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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detect a signal emitted by an defects during damage-failure transition and studied by Chen, Ansari and Fiber (2000). Optical fibers in the interferometer’s measurement system were served as sensors of ultrasonic waves and embedded into composite material, when the sample was manufactured. Acoustic emissions from defects with various locations in the composite structure create stress wave perturbations in the optical fibers, which are 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 using a fiber optic sensor. The analysis by Back, Tang and Wiesenfeld (1987) of sequences time delay revealed the signs of the Self Organized Criticality (SOC) freedoms with the power law for the distribution of delay time and energy, that is characteristic of nonlinear dynamic systems with numerous degrees of. Similar signs were established by Naimark (2004, 2016), Naimark, Bayandin, Uvarov, Bannikova and Saveleva (2021) in damage-failure transition analysis as specific type of critical phenomena (structural-scaling transition in defects ensemble), when the damage-failure staging was the consequence of the self-tuning in term of “structural-scaling”parameter as the integral characteristics of criticality.

Nomenclature R ij

Recurrence Matrix state space trajectory

ˆ i x

ε radius of a small neighbourhood ˆ ˆ i j x x  distance between state space trajectories DET determinism H D (l) histogram of diagonal lines on recurrence plot

2. Material and experimental conditions Experiment а l statement

Quasi-static loading of flat composite samples was carried out on the experimental complex consisting of an electroresonance testing machine Testronic-50 with a maximum load of 50 kN, a La Vizion DIC and the acoustic emission AMSY-6 systems, infrared camera NEC TH9100. Mechanical testing of the composites was accompanied by the recording of acoustic emission signals by two methods: using piezoelectric and fiber optic sensors. The scheme of the experiment on fiber-optic recording of an acoustic signal is shown in Fig.1. Acoustic emission signals were recorded using piezoceramic microphones by Vallen system, model AE204A with a frequency measurement range of 180–700 kHz, an operating temperature range of -20 to +80 º С . The microphones were connected to the signal processing unit through standard preamplifiers from Vallen system with a gain of 34 dB. The AMSY-6 system allows the measurement and analysis of discrete AE signals that cross a pre-set fixed or floating threshold level. The detection system consists of a 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 recording system, which serves as the main device for 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 are detected by interferometer as perturbed light and is used to analyze the damage-failure staging. The time domain signal