An approach for the simultaneous quantification of La, Fe, and Sr in solutions and suspensions of (La, Sr)FeO₃ composites by the TXRF method has been developed to study the effect of lanthanum substitution with strontium on the sensory properties of lanthanum ferrites. A gallium solution with a concentration of 50 mg/liter was used as an internal standard for the determination of the elements. The validity of the obtained results was confirmed for sample solutions by inductively coupled plasma atomic emission spectrometry (ICP AES). No interelement effects were observed for La, Fe, and Sr when present together in solutions. The precision of the results of the determination (S_r) by the TXRF was calculated as 0.04, 0.05, 0.06 for La, Fe, and Sr, respectively. The results obtained for suspensions are caused to the small particle size (15 – 17 nm) and the uniform distribution of the internal standard in the aliquot with the chosen sample preparation method. It is shown that all samples have a single phase corresponding to pure lanthanum ferrite with an orthorhombic crystal lattice (ICDD 37-1493). The absence of extraneous reflexes on the diffractogram indicates the successful incorporation of Sr²⁺ cations into the La³⁺ positions. It is shown that the doping of strontium into lanthanum ferrite made it possible to increase the sensitivity of materials to CO, NH₃, methanol and acetone, as well as to reduce the optimal operating temperature of the sensor by 50 – 150°C. At the same time, the best sensory properties were found for lanthanum ferrite nanofibers with a minimum concentration of introduced Sr (0.01 % at.). The absence of sensitivity of materials to methane and benzene is due to the greater stability of these molecules with respect to the acid-base active surface centers of La_{1 – x}Me_xFeO₃.

A method of studying the radiation effect of low-energy electron beam on the structural characteristics of a number of unsaturated fatty acids present in fish oil: oleic, linoleic, arachidonic, eicosapentaenoic and docosahexaenoic acids using high-resolution liquid chromatography-mass spectrometry has been proposed. The solution used was: 1 μl of commercially available fish oil containing omega-3 and omega-6 polyunsaturated fatty acids in 1 ml of 0. 9 % NaCl physiological solution. The samples were irradiated at the UELR-1-25-T-001 electron accelerated with an energy of 1 MeV at an average beam current of 0.5 μA and a dose rate of 10 Gy/sec at doses of 0.25, 0.5, 1, 5, and 8 kGy. The structural integrity of selected unsaturated fatty acids was analyzed by high-resolution liquid chromatography-mass spectrometry with high-resolution tandem mass spectrometric detection (HPLC-MS/MS). The content of intact unsaturated fatty acid molecules was estimated by comparing the peak areas of analytes in the irradiated solution with a control sample that was not irradiated. Taking into account the optimization of detection conditions, detection limits were calculated for each acid, and two variants of identification of the presence of unsaturated fatty acids in the sample were distinguished: reliably detected and not detected. Using the developed approach, a decrease in the content of omega-3 fatty acids — eicosapentaenoic acid and docosahexaenoic acid in water samples as a result of exposure to low-energy accelerated electrons in the dose range from 0.25 to 8 kGy at an average power of 10 Gy/sec was established.

The development of an accessible procedure for determining methyl methacrylate (MMA) in aqueous media is of great interest, since monitoring the content of the residual monomer released from the denture material — polymethyl methacrylate (PMMA) — into the oral cavity in neccesary prostheses. The proposed technique of electrophoretic determination of MMA is characterized by high precision, short analysis time, and minimal sample preparation. Optimal analysis conditions have been found: the concentration of surfactant (sodium dodecyl sulfate) — 80 mmol/liter, capillary voltage — 25 kV, temperature — 25°C. The developed procedure was tested in the analysis of real samples from dental practice: base materials intended for the fabrication and relocation of orthopedic constructions. Monitoring of MMA releasing from PMMA samples allowed to evaluate the residual monomer content in deionized water and artificial saliva: after 48 hours, MMA concentration in model solution is 35% lower than in water. With direct spectrophotometric detection (λ = 215 nm), the limit of detection of MMA in deionized water and artificial saliva is 0.015 and 0.020 μg/ml, respectively.

The solution of problems in the field of microwave electrotechnology related to mathematical modelling, development of installations or technology of electromagnetic field influence on the processing object requires knowledge of dielectric properties of high-energy radio-absorbing composites. The paper presents the results of computational and experimental study of dielectric properties of composite materials based on epoxy matrix with different absorbing fillers. Dielectric properties of materials were determined using the waveguide method based on the determination of the complex reflection coefficient and passage of electromagnetic waves through the working chamber with the investigated sample. By means of modelling the electric field strength distribution, the optimum geometry of the electromagnetic wave in the measuring microwave line (frequency — 2450 MHz) was found. It was found that the use of silicon carbide as an absorbing filler in the composite is very promising, providing a high temperature of its heating at dissipation of microwave energy. At the same time, the results of in-situ experiment of measuring dielectric properties of composites with different fillers and numerical results showed convergence with an error of 14%. The obtained results can be used in the creation of new radio-absorbing composites on the polymer basis with a given complex of functional properties.

The dimensions of products obtained by additive technologies are limited by the working chamber of the 3D printer. The solution to the problem of scaling products is possible through a combination of additive methods and laser welding. The paper presents the results of quality assessment of welded joints using non-destructive testing methods. The objects of the study were plates made of corrosion-resistant steel 12Kh18N10T (AISI 321) measuring 100 × 100 × 5 mm and pipes with a wall thickness of 6 mm, manufactured by selective laser melting. X-ray computed tomography, digital radiography and ultrasonic testing were used to analyze defects. It was shown that the presence of pores and lack of fusion in welded workpieces leads to the occurrence of local porosity in the weld. The digital radiography revealed the difference in the formation of negative and positive contrast of radiographs. Digital post-processing methods were applied to improve the quality of radiographs (increase in image contrast by 7 – 8 times) and to increase the detection of defects. It was established that the ultrasonic testing method allows for the qualitative determination of the presence of defects in a welded joint, but does not provide a quantitative assessment of their characteristics due to the strongly expressed anisotropy of the acoustic properties of the material. The obtained results can be used to solve the general problem of quality control of additive manufactured products, in particular, in the control of welded joints of corrosion-resistant chromium-nickel steels for aerospace products.

The main disadvantage of the methods used when studying the nature and rate of interaction of hydrogen with structural materials is the difficulty of determining the rate of interaction of components at characteristic concentrations of hydrogen in metals 1 – 5 ppm. The paper presents the results of a study of the interaction of hydrogen with metals in a continuous mode using an installation that allows determining kinetic parameters up to a temperature of 1000°C in the case of both gas release and absorption. The principle of operation of the installation is based on a comparison of changes in gas volumes in two isolated, almost identical cells (an inert sample is placed in one and a test sample in the other). Both cells are pre-filled with the test gas. The relative volume change in the tank with the active sample is measured with a differential zero pressure gauge and regularly compensated to the initial zero pressure drop value by introducing or removing part of the gas from the reaction volume. It is shown that when nickel interacts with hydrogen, the gas absorption pattern has a smooth temperature dependence, which is quantitatively related to the shape of the metal sample. For powdered nickel, the absorption is higher than for sheet nickel. The rate of hydrogen absorption by spongy titanium has a threshold character — it increases abruptly at a temperature of about 600°C. The kinetic characteristics of the interaction of hydrogen with a multicomponent alloy at 820°C were determined. The results obtained and the proposed technique can be used in studies of the interaction of gases with solids, including studies of the kinetic parameters of the interaction of hydrogen with metals and alloys.

Novel experimental technique, which provides quantitative description of damage indicators evolution related to cyclic loading of composite specimens with stress concentrators, is developed and implemented. Involved indicators represent by itself deformation response to narrow notch inserting. This notch is emanated form the edge of through circular hole, located in the centre of plane rectangular coupon, under constant external load. The first indicator is the notch mouth opening displacement. In-plane displacement component directed along the notch line as measured in the notch top serves as the second damage indicator. Both parameters follow from direct physical measurements by counting interference fringes, which are visualized on the base of electronic speckle-pattern interferometry. Damage indicator values are obtained for array of specimens with different damage levels. Dependencies of both parameters from loading cycle number are constructed. Theoretical background essential for quantitative analysis of damage accumulation process proceeding from experimental data, which represent evolution of damage indicators caused by loading cycle number increase, is presented. The approach developed is implemented to a quantitative description of damage accumulation process related to cyclic loading of thin rectangular plates with central through hole. Each plate is made from orthotropic composite material. Specimens under study, which are manufactured from layers with three different angular orientations, are tested under fatigue loading with stress range 262.5 MPa and stress ratio –6.0. The point corresponding to the specimen with maximum cycle number, for which damage indicator values are obtained, is decided as conventional limiting case responsible for explicit form of damage accumulation function. Chosen value is equal to 150,000 cycles that comprises 41% of average lifetime of tested specimens. There are no evidences of any delamination inherent in all investigated specimens. Damage accumulation function is constructed in an explicit form for prescribed cycle range. It is established that both indicators provide the same results. Data obtained show that damage accumulation rate is constant for investigated loading cycle range. Accordingly to currently adopted opinion, revealed character of damage accumulation is related to the first stage of the process considered. It is shown that a decrease in the value of deformation response to artificial notch inserting, which occurs after only 1000 cycles applying, is produced by relaxation of residual stress component directed along external force acting line.

The aim of the work is to demonstrate the application of the cutting method in determining the membrane component of residual stresses in elements of metal structures with continuously distributed eigenstrains, when methods of etching, drilling holes and X-ray diffraction can provide only limited information. The objects of the study area (a) a 250 × 25 × 10 mm bar made of aluminum-magnesium alloy, one narrow face of which is subjected to spot pressure treatment, (b) a 150 × 25 × 10 mm edge made of austenitic stainless steel, surfaced on the basis by wire-arc, (c) sheet ferritic-martensitic steel with a thickness of 14 mm, subjected to mechanothermic treatment. The method used consisted in (1) cutting a sample in the form of a bar cut from a workpiece by an electroerosion method into strips 1 mm thick at a coordinate along which the membrane component of residual stresses was inhomogeneously distributed, and (2) measuring the deflections of the strips and reconstructing from these data the distributions of the sought component of residual stresses and the incompatible part of the eigenstrains that generate these residual stresses, according to the relations obtained by the authors earlier. As the result in all considered problems the method showed fairly good solvability and revealed technologically important differences in the distributions of residual stresses in the height of the edge surfaced by wire-arc with and without layer forging with pneumatic tools, as well as in the thickness of the sheet subjected to unilateral rapid cooling with or without plastic bending in one direction or the other. The method does not require special laboratory equipment, and the cutting method used has a minimal effect on the material, symmetrically on both sides of the strips.

Obtaining a stress – strain diagram using tensile machines involves testing a large volume specimen. An alternative to such tests is the automated ball indentation test (ABI test — automatic ball indentation), which is designed to determine the stress-strain curves of metallic materials and structural elements. The purpose of this work is to study the applicability of the technique, which is developed for the obtaining of the stress – strain diagram using large spherical indenters (diameter 250 – 1500 μm), to work with a microspherical indenter with a diameter of 5 μm. The use of small diameter spherical indenters allows the study of small sized samples of material from which it is not possible to produce samples for a standard uniaxial tensile experiment. It can be applied to study individual phases of heterogeneous materials, intergrain boundaries, as well as thin films, coatings and near-surface layers of the sample. In this work, the shape of the obtained imprints on the surface of the studied samples was studied both by non-contact method — by means of confocal optical 3D profilometry, and by means of contact method — atomic force microscopy. The non-contact method, as having a higher speed, was used to reveal the grain sizes of alloys, the contact method — to measure the diameter of imprints — due to its higher lateral resolution. A series of experiments were carried out on tensile testing of alloys on a universal testing machine and on indentation of specimens made of the same alloys. The values of elastic moduli and time resistances of alloys V95, VT1 and VT6 were obtained, which coincide within the error limits in the results of two different experiments. In this study, stress – strain diagrams were experimentally plotted using tool indentation and residual indentation geometry analysis when a spherical tip made of diamond single crystal with a small radius of curvature (2.5 μm) was used.