The results of measuring gradient strain fields by embedded or mounted point fiber-optic sensors based on Bragg gratings and distributed fiber-optic sensors based on Rayleigh scattering are discussed. Along with the experiment, the results of numerical modeling of strain measurement errors associated with the assumption of uniaxial stress state in the area of the embedded Bragg grating and measurement errors by distributed fiber-optic sensors associated with gage length are presented. Experimental results are presented for 3D printed samples and samples made of polymer composite material. The geometry of the samples was chosen based on the results of numerical simulations, and provides different variants of non-uniform strain distribution under uniaxial tension, including the variant in which the derivative of the strain distribution function changes its sign. A good agreement of numerical results and experimental data obtained by distributed and point fiber-optic sensors in areas where the derivative of the strain distribution function keeps a sign and an increase in the error of strain measurement results by distributed fiber-optic sensors in areas where this derivative changes sign are demonstrated.

The results of strain measuring experiments, with the help of rosettes consisting of fiber Bragg grating sensors (FBG) embedded at the manufacturing stage in a polymer composite material are considered in this paper. The samples were made by the direct pressing method from fiberglass prepregs. A cross-shaped sample was tested under loading conditions corresponding to a complex stress state. A variant of strain calculations based on experimental data is discussed. The calculations were performed under the assumption of a uniaxial stress state in an optical fiber embedded in the material. The obtained results provide a reasonable explanation of the absence in the conducted experiment of two peaks in the reflected optical spectrum, the presence of which follows from the known theoretical principles. The experimental result with two peaks in the reflected optical spectrum was obtained for the same sample under a different loading scheme. The proposed variant of the numerical model of the experiment and the results of numerical simulation made for FBG rosettes embedded in the material allowed to estimate error in the strain values calculated on the assumption of the uniaxial stress state in the optical fiber and in the presence of two peaks in the reflected optical spectrum.

The contemporary construction industry is based on the use of reinforced concrete structures, but emergency situations resulting in fracture can arise in their exploitation. In a majority of cases, reinforced concrete fracture is realized as the process of crack formation and development. As a rule, the appearance of the first cracks does not lead to the complete loss of the carrying capacity but is a fracture precursor. One method for ensuring the safe operation of building structures is based on crack initiation monitoring. A vibration method for the monitoring of reinforced concrete structures is justified in this paper. An example of a reinforced concrete beam is used to consider all stages related to the analysis of the behavior of natural frequencies in the development of a crack-shaped defect and the use of the obtained numerical results for the vibration test method. The efficiency of the method is illustrated by the results of modeling of the physical part of the method related to the analysis of the natural frequency evolution as a response to the impact action in the crack development process.

Compared to traditional machines, superconducting electrical machines have significant advantages, i.e: improved weight and dimensions, higher efficiency, lower values of inductive parameters, reduced noise level, greater stability when operating in electrical networks. Development of such machines requires the solution of a whole series of scientific and engineering problems related to many fields of science and technology. Along with the solution of traditional problems of the usual “warm” electrical engineering, one has to solve the problems associated with cooling of superconducting windings and the stability of their superconducting state under the action of external heat leakage, centrifugal and ponderomotive forces, as well as vibrations. The design of cryogenic machines should provide for the compensation of thermal compression of structural elements and windings during cooling process. This paper presents some interdisciplinary tasks, the solution of which will allow to reach a new level in the field of superconducting electrical machines and to create samples of electric motors and generators, surpassing all existing analogues in specific parameters.

This paper addresses the challenge of strain measurement using distributed fiber-optic sensors based on Rayleigh scattering in the presence of fiber Bragg gratings (FBGs) with a reflectivity level of 70% within the optical fiber. The reflectivity of such FBGs complicates distributed strain measurements that rely on the cross-correlation algorithm. The cases where the scanning ranges of a backscatter reflectometer include the resonant wavelengths of the FBGs and those beyond their limits, resulting in either a complete absence of a useful signal or the emergence of insensitive zones near the FBGs, are considered. An approach is proposed that employs a windowed Fourier transform with Hann window function for signal processing. This method effectively eliminates insensitive zones in distributed strain measurements based on Rayleigh scattering.