Acoustic Emission Phenomenon Research Articles

An acoustic emission activity detection method based on short-term waveform features: Application to metallic components under uniaxial tensile test

The Acoustic Emission (AE) phenomenon has been used as a powerful tool with the purpose to either detect, locate or assess damage for a wide range of applications. Derived from its monitoring, one major current challenge on the analysis of the acquired signal is the proper identification and separation of each AE event. Current advanced methods for detecting events are primarily focused on identifying with high accuracy the beginning of the AE wave; however, the detection of the conclusion has been disregarded in the literature. For an automatic continuous detection of events within a data stream, this lack of accuracy for the conclusion of the events generates errors in two critical aspects. In one hand, it deteriorates the accuracy of the measurement of the events duration, truncating the span of the event, which is undesirable in evaluation applications; and in the other hand, it causes false detections. In this work, an accurate and computationally efficient AE activity detector is presented, using a framework inspired by the area of speech processing, and which provides the required indicators to accurately detect the onset and the end of an AE event. This is achieved by means of a threshold approach that instead of directly operates with the transduced voltage signal it does so over the Short-Term Energy and the Short-Term Zero-Crossing Rate measures of the signal. The STE-ZCR method is developed for an application related to the continuous monitoring of a single AE channel derived from the characterization of metallic components by means of a uniaxial tensile test. Additionally, two experimental test-benches are implemented with the aim to quantify the accuracy and the quality of event detection of the presented method. Finally, the obtained results are compared with four different techniques, representing the current state of the art related to AE activity detection.

Relation between the shear stress distribution and the resulting acoustic emission variation in concrete beams

Acoustic emission (AE) technology is extensively acknowledged as a promising structural health monitoring (SHM) approach; meanwhile, AE monitoring has long been criticised for a lack of quantitative results. This work revealed a strong correlation between the shear stress distribution and the resulting AE distribution, enabling accurate and real-time quantification of the shear stress states in concrete beams using only AE measurements. This paper started by introducing the AE phenomenon and the theoretical distribution of the shear stresses on a beam cross section, which revealed that the distributions of the stresses and the resulting emissions inherently correlate to each other. Twelve reinforced concrete beams were then tested, deploying devices including an AE system. The results showed that the AE source intensity distribution strongly correlated with that of the shear stresses in a beam segment when the beam was in both the working stage and the failure phase and that the matching degree of these two distribution curves varied from 79.20% to 94.12%. The correlation revealed in the paper will boost a wide range of significant AE-based scientific research and engineering applications, including SHM and non-destructive testing.

Experimental Research on Acoustic Emission Characteristics and Felicity Effects during Coal Fatigue Failure under Cyclic Loading

In order to study the acoustic emission characteristics and Felicity effect in the process of coal fatigue failure and reveal the internal relationship between the fatigue damage evolution law and the acoustic emission activity, with the help of MTS815.02 electrohydraulic servo rock mechanics test system and PCI‐2 acoustic emission detection and analysis system, a triaxial cycling loading acoustic emission test was carried out on the coal samples. The results show that the higher the upper limit stress is, the more obvious the degree of fatigue damage will be caused by coal samples. At the same time, the more active acoustic emission signal will appear. The coal samples under linear loading are on the initial damage state, and slight fatigue, moderate fatigue, deep fatigue, and ultimate fatigue failure under cyclic loading. The acoustic emission shows the “L‐” type development evolution law in any previous stress level range, while at the last stress level, it shows the obvious “U‐” type development evolution law. The higher the frequency of the cyclic loading is, the higher the rate of initiation and expansion of the microcrack will be, while the more obvious acoustic emission phenomenon will appear. Furthermore, the ringing counting rate is basically the same as that of the energy counting rate. Under triaxial cyclic loading, a shear failure mode that extends along different directions of fracture surface will be presented. The acoustic emission in the range of different stress levels shows a different degree of Felicity effect. In contrast, it is more reasonable to use the principal stress difference as a parameter to study the Felicity effect of coal under cyclic loading.

Mechanistic Characteristics of Double Dominant Frequencies of Acoustic Emission Signals in the Entire Fracture Process of Fine Sandstone

To determine the intrinsic relationship between the acoustic emission (AE) phenomenon and the fracture pattern pertaining to the entire fracture process of rock, the present paper proposed a multi-dimensional spectral analysis of the AE signal released during the entire process. Some uniaxial compression AE tests were carried out on the fine sandstone specimens, and the axial compression stress–strain curves and AE signal released during the entire fracture process were obtained. In order to deal with tens of thousands of AE data efficiently, a subroutine was programmed in MATLAB. All AE waveforms of the tests were denoised by wavelet threshold firstly. The fast Fourier transform (FFT) and wavelet packet transform (WPT) were applied to the denoised waveforms to obtain the dominant frequency, amplitude, fractal, and frequency band energy ratio distribution. The results showed that the AE signal in the entire fracture process of fine sandstone had a double dominant frequency band of the low and high-frequency bands, which can be subdivided into low-frequency low-amplitude, high-frequency low-amplitude, high-frequency high-amplitude, and low-frequency high-amplitude signals, according to the magnitude. The low-frequency amplitude relevant fractal dimension and the high-frequency amplitude relevant fractal dimension each had turning points that corresponded to significant decreases in the middle and end stages of loading, respectively. The frequency band energy was mainly concentrated in the range of 0–187.5 kHz, and the energy ratios of some bands had different turning points, which appeared before the complete failure of the rock. It is suggested that the multi-dimensional spectral analysis may understand the failure mechanism of rock better.

Experimental investigations of monolithic IGBT transistor acoustic emission phenomena

Many recent researches are focused on the diagnostic methods allowing determination of the condition of working semiconductor components (power transistors, diodes etc.). As any solid material under stresses (mechanical, temperature and electrical) the semiconductors are generating elastic waves in the case of changing conductivity state. Based on the results of experimental research, a correlation can be observed between the transition between the on and off states of a single IGBT transistor and the emitted acoustic signal. Acquisition of acoustic emission signals was obtained with use of a wide band acoustic emission sensor. The received signal initially was prepared by AD input card with amplifier and then were recorded by means of a computer software. Acquired data were exported the to a file, which enabled further processing of the measured signals. The aim of the study was to determine the acoustic emission background signal coming from switching IGBT transistor and preparation of frequency response. The results of analysis will be used as a reference point for a further investigation of early-stage faults of semiconductors elements.

Физико-механические, химические и статистические аспекты акустической эмиссии

This paper presents an overview of the proposed interdisciplinary approach to the effect of acoustic emission (AE) with further prospective development of effective methods for restoring the parameters of structural transformations and damage accumulation from the recorded signals of the accompanying AE. The essence of the approach is to use the kinetic concept of strength, Poisson model of the defect formation process, and experimentally discovered physical and mechanical features of the AE phenomenon (including statistical parameters of the random AE process stable due to a number of limit theorems). The results are obtained by exploiting elements of condensed matter physics, theory of elasticity, physics of strength, fracture mechanics, statistical radio-physics, and the theory of streams of random events. The features of AE during physical and chemical processes in liquid media are outlined. The developed methods and algorithms can significantly improve the accuracy and reliability of the assessment of structural transformation processes in materials by utilizing the accompanying AE.

Utilising elastic waves of acoustic emission to assess the condition of spray nozzles in a marine diesel engine

ABSTRACTThis article presents an original method of using elastic waves of acoustic emission (AE) to assess the technical condition of nozzles in marine diesel engines. The developed method makes it possible to detect the early stages of wear by friction of the needle-nozzle pair. The phenomenon of AE and the possibility of its use in evaluating the condition of marine diesel-engine injectors are discussed. Experiments are presented in which the AEs were used to evaluate the condition of both a new injector and an injector where galling of the needle-nozzle pair is developing. The measurements were processed by time–frequency analysis and wavelet transformation.

The effect of liquid nitrogen cooling on coal cracking and mechanical properties

Liquid nitrogen is a type of super-cryogenic fluid, which can cause the reservoir temperature to decrease significantly and thereby induce formation rock damage and cracking when it is injected into the wellbore as fracturing fluid. An experimental set-up was designed to monitor the acoustic emission signals of coal during its contact with cryogenic liquid nitrogen. Ultrasonic and tensile strength tests were then performed to investigate the effect of liquid nitrogen cooling on coal cracking and the changes in mechanical properties thereof. The results showed that acoustic emission phenomena occurred immediately as the coal sample came into contact with liquid nitrogen. This indicated that evident damage and cracking were induced by liquid nitrogen cooling. During liquid nitrogen injection, the ring-down count rate was high, and the cumulative ring-down counts also increased rapidly. Both the ring-down count rate and the cumulative ring-down counts during liquid nitrogen injection were much greater than those in the post-injection period. Liquid nitrogen cooling caused the micro-fissures inside the coal to expand, leading to a decrease in wave velocity and the deterioration in mechanical strength. The wave velocity, which was measured as soon as the sample was removed from the liquid nitrogen (i.e. the wave velocity was recorded in the cooling state), decreased by 14.46% on average. As the cryogenic samples recovered to room temperature, this value increased to 18.69%. In tensile strength tests, the tensile strengths of samples in cooling and cool-treated states were (on average) 17.39 and 31.43% less than those in initial state. These indicated that both during the cooling and heating processes, damage and cracking were generated within these coal samples, resulting in the acoustic emission phenomenon as well as the decrease in wave velocity and tensile strength.

The Mechanical and Fracturing of Rockburst in Tunnel and Its Acoustic Emission Characteristics

The phenomenon of acoustic emission (AE) is associated with rock failure and rock fracturing. In order to investigate the influence of tectonic stress on rockburst in tunnel, a biaxial loading experiment system was used in this study. The excavation operation is undertaken at the center of samples to monitor the tunnel forming process in situ, and the different horizontal stresses can be studied by using the AE monitoring technique. The dynamical fracturing process of the tunnel model was summarized, and the timing parameters of AE signals in rockburst stages were obtained. The curves of AE energy and cumulative AE energy with time show a “step‐like” rising trend before the occurrence of rockburst. The evolution of macro‐ and mesocracks is captured, and the mechanical conditions for a “V‐shaped” rockburst pit are derived. As the horizontal stress increases, the effect of excavation unloading becomes more pronounced, and the damage caused by the rockburst intensifies. In the early stage of rockburst evolution, the fracturing type follows a model of tensile‐shear mix model. A positive relationship between the ratio of shear fracturing type and the horizontal stress can be noted when the rock is about to burst, and the high intensity and the high energy released of from the rock‐fracturing event have become evident. Thus, the results indicate that one should focus on monitoring both sides of the surrounding rock of the tunnel so as to extract the characteristics of the process of tunnel in tunnel. The applications of biaxial loading system and during an excavation operation provide a useful tool to simulate the rock burst in tunnel at an engineering site.

Research on Acoustic Emission and Electromagnetic Emission Characteristics of Rock Fragmentation at Different Loading Rates

The relationships among the generation of acoustic emission, electromagnetic emission, and the fracture stress of rock grain are investigated, which are based on the mechanism of acoustic emission and electromagnetic emission produced in the process of indenting rock. Based on the relationships, the influence of loading rate on the characteristics of acoustic emission and electromagnetic emission of rock fragmentation is further discussed. Experiment on rock braking was carried out with three loading rates of 0.001 mm/s, 0.01 mm/s, and 0.1 mm/s. The results show that the phenomenon of acoustic emission and electromagnetic emission is produced during the process of loading and breaking rock. The wave forms of the two signals and the curve of the cutter indenting load show jumping characteristics. Both curves have good agreement with each other. With the increase of loading rate, the acoustic emission and electromagnetic emission signals are enhanced. Through analysis, it is found that the peak count rate, the energy rate of acoustic emission, the peak intensity, the number of pulses of the electromagnetic emission, and the loading rate have a positive correlation with each other. The experimental results agree with the theoretical analysis. The proposed studies can lead to an in‐depth understanding of the rock fragmentation mechanism and help to prevent rock dynamic disasters.

The experimental comparison of parameters signals of acoustic emission during destructive test on composites based on cement

The paper reports the analysis of acoustic emission signals captured during compressive strength tests of fine-grained cement-based composites of various composition. Acoustic emission monitoring belongs to a non-invasive and passive non-destructive testing technique. It is one of the most sensitive experimental techniques to monitor cracking of materials. While the acoustic emission phenomenon is directly associated with nucleation of cracks in materials based on cement, the measurement of these kinds of materials is readily applied to detect cracking activity. An understanding of microstructure–performance relationships is the key to true understanding of material behaviour.

ОБ ИСПОЛЬЗОВАНИИ АКУСТИКО- ЭМИССИОННЫХ ЭФФЕКТОВ В КОМПОЗИЦИОННЫХ МАТЕРИАЛАХ ДЛЯ ОЦЕНКИ ДИНАМИКИ НАПРЯЖЕННО- ДЕФОРМИРОВАННОГО СОСТОЯНИЯ МАССИВА В ОКРЕСТНОСТЯХ ГОРНОЙ ВЫРАБОТКИ

ОБ ИСПОЛЬЗОВАНИИ АКУСТИКО- ЭМИССИОННЫХ ЭФФЕКТОВ В КОМПОЗИЦИОННЫХ МАТЕРИАЛАХ ДЛЯ ОЦЕНКИ ДИНАМИКИ НАПРЯЖЕННО- ДЕФОРМИРОВАННОГО СОСТОЯНИЯ МАССИВА В ОКРЕСТНОСТЯХ ГОРНОЙ ВЫРАБОТКИ

Rock Stability Assessment Based on the Chronological Order of the Characteristic Acoustic Emission Phenomena

Sudden inelastic deformations in rock are associated with acoustic emission (AE). Therefore, AE monitoring technique can be used to study the fracture processes of rock. In this paper, AE tests were conducted on the granitic gneiss specimens under the uniaxial compressive loading conditions. The temporal changes in AE hit parameters and spatial‐temporal evolution of AE events during the failure process of the granitic gneiss specimens were studied, and several characteristic AE phenomena (i.e., dramatic increase in dominant frequency, AE energy, and hit rate, the AE event with a high energy level, and the through‐going distribution of the AE events with intermediate energy levels) were statistically analyzed before the failure occurred. It was found that the chronological order of the characteristic AE phenomena was relatively certain and correspondingly had a close relationship with the crack development stage. Because of the difference of the stress level at each crack development stage, the stability at different crack development stages is different. Therefore, a rock stability assessment approach was established based on the chronological order of the characteristic AE phenomena, and then the rock stability was assessed using the proposed approach.

A Method for Determination of the Minimal Thickness of the Cutting Layer during Precision Machining Performed with the Indexable Cutting Tools

Under the influence of the pressure caused by the application of the cutting edge on the surface of the workpiece elastic waves are generated. Waves propagate in the material in every possible direction and can be identify by specialized measuring equipment. Acoustic emission phenomenon was used to determine the beginning of decohesion process. The article presents a new method for determination of the decohesion process during peripheral milling performed with the indexable cutting tools on samples made out of titanium based alloy and nickel based alloy.

Experimental facility for the study of acoustic emission registered in the primary circuit components of WWER power units

This paper is dedicated to the creation of a facility for the experimental study of a phenomenon of background acoustic emission (AE), which is detected in the main circulation loop (MCL) of WWER power units. The analysis of the operating principle and the design of a primary feed-and-blow down system (FB) deaerator of NPP as the most likely source of continuous acoustic emission is carried out. The experimental facility for the systematic study of a phenomenon of continuous AE is developed. A physical model of a thermal deaerator is designed and constructed. A thermal monitoring system is introduced. An automatic system providing acoustic signal registration in a low frequency (0.03–30 kHz) and high frequency (30–300 kHz) bands and study of its spectral characteristics is designed. Special software for recording and processing of digitized electrical sensor signals is developed. A separate and independent principle of study of the most probable processes responsible for the generation of acoustic emission signals in the deaerator is applied. Trial series of experiments and prechecks of acoustic signals in different modes of the deaerator model are conducted. Compliance of basic technological parameters with operating range of the real deaerator was provided. It is shown that the acoustic signal time-intensity curve has several typical regions. The pilot research showed an impact of various processes that come about during the operation of the deaerator physical model on the intensity of the AE signal. The experimental results suggest that the main sources of generation of the AE signals are the processes of steam condensation, turbulent flow of gas-vapor medium, and water boiling.

Effect of steel fibres dosage in alkali-activated slag mortar on acoustic emission obtained during three-point bending tests

The acoustic emission phenomenon is directly associated with nucleation of cracks in structural materials during loading. This paper analyses acoustic emission signals captured during three-point bending fracture tests of alkali-activated slag mortar specimens with different amount of steel fibres. Typical parameters of acoustic emission signals were identified for different mixtures to further describe the under-the-stress behaviour and failure development. The acoustic emission signals from crack growth were continuously monitored using acoustic emission sensors mounted on the specimen surface. Acoustic emission results are accompanied by selected mechanical fracture parameters determined via evaluation of load versus displacement diagrams recorded during three-point bending tests.

汶川地震和芦山地震的有助于预报的地震前兆

是否存在“有助于预报的地震前兆”？马瑾院士由岩样加载实验发现岩石加载临近强度极值进入亚失稳阶段，发出应变、位移、温度变化特征信号，之后岩样破裂。大地震前是否能观测到这些信号？观测到了，如何识别应力已达峰值强度？姑咱地震台YRY-4分量钻孔应变仪汶川大震前550天中接收到3700多个异常应变脉冲，震后衰减。2014年底发现，脉冲出现初期，表征脉冲数据自洽性的k值大于0.99；大震前夕k值逐渐减小至0.4，数据失洽。地层连续无裂隙是应变数据满足自洽的条件，失洽是震源区地层连续性破坏越来越严重，大震将发生的标志。汶川大地震前五个月时出现5天中一个脉冲事件也没有的平静期，脉冲事件再度增多后大地震发生。岩石加载声发射现象，加载接近峰值强度出现声发射平静期，继续加载声发射再现后岩样破裂。在数千脉冲事件背景下，出现数据失洽及平静期，这两项特征有助于判断地层加载进入亚失稳阶段及何时达到强度峰值，地震必将发生。2013年芦山7级地震前的440天中，姑咱台又记录到1000多个脉冲事件，震前2个月时又出现5天平静期。在适当位置布设精密应变观测网，有可能观测到，并能识别出“有助预报的地震前兆”。汶川、芦山地震观测中得到的认识，具有普遍性还是特例，还要在实践中接受检验。 Whether there exist “earthquake precursors that facilitate earthquake prediction”? From rock experiments Ma Jin, Academician of CAS P, found that when the specimen is loaded near to its strength limit and enters a meta-instable stage, it emits characteristic signals of strain, displacement, and temperature, and then the rock specimen breaks. Before a large earthquake can we observe such signals? If we can, how do we know the stress has reached the peak strength? In 550 days before the Wenchuan earthquake the YRY 4-component strainmeter in Guzan seismic station received more than 3700 abnormal strain pulses, which were then attenuated after the earthquake. In the end of 2014 when the pulses started to appear, it is found that the k value, which characterized the self-consistency of pulse data, was greater than 0.99; whereas the k value decreased gradually till 0.4 immediately before the earthquake, and the data lost self-consistency. For self-consistency of the strain data the Earth strata should be continuous and without cracks, the loss of self-consistency indicates that the continuity of strata in the earthquake source region is increasingly damaged and a large earthquake may occur soon. About 5 months before the Wenchuan earthquake there was a quiet period without a single pulse in 5 days, then after the impulsive events increased again the great earthquake took place. This is similar to the acoustic emission phenomenon during rock loading; a quiet period appears when the load approaches to the peak strength, with continuing loading acoustic emission reappears then the rock specimen breaks. On a background of thousands of impulsive events, the loss of data self-consistency and the appearance of quiet period are two features that help to judge whether the loading of strata has entered the meta-instable stage and when it reaches to the strength limit, thus leading to the inevitable occurrence of an earthquake. In 440 days before the Lushan M7 earthquake of 2013, the Guzan station recorded again more than 1000 pulses, and a quiet period of 5 days appeared 2 months before the earthquake. By setting up a precise strain monitoring network in proper locations, we may be able to observe and identify “earthquake precursors that are useful for earthquake prediction”. Whether the knowledge acquired from Wenchuan and Lushan earthquake observations is general or specific, it remains to be tested in future practice.

Оптимизация акустико-эмиссионного контроля прочности сварных соединений

Lack of rigor in the justification of approaches to interpretation of acoustic emission (AE) signal recording results generates the need to improve the methodological aspects of acoustic emission (AE) examination methods and to ensure the validity of diagnosing the strength state of technical items, which would make it possible to correlate the AE parameters with the material damageability parameters and reliability indicators. The stated problem is solved by sequentially constructing adequate, logically interconnected and hierarchically subordinated models of the examined item in decreasing order of their informational content with increasing the level of abstraction and determining the model parameters. Based on this approach, the article formulates the main principles of optimizing the AE-based diagnostic technologies in regard of rules for conducting AE tests, recording and processing primary AE information, and constructing models describing the lifetime governing destruction process, AE phenomenon models reflecting the destruction process, and the time dependencies of its parameters. The functional model is focused at predicting the examined item’s lifetime and selecting the crack formation process and time dependences of the AE parameters related to the lifetime as a subject of study. The physical model that follows from the functional model interconnects the selected functional properties and factors via generalized physical properties and laws. The subsequent construction of the mathematical model boils down to a quantitative description of the selected physical laws in the form of very specific mathematical expressions uniting the metrological and strength factors. The article describes the micromechanical model describing the destruction process and time dependencies of the parameters relating to the acoustic emission accompanying the destruction process. This model, which is constructed in accordance with the above-mentioned principles, makes it possible to propose an approach to determining the informative diagnostic parameters robust to the influence of destabilizing factors and bearing information about the strength of the examined item. The article presents some concentration-kinetic AE indicators characterizing the strength state of technical items, which contain formulas for estimating the strength and lifetime parameters.

Effect of high temperature on mechanical and acoustic emission properties of calcareous-aggregate concrete

In order to investigate the effect of high temperature (25–800°C) on mechanical properties of concrete, uniaxial compression test is carried out to study the relationship between compressive strength and temperature, and the crack development in concrete specimen is monitored based on the acoustic emission (AE) phenomenon to reflect the change of internal cracks of concrete specimen under load. The test results show that the compressive strength of concrete is not obvious when the temperature is below 400°C, but decreases with the increase of temperature and to 20% of that at room temperature when the temperature reaches 800°C. The AE activity in the whole loading process and the cumulative counts and AE energy increase sharply to the critical point C until the specimens are completely damaged. The higher the temperature is, the more seriously the specimens are damaged and the less the acoustic emission signal is generated at the dynamic loading stage.

Parameters of Acoustic Emission Signals Obtained During the Setting and Hardening of Concrete Mixtures with Different Water-Cement Ratio

Concrete hardening and setting processes are the most critical phases during construction work, influencing the properties of concrete structure. For this reason applying non-destructive testing in the early age of concrete lifetime can be useful. Acoustic emission method is a powerful tool for determination of lifetime concrete structures. Nevertheless, its application in civil engineering area is not easy because many building structures are inhomogeneous. This method can describe material changes during concrete lifetime. Acoustic Emission Method monitors concrete structure continuously. Changes in the whole concrete structure are recorded. The acoustic emission phenomenon is directly associated with nucleation of cracks in building materials, therefore the changes result from the volumetric expansion causing formation micro and macro cracking in structure, which we can recognize. Application of Acoustic Emission Method during concrete hardening and setting with different water-cement ratio will be the aim of this article and his influence on parameters of acoustic emission. A comprehension of microstructure-performance relationships is the key to true understanding of material behaviour.