The points of stress concentration in the sections of structural elements are considered. These include, in particular, crack tips that may appear both during operation and as a result of a violation of their production technology. The values of stress intensity factors in the vicinity of cracks in the considered sections with contour corner points are obtained. In addition, the study of indicators in the asymptotic solution of the elasticity theory problem for bodies made of isotropic materials in the vicinity of the structure rod element corner point of the section, where the sides (or one of them) are supported by a thin coating, was carried out. On the other side of the corner region, various conditions for its reinforcement are assumed, including the presence of a thin elastic coating. Mathematically, the solution of the problem is reduced to the transcendental characteristic equation solution, that is, to the problem of finding the equation roots that is constructed from the condition for the existence of a non-zero solution to a linear homogeneous equations system. The characteristics of the stress components were determined for various combinations of boundary conditions, physical and geometric parameters. Qualitative conclusions are made. In particular, values these parameters are established combinations , at which the behavior of stresses at the section corner point becomes singular.

Keywords: stress intensity factor, isotropic elastic bodies, structural element, section corner point , crack, thin elastic coating, boundary conditions, characteristic equation, stress concentration

The article is devoted to modeling the operation of a piezoelectric generator (PEG) in the form of a round bimorph plate with two piezoactive layers and an inertial mass. The considered PEG can serve as an element of the energy storage device, as a source of electrical energy obtained from the vibrations of structural elements and machines. The bending axisymmetric oscillations of a composite elastic and electroelastic body are considered in a linear formulation, taking into account the dissipation of mechanical and electrical energy. The problem is solved using the finite element method (FEM) in ACELAN. Statement of the problem simulates the fixation of PEG in a moving structure. A modal analysis of the device was carried out, the first frequencies of resonance, antiresonance, and electromechanical coupling coefficient were found. Next, the problem of forced harmonic oscillations at the first antiresonance frequency is solved and the output electric potential is determined. The dependences of the output characteristics of PEG on its geometrical parameters are constructed.

Keywords: piezoelectric generator, energy storage, electric potential, finite element method

The possibility of revealing the main defects that arise when strengthening reinforced concrete structures by external reinforcement systems based on carbon fibers is considered. The efficiency of active and passive methods of thermography is compared, and the possibility of using the passive method at negative ambient temperatures is considered. Under laboratory conditions, ferroconcrete samples with defects in the form of air bubbles and glue were made and a comparison of the mapping of these defects on thermograms was made.

Keywords: composite materials, reinforcement, external reinforcement systems, infrared thermography, defect, work quality assessment, technical condition assessment, span structures, bridge supports

The article presents the vibration diagnostics method for pilons of transmission lines. Pilons has defects: inclined cracked faces with a length of 25-30 cm , with a crack width of 0,4-0,7 mm . The article presents an example of analytical modeling of natural vibrations of a reinforced concrete pilons of transmission lines with defects in the base. Analytical modeling was based on the hypotheses of Euler-Bernoulli. Built an equivalent model of the pilons with defect in the form of an elastic element, simulating the damage in the area of trapping. The calculation of natural frequencies of first five modes of transverse oscillations for different values of stiffness of the defect. The result of this work is to obtain the dependencies of the relative frequencies from the stiffness of the defect and establishment of sufficiently informative criterion for predicting the alarm state of structures. The material presented can be used in the development of methods of diagnostics and monitoring of technical condition of different structures of the core type.

Keywords: vibration analysis, pilons of transmission lines, the defect, analytic modeling, transverse vibrations, natural vibrations, natural frequencies

the paper considers the comparison of natural modes for the first and second transverse oscillation modes obtained by numerical simulation and finite element package of analytical calculation of the core model with an elastic element based on the application of the Euler-Bernoulli hypothesis. The analysis compared waveforms for different values of the defect shows their satisfactory agreement.

Keywords: rod design, vibrations, defect, finite element modeling, analytical modeling, waveform