The conditions for sample preparation and determination of total arsenic in fish and seafoods by atomic absorption spectroscopy with electrothermal atomization have been optimized. When using a standard sample preparation procedure (GOST R 53100), a complete decomposition of the organic arsenic compound, arsenobetaine, appeared impossible which leads to underestimated results. A novel sample preparation procedure for the determination of total arsenic, including the addition of concentrated sulfuric acid for complete decomposition of the organic forms of arsenic to inorganic ones is proposed. During the atomization of the sample, an additional stage of drying was introduced with smooth heating from 200 to 250°C, which contributed to a complete removal of sulfuric acid residues from the injected sample volume. The correctness of the proposed methodology was verified using the ICP-MS method and in the analysis of reference samples of fish and seafoods.

The necessity of developing safe methods of processing food products which improve the quality and extend their shelf life entails further scientific research aimed at increasing the efficiency of radiation processing of food products. Ionizing radiation causes lipid peroxidation in the items with a high fat and water content, such as chilled meat and fish products, which leads to formation of organic volatile compounds that render the food the specific flavor and smell. Gas chromatography-mass spectrometry is a technique that provides identification of chemical changes that actually occur in the product after irradiation. Experimental data on the content of organic volatile compounds in chilled turkey and salmon meat samples exposed to irradiation with 1 MeV accelerated electrons in the dose range from 0.25 to 2 kGy revealed both common and different trends in the behavior of dose dependences of alcohol, aldehyde and ketone contents in various types of chilled products. A proposed mathematical model based on the possibility of simultaneous occurrence of two competing processes, i.e., the decomposition of compounds due to their oxidation and the accumulation of compounds due to oxidation of other compounds after exposure to ionizing radiation match a dose dependent character of experimental data.

A lithium-boron alloy (LBA) with a high lithium content (up to 70%) is used as an anode material for molten salt batteries in chemical sources of current. We present a complex of developed techniques for determining mass fractions of free lithium, total lithium, and total boron in lithium-boron alloys containing lithium mass fractions no more than 70%, boron mass fractions — no less than 26%. Optimal conditions for preparation of LBA samples and subsequent free lithium extraction from them are determined. The developed techniques are intended for i) extraction-titrimetric determination of free lithium in a content range of 20 - 50% (the relative total error no more than 1.1%); ii) determination of the total lithium content using flame atomic emission spectrometry in a content range of 59.0 - 96.0% (the relative overall error no more than 2.7%; iii) determination of the total boron content by two methods, i.e., potentiometric titration within a content range of 5 - 40% (the relative total error no more than 1.3%) and flame atomic absorption spectrometry within a content range of 4.9-50.7% (the relative total error no more than 4.9%). The results of analysis of full-scale LBA samples for the content of free lithium, total lithium and total boron are presented. It is shown that the application of two techniques for the determination of total boron content in lithium-boron alloys makes it possible to get the convergent results within the limits of measurement errors. The developed techniques are certified by the metrological service of the enterprise and can be used for the incoming and process control of the LBA production.

The quality control of coatings when selecting a powder material for the restoration of worn surfaces by gas-flame spraying is hampered by the lack of an operational method of non-destructive diagnostics. We present the results of studying coatings applied by gas-flame spraying using ultrasonic diagnostics. The powder coatings obtained using different technologies of gas-flame spraying were studied. Features of the structural state of coatings were evaluated using a model based on the effect of the structural inhomogeneities of the coating on the velocity and attenuation of ultrasonic waves. It is shown that the amplitude-time characteristics of the pulse of surface elastic waves when they pass along the coating are consistent with the data obtained from friction and hardness tests, the characteristics of the pulse being dependent on the quality of the coating material. The obtained results can be used to improve the quality control of coatings formed by gas-flame spraying.

Development of the technology for the synthesis of magnetic nanoparticles of metals and alloys has opened up the possibility of their use in the field of radar-absorbing materials (RAM). The results of studying the properties of nanocomposites, method for the synthesis of metal-carbon nanocomposites by pyrolysis using infrared heating are reviewed. The magnetic, electromagnetic, and radar-absorbing properties of the obtained nanocomposites depending on the synthesis temperature and metal concentration were studied. It is shown that the chosen metals, alloys (FeCo) and carbon material are effective for isolating magnetic nanoparticles when developing hybrid radar-absorbing composites. Moreover, methods for controlling the radar-absorbing properties of hybrid composites and the prospects for improving the impedance matching are considered. An analysis of the efficiency of absorption of electromagnetic radiation by FeCo/C nanocomposites synthesized by different methods is presented. The possibility of controlling the morphology and properties of metal-carbon nanocomposites using certain approaches to synthesis, varying the compositions of precursors, and the orientation of FeCo nanoparticles synthesized in the form of flakes in the composite has been revealed. The results of the study can be used to improve the technique of using FeCo/C nanocomposites obtained by pyrolysis of organometallic precursors based on polyacrylonitrile in the field of radar-absorbing materials.

The goal of the study is the fatigue process in polyimide-based composites reinforced with short carbon fibers. Parameters of mechanical hysteresis loops such as the loop area, secant and dynamic moduli were used in the study. Hysteresis loops were constructed using the developed hardware and software system based on the optical method of strain measurements using a digital image correlation (DIC) technique. Methods for calculating the moduli and the parameters of mechanical hysteresis loops is considered. The results of their evaluation and the experimental data on the fatigue behavior of polyimide-based composites reinforced with short carbon fibers are presented. It is shown that an important quantitative measure of the differences in the fatigue behavior of the studied composites is the hysteresis induced energy loss. For a composite with carbonized fibers, the energy loss level per cycle is 35 kJ/m³, whereas for a composite with graphitized fibers it is 34% lower (23 kJ/m³). At the same time, the fatigue durability of the latter is - 40 times lower. A decrease both in the secant modulus (up to 11%) and the dynamic modulus (up to 3.5%) was observed in cyclic tests. However, the reduction was twice as much in a composite with carbonized fibers possessing a longer durability. Thus, the DIC-based estimation of mechanical hysteresis loops by the parameters of the secant and dynamic moduli, as well as the loop area can be successfully used to interpret the difference in the fatigue characteristics at the stage of scattered damage accumulation, whereas an unambiguous prediction of the residual life appeared impossible. The problem requires further systematic studying using approaches of the fracture mechanics.

The local indices of the crack resistance of a thin-sheet reinforced polymeric carbon composite (CCM) stitched with glass and aramid threads with a double lockstitch were determined by wedging in the framework of linear elastic fracture mechanics under loading mode I using standard samples in the form of a double cantilever beam (DCB). Different number of stitches and stitching lines were used for different directions of crack propagation relative to the laying of the reinforcing fabric and stitches. It is shown that regardless of the type of stitching thread and the crack propagation direction, the average and normalized (relative to non-stitched samples) values of the local crack resistance parameters of stitched CCM samples mostly depend on the crack propagation area and on the density (pitch) of stitching responsible for a pronounced locality and anisotropy of the crack resistance. The highest resistance to crack propagation is observed in the areas of interweaving of the stitching threads as a result of additional energy consumption for deformation and breaking of stitching threads, and the lowest one is characteristic of the areas between stitches along the stitch or step between lines, both in the longitudinal and perpendicular directions of the crack propagation relative to the laying of the fabric and stitching lines. When evaluating the specific average values of the parameters of the local crack resistance of CCM samples related to one line of stitching with a longitudinal crack propagation or to one stitch when a crack propagates across the stitching lines, the effect of increased local crack resistance in the areas of interlacing of threads turns out to be significantly weaker, whereas this decrease in stitch areas and between the stitching lines is significantly more pronounced. For more accurate assessment of the crack resistance of a thin-sheet stitched CCM, it is advisable to determine and use specific local parameters taking into account scale effects.

A Walker-based mean strain correction model of low-cycle fatigue (LFC) life prediction is proposed for high loaded parts. The model is based on a function depending on the strain range and strain ratio controlled in the strain-controlled LCF test of fatigue specimens and a constant reflecting the material sensitivity to strain ratio. The independence from the stress cycle parameters which can change during the strain-controlled LCF test is an obvious advantage of the model. The model was verified using the results of strain-controlled LCF tests of smooth titanium alloy Ti-6A1-4V ELI and iron-based alloy specimens conducted at room temperature. The proposed model was compared to the Smith - Watson - Topper and Walker models that take into account the mean stress effect. The proposed model provided the best prediction accuracy for titanium alloy. For Iron-based alloys the results obtained by the Walker model and the model proposed are close to each other. A simplified model based on the analysis of model parameters tailing into account the mean strain effect for predicting fatigue life of aeroengine critical parts is developed using a limited amount of experimental data when only the results of R_ε = 0 tests are known. A comparison of the predicted life with the number of cycles to failure showed satisfactory results of fatigue life prediction for Ti-6A1-4V ELI and Iron-based alloys specimens.

Among the mathematical models of risk research, an important place is occupied by additive-multiplicative models of risk estimation. The components of such models are: three-stage hierarchical risk systems (built for a specific applied situation); partial risk estimators (determined by experts for a specific project, product, etc.); indicators of the weight of specific types of partial risks (found on the basis of a survey of experts in a particular application area); algorithms for calculating group risk estimators based on partial risk estimators and general risk estimator based on group risk estimators. As examples, three-stage hierarchical risk systems are considered in the production of a new innovative product and in the implementation of projects for the development of rocket and space technology. An algorithm for an additive-multiplicative model for risk estimation of a general form is proposed. Estimates of partial risks are products of weighting indicators by severity indicators, which corresponds to the well-known method of risk estimation in the form of the product of average damage by the probability of an undesirable event. Group risk estimators are built additively from i partial risk estimators, and the final overall risk estimator is calculated multiplicatively from group risk estimators. In previous works of the author, a special case of an additive-multiplicative risk estimation model was considered, in which, in particular, the components of the model were interpreted in terms of probability theory. It is proposed to carry out estimators of partial risks and weight coefficients on the basis of interval mathematics and fuzzy theory. The rules of arithmetic operations on interval and triangular fuzzy numbers are given. The application of the algorithm of the additive-multiplicative risk estimation model based on triangular fuzzy numbers is demonstrated using the example of risk estimation for the implementation of innovative projects. Within the framework of interval mathematics, risk estimators are considered in the implementation of projects for the development of rocket and space technology. The approach developed in this research article corresponds to the main provisions of the theory of stability of mathematical models of real phenomena and processes and to the results of systemic fuzzy interval mathematics.