The project is supported by the grant of the Russian Science Foundation №23-79-10107.
The research results have been published in the journal Optics and Lasers in Engineering (Q1; IF:4,6).
Composite materials and foamed metals are actively used today in new generation space and transportation equipment. Existing non-destructive testing methods are not fully suitable for quality control of such materials with laminated, cellular or porous structure. This determines the importance of creating new methods of non-destructive testing to detect defects in products of complex configuration.
Scientists of Tomsk Polytechnic University have developed an alternative non-contact system for diagnosing the quality of aluminum, carbon fiber and glass fiber composite materials. The main feature of the method is the use of a non-contact broadband radiator to inject an acoustic signal into the inspected products. The process of propagation of elastic waves in materials and their interaction with defective inclusions is analyzed by scanning laser vibrometry. Data processing makes it possible to determine the resonance frequencies of the controlled product and to highlight the areas of defects in their presence.
In order to study the vibration characteristics of the gas-discharge emitter, the scientists examined the air space near the emitter as part of the experiment. For this purpose they used the method of refractovibrometry. It consists in the refraction of the laser beam in the zones of variable pressure in the air created during the propagation of ultrasound. By creating a high density of points in the scanning area, the research team visualized with high accuracy the propagation of acoustic fields emitted by the gas discharge emitter in a wide range of frequencies.The principle of the gas discharge emitter is based on the electro-thermo-acoustic effect accompanying the flow of spark discharge current in air at atmospheric pressure. The flow of the electric current pulse causes a strong heating and expansion of the discharge plasma, which is accompanied by a pressure jump in the gas discharge gap. This leads to the appearance of acoustic vibrations on the surface of the transmitter and, accordingly, in the environment. The transmitter operates in pulse mode - it "shoots" beams of acoustic waves of different frequencies into the air. The discharge pulses are sharp and short-lived, and the generated acoustic signals are characterized by a wide range of frequencies,
"The pulse mode of operation of the gas discharge transmitter allows us to perform modal analysis of materials, i.e. to determine natural frequencies and vibration modes of products. In this case, due to the short duration of the discharge pulse, the spectral composition of the generated acoustic signal contains a number of frequencies, and the plate under test oscillates at different frequencies of the excitation signal present in the pulse. This leads to a multi-frequency resonant response of both the plate itself and its defective inclusions. We have shown that the pulsed gas discharge emitter allows us to detect defects in materials in a single experiment without using a set of resonant emitters and changing them, which significantly reduces the inspection time. This makes it an effective tool for non-destructive, non-contact testing of materials," says Daria Derusova.
Non-contact diagnostics is more accurate because it eliminates the influence of the attached mass on the test results. This method is energy efficient and less expensive because a large amount of energy is transmitted in the pulse for a short period of time. In addition, it can be applied to the inspection of thin, brittle and hydrophilic materials.
The Russian Science Foundation project will continue for the next two years. The scientists plan to improve the stability of the device so that the amount of energy transferred is stable from pulse to pulse. To do this, the researchers plan to adjust the internal parameters of the current pulse generator and study different configurations of the electrode system.