Percolation-induced low frequency plasmonic state in metal granular composite materials

The article is devoted to the investigation of the spectral characteristics of acoustic emission signals that appear under various schemes of composite materials loading. The tests involved samples of composites reinforced with layers sheets of carbon fiber fabric and dispersed carbon fibers. Based on the results of laboratory tests, a comparison is made between the traditional parameters of acoustic emission and the complete spectrograms of the acoustic emission response developed with the use of a special algorithm. The relationship between the emission activity and the change in the spectral composition of emission hits is shown. For example, for some composites, the acoustic emission memory effect (Kaiser effect) manifests itself not only in the time domain but also in the spectral domain in a form of a sharp change in the amplitudes in the frequency range 130/150 kHz. Also, when the samples were loaded according to the Brazilian scheme, the presence of the so-called “inverse” Kaiser effect is observed, in which the memory carrier “remembers” the previously experienced level of tensile stresses and reproduces this information during subsequent unloading. Such effect manifests itself in the form of a sharp change in the amplitudes in the low-frequency region of the spectrum.

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Using Hilbert Transform in Diagnostic of Composite Materials by Impedance Method

Periodica Polytechnica Electrical Engineering and Computer Science ◽

10.3311/ppee.15066 ◽

2020 ◽

Vol 64 (4) ◽

pp. 334-342 ◽

Cited By ~ 1

Author(s):

Volodymyr Eremenko ◽

Artur Zaporozhets ◽

Vitalii Babak ◽

Volodymyr Isaienko ◽

Kateryna Babikova

Keyword(s):

Composite Materials ◽

Nondestructive Testing ◽

Hilbert Transform ◽

Instantaneous Frequency ◽

Information Quality ◽

Low Frequency ◽

Mechanical Impedance ◽

Phase Characteristic ◽

Impedance Method ◽

Materials Testing

The article is devoted to the problem of the increasing of information quality for the impedance method of nondestructive testing. The purpose of this article is to get for the pulsed impedance method of nondestructive testing the additional informative parameters. Instantaneous values of the information signal's amplitude is a sensitive parameter to the effects of interference, in particular friction, which necessitates the use of additional informative features. It was experimentally measured signals from defective and defectless areas of the test pattern. Using of the Hilbert transform gave possibility to determine phase characteristics of these signals and realize demodulation to extract a low-frequency envelope for further analysis of its shape. It was received the informative features as a result of researches. Among them are instantaneous frequency of a signal, the integral of a phase characteristic on the selected interval and the integral of a difference signal phase characteristics. In order to compare quality of the defect detection using selected parameters it was carried out evaluation of the testing result reliability for a product fragment made of a composite material. Considering the influence of the change in the mechanical impedance of the researched area on the phase-frequency characteristics of the output signal of the converter, it is proposed to use as the diagnostic signs: the instantaneous frequency and the value of the phase characteristic of the current signal for certain points in time. The proposed informative features enable to increase general reliability of composite materials testing by the pulsed impedance method.

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