately the powder were studied. Using methods of modeling the process, the samples were tested for 3-point bending. Based on the results of mechanical tests, the elastic module, strength limit, and ultimate strains were obtained. As part of the study of materials, numerical calculations were performed using Digimat software (MSC Software) to model the structure and obtain effective material properties, as well as strength analysis using the finite element method in Ansys Workbench. The calculation was carried out for the volumetric content of inclusions of 5%, 10%, 15%, and 20% order and in the absence of inclusions. The obtained numerical results were compared with an experimental study. Based on the numerical calculations, the dependence of the percentage of inclusions on the strength limit and elastic module was obtained.

This work investigates the effect of carbon nanomodification on the residual stress-strain state (SSS) after molding. One of the ways to reduce residual stresses and deformities is nanomodification. The main objective was to determine the degree of influence of the nanomodification parameters on the residual SSS. Within the framework of this study, 4 slabs were made. Two slabs are made of a conventional binder with laying [010/9010] and [010/4510] and two slabs of a modified binding material with the same layer structure. For the fabricated plates, deflections were measured on each of the four sides, during which residual strains were obtained in the panels of nanomodified carbon fiber for the considered layings with and without modified binding material. To analyze the residual stress-strain state, a numerical and analytical calculation was performed. The numerical calculation was carried out by means of the finite element method for the case when the slab is fixed at the point of the geometric center, with no power load, and the temperature load is a difference of 100 °C. An analytical calculation was carried out for the case when the slab is free from fastening and external power load, and the temperature load is a difference of 100°C. During the study, variants of the physicomechanical properties of the monolayer were obtained using the Digimat software and the Mori-Tanaka averaging method. The results obtained by analytical and numerical methods have a good correlation between each other, and in the course of comparison with the experiment, a method for calculating the characteristics of the monolayer that was closest to the experimental result was determined. On the basis of the obtained results, conclusions were made on the possibility of reducing residual SSS and deformation in structures with asymmetric reinforcement schemes using a matrix containing carbon nanoparticles.

In this work we solve a higly-nonlinear structural optimization problem for the sandwich panel with external thermal protection layer that can be used in the spacecraft systems. Objective function of the problem is the mass per unit area of the panel. Constraints are formulated based on the simplified analytical solutions of structural mechanics and heat transfer problems, which are suitable for the preliminary design considerations. The set of design variables includes the geometric parameters of the panel and additional microstructural parameter—porosity of the heat protection material. Direct random search and simulated annealing method are applied to solve considered problem. Change of limit states and optimal configurations of the panel are studied for different levels of the mechanical loading.

The scientific paper presents a technique for calculating a thick-walled axially symmetrical construction consisting of a steel rod (reinforcing component) and an external thick-walled shell made of carbon fiber. The construction is loaded with linear load distributed along its length, associated with the operating external pressure, and inertial forces. The technique is based on a one-dimensional model of a composite rod of variable cross-section, roughly taking into account transverse deformations, which is necessary when analyzing a thickwalled construction operating under pressure. In the proposed approach, the geometry of the product is divided into sections and approximated by fragments in the form of truncated cones and, in the particular case, in the form of cylinders. As a result of calculations, the distribution of normal tensile/compression stresses in the shell and in the reinforcing rod, as well as tangential stresses at the boundary of their contact, are determined. As a result of test calculations, a fairly good consistency of the considered one-dimensional model with refined finiteelement modeling is shown. It has been established that the concentration of shear stresses is realised due to the presence of substantially inhomogeneous deformations in the areas of sharp changes in geometry, a reduction in the radius of the shell (the appearance of edge effects), and in the area of a sharp increase in the radius of the bevel of the shell where external pressure is in place.

Magnetic properties of trilayer double-exchange biased Si/Ta(30 nm)/NixFe(1−x)(10 nm)/IrMn(tAF)/NixFe(1−x(10 нм)/Ta(30 нм) thin film structures with x = 0.4 and x = 0.75 were investigated. The exchange bias, noncollinearity of unidirectional and uniaxial anisotropy and magnetization in both bottom and top ferromagnetic layers as a function of the antiferromagnetic (AF) layer thickness in the range from 2 to 50 nm were investigated. The obtained effects support the model of ferromagnetic coupling through the antiferromagnetic spacer and the model of rotatable anisotropy contribution at small AF thickness. It was found that usage of low-nickel permalloy in exchange biased systems has advantages of higher magnetization, a higher magnetic ordering at the interface and smaller critical thickness of antiferromagnetic layer to set the exchange bias, though provides a lower exchange bias compared with normal permalloy composition.

The regular shape of the magnetoresistance as a function of applied magnetic field, R(H), is important for numerous spin valves applications. Nevertheless, in many practical studies the shape of the R(H) curve is unpredictably complicated. We draw attention to the close connection between R(H) and magnetization hysteresis loop and propose a simple technique, which allows interpreting the R(H) features and calculating R(H) curves from known hysteresis loops of ferromagnetic layers, composing spin valves. And vice versa, the shape of the hysteresis loops of the composing ferromagnetic layers can be obtained from R(H) curves. The method is suitable for prompt selection of promising spin valve stacks.

Ferromagnetic resonance (FMR) linewidth (LW) is a tool for studying the high frequency properties of magnetic materials for their application in high-speed devices. Here, we investigate different mechanisms which determine FMR damping in bilayer ferromagnetic/antiferromagnetic (F/AF and AF/F) exchange bias systems. Variations of FMR LW with the thickness and deposition order of the F and AF layers were studied, as well as their correlation with the exchange bias field and roughness of the sample surface. We observed much larger LW in AF/F structures compared with F/AF samples. It was found that neither the exchange bias nor surface/interface roughness in the samples could explain the difference in LW for F/AF and AF/F samples. Instead, the different underlayer microstructure influenced the grainsize, leading to different angular dispersion of magnetization and different internal stray field in F-layers, promoting a different intensity of magnon scattering and FMR damping in F/AF and AF/F samples.

Magnetic field sensors based on the giant magnetoresistance (GMR) effect have a number of practical current and future applications. We report on a modeling of the magnetoresistive response of moving spin-valve (SV) GMR sensors combined in certain cluster networks to an inhomogeneous magnetic field of a label. We predicted a large variety of sensor responses dependent on the number of sensors in the cluster, their types of interconnections, the orientation of the cluster, and the trajectory of sensor motion relative to the label. The model included a specific shape of the label, producing an inhomogeneous magnetic field. The results can be used for the optimal design of positioning devices.

The paper presents an analytical estimate for an area of contact for a thin-walled noncircular cylindrical shell placed between two parallel rigid plates with an initial gap and then pressurized hydrostatically up to the contact appearance. The Euler–Bernoulli beam is used to model the shell deformation under the plane strain assumption. Such a simplification allows one to obtain the simplest closed-form estimate for the contact zone area. The first approximation is obtained neglecting the deformation of the curvilinear segments of the flat oval shell cross-section while the solution for the curved beam loaded by the homogeneous pressure is considered as a second approximation. The accuracy of the proposed analytical solutions as well as their usability in the preliminary design of thin-walled elements of various cooling systems is validated by the results of both numerical simulations and experimental tests.

The results of the digital image correlation (DIC) analysis for the three-point bending tests with GLARE1-9/8 laminates (9 aluminum and 8 unidirectional GFRP layers) are presented in this paper. The findings show that, in samples with a small span-to-thickness ratio, an intensive concentration of the plastic shear strain arises inside the GFRP layers, which significantly affects the load-bearing capacity and apparent interlaminar shear strength of GLARE. Previously, such effects were predicted based on numerical simulations. In the present paper, we validate these theoretical predictions based on the full-field DIC analysis of the shear strain distribution across the GLARE thickness. For this analysis, samples with longitudinal and transverse orientation of glass fibers in the GFRP layers were studied and compared. For the transverse samples, we also found that the matrix cracking in the GFRP layers becomes an additional source for the overall non-linear behavior of GLARE, such that the pure failure mode related to the interlaminar shear cannot be achieved.

Nowadays, additive technologies are used to create physical models, prototypes, samples, tooling, and the production of plastic, metal, ceramic, glass, composite components, and components made of biomaterials. The greatest technological interest is the production of final parts from metal alloys. This paper presents the results of studies of the topography of differently oriented surfaces of PH1 stainless steel samples made using the method of selective laser melting. The surfaces were studied in the plane of construction, perpendicular to the platform, at angles of 45o and 135o. For each surface under consideration, the roughnesses Ra, Rz were determined and a profile was constructed. The findings showed high stability of the topography of the surface layer of the grown material. To confirm the quality of the obtained samples, they were synthesised and tensile tests were carried out. The established characteristics of the elastic modulus, the tensile strength and the corresponding deformations are consistent with the previously determined properties of samples grown using selective laser melting technology and datasheet specifications. According to the results of mechanical tests, the microstructure of the fracture surfaces of the samples was investigated. It is established that the destruction of samples under tension occurs by a viscous mechanism with the implementation of a combination of shear and pit-porous types of destruction. The study of the topography of differently oriented surfaces is carried out – in the plane of construction, perpendicular to it and at angles to the platform 45 and 135o. It is shown that the best surface quality corresponds to two planes – parallel and perpendicular to the plane of the construction platform. The average values of their roughness were Ra ~ 0.6 µm and Rz ~ 4 µm. The quality of the surfaces located at an angle is significantly inferior to the first two. A change in the surface quality depending on the angle of inclination was also observed.

Residual stresses arising from the technological processes of manufacturing aircraft structures can considerably affect the bearing capacity of the structure, which justifies the need to assess the level of these stresses. The study analysed the speckle interferometric images in terms of the parameter image intensity. This method allows assessing the picture of the change in this parameter both in a particular band, and performing a comparative analysis in a number of bands. Due to the presence of a correlation between the material deformation and the intensity of the image, the dynamics of the variation of the stress state (residual stresses) is estimated. When decoding the holograms, the authors used the Aleksandrov-Bonch-Bruevich vector equation. Double exposure of speckle holograms was applied and photo processing of the hologram was performed. It is shown that, depending on the position of the beam from the hole, there is a change in the image intensity. It was proved that the method employed in the study does not depend on external factors. The proposed approach allows taking a fresh look at the picture of stress state analysis and evaluating the qualitative and quantitative processes in the deformation zone, namely around the drilled hole in the plate.

An analysis of the behavior of nanosized colloidal particles in a supersaturated solution made it possible to substantiate the possibility of increasing the heat-transfer efficiency in a heat exchanger during magnetic treatment of a heat-transfer agent. A model is proposed to weaken the scale during magnetic treatment of a water stream. A colloidal solution is shown to decrease its stability—the coagulation of colloidal particles begins—because of the deformation of the double electrical layer. As a result of increasing the effective radius of curvature of nanoparticles, the solution becomes strongly supersaturated with respect to forming aggregates, which accelerates the solidification of dissolved salts on them. The influence of the interfacial layer of nanoobjects decreases the energy of formation of critical nuclei (size effect) and their sizes. Since coagulation tends to decrease the concentration of critical nuclei in the solution, their loss should be compensated via the homogeneous generation of new nuclei. As a result, the concentration of suspended particles increases additionally and the antiscale effect is enhanced. The solidification flux of dissolved salts is shown to deposit mainly on suspended nanoparticles due to an increase in their total surface area and to the fact that the coefficient of mass transfer to suspension is higher than that to the wall by four orders of magnitude. The mathematical model constructed on the basis of the detected set of physical processes can be used to perform quantitative estimates of the antiscale effect in real power plants.

The influence of powder coatings based on an epoxide polyester mixture on the mechanical properties of the plates made of rolled sheet steel is studied. The influence of 100-μm-thick coatings on the mechanical properties of specimens 0.7–1.5 mm thick is considered. The bending and tensile tests performed at room and elevated temperatures show that the thin coatings weakly affect the mechanical properties of the plates. In particular, the stiffness of the coated plates during tension and bending remains almost the same despite the fact that the elastic modulus of the coated plates is always slightly lower than Young’s modulus of steel because of an increased specimen thickness determined with allowance for the presence of a coating. The influence of the coatings is substantial in compressive stability tests. Under supercritical deformation conditions, the bearing capacity of the coated plates decreases substantially, and their critical stability load on the loss of stability falls by 20–30% (depending on the substrate thickness). This effect can be explained by the influence of the residual thermal stresses that appear in the specimens during coating deposition.

We demonstrate the magnetization reversal features in NiFe/IrMn/NiFe thin-film structures with 40% and 75% relative content of Ni in Permalloy in the temperature range from 80 K to 300 K. At the descending branches of the hysteresis loops, the magnetization reversal sequence of the two ferromagnetic layers is found to depend on the type of NiFe alloy. In the samples with 75% relative content of Ni, the bottom ferromagnetic layer reverses prior to the top one. On the contrary, in the samples with 40% of Ni, the top ferromagnetic layer reverses prior to the bottom one. These tendencies of magnetization reversal are preserved in the entire range of temperatures. These distinctions can be explained by the morphological and structural differences of interfaces in the samples based on two types of Permalloy., 11 pages, 5 figures

The influence of the antiferromagnetic layer thickness on the magnetic properties of the trilayered thin-film structures with the exchange bias phenomenon was studied in the temperature range from 100 up to 295 K. Dependences of the coercive force and exchange bias field on AF-layer thickness were analyzed for all structures with AF layer thickness from 2 nm up to 50 nm at room and low temperatures. The explanation in terms of the anisotropy and thermal energies competition was given for disclosure of an exchange bias for structures with 2 nm AF layer thickness at low temperatures.

The combustion temperatures under limiting conditions for propagation of combustion were determined for a variety of water-vapor/air/gas/dust mixtures, and a methodology was developed for calculating the concentration limits for flame propagation in suspensions [of powders] in air for various concentrations of combustible gases.

As of now, many investigations are performed in order to develop methods of correlation with the help of relevant algorithms. This is especially helpfull for plotting vectors of displacements in order to estimate deformation of various materials, as well as to determine correspondence between sections of two images through calculation of the cross-correlating functions and to ensure seeking of the extremum. The aim of this study was to develop relevant method to estimate mechanism of fracture of materials in accordance with the data of analysis of a photographic image in respect of the parameter of the image intensity. In addition, this method is to be used with the help of the multivariate analysis (multi-factor analysis) of the interrelationship between image intensity, surface roughness, and possibility to determination the geometrical parameters of the deformation area/deformation volume under different conditions of operation. Digital method of processing of photographs/video frames has been used in order to investigate microstructure and surface of materials in respect of criterion of the image intensity in the course of mechanical tests in accordance with deformations. Quantitative parameters of the image intensity were compared to the structure of material, as well as to the surface roughness before and after destruction of samples. The images used were obtained during mechanical testing of aluminium samples. To ensure the validity of the test results, six specimens of the same type were tested. A stress-strain diagram was drawn up for each specimen. Stress-strain diagrams from the mechanical tests were compared with those from the photo analysis using the method described above. The results correlate well with each other, but unlike the experiment, where the strain is measured only at the strain gauge location, the photo analysis provides a complete picture of the strain distribution over the entire specimen area. In addition, a multivariate analysis has been carried out to evaluate the geometric dimensions and shapes of the structure elements.