A brief review of the methods for determining the total base number of engine oils (TBN) is presented. This integral indicator characterizes the total content of basic impurities (additives) in terms of the amount of potassium hydroxides in one gram of engine oil (mg KOH/g). Used engine oils are usually titrated with hydrochloric acid in a non-aqueous medium, the potential of the indicator electrode being under control. The same technique can be successfully used in analysis of commercial (fresh) oils. Titration curves are recorded with an indicator glass electrode. TBN of fresh and used engine oils are determined with approximately the same convergence (S_r < 2 %). To check the compatibility of redetermined TBN values, the repeatability and reproducibility limits specified in GOST 11362–96 were used. Using the M-10G2 oil as an example, different variants of potentiometric titration are compared, the corresponding metrological characteristics were determined, and recommendations for testing laboratories were developed. Titration of oil to a certain fixed potential recommended in GOST 11362–96 results in underestimated TBN values compared to other options used for identification of the equivalence point and worsens the reproducibility of the results when using samples of different weights. We recommend to determine TBN values for fresh or used engine oils by direct potentiometric titration using three-tangent method. The accuracy of the obtained results is checked by the standard method of additives (spike recovery test); the error of determination being less than 15 % rel. It is shown using Shewhart maps, that the metrological characteristics of the repeatability and reproducibility are stable, but the results of analysis of control samples often go beyond the warning limits, especially for the samples of used oil. Promising directions of future studies are proposed.

Historical glasses are complex multicomponent systems that can be modeled by restricting their composition to three or four most important main components and considering the other ones as additives. We present an analysis of glass samples in K₂O – CaO – SiO₂ system, some of them contain sodium along with potassium and small amounts of different additives (oxides of iron, antimony, arsenic, manganese). Study of the aforementioned objects does not provide for their removal outside the museum storage areas, which substantially limits the range of the methods to be used for their analysis. We have demonstrated the possibility of using a portable X-ray fluorescence analyzer in determination of the compositions of historical glasses, including objects of cultural heritage, the study of which can only be carried out by non-destructive methods of analysis. Determination of compositions of silicate glasses that do not contain lead or with a low lead content is considered. The proposed procedure suggests using the programs for fundamental parameters to determine the elemental composition of the glass with subsequent recalculation of the content of elements into oxides, which makes it possible to estimate the oxygen content in the sample. The content of the other light elements that cannot be determined by an XRF-analyzer used (elements with atomic numbers less than 13) is determined as follows. The literature data indicate that the objects under study do not contain lithium, boron, carbon, nitrogen and fluorine. Magnesium was not specially introduced into the composition of historical glasses, but appeared only as an admixture to limestone or potash thus providing only a semi-quantitative estimation of the magnesium content from the known experimental value of the potassium and calcium content and recalculation to oxides. We determined the sodium oxide content in glass by the difference subtracting the content of all oxides from 100%. Although this technique provides only estimation of the sodium content in glass, it is important in answering the question of whether sodium was added to glass specially or entered it as an impurity in potash.

Synthesis of dimethylmethylphenylsiloxane rubbers with terminal hydroxyl groups by copolymerization of cyclosiloxanes can be accompanied by formation of low molecular weight compounds, impurities, which are difficultly removed (due to target product affinity) and can lead to rubber opalescence. Identification of the impurities (the content of each impurity ≥10^–4 wt.% in 1 μl of the sample) can be carried out using a sensitive gas chromatography-mass spectrometric method. The method allows separation of the analyzed mixture into individual components on a capillary column. These components enter a mass analyzer and undergo electron ionization which leads to their dissociation into pairs «cation – neutral fragment». Only positively charged ions are observed in the mass spectra, which provides the possibility of predicting the structure of the analyzed siloxane impurities. Rearrangement of linear and cyclic molecules occurring upon mass spectrometric fragmentation result in their transformation into cyclic and bicyclic cations. The structure of the cations formed under ionization conditions depends on the number of silanol bonds and their location in the molecule. To prove the presence of compounds with hydroxyl groups in the composition of impurities and to demonstrate the effect of electron ionization on the fragmentation of compounds with silanol bonds, a sample of oligomethylsiloxane with terminal trimethylsiloxy groups was synthesized in a similar way using the copolymerization method. Compounds with silanol bonds present in the composition of the impurities appear as chromatographic asymmetric peaks with ascending and descending gently sloping zones. Those compounds are rearranged either when passing through a chromatographic column due to sorption-desorption and enter the detector in a modified form or drift through the column and undergo rearrangements already under conditions of electron ionization. The impurities contained linear and cyclic methylsiloxanes with silanol and phenyl bonds. The chromato-mass spectrometric method provide a reliable control of the composition and content of undesirable impurities which cause rubber opalescence.

Thermoporometry is a calorimetric method for characterizing pore structure from the melting or freezing point depression of a liquid confined in a pore, by the reason of the added contribution of surface curvature to the phase-transition free energy. Porous materials are widely used in the production of noise and vibration-absorbing coatings, thermal insulation, filters, etc. We present the results of studying the porous structure using thermoporometry, a method based on lowering the melting point of the working substance (penetrant) which previously filled micro- and mesopores of the sample under study. The open porosity of carbon materials based on phenol-formaldehyde resins and a pore former obtained after pyrolysis under different conditions of microphase separation induced by polymerization is analyzed. The tests were carried out using a differential scanning calorimeter. Bidistilled water, which has a relatively high value of the enthalpy change upon melting of the crystalline phase is used as a penetrant to lower the error of measurements. Differential and integral curves of the size distribution of micro- and mesopores are presented. It is shown that an increase in the microphase separation temperature entails an increase in the total porosity. Moreover, an increase in the polymerization rate of phenol-formaldehyde resin due to resin modification with m-cresol also facilitated an increase in the cumulative volume of micro- and mesopores. It is shown that replacement of phenol with paracresol leads to an increase in the total porosity even under a significant decrease in resole resin polycondensation rate. The results obtained can be used in the development of carbon matrices with controlled parameters of the mass transfer.

X-ray diffractometers are widely used in studying the atomic structure of mono- and polycrystalline substances. The radiation source of conventional laboratory diffractometers is a soldered x-ray tube with the maximum power consumption 1 – 3 kW. The radiation spectrum of the tube is determined by the anode material (usually, these are spectrally pure metals Cr, Ni, Fe, Cu, Mo, Ag). The wavelengths of the characteristic radiation range within 0.56 – 2.29 Е. We present the results of studying the effect of X-ray radiation power on the structure of barium titanate. Comparison of the diffraction spectra of BaTiO₃ (laminar polydomain ferroelectric single crystal and nanopowder samples) showed that the spectrum structure changes significantly with an increase in the power of X-ray beam (CuKα radiation) from 100 (5 mA, 20 kV) to 800 W (20 mA, 40 kV). For example, a rearrangement of the domain structure and, hence, a change in the dielectric characteristics of the material were observed for BaTiO₃ single crystal. The rearrangement was accompanied by the formation of continuous transition zones (between domains) containing a cubic phase. As for the BaTiO₃ nanopowder, a change in the structure was observed in the direction of the axis of spontaneous polarization c and an invariance of the structure in the plane a – c. The results obtained can be used to control the physical properties of ferroelectric and ferroelastic materials, in particular, the memristor characteristics of epitaxial films based on YBa₂Cu₃O_7–δ due to changes in their twin structure under X-ray irradiation.

We consider the manufacturing process of forgings for turbine blades of extra-large dimensions (length >2 m) from electroslag remelting steel 15H11MF-Sh. With an increase of the workpiece dimensions (weight >450 kg), we face the problem of choosing the technology for obtaining the original billet. The production technology is known to affect the structure of the material and, as a consequence, the final properties of the product. We present the results of studying the influence of the method of obtaining the original metal blanks (hot-rolled steel bars and forged billets) on the properties of large-sized forgings of turbine blades. The mechanical characteristics, microstructure properties, chemical composition and content of δ-ferrite were determined by examining the initial samples of long products and forged rods. It is shown that billet in the forged state exhibit higher strength characteristics. However, after the stamping process, the properties of the blades equalize, i.e., after stamping and heat treatment, the same structure is formed, regardless of the method of obtaining the original workpiece. The results obtained can be used in the serial production of large-sized turbine blades of a new profile.

Strength of a unidirectional composite along the fibers is the most important characteristic for the design calculation of composite products, being, however most difficult for correct determination in the experiment. The main problem is attributed to the shape and methods of fixing the specimen, providing the minimum impact of the stress concentration near the grips on the strength. The impossibility of direct use of standard self-tightening grips due to lateral crushing of the sample led to the necessity of using either samples with glued pads, or special grips with a constant transverse force. Specimens with fillets should not be used for unidirectionally reinforced plastics. When using standardized specimens in the form of rectangular strips with abruptly varying shear stresses applied to their lateral surface which results a significant concentration of tensile stresses, the incorrect result can be gained. We present the calculated values of the stress concentration factor (SCF) near the grips using a simplified model of shear analysis and the finite element method (FEM). Since the strength reduction factor is always less than the theoretical stress concentration factor, a phenomenological parameter of the material with the dimension of length, as a characteristic size of the stress averaging zone should be introduced to assess the strength value. Three methods are proposed to find this characteristic size according to the results of testing specimens of different kind: 1) smooth with various thicknesses; 2) smooth with various thicknesses and with holes in which the failure occurs at the hole, away from the grips; 3) with a series of holes with a decreasing radius, to find that small radius, the influence of which on the strength decrease is equivalent to the influence of grips. Proceeding from the experimentally determined characteristic size, the dependences of the strength on the specimen thickness, on the ratio of Young’s and shear modulus, on the length of the grips and the working zone, and on the degree of stress smoothing near the grip edges are calculated. The proposed calculation and experimental technique provided more accurate assess of the «true» tensile strength of the composites, which can be approximately 10 % higher than that determined on the specimens of large thickness. Taking this correction for the effect of grips into account, it appeared possible to reduce the safety factor, and, hence, to reduce the mass of composite structures.

Modern aircraft are exposed to intense pulsations of sound pressure arising both from engine noise, and from turbulent effects of the environment during flight. The pulsations cause vibrations of the structure leading to fatigue damage of the fuselage skin and primary elements of structure, as well as to the equipment failure. The operating experience shows the necessity of taking into account the acoustic fatigue starting with loads of 130 – 135 dB. At a load value above 160 dB, the acoustic fatigue becomes one of the main factors determining the strength of aircraft and space structures. Despite the development of computational methods for estimating durability under acoustic loads, the most reliable methods are still based on experimental studies. The frequency spectrum is the main characteristic of acoustic loading. Reproducing of acoustic loads in a controlled frequency range 150 – 600 Hz with the intensity of pulsations specified above appeared enough for testing most aircraft structures. However, space apparatus and equipment must be tested for the effect of acoustic noise within the frequency range from 150 to 1200 – 2000 Hz. Domestic low- and medium-frequency generators operating in a frequency range of 20 – 600 Hz are currently used in reverberation chambers in Russia. To generate higher frequencies of acoustic vibrations, we used an ERT-200 electropneumatic converter (LING (USA), the maximum frequency 1000 – 1250 Hz) and a most advanced SEPMOD modulator [SEREME (France), the maximum frequency is 1000 – 2000 Hz]. Information about the design of those sound modulators is not available to consumers. Further development of aerospace technology necessitates developing of domestic high-frequency sound generators for acoustic tests. We propose a method which ensures operation of the sound generator in a controlled frequency range of 150 – 1200 Hz. The essence of the method consists in designing a sound modulator (being part of the generator) which provide that an increase in the electromotive force, driving the movable element of the valve assembly into reciprocating motion, will not entail an increase in heat generation in the electromagnetic propulsion device. For this, we propose to perform the electric propulsion device in the form of synchronously operating two parts located at opposite ends of the movable element of the valve. Supplying each part with the maximum permissible current, we managed to increase the total excitation current by half. The calculations showed that the use of more energy-intensive permanent magnets of neodymium type NdFeB and considered principle of forming a propulsion unit provide a range of sound frequency control of 150 – 1200 Hz at a pulse acoustic load up to 160 dB.

Ordering of classification methods should increase their role in solving applied problems, in particular, in diagnostics of materials. Development of the requirements to be met by classification methods is the first concern. The initial formulation of the requirements is the main content of this work. Mathematical methods of classification are considered as a part of the applied statistics methods. The natural requirements to the considered methods of data analysis and presentation of the calculation results arising from the achievements and ideas accumulated by the national probabilistic and statistical scientific school are discussed. Specific recommendations are given on a number of issues, as well as criticism of individual errors. In particular, methods of data analysis must be invariant with respect to the permissible transformations of the scales in which the measured data are gained, i.e., the methods should be adequate in the terms of measurement theory. The basis of any statistical method of data analysis is always a particular probabilistic model which must be clearly described and the premises must be justified either from theoretical considerations, or experimentally. Data processing methods intended for use in real-world problems should be tested for robustness with respect to the acceptable deviations of the initial data and model assumptions. The accuracy of the solutions provided by the method should be determined. When publishing the results of statistical analysis of real data, it is necessary to indicate their accuracy (confidence intervals). As an estimate of the predictive power of the classification algorithm, it is recommended to use predictive power instead of the proportion of correct forecasts. Methods of mathematical research are divided into «exploratory analysis» and «evidence-based statistics». Specific requirements for data processing methods arise in connection with their «docking» during their sequential execution. The limits of applicability of probabilistic-statistical methods are discussed. Specific statements of the classification problems and typical errors in application of different methods of their solution are also considered.