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Results of calculations of values of static and cyclical strength of steels used in the structural design and based on the method of experimental and analytical coordination of hardness numbers are presented in the article. Strength measurements taken on the basis of the Rockwell method make it possible to research into the strength characteristics of small-size samples of steel in cases of restoration and inspection of the technical condition of the metalwork. Besides, the Rockwell method is universal and faster than the Brinell method.Thus, the availability of hardness values of small-size samples makes it possible to provide a definition of standard indicators of static and cyclical strength. Moreover, development of the definition of structural and power (synergetic) criteria of reliability of metalsusing the equation of relative strength turn into reality. The solution to this equation ofuniform plastic deformations of dmakes it possible to identify S , S , W , W values.р B K P C The initial experimental value of the hardness number may be used to calculate avariety of static and cyclical properties of steel and to identify the standard strength group and the approximate steel type counterpart.

The objective of the study is research into interrelation between values of plasticity(d, y) and hardness (HB).Numerical values of hardness are insufficient to make accurate assessments of plasticity values. Meanwhile, hardness is the property identified using small-sized samples extracted from the metalwork of restored and reconstructed buildings. The most suitable method is the Rockwell one used to obtain HRB or HRC hardness values. However, these values maintain an analytical relationship neither with durability, nor with plasticity values. The difference between metal testing methods consists in their relation to dimensions: HRB and HRC values are dimensionless, while HB values are size dependent (kgf/mm2, or MPa). Therefore, the approach employed in this article can be used to generate supplementary information about the properties of metals using HRB or HRC hardness measurements.It is noteworthy that the proposed technique of coordination of HRB hardness val-ues with HB hardness values may be employed to, first, analyze σ and σ sizes using HBт вvalues, and second, to identify the nature of relationship between HRB, on the one hand,and d and y values, on the other hand, to compose the equation of relative strength and plasticity values and to assess the most important factor of reliability of metals.

In this paper, the authors study the influence of the drawback temperature of metal-ceramics composites on their mechanical properties, if composites are produced using the iron-graphite powder method. The authors have studied the microstructure of the materials and the influence that the thermal treatment produces on their strength, plastic properties and toughness. The authors have also identified specific thermal treatment parameters aimed at the improvement of mechanical properties of parts of machines and mechanisms made of the above composites. The analysis of the authors’ findings is applied to find the ways of improving the mechanical properties of machine parts produced using powder metallurgy methods.The analysis of the microstructure confirms the presence of changes in the mechanical properties of materials, namely, their plastic properties and toughness. The combination of the most efficient sintering regime (using double pre-pressing) and subsequent thermal treatment in the form of hardening and tempering can improve the mechanical properties of machine parts. The authors performed experiments to identify the best sintering conditions and improve the mechanical properties of the Fe-C composition, including its tensile and flexural strength, as well as compressive and impact strength using the above process parameters and other data obtained from the reference literature. The authors have discovered that if the sintering speed and the shrinkage ratio are maximal and vary insignificantly at the temperature near the Ac3 value and slightly above it, the mechanical properties after sintering, for example, at 870 °C and 1100°C will differ slightly.

Introduction. Presented the approach to optimal choice of materials, in particular, composite materials. An important task of modern materials science is the development of effective composite materials, which is associated with numerous scientific studies in this area and the search for materials with certain additives in order to obtain the necessary properties. First of all, it is an indicator of the hardness of the composite material. Materials and methods. Traditionally, different compositions are studied and property values are analyzed, and experimental results are processed in different ways. Multi-criteria optimization occupies a special place in the theory of optimization of objects, which include composite materials, in particular concrete with various additives. For this it is necessary to formulate a multicriteria optimality problem, in particular a two-criterion minimization problem. Results. Two heuristic optimization criteria are considered, according to which a vector criterion is formed, which allows to carry out the selection of composite materials from experimental data at its minimization. Vector criterion connects the change of the studied properties of the composite material with the simultaneous preference for the choice of the composition that optimizes the given criterion of optimality. The basis of the construction of the optimization scheme of choice of materials is a piecewise linear approximation of the test results, which allows to determine the scalar criteria on the basis of which the vector optimization criterion is constructed. To demonstrate two-criterion optimization, the results of experiments for cement composites exposed under the cyclic influence of negative and positive temperatures are considered. The search for the optimal composition in terms of hardness from the time of exposure. Conclusions. The proposed approach of optimal choice of materials, in particular, composite materials, can be tested on large numbers of test samples, or to automate calculations. This approach has a certain heuristic character. But its practical significance is confirmed by the expert evaluation of the quality of composite materials due to the existing methods of evaluation of materials, for example, in terms of changes in its hardness.

Introduction. Application of renewable raw materials for manufacturing non-toxic components of polymer materials is of great practical interest. Cyclic carbonates on the base of epoxidated rubber tree oil could be seen as a promising alternative of fossil fuels. The ability of compounds containing cyclic carbonates to interact with primary amines and to form urethane and hydroxyl groups makes them rather efficient modifiers of amine-toughened epoxy compounds on the base of low-molecular diane oligomers. Introduction of cyclic carbonates enhances impact behavior of epoxy materials as well as their adhesion and strength properties. Materials and methods. Epoxy resin ED-20 was used for the research, as a cross-linking agent for cold toughening aminealkylphenol AF-2 was used; cyclic carbonates of epoxidated soy oils and rubber tree oil were applied as modifiers. Adhesional strength of bond joints has been determined in compliance with the GOST 28840-90, abrasive hardness of epoxy compound samples has been tested by the vertical optical caliper IZV-1. Results. When applying two-stage technology for obtaining epoxy cyclic carbonate compounds, there has been appeared a significant increase of adhesion to aluminum. This effect could be even more noticeable with increasing temperature during the stage of mixture of the amine toughener with the cyclic carbonate modifier. High viscosity of cyclic carbonate modifiers complicates the process of mixing components of the epoxy compound and correspondingly its application as a backing of glues and linings. The authors researched cyclic carbonates of epoxidated soy oil with various averaged functionality as modifiers. Application of epoxy materials CESO-75 as a modifier has proven to be more forward-thinking for the reasons of cost-efficiency and for operating and technological properties. CESO lowers the coefficient of static friction for epoxy materials together with enhancing their abrasion hardness. Conclusions. Cyclic carbonates of epoxidated plant oils (soy oil and rubber tree oil) as rather efficient non-toxic modifiers of epoxy polymers are of practical interest. They are produced on the base of annually renewable plant raw materials. Their application enables to enhance abrasion hardness and adhesion properties of epoxy compounds and also improve their antifriction properties.