PSI - Issue 47

Oleg Naimark et al. / Procedia Structural Integrity 47 (2023) 782–788 / Structural Integrity Procedia 00 (2019) 000–000

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(v) Carrying out the polymerization of samples with embedded FOSs in the S с holz autoclave complex; vi) Obtaining the composite plate with embedded FOSs, from which samples are made. For additional control of the technological mode of forming samples with embedded FOSs, sensors based on the Bragg gratings with a connected ASTRO X327 interrogator were installed in the autoclave complex. During the process, the pressure and temperature were monitored by the control computer and according to fiber optic sensors. Registration of acoustic signals Optic fibers in the interferometer’s measurement system served as sensors of ultrasonic waves and were embedded into composite material when the sample was manufactured. The detection system consists of fiber optic sensor and two acoustic emission sensors. The fiber optic sensor was included in one of the interferometer arm. The result of the interference is recorded using a photodetector directly connected to the input of the oscilloscope, which serves as both a recording device and a signal preamplifier for the Vallen AMSY-6 acoustic emission system to provide recording and analyzing the signal from both a fiber optic and acoustic emission sensors. Acoustic emissions from defects with various locations in the composite structure create stress wave perturbations in the optical fiber that is detected by interferometer as perturbed light and is used to analyze the damage-failure staging. The time domain signal acquired from the optical fiber discerns the damage zones located in epoxy matrix or brittle carbon fabric or the interfaces in composite materials. Three channels were combined for the recording with sampling frequency 2 MHz: the signals on the first and second channels were obtained using piezoelectric transducers, and on the third channel using a fiber optic sensor. The amplitude threshold method of event registration with a sampling frequency of 2 MHz was used. The threshold was set on the first channel, the other two channels were in the slave mode. When the set threshold is exceeded by the amplitude of the signal on the first channel, the recording of waveforms on all three channels begins, until the signal again goes below the threshold level. Figure 3a shows an example of detected events.

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Figure 3. a-Acoustic emission signal by channels; b - Cumulative Renyi entropy

The methods for cluster and multifractal analysis of spatio-temporal dynamics of multiscale damage kinetics of composites were developed by Naimark, Uvarov, Bannikov, Bayandin and Nikityuk (2022) using acoustic emission in order to substantiate the criticality of damage-failure transition stages related to the duality of two-parameter fracture criteria. Analysis of acoustic emission data The data recorded on the first and second channels using piezoelectric transducers, and on the third using the fiber optic sensor, were analyzed with a sampling frequency of 2 MHz (Fig. 3a). The AE events can be considered as a fast response sequences of the material under the loading. The class of open systems that demonstrate avalanche-like fast relaxation under slow energy pumping is represented by many examples (earthquakes, plastic deformation, solar flares) and often appeals to the concept of Self-