Vol 55, No 9 (2019)

The work is devoted to experimentally studying regularities of inelastic strain and fracture in CFRP samples with pre-embedded technological defects corresponding to possible nonpressings and starved joints between material layers within a given bounded domain. The evolution of inhomogeneous strain fields at the surface of CFRP samples with an internal starved-joint type defect in a complex stressed state is analyzed. Faulty structures were located in the composite material using the acoustic emission method. This method allowed analysis of damage accumulation processes in complex loaded samples. The experimental data will be used in further tests to assess the adequacy of signals received from embedded fiber optic sensors subjected to complex-form loads.

The ill-posed problem of the ultrasonic inverse scattering equation is presented as existence, uniqueness, and stability. Among these three points, stability plays a significant role. Generally speaking, solving the stability problems requires the use of regularization method. The Tikhonov regularization method is at the core of the regularization method. This method has some disadvantages, such as not considering the coefficient matrix error, the regularization parameter is difficult to adjust, etc. Based on the all above reasons, truncated full least squares regularization method that considers the existence of errors in both the data term and the coefficient matrix is introduced into solving the ultrasonic inverse scattering equation. It is verified by simulation experiments that the truncated complete least squares regularization method can not only improve the data fitting degree, but also has higher imaging quality.

We propose a dual-frequency eddy current procedure for quality control of soldering in superconducting current-carrying joints of electromagnets. The advantage of the procedure is that the quality control result is independent of inevitable manufacture- and soldering-induced variations in the cross section of the joint being tested. The measurements are taken in two stages with an eddy current device using a transformer-type probe with a U-shaped core. At the first stage, measurements are taken at a high frequency, with the eddy current device readings depending only on the cross section of the joint but not on the degree of soldering. At the second stage, measurements are taken at a low (main) frequency, with the eddy current device readings depending on both the soldering of superconducting cables with each other and the outer section of the copper stabilizer. The degree of soldering in the tested joint is evaluated taking its cross-sectional area into account, based on the results of measurements at the two frequencies. Prior to testing, the eddy current device is pre-configured using three sample joints: two 100%-soldered samples of the same thickness but different heights and one sample with 0% degree of soldering.

The mathematical and simulation models of image formation in a system for the recognition of materials of internal fragments of containers by the dual-energy method are developed. A series of computational experiments were carried out on the recognition of materials inside shipping containers without and with compensation for the influence of the factor being analyzed on the quality of identification. The thickness of the prefilter, the ADC digit capacity, the ratio of the numbers of low- and high-energy bremsstrahlung pulses, and the dimensions of the averaging filter window were varied. An algorithm has been developed to compensate for the influence of the container wall thickness on the identification quality. The algorithm is based on the statistical processing of radiographic images of the object. Its effectiveness has been experimentally proved.