Key Engineering Materials Vol. 887

Abstract: The optimal compositions of fine-grained concrete (FGC) with two-level reinforcement with fiber are determined via the extreme modelling of experimental data based on the Scilab engineering and scientific computing environment. At the macro level brass plated fibre of the wave profile FSW LV 15/0.3 made of steel grade 70-85 with the fiber length of 15 mm and the diameter of 0.3 mm was used for reinforcement. At the micro-level the halloysite nanotubes NN-RTE 200 with the particle sizes from 0.05 to 5 microns were applied. Having calculated the models the designed program Extr.sce determined the extrema of the required characteristics of fine-grained concrete Max_z and their coordinates max_x and max_y, corresponding to the contents of the brass plated fiber (x) and halloysite nanotubes additive (y). The graphic dependences of the compressive strength, bending strength and water absorption of fine-grained fiber concrete on the content of brass plated fibre and halloysite nanotubes additive with minimum, average and maximum cement content in it in the form of contour and 3d graphs of the interpolation surface are obtained. Two-level reinforcement of FGC, optimized by the program Extr.sce, proved that fine-grained concrete with 10% of brass plated fibre, 20% of halloysite nanotubes additives, and cement content of 600 kg had the maximum compressive strength of 70.26 MPa. In order to obtain FGC with maximum bending strength (17.43 MPa), there should be 5% of brass plated fibre, 10% of halloysite nanotubes additives, and 600 kg of cement in it. The fine-grained concrete without any reinforcement additives will have the minimum water absorption (3%).

Abstract: The paper presents the results of experimental studies on the determination of corrosion products on the surface of reinforced concrete structures. This paper also discusses methods for creating samples with artificial electro corrosion under conditions close to real operation. The paper presents the results of testing samples using laser-inducted breakdown spectrometry (LIBS) devices.

Abstract: Nowadays, a lot of information on structure and properties of a wide variety of substances and materials has been accumulated. Yet, there is a lack of systemic universal approaches to assessing their structure and properties, including developing the effective approaches for monitoring and analysing various materials. It is of special interest in this respect to assess the effects of the chemical bond type on structure and properties of substances and materials. However, searching for necessary data on the effects of chemical bonds on structure of substances and materials is a rather laborious process. The authors, relying on the intermediate nature of chemical bonds of compounds of elements in any metallic and non-metallic material, as well as the system of chemical bonds and compounds developed by them in the form of a “Chemical Triangle”, produced an algorithm for creating a computer programme. It implies systematising of the database on the effect of chemical bond type on its length and energy, structure and various physicochemical and mechanical properties of homo-and heteronuclear compounds and materials. Development of such a specialised computer programme greatly simplifies this process, providing more efficient analysis and control of materials.

Abstract: The spreading process of drying and coalescing nanodispersion was simulated using the method of analogies. A mathematical description of the energy processes in the proposed physical model was obtained in the form of a system of differential equations of the first order. A transition function that describes the dynamics of the change in the contact angle when the nanodispersion drop spreads was obtained as a result of solving the system of differential equations. The physical meaning of the transition function coefficients was established. Based on the analysis of the ratio of the transition function coefficients, a theoretical justification for the results of experiments on choosing the optimal amount of desiccant introduced into styrene-acrylic nanodispersion was given.

Abstract: In the paper the research has been performed to obtain the stress distribution through the thickness of the rolled products along the deformation zone in the conditions of roughing rolling and in the conditions of quasi-stationary temperature distribution during finishing rolling at the Steckel mill. The research has been performed by the simulation based on the Abaqus CAE 6.14-2 software and analytical modeling of the hot rolling process of coils at the Steckel mill with dimensions of 15 mm × 1500 mm, made of steel grade S355JR+AR, according to the requirements of EN 10025-2. The obtained deviations of the rolling force between simulation, analytical modeling and actual data have comparable results and a similar trend of changes through the passes, the average value of which does not exceed 1.54 % and - 1.77 %. The beginning of the continuous layer formation of equivalent stress during roughing rolling has been determined, and, accordingly, the beginning of the deformation penetration through the entire thickness of the semi-rolled product has been also determined that occurs in the pass 6 when reduction equals 14 %.

Abstract: Currently, the most promising high-tech and productive process is friction stir welding. An important element of this technology is the determination of the material temperature in the stir zone, which can be determined by calculation based on the amount of heat input introduced into the welding zone. To determine this value, experimental of the dependence of heat input on the tool rotation speed and welding speed were carried out. For this, a scheme of experiments has been selected in which the material to be welded (aluminum alloy AMg5) is modeled as an experimental tube with a diameter of 20 mm, and the tool (made of tool steel R6M5) is modeled as a working plate. On the designed and manufactured stand, studies of the dependence of the heat-liberation value for the speeds of rotation of the experimental tube 42-105 rad/s were carried out. In this case, due to the pressing force of the experimental tube and the working plate, a constant temperature of the place of friction was maintained. The obtained experimental data were used to calculate the heat-liberation value and heat power on each concentric ring 2 mm wide at the end of the working tool with a diameter of 20 mm, as well as the total heat power for different speeds of rotation and welding.When carrying out experiments on the bench, heat losses were determined by thermal conductivity along the rod on which the experimental tube is fixed, as well as from the working plate made of tool steel through the gasket onto the working table and by convection from the surface of the rotating experimental tube into the environment. The calculation results showed that each of these losses does not exceed 3-10%. These losses are taken into account in the heat supply calculations.

Abstract: This article provides a theoretical study of the possibility of reacting acetone, a common volatile organic compound (VOC) in human respiration, with carbon nanotubes modified with functional groups - carboxyl and amine. Analysis of efficiency of processes of sorption interaction of acetone molecule with modified nanosystem for development of recommendations for creation of perspective highly sensitive sensory devices using modified carbon nanotubes for detection of VOCs contained in human exhalation and diagnostics of various diseases.

Abstract: It is introduced to use a portable spectrometer along with a calibration model for rapid quality control of metakaolin in situ. Verification of the calibration model for predicting the values of two indicators: total acid solubility and mass loss during calcination, indirectly characterizing the pozzolanic activity of metakaolin.

Abstract: Despite the fact that the classical theory of combustion (CTC) operates with the simplest, elementary objects and concepts, such as: flat or slightly curved combustion fronts, elementary combustion models and potential flows. there are some problems that the CTC is only facing with a sufficiently strong curvature of the front. For example, Markstein's solution in the problem of hydrodynamic instability of a plane combustion front. In the work presented by the authors, the problem of stabilizing the titanium carbide synthesis front at moderate temperatures, which cannot be plane due to the thermo physical features of the system under consideration (Le<<1, Ze=6.03 at Тad=3300К), is similarly solved. A model of vortex combustion with a spirally curved front is proposed, the numerical analysis of which showed the stability of similar front of the TiC synthesis in the field of vortex hydrodynamic currents. The resulting solution can serve as a complete alternative to the mode of spiral spin combustion (or rather, to its branch with a low orbital speed and a low combustion temperature) of such systems, not only considered conditionally unstable in CTC, but also actually manifesting this instability during numerical calculations of the area of the existence of a spinal spot with a small radius and great curvature.

Abstract: This paper presents a model of a thin film formation process of an amorphous alloy as a sequential procedure when a conditional unit of substance is randomly thrown onto a substrate at each next step. The islands of a precipitant are generated on the substrate with an increase of number of steps (density defects of substance). We determine the probability distribution of an island area, which shows the maximum informational entropy. An algorithm for computing estimates of parameters of this distribution is obtained. The results of processing experimental data are presented. We demonstrate that the proposed distribution is more consistent with the experimental data than the Pareto distribution.