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Abstract. The aim of this study is to determine the influence of design factors of butt-welded sheet joints on the level of elastic stress concentration in joints. The finite element method was used to model the stress-strain state in the zones of constructive concentration of butt sheet joints with double-sided seams. The design model simulated the form of the joint in all the elements since the distribution of stresses and strains in the cross section depends on the joint configuration. The following parameters for butt sheet joints such as sheet thickness, the width of the joint, the bead width and bead height in butt welding joints were varied in the study. A nonlinear model was used to approximate the values of the elastic stress concentration factors obtained for different values of the geometric parameters for butt-welded sheet joints. This model is in good agreement with the values of the elastic stress concentration factors in the transition zone between the weld seam and base metal obtained by the stress-strain state modelling in joints with the help of FEM (the coefficient of determination R 2 ≥0.856).

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Despite the fact that concrete and reinforced concrete are the main construction materials, to date there is no complete theory of deformation and destruction. Structural concrete is considered at the level of macrostructure, has a number of features that do not allow you to directly transfer some of the provisions obtained for homogeneous materials. Available experimental data on the resistance of the concrete crack propagation relate mainly to the laboratory samples. In the paper, a new method for obtaining the fracture mechanics parameters of concrete, which is one of the most promising areas of research of fracture of composite materials. The study investigates the characteristics of cracks at different parameters of the segment breaks off. The study was carried out on finite element models. The authors studied the influence of the tilt angles formed by the segment on the stress state at the tip of the crack. In addition, the research separately considered the changes in mechanical properties of a break-off segment. As a result, the authors built regression tables and graphs. In conclusion, the research provides recommendations for the implementation of a shape for the break-off segment.

The article analyzes the sizes of concrete samples. We revealed a possibility to reduce sizes of samples. We simultaneously carried out tests of standard and small (25x25x100 mm) concrete samples. Small samples were obtained by cutting standard samples. In the course of study, the density, strength, and deformation of standard and small specimens were measured. The results are presented in tables and graphs. The strength of small samples was lower than the strength of reference samples. We identified loss of strength of the samples when cutting concrete. The average characteristics of deformation of concrete remained. Small samples are recommended for use in assessing the stress-strain state of reinforced concrete structures.