Conditions for determining oxysulfides in construction steel by spark atomic emission spectrometry (SAES) using an ARL iSpark 8860 spectrometer which is equipped with a Spark-DAT software function for processing spark diagrams are studied. To improve the characteristics of the calibration curves for the determination of Al, Ca, Mn and sulfur forming non-metallic inclusions (NMI), we used certified reference materials of the composition of construction steels. An increase in the sensitivity of Al and Ca determination and correlation coefficients of calibration curves for the determination of Mn and S is shown. The concentration of Al₂O₃MnS, Al₂O₃MnSMgO, Al₂O₃MnSCaS, Al₂O₃CaOCaS, Al₂O₃CaOMgOCaS in steels was preliminarily determined using a combination of scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) according to ASTM E1245 (method 3) in the lack of certified reference materials with oxysulfides. It is shown advisable to determine the concentration of oxysulfides in construction steels by SAES using corrected and developed algorithms for software processing of the integrated spectrum in combination with a pseudo-formula. It is shown expedient to select the appropriate algorithm and pseudo-formula on the basis of Student’s test statistics by comparing the NMI concentrations obtained by SEM-EDS with SAES results. The spark intervals and the delay time of the analytical signal integration for Al, Ca, Mg, Mn, and sulfur are compared. The correctness of the oxysulfide determination by SAES was confirmed in the range of 500 – 1900 sparks (t_exp = 0.01) and the signal integration delay of 110 μsec (t_exp = 0.23). Test method for measuring the total concentration of oxysulfides by SAES was tested on production samples of construction steels. The absence of a systematic error and the correctness of the measurement results (t_exp < 4.30) were proved. It is shown that the developed method for determining the NMI concentration provides drastic reduction of the duration of the analysis from 18 hours (SEM-EDS) to 10 min.

A technique for non-destructive analysis of drugs for fluoroquinolones by diffuse reflection of IR radiation using a smartphone and a device printed on a 3D printer is proposed. It is shown that the diffuse reflection of IR radiation (850 nm) from tablets containing fluoroquinolones as an active substance can be recorded by a smartphone camera. The blister pack and the shell of tablets do not interfere with the passage of IR radiation, which is confirmed by a comparative analysis of the results of the colorimetric determination of fluoroquinolones in drug samples in a package, without it, and on a tablet split. A correlation of the analytical signal with the concentration of the active substance is observed regardless of the test option. The possibility of using chemometric methods providing the reduction of the time of analysis and visualization of the data obtained is shown. The dataset was processed by the principal component analysis (PCA), hierarchical cluster analysis (HCA), partial least squares regression (PLS), and the method of least squares using PhotoMetrix PRO^® software. The aforementioned algorithms also provided identification of drugs by the manufacturer. Colorimetric signals from tablets of the same manufacturer form separate clusters on the charts constructed using the HCA algorithm. Data obtained using PCA indicate the location of signals from tablets from different manufacturers in separate quadrants, which makes it possible to identify the pharmaceutical company, as well as the country of manufacture, e.g., the drug Ciprofloxacin with different concentrations of the active substance manufactured in Russia is located in quadrants 2 and 4, whereas the drugs manufactured in India are located in quadrants 1 and 3. The relative standard deviation of the analysis results did not exceed 0.07. The use of chemometric methods of analysis in determination of active substances is considered in detail.

Data on the expanded oil microelement composition (for various oil types) is of practical importance and interest both for scientific research and for the development of technological processes of oil refining. From a geochemical point of view, the data on the features of the quantitative distribution of microelements in oil provide an opportunity to identify the genetic differences in view of oil exploration goals. Data on the microelement composition of oils provide assessing the oil composition at the stage of production and monitoring the quality of petroleum products at different stages of oil refining. Analysis of the distribution of microelements in oil hydrocarbon groups (so called SARA-groups) was carried out in the case study of two samples of commercial oils of Russian origin that differ in the physicochemical properties (heavy HI-VIS and bituminous extremely high viscosity index oil). The content of microelements was determined by inductively coupled plasma mass spectrometry in oil samples, and both in their maltenes and asphaltenes, as well as in paraffin-naphthenic hydrocarbons, aromatic hydrocarbons and resins isolated from the maltene part using open-column liquid adsorption chromatography in accordance with the method developed at the Joint-Stock Company VNII NP. It is shown that the majority of microelements are present in the oil samples in three concentration ranges: more than 1.0 μg/g, 0.1 – 1.0 μg/g, and less than 0.1 μg/g. The concentrations of other elements lie below the detection limits (0.3 – 9 ng/g). Both oils under study turned out to be enriched with microelements and can be classified as «vanadium» type oils. The main trends in the distribution of microelements in hydrocarbon groups indicate to their concentrating in polar poly condensed structures (resins and asphaltenes).

Measuring of the magnetic characteristics of metal objects makes it possible to study the entire volume of the material simultaneously, while the commonly used metallographic and X-ray (phase) methods provide information only about a thin subsurface metal layer. The results of determining the percentage ratio of the paramagnetic — ferromagnetic phase in metallic materials by the magnetometric method are presented. An equation that relates the magnetic permeability and the parameters of the sample is derived. A relative change in the magnetic permeability, which characterizes the phase relationships, was determined by recording the oscillation frequency of the electric circuit built on the chain capacitor — inductor (measuring coil), in which the sample was placed. A two-phase structure (ferrite + austenite) was simulated by placing ferro- and non-ferromagnetic samples (Fe + Cu or Fe + X19H10T) in different proportions into the measuring coil. The relative magnetic permeability of 160Cr12MoV steel samples quenched at 1030 – 1250°C was studied. It has been revealed that a quenching temperature should not exceed 1120°C to provide a hardness value of 62 HRC. The results obtained can be used in the search for optimal heat treatment regimes, primarily for high-speed steels with a high austenite stability.

The thermo-physical properties of molding materials for sand casting depend on changes in the composition of binders under thermal action on the technological equipment made from sand-based mixtures. We present the results of developing an algorithm for modeling the thermo-physical properties of molding materials used in sand casting. We used the solution of the inverse problem of heat conduction by the Levenberg – Marquardt method which suggested using iterations to the results of solving the direct problem of calculating the non-stationary temperature field. The direct problem of the nonlinear thermal conductivity upon solidification of a casting in a sand mold was solved using the LVMFlow program. Data on the temperature field during solidification of the AK7 alloy casting in a sand mold were obtained using thermocouples. The accuracy of temperature measurements with thermocouples was assessed in relation to sand casting processes depending on the casting dimensions and the melting temperature of the casting alloy. Thermocouples with chromel-constantan electrodes are recommended for the experimental determination of temperature fields in aluminum alloy castings. The proposed algorithm is intended for processing data on temperature fields measured by thermocouples upon solidification of castings in a sand mold and calculated by simulating the identical casting process in the LVMFlow program. The developed algorithm is implemented in the SciLab software environment and ensures the correct construction of the Jacobian matrix. The results obtained can be used in computer simulation of casting technology, taking into account the thermo-physical properties of mold materials, which reduces the time spent for the development of technological processes and equipment.

A technique for probabilistic risk analysis of technical objects with accumulated irreversible damage is proposed. Damage is considered as a stochastic irreversible cumulative process with an absorbing boundary. The gamma process is used as a model of damage accumulation with a time-dependent probability density distribution. The probability distribution function of life before failure and the probability (risk) of failure are determined by integrating the probability density of accumulated damage over the risk area. The damage accumulation rate is considered as a non-stationary function of time. The parameters of damage distribution function can be determined from the data of non-destructive testing using the maximum likelihood method or the method of moments. The potentiality and features of the proposed method are exemplified in the risk analysis of the corrosion damage of critically important technical objects, e.g., offshore pipelines. The results of calculating the pipeline failure probability at various shape parameters and the scale parameter of the damage distribution function are presented. It is shown that the shape parameter which directly depends on the time of damage accumulation most strongly affects the damage probability. The main difference between the proposed methodology and other schemes and methods of damage risk analysis is the explicit time dependence of the gamma model parameters, which makes it possible to predict the probability of failure for a given service interval of technical objects. The proposed technique can be adapted for other types of damage, in particular for processes of long-term damage with the growth of corrosion, corrosion-fatigue and fatigue cracks.

The concept of staging of fatigue crack kinetics (FCK) is presented. According to the developed concept the staging of FCK is attributed to changes in critical (preceding the fracture) deformation structures localized at the crack front and in micromechanisms of fracture operating in these structures. At the first stage of the FCK, these critical structures are clusters of dislocation braked near various barriers. In this case, the crack propagates through the low-energy-type mechanisms of brittle fracture with the formation of cleavages of various scale. At the second and third stages of the FCK, a critical two-level fragmented structure (two-level nanostructured state) is formed near the crack front. Brittle microlaminations along the boundaries of large-scale fragments of this structure oriented in the direction of maximum principal deformation play a key role in the high-energy-type mechanism of stable crack growth at the second stage of the FCK and form fatigue striations on the fracture surface. At the third stage of the FCK the mechanism of stable crack growth is added with the mechanism of origination and development of fracture at the boundaries of small-scale fragments of the critical fragmented structure with the formation of micropores which results in the formation microdimples in the corresponding areas of the fracture surface. The universal nature of the FCK staging and features of manifestation are illustrated by fractographic study of the fatigue crack propagation in highly stressed parts of aero-engines under various cyclic loading conditions, i.e., under self-induced and random vibration of compressor blades, repeated-static loading of compressor disks in the course of a cyclic test under vacuum conditions and during operation in the presence of crystallographic texture.

The results of studying creep of polymethyl methacrylate (PMMA) in the temperature range from 0 to +30°C at a strain rate from 0.02 to 2% per minute and holding for up to 100 h under stress values within a range of 48 – 72 MPa are presented. The viscoelastic behavior of PMMA is analyzed under normal operating conditions before the onset of the material damage. A unified power dependence of the creep deformation on time was obtained for the entire holding period, without any division into the stages of the unsteady and steady creep. Formulas to be used for approximating the results of isothermal tests of samples at a constant strain rate and holding under a constant load are proposed. The dependences of the approximation parameters on the strain rate, stress level, and temperature of PMMA tests are obtained. A comparison of the creep strain diagrams for the same holding stress after deformation at different rates showed that the diagrams lie on a single curve with a time shift. This indicates the possibility of describing the totality of the experimental data obtained by a single equation of state linking the creep rate, stress and temperature. Differentiation of the approximating formulas made it possible to reveal the regularities of changes in the creep rate during testing and repeated differentiation allowed us to obtain an equation for the creep acceleration upon deformation at a constant rate and to exclude the time variable from it. Similarly, the time variable was also excluded from the creep deceleration equation obtained for holding under constant stress. In this form, these two equations can be considered special cases of the equation of state of a viscoelastic material which behavior is independent on the loading prehistory. Creep under continuous deformation is a superposition of two processes: creep acceleration due to the stress growth and creep deceleration with time. On this basis, a unified equation of state for a viscoelastic material was derived for a process with an arbitrary law of the strain and stress growth. The parameters of this equation are the temperature, creep velocity and acceleration, stress and the rate of stress change. The accumulated creep strain is not a parameter of equation. The applicability of this equation under more complex conditions of a nonmonotonic thermopower loading of materials requires additional experimental justification, as well as identification of the equation parameters.

When solving the calibration problem within the statistical approach, ignoring the fact that interference models in experimental and in real conditions have different sources and are generated by different factors can lead to a significant distortion of error estimates of the measuring system and the formation of an inadequate transformation characteristic. Moreover, there are known theoretical difficulties in constructing a model inverse to the regression model and in determining the error corridor of the model, e.g., there is a problem of determining the distribution of a random variable inverse to a normally distributed. Here we use an interval approach as an alternative to the statistical approach, under the assumption that all variables are measured inaccurately during the experiment and the results of the calibration experiment are presented in the interval form. It is also assumed that the interval certainly contains an unknown true value. The developed approach is used in analysis of single-factor multisensory systems under the assumption that the errors of the calibration experiment are limited in magnitude. The problem of constructing a calibration characteristic of a separate sensor which can be solved using methods of constructing direct and inverse static characteristics is also briefly considered. Thus, we have developed: a new approach to the analysis of interval data at the output of single-factor multi-sensor systems, which, on a set of specified sensors, allows solving the problems of rejecting obviously unsuitable sensors and choosing the best sensor; the procedure for constructing a calibration characteristic in the form of a spline function integrating the readings of several selected sensors in the absence of the best sensor. Various estimates are proposed to integrate the information obtained from different sensors, including the arithmetic mean of intervals, which provides determination both of the point value of the average and the error of determination (which is applicable for any intervals, including non-intersecting ones); the weighted mean of intervals, which allows the use of a priori information about the reliability of sensor readings (accuracy, reliability, character of the dependence, etc.); the intersection of intervals, tending to the true value of the measured variable as the number of experiments increases; the intersection of the intervals with a given level, which is applicable in case of a very narrow area of the intersection of measurement error intervals and can also be useful at the stage of preliminary analysis of the reliability of predicted values.