Application of revitalisants for extension of resource and restoring worn‐out friction units of aviation axial ‐ piston hydromachines

The perspectives of application of using RVS technique for repairing and prophylactic of hydraulic systems’ units, particularly axial‐piston machines are considered. Physical background of revitalization processes, which took place on the friction surfaces during drifting of cermets coating (CC) are uncovered. The results were received from numerous investiga‐tions. First Published Online: 14 Oct 201

Acoustic emission under temperature tests of materials

The theoretical research of the influence of temperature on the parameters of the alteration of acoustic emission signals from plastic deformation is considered. It is shown that increasing temperatures cause an increase in the amplitude of acoustic emission signals in an area of low temperatures and a decrease in an area of high temperatures. At the same time, there is an intermediate area of temperatures in which the amplitude of acoustic emission signals remains constant when temperature is increased. As shown in the article, this fact is connected with the alteration of the process of plastic deformation. First Published Online: 14 Oct 201

Model of acoustic emission signal at self‐accelerated crack development

The article is devoted to the theoretical analysis the problem of acoustic emission signals application for the detection of self‐accelerated crack development. The acoustic emission signal model has been proposed which takes into account the change of crack propagation velocity in the process of material loading. The process of self‐accelerated crack development results in growth of acoustic emission signal amplitude and compression the signal in time. First Published Online: 14 Oct 201

Using Hilbert Transform in Diagnostic of Composite Materials by Impedance Method

The article is devoted to the problem of the increasing of information quality for the impedance method of nondestructive testing. The purpose of this article is to get for the pulsed impedance method of nondestructive testing the additional informative parameters. Instantaneous values of the information signal's amplitude is a sensitive parameter to the effects of interference, in particular friction, which necessitates the use of additional informative features. It was experimentally measured signals from defective and defectless areas of the test pattern. Using of the Hilbert transform gave possibility to determine phase characteristics of these signals and realize demodulation to extract a low-frequency envelope for further analysis of its shape. It was received the informative features as a result of researches. Among them are instantaneous frequency of a signal, the integral of a phase characteristic on the selected interval and the integral of a difference signal phase characteristics. In order to compare quality of the defect detection using selected parameters it was carried out evaluation of the testing result reliability for a product fragment made of a composite material. Considering the influence of the change in the mechanical impedance of the researched area on the phase-frequency characteristics of the output signal of the converter, it is proposed to use as the diagnostic signs: the instantaneous frequency and the value of the phase characteristic of the current signal for certain points in time. The proposed informative features enable to increase general reliability of composite materials testing by the pulsed impedance method

Safety of Live Activity

Курс містить інформативні матеріали, що стосуються проблем життєдіяльності людини, та систему графіки для візуального відтворення і фіксації його основних положень

Safety of Live Activity

Курс містить інформативні матеріали, що стосуються проблем життєдіяльності людини, та систему графіки для візуального відтворення і фіксації його основних положень

Some Features of Modeling Ultrasound Propagation in Non-Destructive Control of Metal Structures Based on the Magnetostrictive Effect

A method and mathematical models of direct and inverse problems of ultrasonic testing and diagnostics of complex metal structures for defects were developed and tested. A prototype of a system for magnetostrictive control of elements of the objects under study was manufactured and experimentally tested. Mathematical simulation of ultrasonic testing processes using MATLAB and the COMSOL Multiphysics software environment was carried out. The adequacy of the mathematical models was verified by the results of their comparison with real physical experiments. Information support and a methodology that implements it was developed, which ensure the functioning of the control facilities for these objects based on the use of small-aperture magnetostrictive transducers. The mathematical identification of the vibration generator in complex building structures was developed, which consists in finding the locations of the generator of ultrasonic vibrations, as well as the characteristics of this vibration generator based on data obtained from sensors in the form of time series

Analysis of Low-Density Heat Flux Data by the Wavelet Method

When evaluating the energy efficiency of buildings and implementing the necessary measures to increase energy efficiency levels, thermal technical characteristics are determined. For this purpose, in situ measurements of the thermal resistance of external enclosing structures were carried out. One of the methods most often used by researchers is the non-destructive method—the heat flow meter (HFM) method regulated by ISO 9869. In the case of surveying a building with a high level of thermal resistance, researchers are faced with low-density heat flux measurements, which is always a difficult task due to significant fluctuations and the influence of external factors on the measurement results. This is due to the fact that it is difficult to determine what is a useful signal and what is a consequence of the effects of non-stationarity and heat transfer conditions. The article provides an example of low-density heat flux measurements when determining the thermal resistance of a building and proposes a data pre-processing procedure that allows for the reduction of heat flux fluctuations, which has a significant impact on the final result at low density. The proposed use of wavelet analysis in the pre-processing of low-density heat flux measurement data makes it possible to reconstruct them or reduce disturbances that occur during research. A comparison of the obtained results with the results of the calculation according to ISO 9869-1 showed a decrease in the standard deviation of the measurements from 5.74 to 2.81%. The results of this study can be used to reduce the noise of low-density heat flux and, as a result, reduce the standard deviation of the measurement when applying the HFM method of determining the thermal resistance of external enclosing structures

Вплив на теплофізичні властивості нанокомпозитів тривалості змішування компонентів у розплаві полімеру

A set of experimental studies has been carried out to establish the effect of the mixing time of components of nanocomposite materials on their thermal conductivity, specific heat, and density. The physical properties of polypropylene-carbon nanotube composites were to be studied. During the experiments, the duration of mixing of the components in the melt of the polymer varied from 5 to 52 minutes, the mass fraction of the filler ‒ in the range of 0.3...10 %, and nanocomposite temperature – from 290 K to 475 K. It was found that an increase in the mixing time of components of nanocomposite materials could lead to a significant (more than 70 times) increase in their thermal conductivity. It is also shown that the influence of the specified time is limited to its value equal to 27 minutes, above which the change in the thermal conductivity of nanocomposites can be neglected. It was found that the sensitivity of the thermal conductivity of nanocomposites to the time of mixing of their components decreases with a decrease in the mass fraction of the filler. Temperature dependences of the specific heat capacity of the studied composites were obtained by varying the mixing time of their components and the mass fraction of the filler. It was found that with an increase in the specified time, there is a decrease in the heat capacity of nanocomposites, which is significantly manifested only in the region of temperatures close to the melting point of the composite matrix. It is shown that the dependence of the density of nanocomposites on the mixing time of their components in qualitative terms is similar to the corresponding dependence for their thermal conductivity. The obtained data can be used to choose the mixing time of components of nanocomposite materials in the development of appropriate technology for their productionВиконано комплекс експериментальних досліджень щодо встановлення впливу часу змішування компонентів нанокомпозиційних матеріалів на їхню теплопровідність, питому теплоємність та густину. Дослідженню підлягали фізичні властивості композитів «поліпропілен-вуглецеві нанотрубки». При проведенні експериментів тривалість змішування компонентів у розплаві полімеру змінювалася від 5 до 52 хв, масова частка наповнювача – у діапазоні 0,3…10 % і температура нанокомпозитів – від 290 К до 475 К. Встановлено, що збільшення часу змішування компонентів нанокомпозиційних матеріалів може призводити до суттєвого (більш ніж 70 разів) підвищення їх теплопровідності. Показано також, що вплив зазначеного часу обмежується його значенням 27 хв, при перевищенні якого зміною теплопровідності нанокомпозитів можна знехтувати. Встановлено, що чутливість теплопровідності нанокомпозитів до часу змішування їх компонентів знижується зі зменшенням масової частки наповнювача. Отримано температурні залежності питомої теплоємності досліджуваних композитів при варіюванні часу змішування їх компонентів та масової частки наповнювача. Встановлено, що при підвищенні зазначеного часу має місце зменшення теплоємності нанокомпозитів, яка суттєво проявляється лише в області температур, близьких до температури плавлення композиційної матриці. Показано, що залежність густини нанокомпозитів від часу змішування їх компонентів у якісному відношенні є подібною до відповідної залежності для їх теплопровідності. Отримані дані можуть використовуватися для вибору часу змішування нанокомпозиційних компонентів матеріалів при розробці відповідної технології їх отриманн