scholarly journals Spectral Characteristics of Acoustic Emission in Carbon Fiber-Reinforced Composite Materials Subjected to Cyclic Loading

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Vladimir L. Shkuratnik ◽  
Petr V. Nikolenko
Keyword(s):  
Acoustic Emission ◽  
Composite Materials ◽  
Carbon Fiber ◽  
Spectral Characteristics ◽  
Spectral Composition ◽  
Low Frequency ◽  
Sharp Change ◽  
Kaiser Effect ◽  
Emission Activity ◽  
The Time Domain

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.

Research on Failure Mechanism of Carbon Fiber Composite Materials Basing on Acoustic Emission

2013 ◽  
Author(s):  
Yan-Lei Liu ◽  
Wei-Zhong Li ◽  
Fu-Yong Xia ◽  
Bing Wang ◽  
Shu-Xin Han ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Composite Materials ◽  
Carbon Fiber ◽  
Composite Laminate ◽  
Fiber Composite ◽  
Acoustic Emission Technique ◽  
Carbon Fiber Composite ◽  
Emission Testing ◽  
Different Characteristics ◽  
Fiber Composite Materials

Tensile process of carbon fiber composite laminate was monitored by acoustic emission technique. And the acoustic emission signals by tensile specimens of different winding angles were analyzed. The results show that carbon fiber released signals of different characteristics in different stages. So, the acoustic emission technique can effectively distinguish the different stages such as delaminating, detaching and fracture. Also, different angles in specimen’s layers of carbon fiber had different mechanical properties and failure mechanisms. Analysis on experimental data showed that acoustic emission testing technique can determine the process of different internal activities in carbon fiber composite laminate. Therefore, it can be used in the integrity evaluation for carbon fiber composite materials.

Kaiser effect performance in anthracite as an indicator of the rock resistance to cryo-thermal treatment

2020 ◽  
pp. 5-12
Author(s):  
V. L. Shkuratnik ◽  
P. V. Nikolenko ◽  
P. S. Anufrenkova
Keyword(s):  
Acoustic Emission ◽  
Thermal Treatment ◽  
Experimental Studies ◽  
Thermal Action ◽  
Kaiser Effect ◽  
Stress Memory ◽  
Freeze Thaw ◽  
Before And After ◽  
Emission Activity ◽  
Number Of Treatment

The article presents the experimental studies into the stress memory in acoustic emission (Kaiser effect) in anthracite samples subjected to different number of freeze-thaw cycles. All in all, 6 groups of relatively uniform samples were tested; one group (0) was a reference set unexposed to cryo-thermal effects; the number of a group conformed with the number of treatment cycles. After the cryo-thermal action, all samples were subjected by two cycles of mechanical loading up to maximum stresses of 10 and 14 MPa, respectively. During a loading cycle, acoustic emission activity of a sample was measured, and the Kaiser effect in the second cycle of loading was assessed by two characteristics. These characteristics were the factor of retention FR of the stress memory, or the ratio of the stress of emission initiation in the second cycle to the maximal stress of the first cycle, and the index Δ, or the ratio of the averaged acoustic emission activities before and after the moment of the Kaiser effect. The values of FR and Δ are obtained and analyzed as functions of the number of anthracite freeze-thaw cycles. The value of FR drops but Δ grows with increasing cryogenic disintegration of coal. The maximal change in FR and Δ, and, accordingly, the highest dynamics of damage in anthracite takes place in the first cycles of cryo-thermal treatment.

Estimation of Rock In-Situ Stress by Acoustic and Electromagnetic Emission

2006 ◽  
Vol 13-14 ◽  
pp. 357-362 ◽  
Author(s):  
Yasuhiko Mori ◽  
P. Sedlak ◽  
Josef Sikula
Keyword(s):  
Acoustic Emission ◽  
Simultaneous Measurement ◽  
Rock Sample ◽  
Electromagnetic Emission ◽  
In Situ Stress ◽  
New Method ◽  
Acoustic Emission Activity ◽  
Kaiser Effect ◽  
Emission Activity

The Kaiser Effect in acoustic emission is often used for an estimation of the stress to which rocks have been subjected. However, there are cases in which the Kaiser Effect is not clear, since the noises due to the contact and/or the stick slip between the pre-induced fracture surfaces are measured during the reloading process. In such cases, estimation of previous stress is difficult by the conventional method which is based on the acoustic emission activity observed under reloading process. In the tests for the Kaiser Effect on rocks, therefore, the noises must be eliminated from the acoustic emission generated from newly created cracks during the second loading process. Such techniques as analysis of the difference between the acoustic emission activity observed in the first and second reloading and the analysis of the change in the slope of the acoustic emission amplitude distribution have been proposed. In this paper we present a new method by which the maximum previous stress in rocks can be directly estimated without any post signal analysis. In the new method, simultaneous measurement of acoustic and electromagnetic emission during loading test of rock sample is employed. The electromagnetic emission in the deformation of rock sample generates only when the fresh surfaces due to cracking are created in the material, and the source of electromagnetic emission is the electrification between the fresh crack surfaces. This paper describes the simultaneous measurement of acoustic and electromagnetic emission useful for estimating the rock in-situ stress.

DESIGN OF THE VIRTUAL DEVICE FOR THE SIGNAL SPECTRUM CALCULATION IN THE LABVIEW ENVIRONMENT

2019 ◽  
Author(s):  
Tossenko O.M.
Keyword(s):  
Virtual Instrument ◽  
Spectral Characteristics ◽  
Spectral Composition ◽  
Automated System ◽  
Signal Spectrum ◽  
Measuring Instruments ◽  
Specific Information ◽  
Measuring Device ◽  
Virtual Device ◽  
Graphical Tool

The development of measuring instruments requires a specialist to know the principles of operation of advanced measuring systems. This article describes guidelines for creating a virtual appliance in LabVIEW. LabVIEW (Laboratory Virtual Instrument Engineering Workbench) is a graphical application programming environment used as a standard tool for measuring, analyzing their data, further ma­ naging devices and objects under study. LabVIEW language is not like other programming languages. It does not create a program, but a virtual tool, designed not only for the simulation of certain processes, but also for the management of hardware and the study of real physical objects. The article deals with the task of designing application software for a specific information-measuring device, analyzes the capabilities of the LabVIEW environment for spectral analysis of various signals, outlines the basic principles and techniques of programming within the framework of the LabVIEW graphical environment during the basic stages of development. The procedure for creating a virtual device is described, which allows to evaluate the spectral composition of the signals, presents a graphical code of execution (diagram) to the program and a graphical tool interface of the virtual device. A number of basic elements used to develop the program are described. The simplicity of the graphic designs, the ease of installation on the field of the program, the clarity and readability of the program — all of which makes LabVIEW preferred over other languages of programming. In most cases, the experiment is the only source of reliable information. And the result is achieved much faster than the methods of "pure" theory. The article substantiates the effectiveness of using a development tool that allows to obtain a software product and ensure the fulfillment of all the basic functions of an automated system. Developing a software algorithm for calculating statistical parameters will help engineering students understand the order of determining spectral characteristics and their place in the structure of experimental research.

Changes in the Total Power of Beta and Theta Bands When Using EEG Biofeedback in Primary School-Age Children Having Difficulties with Voluntary Regulation

2020 ◽  
pp. 331-340
Author(s):  
Yuliya S. Dzhos ◽  
◽  
Irina A. Men’shikova ◽  
Keyword(s):  
Left Hemisphere ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
School Age Children ◽  
Total Power ◽  
Eeg Biofeedback ◽  
Beta Band ◽  
Bioelectric Activity ◽  
Voluntary Regulation ◽  
The Brain

This article presents the results of the study on spectral electroencephalogram (EEG) characteristics in 7–10-year-old children (8 girls and 22 boys) having difficulties with voluntary regulation of activity after 10 and 20 neurofeedback sessions using beta-activating training. Brain bioelectric activity was recorded in 16 standard leads using the Neuron-Spectrum-4/VPM complex. The dynamics was assessed by EEG beta and theta bands during neurofeedback. An increase in the total power of beta band oscillations was established both after 10 and after 20 sessions of EEG biofeedback in the frontal (p ≤ 0.001), left parietal (p ≤ 0.036), and temporal (p ≤ 0.003) areas of the brain. A decrease in the spectral characteristics of theta band oscillations was detected: after 10 neurofeedback sessions in the frontal (p ≤ 0.008) and temporal (p ≤ 0.006) areas of both hemispheres, as well as in the parietal area of the left hemisphere (p ≤ 0.005); after 20 sessions, in the central (p ≤ 0.004), frontal (p ≤ 0.001) and temporal (p ≤ 0.001) areas of both hemispheres, as well as in the occipital (p ≤ 0.047) and parietal (p ≤ 0.001) areas of the left hemisphere. The study into the dynamics of bioelectric activity during biofeedback using EEG parameters in 7–10-year-old children with impaired voluntary regulation of higher mental functions allowed us to prove the advisability of 20 sessions, as the increase in high-frequency activity and decrease in low-frequency activity do not stop with the 10th session. Changes in these parameters after 10 EEG biofeedback sessions are expressed mainly in the frontotemporal areas of both hemispheres, while after a course of 20 sessions, in both the frontotemporal and central parietal areas of the brain.

scholarly journals Acoustic Emission and K-S Metric Entropy as Methods for Determining Mechanical Properties of Composite Materials

Sensors ◽  
2020 ◽  
Vol 21 (1) ◽  
pp. 145
Author(s):  
Lesław Kyzioł ◽  
Katarzyna Panasiuk ◽  
Grzegorz Hajdukiewicz ◽  
Krzysztof Dudzik
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Composite Material ◽  
Composite Materials ◽  
Testing Machine ◽  
Measurement Data ◽  
Entropy Method ◽  
Displacement Sensor ◽  
Metric Entropy ◽  
Plastic Phase

Due to the unique properties of polymer composites, these materials are used in many industries, including shipbuilding (hulls of boats, yachts, motorboats, cutters, ship and cooling doors, pontoons and floats, torpedo tubes and missiles, protective shields, antenna masts, radar shields, and antennas, etc.). Modern measurement methods and tools allow to determine the properties of the composite material, already during its design. The article presents the use of the method of acoustic emission and Kolmogorov-Sinai (K-S) metric entropy to determine the mechanical properties of composites. The tested materials were polyester-glass laminate without additives and with a 10% content of polyester-glass waste. The changes taking place in the composite material during loading were visualized using a piezoelectric sensor used in the acoustic emission method. Thanks to the analysis of the RMS parameter (root mean square of the acoustic emission signal), it is possible to determine the range of stresses at which significant changes occur in the material in terms of its use as a construction material. In the K-S entropy method, an important measuring tool is the extensometer, namely the displacement sensor built into it. The results obtained during the static tensile test with the use of an extensometer allow them to be used to calculate the K-S metric entropy. Many materials, including composite materials, do not have a yield point. In principle, there are no methods for determining the transition of a material from elastic to plastic phase. The authors showed that, with the use of a modern testing machine and very high-quality instrumentation to record measurement data using the Kolmogorov-Sinai (K-S) metric entropy method and the acoustic emission (AE) method, it is possible to determine the material transition from elastic to plastic phase. Determining the yield strength of composite materials is extremely important information when designing a structure.

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

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