The processes of superstructure formation were investigated using nanocomposites composed of inorganic scintillators based on lanthanum bromide and cesium iodide and an organic luminophore based on polystyrene, under deformation, electrical, ultrasonic and laser exposures. It was shown that for certain combinations of nanocomposite compositions and exposure parameters, structuring develops at molecular‑cluster and optical scales, which is of interest for the development of improved radiation detectors.
This study examines the flow patterns of viscoelastic-plastic filler in a molded volume during the manufacturing of repair parts for mining machinery and equipment. Promising technologies for the rapid manufacturing of metal-composite mining machine parts, such as metal-composite technology, require a mathematical description and functional dependencies describing the flow of metal-polymer composite materials (MPCMs) in complex channels formed by mold voids. The objectives of this study are to mathematically describe the MPCM flow process in mold channels and to derive mathematical dependencies describing the optimal channel shape. The paper analyzes a number of studies related to the search for the optimal surface shape ensuring minimal descent time when solving various engineering problems. It is revealed that all solutions are based on the properties of brachistochrone. However, in the process under consideration, additional conditions are imposed when formulating the problem, such as resistance, viscous or dry friction, the movement of solid or viscoelastic-plastic bodies, and others, resulting in a brachistochrone shape other than a cycloid. An equation was obtained for the generatrix that ensures the least work done by the friction forces of the wall-adjacent layers of the MPCM on the mold walls. The resulting mathematical relationship can be applied to the design of internal mold channels using specialized computer programs.
Steady‑state and pulsed X‑ray luminescence of nanocomposites based on polystyrene and inorganic scintillators (cerium‑doped lanthanum bromide LaBr3(Ce) and thallium‑doped cesium iodide CsI(Tl)) were investigated. The formation of high‑speed emission pulses of nanosecond duration with substantially enhanced intensity was observed. For certain combinations of composition and preparation conditions, the primary emission is concentrated in a fast nanosecond component with high light output. This is explained by the formation of molecular‑cluster assemblies in which interaction between the electronic and vibrational states of the organic and inorganic components initiates a new shock‑vibronic (impact‑vibronic) excitation mechanism.
The effect of selective laser melting (SLM) modes on melt bath geometry and defect porosity of solid materials and lattice structures made of medical-grade Ti–Zr–Nb alloys was studied. Based on the analysis of melt bath geometry formed by single and multiple laser passes, an approach was developed to optimize SLM modes for producing porous materials based on lattice structures made of Ti–Zr–Nb alloys with thin (250–340 μm) structural elements and a low defect count. It was found that modes with reduced scanning speed (700–1000 mm/s) and laser power (45–60 W) ensure high geometric accuracy due to reduced melt bath size and low defect porosity (<0.75
For the first time, the relationship between the firing time of ceramics based on the solid solution (Ba,Ca)(Ti,Sn)O3 containing 12 wt
A comprehensive assessment of the climatic durability of SKEPT‑based rubbers was carried out under prolonged natural and accelerated laboratory testing. The suitability of SVMPE as a modifier for SKEPT‑based rubbers was substantiated. It was shown that the modified rubbers exhibit a high degree of retention of physicomechanical and low‑temperature properties during aging due to an increased fraction of saturated bonds, which confer resistance of the polymers to destructive factors, as well as enhanced interfacial interaction between SVMPE and the rubber.
The influence of the following factors on the strength of composite geopolymers based on thermal power plant ash and nepheline was studied: ash type, composition of the initial component mixture, mechanical activation parameters, and curing conditions.
A comparative analysis of modern methods to estimate the adhesive strength between carbon fiber and epoxy binder is outlined. A new method for studying adhesive strength is proposed. It makes use of analyzing properties of carbon fiber bundles combined with accounting for the process of obtaining microplastics. Two grades of carbon fibers—UMT42S-3K-EP and UMT49S-12K-EP—manufactured by Alabuga-Volokno LLC are selected as the objects for the study. An epoxy binder of the VSE-30 brand, developed at the National Research Center Kurchatov Institute—VIAM, is used as the matrix. The features of testing samples to determine adhesive strength using the improved knot method are presented. Optimal parameters for forming the adhesive cell are proposed. The fracture zone of the adhesive joint between the carbon fiber and the epoxy matrix is examined using optical microscopy.
Ceramic materials based on [97Zr3Yb]O2 nanopowder are obtained using the hydrolysis sol-gel method. The phase composition of the base material and that modified by aluminum, yttrium, and neodymium cations is represented by solid solutions based on ZrO2 in the tetragonal system. The ceramic materials exhibit high strength that grows with increasing the modifier content. It is established that barothermal treatment reduces the porosity in ceramic materials and increases microhardness, strength, and elastic moduli, as well as the translucency coefficient. The new materials are promising as structural materials for engineering and medicine.
A method is developed to obtain composite materials from PVDF copolymer (polyvinylidene fluoride/trifluoroethylene having ratio of 94/6) with titanium dioxide particles included in its structure. Using IR spectroscopy, the phase composition of PVDF is estimated for composite materials with different contents of titanium dioxide particles. The crystallinity of the polymer is assessed using DSC analysis. The free surface energy of composite polymer films is estimated using the contact angle analysis for materials having different amounts of included titanium dioxide particles. The electron microscopy technique confirmed that including the titanium dioxide particle affects the surface morphology. Quantitative analysis of included titanium dioxide particles is carried out using thermogravimetric technique. The strategy proposed presents a new approach to obtain and control the phase composition of PVDF-based polymer films.
The effect of powder fillers (silica ZC-120, natural chalk, kaolin and carbon black of P 803, P 324 and N 220 grade) is estimated on the rubber mix rheology, on the physical, mechanical and operational properties of the vulcanized rubber product obtained from the ethylene propylene diene rubber S 505A. This rubber grade is used as a metal liner. It is established that rubber containing 60.0 parts per hundred parts of rubber (phr) of N 220 carbon black has the best physical and mechanical properties. The material is resistant to aggressive alkaline and acidic media. It is frost-resistant and is can be recommended for lining tanks to transport liquids.
The article examines the microstructure, phase composition, mechanical properties, and fracture mechanism of titanium alloys of the Ti–Zr–Nb system with the addition of silver. The elemental composition of the system was selected from non-toxic elements that can provide a level of mechanical properties at the same level as Ti–6Al–4V, but with a lower Young’s modulus to eliminate the “stress shielding” effect. Samples of the TiZr38Nb11 alloy and its modifications with the addition of silver (1–3 at
The resistance of four polyurethane elastomers to hydroabrasive wear is investigated under similar conditions. The work is made using a new experimental setup that allows testing simultaneously several polymer samples. The material synthesized on the basis of an oligoether of the polyfurite type with a molecular weight of 1000 shows the lowest wear under hydroabrasive conditions. The relationship between the abrasive resistance of the investigated elastomers and their physical and mechanical characteristics is discussed.
The areas of effective applying the instrumented indentation are discussed to evaluate the mechanical parameters of materials, welded joints, coatings and surface layers in materials obtained using various deposition and processing techniques. It is demonstrated that the technique is capable of not only determining the hardness and Young’s modulus as required by effective regulatory documents, but also the parameters of strength, creep and fracture resistance. It is shown that modern methodological and instrument developments allow testing materials both under laboratory and industrial conditions. Examples of applying the indentation testing are given for solving various tasks of controlling the mechanical properties in materials, products, as well as in operating assemblies.
A new statistical model is applied to calculate the properties of previously unstudied alloys. The calculation is based on the published data on the thermodynamic parameters of hydrogen desorption reactions developing in alloys having the CaCu5 structure. Isotherms of hydrogen desorption are plotted. A comparison of calculated and experimental data is given together with the estimate of the accuracy of the predictive model.
The method is outlined to determine the creep parameters of structural steels at high temperatures using the instrumented indentation testing. The existing methods of high-temperature long-term indentation testing are reviewed from the standpoint of the accuracy of assessing the mechanical properties. The main challenges and bottlenecks in implementing this approach are explained. The results are given on the long-term high-temperature indentation testing steel grades, on plotting the creep diagram in the strain—time coordinates during loading at temperatures up to 700°C. For structural steel 15Kh2NMFAA, widely used in the power engineering to manufacture equipment operating at high temperatures, the relationships are obtained linking the creep rate with the temperature at a constant initial stress. Also, the functions of the creep rate against the initial stress are derived for a constant test temperature.
The issue of detecting defects is explored for products made using the selective laser sintering during automated ultrasonic testing. An adaptive algorithm is proposed to detect and localize defects in automated ultrasonic quality control. It is based on combined use of recurrent neural network methods with long-term short-term memory (LSTM). It allows localizing defects based on the amplitude of the ultrasonic signal exceeding a given threshold value. A convolutional neural network (YOLOv5 architecture) is used to classify defects based on the B-scan image. The algorithm automatically determines the type, size, and location of defects, including the depth. The developed algorithm is capable of quickly matching the software settings for any type and size of control objects, provided the matching is made using artificially generated defects.
The influence of the Portevin-Le Chatelier effect on the mechanical properties of AMg6 aluminum alloy specimens under static, dynamic, and cyclic loading was studied. It was found that this effect has little effect on the yield strength, tensile strength, and elongation determined under static tension at a strain rate of 5 mm/min. However, it significantly reduces impact toughness and its components-the work of crack initiation and propagation-and also reduces the number of cycles to complete failure under cyclic loading of the specimen at the same maximum cycle stress.
