The effect of treatment with a pulsed magnetic field on the triboacoustic characteristics of polymer friction composites containing up to 20 wt

In this paper, we study the effect of corrosion inhibitors in compositions of friction composites on corrosion processes and noise generation in friction units. Model composites containing complex corrosion inhibitors as target additives were prepared. Tribological tests of the friction composite were performed using the “plane-to-plane” scheme. Transfer films on the surface of a steel counterbody are shown to be formed predominantly by laminar wear particles of the composite with sizes up to 50 μm. X-ray photoelectron spectroscopy data confirmed the presence in the transfer films of all elements related to the main components of the friction material, including corrosion inhibitors. Climatic tests were carried out. In a friction pair with a composite containing no corrosion inhibitor, continuous corrosion of the metal counterbody is shown to be predominant while pitting actively develops over time. The degree of corrosion damage to the surface reaches 90–95

The paper presents the results of experimental studies of the influence of treatment by an amplitude modulated high-frequency electromagnetic field on the dynamic mechanical and triboacoustic characteristics of friction composites with a polymer matrix intended for operation in unsteady friction units of brake devices of machines. It was found that in the dynamic mechanical characteristics, the effect of magnetic field treatment manifests itself most significantly in the change in the tangent of the angle of mechanical losses (a decrease in the maximum values of the tangent of mechanical losses to 52%), as well as in the change in the dynamic instability of friction and the spectral characteristics of frictional noise components in the range above 2 kHz.

The paper discusses promising way of utilization of the buckwheat husks for production of noise abating epoxy based composites for transport infrastructure and buildings industry. Composites of different densities from 400kg/m3 up to 650 kg/m3 have been prepared. The measurements of normal coefficient of sound absorption and sound transmission loss in the range from 500 Hz up to 6400 Нz are carried out. The absorption coefficient posses local maximum depending on the density of composites approaching the value of 0.99 at 3120 Hz for the density 400 kg/m3. The sound transmission loss of composites increases with density from the mean value of 10 dB for 400kg/m3 up to 60 dB for 650 kg/m3 that is comparable with well-developed artificial materials. The pristine buckwheat husks is thermally stable of up to 200-250°С that gives thermogravimetric analysis in the range from 30°С up to 500°С. The husks is suggested as the filler for production of epoxy resin based noise abating composites.

The results of experimental studies of the influence of non-equilibrium low-temperature plasma on the dynamic mechanical characteristics that determine the vibroacoustic activity of tribocouplings and the tribotechnical properties of friction polymer composite materials with a polytetrafluoroethylene matrix are presented). The aim of the study was to establish the effect of surface treatment of composites with low-temperature plasma of a high-frequency capacitive discharge in air on their dynamic mechanical characteristics and tribotechnical properties. Using non-resonant dynamic mechanical analysis methods, it has been established that plasma treatment leads to a decrease in the values of the tangent of mechanical losses of composites in the surface layer in the entire investigated temperature range (293–473 K), while there is a shift in the peaks of the tangent corresponding to the α- and β-transitions of the polymer matrix of the composite, to the area of higher temperatures. The values of the dynamic modulus of elasticity of the composite showed a tendency to a slight increase; however, this increase is at the limit of the sensitivity of the method. It was found that plasma treatment of friction composites results in stabilization and an increase in the dynamic friction coefficient, as well as a decrease in the wear rate.

The paper presents results of the tribotechnical and acoustic characteristics of copper-based frictional composite materials depending on the composite structure and content of metallic (tin, iron) and carbon (coke, graphite) additives in the composition. Changes in the studied characteristics are most pronounced under dry friction conditions. The introduction of the additives leads to reduced friction components of noise to 56 dB. In the boundary friction mode, the greatest effect of introduced target additives on the acoustic characteristics does not exceed 11 dB relative to the material without additives. For a composite based on 12% tin bronze, an increase in the graphite content from 10 to 30 vol % results in a 5 dB noise reduction.

This part of the paper devoted to the development of mechanism and machine mechanics in Belarus and cooperation with Bulgarian official and public organizations (see the first part of the paper). Successively the input in mechanism and machine terminology, standardization (elaboration of complex of standards on reliability, tribo-fatigue, gear failure modes etc.), quality management (system, techniques and tools, quality factors of machines and their components, methods of designing gear manufacturing processes etc.) are covered. It is considered informational support above mentioned topic through the edition of scientific journals; participation of Belorussian and Bulgarian scientist and engineers in international conferences, provided by one or other parties, as well as third one; interaction between scientific institutions.

При создании акустических композитов особое внимание уделяют получению легких, высокопрочных, экологически безопасных, биоразлагаемых композитов; технологиям пористых волокнистых композитов и повышению их звукопоглощающей способности.Цель работыанализ исследований и коммерческих достижений в области создания акустических композитов и шумопонижающих конструкций на основе экологически безопасных компонент и нанонаполнителей.На основе проведенного обзора патентной и научно-технической информации показано, что традиционные пути и методы создания акустических материалов в значительной мере исчерпаны

БолгарияЦель работысоздание акустических композитов на основе полимерных связующих и природных наполнителей, сочетающих одновременно высокие характеристики звукопоглощения и звукоизоляции

Study contains analysis of spatial arrangement reinforcement structure forming process of semi-finished composite billets. Modified technology of tufting opportunities for industrial use introduced. It may allow to appear wide application a new class of spatial arrangement reinforcement composites - thick-walled materials with adjustable anisotropy and physic-mechanical properties same to convenience laminated composites. Application of presented thick-walled laminates spatial arrangement reinforcement technology will allow production preforms with increased density. Experimentally usage of modified tufting technology approved in carbon-carbon composite transverse preform reinforcement application. Tufting step 5x5mm, preform thickness 50 mm, 0.793 kg/m(3) preform density reached. Modified technology have shown much less fiber damage compare to convenience KSL-tufting. (C) 2019 Elsevier Ltd. All rights reserved.

The influence of surface roughness of a steel counterbody on friction (coefficients of static and dynamic friction) and wear parameters is investigated for friction composite materials that operate in a transmission oil medium. The wear rate of composites and the level of dynamic instability of tribological conjugations (chatter, vibration, and noise) are shown to exhibit a non-monotonic dependence on the roughness of a steel counterbody with a common local minimum, which is typical of various friction materials. A rapid diagnostic method of tribotechnical and NVH-testing of friction materials intended for operation in oil is proposed as well.

In this paper a direct measurement approach able to determine the normal acoustic impedance of sound-absorbing materials using laser Doppler vibrometer (LDV) is presented. The results of measuring a number of typical soundabsorbing materials are given in comparison with the results obtained by standard two-microphone method (ISO 10534-2) using impedance tube. It is shown that the results obtained by the direct method differ significantly from the results of standard measurements in some individual frequency bands, but have good agreement in wide frequency intervals.

For determination of actual mechanical properties of composite material used in the manufacture of natural samples the original technique was proposed. Experimental characterization of composite material, intended for the repair of damaged pipelines during optimization of its service characteristics, revealed that introduction of disperse fillers in epoxy resin had a positive effect on the mechanical properties. Intensive experimental study showed that concentration of montmorillonite nanofiller had a significant impact on dynamic modulus of elasticity of composite materials based on epoxide resin while application of perforated metal tape in polymer resin composites demonstrated increasing of composite mechanical strength.

The given chapter presents a comparative analysis of the technologies presently employed for the repair, using reinforcing wraps/sleeves made of polymeric composite materials, of the areas with volumetric surface defects (also named local metal loss defects) of the transmission pipelines intended for hydrocarbons (petroleum, liquid petroleum products, natural gas, etc.) or other fluids. The above-mentioned technologies are also compared with other pipeline repair technologies (using metallic components and eventually requiring welding operations to be performed) in order to underline their advantages especially in the conditions in which it is preferable, due to the economic benefits, to perform the repair works on the in-service pipeline (without stopping the fluid supply). In addition, the technologies used to apply coating systems (containing polymeric composite materials) intended for the corrosion protection of the transmission pipelines or for the repair of such protection system are also compared and analysed.

In addition to the friction coefficient and the linear wear intensity of the frictional materials, the vibroacoustic characteristics are of importance, especially for the stationary friction units. Noise and vibration in the friction units lead to the problems connected with the technological operation of materials. This paper presents the results of studies of tribotechnical and vibroacoustic characteristics of highly filled friction composites depending on the content of iron oxide (Fe 2 O 3 ). Based on the results of tribotechnical tests and noise measurement generated by stationary friction, it is established that the optimum tribotechnical and vibroacoustic properties of friction composites are obtained within the range of low concentrations of iron oxide (0.6–1.2 wt %).

Extensive knowledge is required for proper use of phased array technology with long-range ultrasonic technique (LRUT) and subsequent interpretation of the results in connection with the study of the interaction of low-frequency ultrasonic waves with discontinuities in pipelines. This chapter presents the basic operation principles of the phased array technology, as well as physical processes of spreading of low-frequency ultrasonic waves in pipes. An attempt is performed at summarizing the advantages and shortcomings of pipelines' control with low-frequency ultrasonic waves, using phased array technology. Advantages, shortcomings, applications, and limitations of the method are present. Sensitivity of the method is analyzed to discontinuity and constituents of the pipeline.

The given chapter presents a review of the materials, presently employed within the composite repair systems (based on reinforcing wraps/sleeves made of polymeric materials), and intended for the areas with volumetric surface defects (also named local metal loss defects) of the transmission pipelines for the transportation of hydrocarbons (petroleum, liquid petroleum products, natural gas, liquefied petroleum or natural gas) or other fluids (water, ammonia, etc.). The categories of materials investigated are polymeric fillers (used to fill the volumetric surface defects and to reconstruct the external configuration of the pipe before repairing it), fibre reinforced composites (the main component of the repair system ensuring its mechanical strength), adhesive materials (used to bind the successive layers of the reinforced composite wrap).

Numerical modeling of surface wear proves to be a very challenging mathematical and numerical problem. Basically nonlinear processes of wear and creation of plastic zones are only the beginning of a large list of factors that have to be incorporated into a numerical model to adequately describe the frictional interaction of solid bodies. This article presents a new approach to numerical modeling of abrasive wear of friction composites under nonstationary friction. It utilizes the meshless smoothed particle hydrodynamics method together with the standard finite element method. The presented numerical examples illustrate both verification of the new approach, as well as results of abrasive wear modeling.