Table of Contents


    • The strenous state of the contact at the sliding – flip pairs

      pg(s) 258-261

      The exact determination of strain on the load application area, regards to changing material or shape is one of the main problems of the mini structure constructions, which it does not interfere with the classical methods of linear elasticity. The main purpose of this article is to demonstrate accomplishments in the knowledge of linear elasticity with different mathematical methods, in order to penetrate into the area or into the contact lining, taking into consideration the friction between the bodies in contact. The methods and hypotheses are related to the analysis of different classical half-plane problems in loads of different types of linear elasticity. This material shows a clear original solution of the strained state in the contact area including the surface lining; it serves as a solution to the various contact plan problems. The details and the elements of the vehicles are part of a broad field, which should be optimized considering different analytical solutions and using various computer programs. These solutions can be installed in their structure. Classical methods in the details apply only when the hypotheses on studied subjects are being met, such as Material Resistance studying the Rod. A detail with a length of ten times greater than the transverse dimension. That’s the reason why extreme problems or problems out of the different hypotheses are solved and proven in practice with the most creative and sophisticated methods. The solution given in this article is an important contribution to constructive calculations, which is also associated with other works carried out by me on the friction coefficient on the flip-flop slippery contact.

    • Comparison of the Precision of Dry Sieve Analysis versus Wet Sieve Analysis for Some Selected Natural Clay Varieties

      pg(s) 262-267

      Clay is a specific soil type that composed with relatively finer particles usually less than 0.002mm according to most of standard definitions including the behaviours of cohesive and the clay particles may have different sizes less than 0.002mm and most of occasions the clay bulk is contaminated with some more coarse particles such as sand and silt even though those particles are comprised in a same deposit or a same massive body. Most of clay varieties are frequently condign in the advanced technological uses. Therefore, the investigation of the particle sizes of some of clay and categorization are important tasks in the selection of a clay type for some particular technological application. The well known methods for the grain size analysis are the wet sieve analysis and dry sieve analysis in order for cohesive soils and non-cohesive soils as usual. In the existing study, there were anticipated to compare the accuracy of dry sieve analysis results with the wet sieve analysis results of three different selected clay verities in Sri Lanka. As the experiential works those clay samples were separately analyzed using a sieve range of 2mm- 0.037mm and pan (<0.037mm) using dry sieve method. Also those clay types were wet sieve analyzed with respect to the sieve size of 0.075mm. According to dry sieve analysis results the finer portions (<0.075mm) were obtained as ~17%, ~6% and ~16% from clay 1, clay 2 and clay 3. The results of wet sieve analysis showed ~60%, ~37% and ~72% of finer portions (<0.075mm) in clay 1, clay 2 and clay 3 while the average grain sizes (D50) of them were 0.25mm, 0.27mm and 0.19mm. When comparing of those results the minimum deviation between wet sieve analysis result and dry sieve analysis result was found from clay 2 which is having maximum average grain size (D50) while the maximum deviation was observing from clay 3 which is having minimum average grain size (D50).


    • Features of creation of multiprobe system for nanometric measurements of geometrical and mechanical properties of surfaces of microsystem devices

      pg(s) 268-271

      The article considers the peculiarities of the technology of creating a multiprobe system for nanometric measurements of geometric and mechanical properties of the surfaces of microsystem devices. This system is built on the sites of domain-dissipative structures formed by the method of combined electron-beam micromachining on piezoelectric ceramics of the grade “lead zirconate-titanate”. The fundamental problem of creating such a nanoinstrument – measuring probes is the difficulty of determining the exact location of the contact regions of these probes. A fundamentally new method of high-precision formation of contact regions by the electroplating capillary method is considered. It is shown that the application of this method will speed up 3.5 – 5.5 times the process of measuring geometric and mechanical surface parameters, as well as the sensitivity of the measurement process by 10 – 18%, which, in general, increase the productivity and reliability of determining these parameters of surfaces of microsystem devices on average – by 15 – 25%.

    • Complex study of the bioaerosol composition of the atmosphere over urban areas based on lidar monitoring during the quarantine COVID-19

      pg(s) 272-276

      A comprehensive study of the air condition in urban areas was conducted, based on lidar monitoring. The subject of monitoring are two districts of Sofia the capital of the R.Bulgaria. The time period of the study is May-June 2020 and coincides with the introduced quarantine period in connection with the COVID-19 pandemic. The study includes lidar monitoring of the selected urban areas taking into account the mass concentration of particulate matter (PM). The method is combined with in situ sampling taking into account also the size control in μm – PM2.5 and PM10. The data are compared with those from the indications for the period of the licensed laboratories of the Ministry of Environment and Water and the Civil Network. A physicochemical study of the phase composition, structure and dispersion of the collected PM was performed by the methods of powder X-ray diffraction and Mössbauer spectroscopy. Predominant pollen and spore contamination was reported using Cascad Impactor measurements. Most part, the PMs studied show a conglomerate of several particles.

    • Experiment on charging an electric vehicle LiFePO4 battery after over-discharge

      pg(s) 277-279

      The efficiency and technical and economic properties of the electric cars depend mainly on the rechargeable traction battery. LiFePo4 batteries belongs to the lithium-ion type and has a number of advantages such as high capacity, long life cycle, resistance to fire at high temperatures or shock. They have safe and stable over-charging and over-discharging performances. This paper describes the process of charging the individual cells of an electric car battery after their over-discharge.


    • Fabrication, structure and use of nanocellulose as reinforcement in polymer composites

      pg(s) 283-287

      Nanocellulose is defined as term refers to the cellulosic materials with defined nano-scale structural dimensions. Nanocellulose can be mainly categorized into three main types; nanocrystalline cellulose (NCC), nanofibrillated cellulose (NFC), and bacterial nanocellulose (BNC). The special attention is the size of nanocellulose fiber which generally contains less than 100 nm in diameter and several micrometers in length. The NCCs have very attractive fundamental properties such as high strength and stiffness, low density, biodegradability, transparency, and extremely low thermal expansion property. They have extremely strong mechanical properties, e.g., a Young’s modulus of 130-140 GPa. As a results of the recent developments in the nanotechnology in the last deceade, nanocellulose has garnered much attention for its use in biocomposites, biofilms, medicine, coatings, thermoplastic and thermosetting resins. The production cost of nanocellulose is gradually decrasing due to increasing utilization by many industries all over the world. In this study, structure of use of nanocellulose and its use in polymer composites was reviewed.

    • Synthesis of energy-efficient control methods of the electromechanical disintegrator operating modes

      pg(s) 288-291

      The present trend in the development of highly efficient technological equipment for the production of nanomaterials is being analysed. It is associated with the synthesis of energy-efficient control methods for the operating modes of electromechanical disintegrator of multifactorial action. As a result of genetic modelling, the deterministic relationship between the genetic information of generative electromechanical chromosomes, structure of the resulting magnetic flux in the active zone of electromechanical disintegrator and its functional operating modes has been established. According to the results of structural synthesis, methods for technical implementation of energy-efficient modes of material processing, which ensure the increase of productivity of the electromechanical disintegrator, have been optimized and developed. The credibility of theoretical results was confirmed by experimental studies.

    • Effects of various fire retardants on mechanical and fire properties of plywood

      pg(s) 292-295

      Effects of various fire retardant (FR) chemicals on mechanical and fire properties of plywoods were investigated. Boron compounds such as, borax and boric acid; and phospate compounds such as, monoammonium phosphate and diammonium phospahate were used as fire retardant chemicals in the plywood panels. An exterior liquid phenol formaldehyde resin with 47% solids content was used as adhesive. The 2.2 mm thick Tetraberlina wood veneers were treated with the liquid solution of FR chemicals. The plywoods having 5-layers were produced from the treated wood veneers. The mechanical properties of the plywoods produced with treated veneers was found to be lower than that of the control group. Among the treated plywoods, The plywoods treated with borax had highest mechanical properties, followed by diammonium phosphate (DAP), monoammonimum phosphate (MAP), and, boric acid, respectively. The FR chemicals improved the fire resistance of the plywoods. The chemicals showed individually different effects related to improvement of fire resistance of the panels. For example, the OSB panels treated with diammonium phoshate were the latest ignited group (52.8 s) which were followed by the panels treated with boric acid (49.2 s), borax (44.5 s), and monoammonium phosphate (41.2 s), respectively. As compared to the control group (7.5 cm), the plywoods treated with borax (3.6 cm) had the shortest flame length after burner was turn off, followed by diammonium phosphate (4.2 cm), boric acid (5.1 cm), and monoammonium phosphate (5.8 cm).

    • A composite magnetic material with insulating anticorrosive coatings

      pg(s) 296-298

      We have studied electromagnetic and corrosive properties of new soft-magnetic composite materials made from iron powder ASC 100.29 and Atomet 1001HP, surface of which is encapsulated by insulating anticorrosive oxide coating. The results demonstrate that the use of such materials in power supplies, chokes, transformers, stators and rotors of electrical machines and other devices ensures their stable operation under various conditions.