Influence of non-metallic inclusions in constructional S355J2 steel on mechanical properties has been evaluated by using fractal theory. Since point evaluation of non-metallic inclusions is fault tolerant to mechanical properties change. Point evaluation of experimental steel grades has been evaluated by 1-2 points. Correlation between mechanical properties of the steel (KV20, σ0.2, σB, δ) and fractal dimensions of non-metallic inclusions has been found. Mechanical properties of the steel have been ranking according to influence of fractal dimensions of non-metallic inclusions on the properties. It has been revealed that non-metallic inclusions, evaluated by their fractal dimensions, have strong effect on impact toughness of the steel S355J2 (R² = 0.89). It can be explained by reducing the metal matrix resistance to crack propagation due to non-metallic inclusions in the matrix. Method of mechanical properties ranging by non-metallic inclusions fractal dimensions allow to vary chemical composition of steel for main parameter obtaining. In this particular case for necessary impact toughness of constructional S355 steel narrower chemical composition of the steel should be chosen.

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 σВ, σ0,2 and specific elongation δ. Areas with suboptimal relations σВ/δ and σ0.2/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.

Actuality. Three-dimensional (3D) printing (Construction 3D printing (c3Dp), 3D Construction Printing (3DCP), additive manufacturing) is an advanced manufacturing process that can produce construction component or buildings automatically from a 3D computer-aided design model [1]. To use 3D printing technology in construction, it is necessary to develop or improve mechanical equipment for 3D printing, development of mixtures and technological parameters of mortars, development of methods for controlling the physical and mechanical properties of materials, development of constructions of buildings and structures made by 3D printing. The purpose. The main objective of the presented research is to develop scientific bases and to create innovative architectural, structural and technological system of construction by 3D printing method of construction objects. Methodology. Engineering design has been applied to develop the mechanical equipment and structures made by 3D printing, laboratory study has been realized for development of mixtures and technological parameters of mortars, methods for controlling the physical and mechanical properties of materials. Finding. Theoretical and experimental studies were carried out at the SHEI PSACEA (Dnipro, Ukraine). Mechanical equipment for 3D printing was improved during the research. The developments were protected by patents of Ukraine. In the technological part of the research, compositions of mixtures with accelerating curing were developed. Concrete quality control methods were substantiated. The structural elements of buildings that are erected by 3D printing method are proposed and investigated. The results of the research were put into practice in construction. Scientific novelty and practical value. The results obtained are a significant contribution to the theory of technological innovation development, which make it possible to improve the efficiency of construction production while reducing the consumption of material and energy resources.

Introduction. The study of the influence of chemical composition of materials on their mechanical properties is most often realized through modeling. This approach makes it possible to establish a one-to-one correspondence between composition and properties in the form of the obtained regression equations. The estimation of the magnitude of the coefficients of the equations allows us to determine the degree of influence of chemical composition elements of the materials on mechanical properties. It is therefore proposed to use this approach to evaluate the effect of chemical composition of S420M on its strength. Materials and methodology. The chemical composition and the tensile strength в of the S420M structural steel were varied within the limits of the ДСТУ EN 10025-4 standard for metal products. Using a technique of experiment planning, a fractional replica of the 2 4 experiment matrix was implemented. The results of the experiment. Multiparametric regression equations for the estimation of the tensile strength depending on the percentage of carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, molybdenum, niobium and vanadium were obtained. The greatest impact on the tensile strength, depending on the percentage, is 125,25 carbon, 29,50  manganese, 29,50  chromium, 24,50  vanadium and 16,50  molybdenum. The calculation of the effect of the elements of the chemical composition on the strength was carried out on the basis of the analysis of the coefficients of the obtained mathematical model. Thus, the approach to the prediction of the strength limit of S420M steel is implemented, which allows to control its performance during production by changing the chemical composition. The performance of the model is confirmed by the statistics of Fisher and Kochren. Conclusions. On the basis of the analysis of the influence of the chemical composition of S420M steel on its ultimate

Introduction. As a result of the formation of the steel structure in open systems, their elements often have a complex geometric configuration. From these positions, the approximation of structural components by Euclidean figures introduces an error in their analysis. Carbon is one of the main components of the chemical composition of steels, significantly affects their structure and performance characteristics. It is proposed to study the effect of carbon on the fractal dimension of steel. Materials and methodology. As the materials for the study, Cт3пс, 20, 40, and У8 steels were chosen. Steel had a ferrite-pearlite structure. The chemical composition of steels has changed within the existing industry standard (ГОСТ). The fractal dimension of the ferrite-pearlite structure was determined using the developed method based on the convergence of the cellular and point dimensions. The results of the experiment. Dependencies are obtained that describe the relationship between the carbon content in the range 0,14…0,84 % and the fractal dimension of perlite, ferrite and their grain boundaries. These dependencies have an exponential form due to an increase in the perlite content to the limiting values that is observed in eutectoid steels. The pair correlation coefficients of the obtained exponential models vary within 0,75…0,80, which confirms the influence of the perlite content in steel on its fractal dimension. A comparative analysis of the fractal dimensions of the ferritepearlite structure with hardness indices of HB steels after annealing according to standard production technology indicates the existence of sensitivity between these indices. Conclusions. The influence of carbon on the ferrite-pearlite structure of the hypereutectoid and eutectoid steel, which is fixed using the fractal dimension, is studied. The results can be used to study the effect of carbon on the geometric shape of perlite, ferrite and grain boundaries.