Laser Doppler vibrometry has found application both in nondestructive testing (NDT) of polymer composite materials (PCMs) and in studies of the amplitude-frequency characteristics of acoustic emitters in a wide frequency range. The use of air-coupled systems for the excitation of acoustic vibrations in the tested objects makes it possible to carry out a non-contact NDT procedure. This expands testing facilities of composites, simplifies the quality control procedure, and minimizes external influences on the test objects in comparison with traditional acoustic NDT methods based on contact emitters. In this paper, we have investigated the features of NDT of composites by a non-contact method using scanning laser Doppler vibrometry. The results of NDT of impact damage to PCMs using several types of air-coupled systems for excitation of acoustic vibrations, namely, based on piezoelectric, magnetostrictive, and gas-discharge transducers are presented.

Air-coupled ultrasonic excitation is a relatively poorly studied method of nondestructive testing of polymer and composite materials. The combination of noncontact ultrasonic stimulation in conjunction with laser vibrometry can provide an assessment of the quality of the product without external influence on the tested material. This work is devoted to the study of an ultrasound diagnostic system based on the combined use of a noncontact magnetostrictive transducer and scanning laser Doppler vibrometry for nondestructive testing of polymer and composite materials. We believe that such combination can provide sufficient power for rapid detection of defects, while the optimization of the experimental conditions increased the efficiency of testing results. Measurement of the directional diagram of the magnetostrictive transducer has made it possible to determine the features of the radiation of the magnetostrictor in an assembly with a titanium step-type waveguide.

In this study, a gas discharge electroacoustic transducer (GDEAT) based on a pulsed electric discharge in the air under atmospheric pressure has been investigated. The acoustic characteristic of GDEATs have been determined in the frequency range from 40 Hz to 4 MHz by evaluating acoustic pressure and recording amplitude–frequency characteristics of membranes. The electrothermoacoustic processes have been studied in open type gas discharge systems where the electrode space is in a direct contact with the environment. Some features of using the above-mentioned GDEATs in material nondestructive testing (NDT) have been demonstrated. It has been shown that, on the one hand, the wear of both electrodes and insulation limits the work life of transducer’s electrode system; however, on the other hand, this may lead to deposition of microparticles on the test object surface. The wear of the electrode system was evaluated quantitatively. The results of the chemical analysis of the deposited microparticles are presented. The possibility of using GDEATs for noncontact stimulation of local resonant vibrations in subsurface defects and visualizing vibrations by means of laser Doppler vibrometry is shown in the case of NDT of a glass fiber composite.

The results of the study of a gas-discharge electroacoustic transducer operating based on a pulse discharge in air at atmospheric pressure are presented. The influence of the electrode system configuration on the acoustic characteristics of the transducer is considered. It is shown that changing the discharge chamber volume and the interelectrode gap significantly affects the radiation intensity. Features that arise when using electroacoustic transducers of open and closed types for NDT tasks are identified. It is demonstrated that the open-type gas-discharge electroacoustic transducer is a sufficiently powerful broadband excitation signal source and has prospects for application in non-destructive testing. The closed-type gas-discharge electroacoustic transducer has advantages when studying materials with special requirements for surface cleanliness or the magnitude of the applied external electric field.

This study is devoted to the development of fusion techniques for data obtained by one or several nondestructive testing (NDT) methods. Experimental results were obtained by applying laser vibrometry and optical infrared thermography to evaluation of impact damage to carbon fiber composites. These NDT techniques are different by their physical nature and supply specific testing results. The proposed data fusion method allows increasing the reliability of inspection results and enables estimating defect parameters. It involves both averaging data of each single NDT technique and merging the results obtained by two methods. Vibrograms obtained by laser vibrometry are used to analyze acoustic response of the test sample to stimulation at various frequencies. In turn, infrared thermographic NDT supplies the sample response to thermal stimulation. It has been shown that the fusion of these two techniques supplies a comprehensive information on defect size and location. Also, the automation of the fusion procedure increases NDT productivity and reduces subjectivity of testing results.

This paper presents the results of a gas-discharge electro acoustic transducer of two configurations, operating on the basis of a pulsed discharge in air at atmospheric pressure. The influence of the electrode configuration on the acoustic characteristics of the transducer is considered. It is shown that a change in the volume of the discharge chamber and the inter electrode gap have a significant effect on the radiation intensity of the transducer. The features that arise when using open and closed type electro acoustic transducers in flaw detection problems are revealed. It is shown that an open type gas-discharge electroacoustic transducer is a sufficiently powerful broadband source of the excitation signal and has prospects for use in non-destructive testing. A closed type gas-discharge electroacoustic transducer has advantages when testing materials with special requirements for surface cleanliness or the magnitude of the applied external electric field.