Key Engineering Materials Vol. 864

Abstract: The sustainable development of industry and society requires new approaches to the building structures design. The article presents the indices of strength, crack resistance and width of crack opening obtained as a result of experimental testing of beams with hybrid reinforcement with basalt plastic and metal armature. The following beams were examined for comparison purposes: the ferroconcrete beams of the control-series, and the twin beams reinforced only with basalt-plastic reinforcement. It was found that the replacement of the metal armature with basalt plastics led to an increase in strength, on average, by 40%. Similar strength indices were obtained for hybrid reinforcement beams. Crack resistance indices of hybrid reinforcement beams were found to be close to ferroconcrete beams of the control series. Crack resistance indices for these beams were also by 84... 89% higher in comparison with beams reinforced with basalt-plastics. The width of crack openings in hybrid reinforced beams did not exceed the maximum permissible norms at the operational level of loads (70% of destructive) and were smaller than in beams reinforced with basalt plastic reinforcement. Hybrid reinforcement efficiency has been established to improve the performance criteria of beams reinforced with composite armature.

Abstract: The article presents the studies of the processes of structure formation in the system "cement-plasticizer - crude carbon nanotubes", established the relationship with the parameters of the structure, physical-mechanical and operational properties of composite materials from the standpoint of physicochemical mechanics of dispersed systems and shows the influence of processes on the physical-mechanical properties of cement composites.

Abstract: During the last decade, the drying up of medieval, arriving and mature stands of pine (Pinus sylvestris L.), which is the dominant breed in domestic forests (33% of the total area, about 45% of the volume of logging), acquired a threatening scale in Ukraine. Dated 2019, the total area of arable crops has reached 413 thousand hectares (of which pines - 222 thousand hectares), or about 4% of the area of the forest fund of Ukraine. One of the main and most effective means of preventing the widespread pathological processes in forests, which cause their drying, is sanitary and other felling of forest care. As a result, a significant amount of untreated low-quality timber, which is classified as deadwood is formed. Timber from deadwood trees is characterized by features such as mycological and insecticidal lesions, cracks, etc., the impact of which on the strength and operational characteristics of timber products has not yet been studied. The interest of using of the wood in the construction as a material from renewable eco-friendly raw materials has traditionally increased. One of the possible uses pine deadwood trees may be the production of structural lumber. The lack of timber characteristics of such timber makes it impossible to predict its behavior during processing and operation and, accordingly, complicates the determination of directions of its rational use, especially in structures. The significantly lower cost of timber from pine deadwood trees, compared with timber from non-attenuated drying out pine trees, is an attractive feature of such raw materials from an economic aspect.

Abstract: The article analyzes the causes of the destruction of road concrete in the winter. The basic theories of concrete failure during freezing are presented. Hypothesis of R. Collins according to which the destruction occurs as a result of the pressure of ice, which is formed when water freezes onto the pore walls. The hydraulic pressure hypothesis of T. Powers, according to which the main cause of concrete destruction during cyclic freezing and thawing, is the hydraulic pressure that creates water in the pores and capillaries of concrete under the action of ice. The hypothesis of thermal destruction of concrete due to the difference in the coefficients of linear thermal expansion of its components. In winter, sodium chloride (NaCl) solutions are most often used to combat ice on the surface of road surfaces. Therefore, an important consequence of this may be osmotic pressure. To calculate the osmotic pressure, the Vant-Hoff formula for true solutions was used. The maximum values of the osmotic pressure were determined at temperatures of 255...293 K. The critical concentrations of sodium chloride solutions at which concrete was destroyed were calculated. It was established that at the initial stage of freezing-thawing of concrete with the simultaneous action of an aqueous NaCl solution, the structure of concrete is densified and its strength is increased.

Abstract: The paper discloses results of durability studies of alkali activated concretes based on different alkali sources using aggregates capable to alkali-silica reaction (ASR). Active aggregates are representing by perlite, andesite, basalt and sandstone. It is shown that the alkali-reactive aggregates, in degree of their influence on expansion deformations occurring in the slag alkaline concretes may be placed in the following row: perlite< sand< sandstone< basalt< andesite, and a growth of expansion deformations is observed with increase in the active silica content in the aggregate. Also it is set that alkaline components, in degree of their influence on the rate of expansion deformations development in the slag alkaline concretes made with reactive aggregates, may be placed in the following sequence: Na₂CO₃<Na₂O SiO₂ < NaOH< Na₂O 2SiO₂.

Abstract: The possibility of increasing crack resistance, strength and elastic modulus of polymer-containing compositions due to the directed organization of their structure by internal, external and complex activation is investigated. Filled polymer compositions are presented as open complex dynamic systems. This made it possible to use rational fillers and special matrix-transformer of external electromagnetic influences as factors for controlling the processes of their structure formation and hardening to obtain materials with the required properties.

Abstract: The method to determine thermal fields considering dependence of thermophysical and mechanical properties of coating materials and a base from the temperature, the running of plastic deformations and stresses relaxation at plasma spraying is suggested. The mathematical model of calculation of thermal field with moving boundary considering nonlinear feature of coating growth at layer-by-layer deposition and dependences from thermophysical properties of materials of the system «coating-base» is developed. The model application helps to estimate the effect of the parameters of plasma spraying process on the level of the residual stresses in the increased coatings.

Abstract: A procedure has been developed for calculating the geometric, kinematic and energy-power parameters of helical rolling, which allows a comparative analysis of the processes carried out in stands of various designs. Based on the results of this analysis, a helical rolling mill was designed and manufactured which allows to roll materials with high deformation resistance at high temperatures. The results of the study of the mechanical characteristics of molybdenum bars and wires made by new technology are presented.

Abstract: The work considers the approach determining suboptimal relation of strength and plasticity by the example of low-carbon constructional steel 3 (0.14...0.22 % С), which is widely used in metal structures. As parameters for the research, the elements of chemical composition and properties of ferrite-pearlite structure of steel were taken. For the reliability of the obtained results for the evaluation of structure, its quantitative analysis was carried out either by traditional methods or by fractal approach. Combining operating regions of the values of steel properties depending on the chemical composition and area and fractal dimension of pearlite, we got the diagram of the region of compromise for indices of strength limit σ_В, σ_0,2 and specific elongation δ. Areas with suboptimal relations σ_В/δ and σ_0.2/δ were defined in the region of compromise for quality criteria. The application of the given approach allows (while adhering to steel production process) to predict areas with stable suboptimal relations for strength and plasticity indices by selecting value range for the elements of chemical composition and analysis of structure.

Abstract: The results of experimental studies of a separate contact dynamic interaction of a spherical non-deformable pellet with a plastic flat metal surface at different angles of attack (20° ≤ α ≤ 90°) at high speeds (v ≈ 100m/s) are presented. A method is described for determining the nature of the viscoelastic resistance of a surface layer attacked by a pellet during contact displacement along the normal to the surface and rigid plastic resistance during tangential displacement, which can be used to establish the processing regimes of products by a mass flow of abrasive particles, in particular, shot-blasting cleaning. The results of comparing the obtained and known theoretical data with each other and with experimental studies are presented.