Vol 54, No 8 (2018)

When developing ultrasonic testing techniques for such complex objects as composite welds, the method of finite differences in time domain (FDTD) can be used to calculate echo signals in numerical experiments. Since the FDTD method is based on explicit numerical solution of the wave equation for an elastic medium, it can be used to take account of such effects as the emergence of a run round wave on a volume reflector, the transformation of a longitudinal wave into a lateral one under scattering of ultrasound by a crack, and the rescattering of pulses between reflectors and test-object boundaries. Applying the FDTD method to modeling the propagation of ultrasound in the sample with a high pattern noise and in the samples made of anisotropic inhomogeneous materials is substantiated. The FDTD calculation of the direct problem of propagation of elastic vibrations in a solid may prove useful when solving the inverse problem of ultrasonic nondestructive testing.

Dedicated low-frequency acoustic-testing methods are widely used to detect flaws in three-, five-, and seven-layer structures with a honeycomb core made of polymer composite materials (PCM), with the impedance technique being the main one. However, this technique allows one to establish only the mere fact of the presence of a flaw but not the depth of its occurrence. To obtain information on the depth of occurrence, it is necessary to numerically measure the mechanical impedance on the surface. The complete impedance-transducer frame system has been simulated by the electromechanical analogy method in order to establish the relationship (and derive respective dependences) between the external load applied to the sensor, expressed as the total mechanical impedance on the article surface, and the change in the values of measured electrical parameters on sensor’s piezoelectric elements. Relevant dependences have been derived for the transmission factor, which is the modulus of the ratio of voltages across receiving and emitting piezoelectric elements, and for the phase shift between these voltages. By combining these dependences, hodographs have been produced that represent the graphs of the dependences in the amplitude-phase plane, similar to how information is displayed in state-of-the-art impedance flaw detectors. The dynamic contact compliance (significantly affecting the efficiency of impedance testing technique) of a dry point contact between materials of the outer PCM layers and widely distributed and commercially available impedance sensors (for example, PADI-8) has been determined. Model hodographs constructed with allowance for contact compliance were used to run an experiment on revealing delamination and starved-joint flaws at various depths in a seven-layer honeycomb structure of an aircraft engine nacelle. It has been confirmed that the depths of defects are effectively discriminated both by the magnitude of mechanical impedances and by the characteristic indication from cell walls on the C-scan over the entire article surface.

Dependence of the readings of the sensor in a permanent-magnet structuroscope with a two-pole magnetizing device has been investigated for different directions of the magnetic-field transducer sensitivity axis with respect to the magnetization of a test article. The possibility for the devices to operate in a sensor rotation mode has been shown as applied to testing the mechanical properties of articles and the stressed-strained state of objects made of ferromagnetic materials.

A mathematical model has been developed to describe the radiation transparency of a test object with allowance for quantum noise. The technique of estimating the effective atomic number of the test object by the dual-energy method has been improved based on the analysis of radiation transparency with regard to necessary restrictions and recommendations. An algorithm is presented for the statistical evaluation of the influence of quantum noises on the quality of test-object material identification by the dual-energy method. An example is given of using the algorithm in a baggage and carry-on inspection system that has the maximum X-ray energies of 80 and 160 keV and is equipped with total-absorption detectors.

Historic buildings have a great cultural and architectural value. It is necessary to analyze their state of conservation, but sometimes it is difficult to perform laboratory tests without damaging this heritage. In the field of architecture, infrared thermography is usually used to provide descriptive information about the surface temperature of building materials. This current research presents a methodology widely applicable to historic buildings. As an example of application, the study is focused in the Seminary-School of Corpus Christi of Valencia (Spain), a very outstanding building from the 16th Century. This research presents an analytical study to be able to differentiate the temperature distribution of all pixels of a thermographic image. Thermal images are a matrix of data and their study helps us in decision-making based on objective data.