Acoustic Emission Signal Amplitude Research Articles

Experimental study of acoustic emission multi-parameter information characterizing rock crack development

Monitoring the acoustic emission (AE) signals released during rock fracture process can reflect the crack development and damage in the rock in real time. As that there are few rock damage indicators at present, it is unsuited to in-situ monitoring and early warning. Based on small-scale AE uniaxial compression experiments in the laboratory, through adopted phased AE source location and wave velocity tomography, it was found that the process of crack development and stress evolution in the rock would show discrete stages, and the regional damage and excessive local stress difference in the rock would accelerate failure of the rock. The phasic variation of the AE multi-parameter indicators introduced from the field of seismology can better characterise the four internal stages of the rock crack development (crack compaction—crack elastic deformation—crack expansion—crack propagation”), which is coupled with the internal crack distribution and degree of damage. The acoustic emission activity (AEA) and the acoustic emission fault total area (AEFTA) are positively correlated with AE signal amplitude, number of AE events and release AE energy of micro-fracture, while the AE b value is negatively correlated therewith. Based on this, the AE multi-parameter damage evaluation indicators which are suitable for actual engineering guidance of excavation and support operations can be established. In practical application, a large amount of data gathered on site is needed to correct the precursors of failure, so as to make the AE monitoring and warning more accurate.

Вплив температури процесу різання на амплітуду сигналів акустичної емісії

Вплив температури процесу різання на амплітуду сигналів акустичної емісії

Acoustic-Emission Procedure for Rejecting Defects in Multiple-Pass Girth Welds

A procedure is proposed for rejecting girth welds based on an analysis of the main parameters of acoustic emission (AE) signals recorded during multiple-pass welding. The accuracy of locating AE signals recorded from defects and their filtering from noise and interference were ensured by the use of a modified tabular method and rejection grid. Normalized coefficients were calculated from the energy and amplitude of localized AE signals and used for in-process assessment of weld quality. Threshold values were determined for the normalized coefficients above which the weld is rejected. Defects in girth welds were identified using this procedure, and the possibility of determining defect hazardousness in real time was demonstrated.

Flexural damage behavior of carbon fiber three-dimensional braided composites using acoustic emission and micro-CT

Some factors such as braiding architectures and braiding angles may cause differences in the damage mechanism of three dimensional braided composites. To address this issue, the damage evolution and deformation process of three dimensional (3D) four-directional (4D) and three dimensional (3D) five-directional (5D) braided composites are detected by digital image correlation (DIC) methods and acoustic emission (AE) technology under three-point bend loading conditions, respectively. Furthermore, the internal damage characteristics of the fractured composite specimens are observed by micro-computed tomography (mirco-CT). The microscopic damage morphology observed by micro-CT has a good correlation with the distribution characteristics of displacement and strain fields, while peak amplitude and peak frequency distributions of AE signals can explain the whole process of damage evolution of the composites. The AE characteristics, microscopic damage morphology and damage-related out-of-plane deformation of 3D4D and 3D5D braided composite specimens with different braiding angles are compared with each other and cross validated. The results show that 3D5D braided composites is strengthened by adding axial yarns in the braiding direction, so it has higher delamination resistance. In addition to this, due to the degree of orientation of the fibers of the specimen with small braided angle is high, the process of damage is shorter and the deformation is smaller.

Wear-resistant electrophoretic deposition (EPD) layer of titanium carbide

A wear-resistant EPD layer of TiCsub (i.e. sub micrometer titanium carbide) was synthesized by pressureless infiltration sintering. EPD is an ideal technique to form a porous layer that could be thickness modulated by easily change of applied voltage/current. Full melt spreading of NiCrBSiFe on TiCsub EPD layer and suppression of TiCsub grain growth can be achieved by substituting TiCsub with core-shell structure of NiP electroless plated on TiCsub. In an infiltrated layer, lowering of TiCsub pushing by solidification front hence homogeneous distribution of TiCsub along with eliminating porous TiCsub solid skeletons are essential factors to improve the wear properties. Wear measurement results showed decrement in friction coefficient of NiCrBSiFe (0.29–0.17), amplitude of acoustic emission signals and wear coefficient (variation between 10−5 and10−6) by embedding TiCsub into the NiCrBSiFe layer. It is postulated that melt infiltration of an EPD layer is a practical way to clad wear-resisting layers on the surface.

Research on AE and EMR response law of the driving face passing through the fault

In this paper, the response characteristics of acoustic emission (AE) and electromagnetic radiation (EMR) to the driving face crossing a fault are analysed and tested. The method of real-time monitoring of the fault in front of the driving face by AE and EMR form coal is put forward. The results are as follows: (1) When passing through the fault, the large increase of stress in mining and fault superimposed stress, which makes it more likely to accumulate and release energy in the coal seam, is the main reason for the high risk of coal and gas outburst. (2) During crossing the fault, AE and EMR signals vary in stages, both the intensity and amplitude of the main frequency points of AE and EMR increase first and then decrease. (3) When the driving face is close to the fault, the main frequency of AE and EMR signals decreases and the frequency band concentrates. The main frequency ranges of AE and EMR signals are 3.66–22.5 kHz and 0.3–17.3 kHz, respectively. (4) The amplitudes of the main frequency points of the AE and EMR signals to the fault response. The change of the main frequency amplitude of AE and EMR signals can be used as the response index of the fault, and the response range is about 10 m. The research provides an effective monitoring method for structures in coal seam, which is of great significance to the safety production and rapid excavation of coal mines.

Applying Impact Loading for Revealing Cracks in Glass by Acoustic Emission Method

Results of studying regularities in the development of cracks in glass under impact loading using the method of acoustic emission (AE) and tensometry are presented. An experimental setup has been developed that provides a single dynamic action with further damping of elastic vibrations in a test object. It has been established that the relaxation of elastic stresses occurring near the crack after the impact is described by a logarithmic dependence. The parameters of the amplitude and time distributions of AE signals have been determined. A technique is proposed for dividing the total flow of AE signals into stationary groups with an exponential distribution of time intervals between the signals.

Modeling of acoustic emission based on the experimental and theoretical methods and its application in face grinding

Acoustic emission (AE) is widely used in the application of grinding monitoring, but few studies have been conducted on the quantitative relationship between the amplitude of AE signal and grinding parameters. In order to obtain the quantitative description and solve the problem of threshold recommendation in using AE signal to monitor grinding process, this paper proposes an amplitude model of AE signal of face grinding based on experimental and theoretical researches. The exponential relationship between grinding force and amplitude of AE signal under a certain condition of the fixed grinding wheel speed is achieved by experimental study. By establishing the theoretical model of the grinding force and cutting depth, the mathematical model between the amplitude of AE signal and the grinding parameters of face grinding is obtained indirectly. The experimental results prove the validity of the amplitude model of AE signal and its effectiveness in the automatic recommendation of the threshold for collision detection in face grinding.

SOME ASPECTS OF ACOUSTIC EMISSION AT MACHINING COMPOSITE MATERIALS

The processing of outcomes acoustic emission signals simulation is conducted at ascending composite machining speed and cutting depth, change of treated composite physical-mechanical characteristics with definition the ratio of acoustic emission signal amplitude average level to acoustic emission signal amplitude average level standard deviation. Are determined the regularity of dimensionless coefficient change, which characterizes the ratio of acoustic emission signal amplitude average level to its standard deviation at change of the influential factors. The processing of experimental acoustic emission signals is conducted at composite machining speed ascending and ascending cutting depth with definition the regularity of dimensionless coefficient change, which characterizes the ratio of acoustic emission signal amplitude average level to its standard. It is shown that the theoretical and experimental regularity of investigated coefficient value change at ascending machining speed and cutting depths will be agreed one another.

An Experimental Investigation on the Relationship between MS Frequency Response and Coal and Gas Outburst

Microseismic (MS) frequency response is an important part of high‐efficiency data mining to achieve the aim of coal and gas outburst (CGOB) early warning. Based on the variation pattern of acoustic emission (AE) signal in the coal failure process, the experimental characteristics of MS activity and typical signals CGOB were obtained in this study. First, the AE behavior of coal failure experiment was studied, and an explanation of laws was provided as follows: the fracture behavior of coal sample exhibits certain characteristics of AE response in terms of AE event count, signal amplitude, and frequency; each stage has its own physical meaning during the process of loading test. Based on these laws, CGOB experiments were carried out using a large CGOB physical simulation system with a MS monitoring system. Notching filter and wavelet packet transform technique were used in the denoising and feature extraction of six typical MS events (signals). The features of each stage, including the time‐frequency domain, were extracted and quantitatively expressed. We finally arrive at the following conclusions: (1) CGOB exhibits significantly periodic characteristics, and each CGOB stage corresponds to the significant response characteristics of MS. CGOB presents varying characteristics, such as “valley‐peaks‐valley”. (2) From the incubation stage to happen stage of outburst, the spectrum significantly moved from extremely low frequency (100‐200 Hz) to high‐frequency band (approach to 1600 Hz). During the residual stage, MS frequency manifested the concentration distribution (50 Hz) and offered the advantage of energy concentration. (3) The phenomenon of signal energy also shows the trend of energy transform low to high and to low modes along with the process. Signals total energy distribution (42.81%, 1,437.5‐1,812.5 Hz) in the happen stage are markedly larger than those of events in incubation stage (7.01%) and residual stage (1.44%). The methodology presented in this paper for CGOB signal analysis provides a new method to obtain MS response precursor and predict CGOB disaster. This approach can be useful for rockburst anticipation and control during mining in gas and highly stressed coal mines.

Experimental acoustic emission signals at composite material machining

The results of acoustic emission signals experimental researches at composite material machiningare reviewed. It is shown, that the registered acoustic emission signal is a continuous signal withthe hardly bluffly form. The statistical acoustic emission amplitude parameters at increase of compositematerial machining speed are determined. It is shown, that the ascending of machining speed results inascending all acoustic emission amplitude parameters. However greatest ascending there is a dispersionof registered acoustic emission signal amplitude average level. The results of acoustic emission analyticalinvestigations at composite material machining for a prevailing mechanical destruction its surface layerare reviewed. It is shown, that the simulation results have a good coordination with the results of experimentalresearches

Vibration and acoustic emission monitoring the stability of peakless tool turning: Experiment and modeling

Acoustic emission (AE) study of steady and chatter mode peakless tool turning has been carried out in order to reveal an acoustic emission response to the workpiece chatter during fine turning. Molecular dynamics simulation of acoustic emission response to chatter was used to find out fundamental system characteristics. Experimental dependencies of AE signal amplitude, median frequency and power spectrum have been obtained and compared to those obtained from the molecular dynamics (MD) simulation. Both experimental and MD simulated AE signal spectral characteristics proved to be sensitive to chatter mode vibrations. Median frequency showed a drop in chatter mode cutting as well as power spectrum shifted to the low frequency range. Such a relationship has been attributed to the growing level of the system potential energy.

Scratching of SiC ceramics at two dimensional pre-stressing

A stress field model was built to study the effects of pre-stressing value, normal and tangential load on the three principal stresses and maximum shear stress when the silicon carbide (SiC) ceramics were scratched under two dimensional pre-stressing, and the scratching tests of SiC ceramic were conducted by using a Rockwell diamond indenter at different pre-stress values and normal loads. Scratching induced damage was assessed and characterised via destructive inspection techniques and progressive lapping techniques combined with the digital microscope. Acoustic emission (AE) technology was also used for the online monitoring of the damage. The results showed that, for a given scratching load, the amplitude of AE signals was reduced as the pre-stress values increasing, and surface/subsurface damage of SiC ceramics induced by two dimensional pre-stress scratching was less than that by conventional scratching. So one can believe that the two dimensional pre-stress method can contribute to decreasing the machining damage of brittle materials.

Piezoelectric-film-based acoustic emission sensor array with thermoactuator for monitoring knee joint conditions

This paper presents a novel piezoelectric lead zirconium titanate (PZT) thin film acoustic emission (AE) sensor array equipped with thermoresponsive polymer actuators that enhance its sensitivity for monitoring knee joint conditions. A hydrothermal PZT film was grown on a micromachined titanium-film four-beam array for use as an acoustic sensing material. The thickness of the grown film was 10μm and its grain size was less than 1μm. Moreover, it had a perovskite structure and demonstrated strong piezoelectric properties. A thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPA) was formed on the beam array to electrically control the pressure on the sensing beam array and the underlying micropins. Such control was required for achieving an excellent couple for detecting a target, thereby increasing the sensitivity to AE signals. The fabricated PNIPA actuator was observed to generate more than 0.5% strain under a load six times its weight. Furthermore, the array configuration rendered the AE source detection more accurate compared with a regular single-detection-head sensor. The developed AE sensor was used for noninvasively examining the knee joint condition of a porcine leg when executing continuous back-and-forth motion. The result indicated that a joint under moderate extensive motion yielded higher AE signal amplitude and a wider bandwidth at major dominant frequencies compared with the joint before its extensive motion. An over-exercised joint with obvious cartilage degeneration yielded considerably high AE amplitude and a change in the pattern of dominant frequency peaks.

Acoustic emission partial discharge detection technique applied to fault diagnosis: Case studies of generator transformers

In power transformers, locating the partial discharge (PD) source is as important as identifying it. Acoustic Emission (AE) sensing offers a good solution for both PD detection and PD source location identification. In this paper the principle of the AE technique, along with in-situ findings of the online acoustic emission signals captured from partial discharges on a number of Generator Transformers (GT), is discussed. Of the two cases discussed, the first deals with Acoustic Emission Partial Discharge (AEPD) tests on two identical transformers, and the second deals with the AEPD measurement of a transformer carried out on different occasions (years). These transformers are from a hydropower station and a thermal power station in India. Tests conducted in identical transformers give the provision for comparing AE signal amplitudes from the two transformers. These case studies also help in comprehending the efficacy of integrating Dissolved Gas is (DGA) data with AEPD test results in detecting and locating the PD source.

Detection of the deterministic component in acoustic emission signals from mechanically loaded rock samples

Using the Takens theorem, the attractor was reconstructed for amplitudes of acoustic emission signals measured during fracture of granite samples. Systematic features of the temporal behavior of system dynamic characteristics, such as the embedding dimension, fractal dimensions, recurrence plots, and their numerical parameters, were determined. For a preliminarily water-saturated sample, an order–disorder phase transition was detected in the structure of acoustic emission signals.

Acoustic emission study on the activity of slip and twin mechanisms during compression testing of magnesium single crystals

Magnesium single crystals with various crystallographic orientations were uniaxially and channel-die compressed at room temperature (RT) and at a constant strain rate of 10−3s−1 in order to obtain a comprehensive set of acoustic emission (AE) data, which can be applied in studies of twinning and dislocation processes in polycrystalline Mg alloys. Loading along the <11.2> axis led to a preferable activation of basal slip and it was accompanied by a low amplitude AE signal. Twinning was observed exclusively during compression along the <10.0> and <11.0> axis. The twin nucleation was associated with burst AE signals with high amplitudes.

Detection of Damaged Tool in Injection Molding Process with Acoustic Emission

ABSTRACTThe measurement of acoustic emission (AE) signals during injection molding of polypropylene with new and damaged mold is presented. The damaged injection mold was fitted with a steel insert with cracks induced by laser surface heat treatment. Two resonant piezoelectric AE sensors were attached to the mold via AE waveguides. To improve the mold integrity prediction with smaller defects, AE signal frequency characteristics and a measure of AE signal amplitude probability distribution are implemented. A 5-dimensional feature vector with real-valued explanatory variables is proposed, providing the defining points in an appropriate multidimensional space to characterize the state of injection molding tool. Feature vectors are classified with neural network pattern recognition. The results confirm that presented AE technique offers characterizing the integrity of molds also with resonant sensors.

Simulation Experiment on Acoustic Emission of Pipeline Leakage

With the heater pipeline leakage experiment conducted on the experiment table, inner pipeline leakage of heater was studied through the leakage failure detection system. The frequency distribution and the amplitude of acoustic emission signals of leakage versus internal pressure were analyzed. Variations of signals versus leakage aperture and dissemination distance were summarized. According to the mapping relationship between the leaking spot and acoustic emission signals, and between the leakage flow and acoustic emission signals, reasons of leakage failure were concluded. The results would be applied to heater leakage failure detection. And an on-the-spot detection in the power plant was conducted to test the heater under pressure in order to verify the results.

Estimation of Stress Corrosion Cracking Initiation and Propagation in High-Pressure, High-Temperature Water Environment Utilizing Acoustic Emission

The stress corrosion cracking (SCC) of type 304 stainless steel during a creviced bent beam (CBB) test in a high-temperature, highpressure water environment was monitored by an optical fiber acoustic emission (AE) sensor. By examining the number and type of cracks formed by different durations of CBB testing an SCC initiation and propagation behavior model was developed. This model was then used to examine the AE event rate, which was found to agree well with the observed changes in the number and size of the cracks formed. Through analysis of the relationship between crack size and AE, the weaker AE signals were assumed to be produced by the initiation of small cracks, whereas the coalescence of cracks produces moderate and large AE signals. On the basis of these findings, it is concluded that the SCC propagation behavior can be reliably estimated from the event rate and amplitude of AE signals. [doi:10.2320/matertrans.M2014357]