AE Source Research Articles

Feature Selection for Robust Localization of Acoustic Emission Sources in Ship-Hull Structures

In this article, a novel feature selection method based on the Fisher ratio (F-ratio) and k-means clustering algorithm is presented and evaluated for nondestructive monitoring of acoustic mission (AE) sources in ship-hull structures. Avoiding complex and time-consuming implementations, the proposed approach use the advantages of the discrimination measure of the F-ratio and the fast convergence rate of a k-means algorithm in the feature selection problem. An extremely efficient set of only four features per sensor is selected for AE sources localization using a radial basis function (RBF) neural network (NN) giving error-free localization accuracy. In the presence of additive white Gaussian noise, different type of information has been selected from the original set of 90 features. Extensive experiments show that even in the very noisy environment of 0 dB SNR, a small set of four features can be used for robust neural localization of AE sources giving localization rates better than 94%.

Investigation on acoustic emission source of bridge crane

In order to draft an acoustic emission testing standard for bridge cranes, the characteristics of acoustic emission sources were studied by performing AE tests for more than 20 bridge cranes. The attenuation curve and linear locations of the AE signals on the box beam were investigated. The results indicate that the linear location method can be used effectively in AE source location in the box beam structure. AE sources of bridge cranes arise mainly from cracking, plastic deformation, structural friction and the noise of vehicle and trolley. The characteristics of each acoustic emission source are shown respectively in this paper.

S0304-3-2 水中計測用干渉型光ファイバAEセンサの基礎特性評価([S0304-3]光学的手法)

We have discussed the characteristic of interferometer type optical fiber sensors to detect acoustic emission signals in the water. It was demonstrated that the proposed sensor is useful to obtain waveform data corresponding to the longitudinal wave propagated in the water. The influences of the size of the sensing head on the sensitivity was revealed based on the experiments using the simulated AE source. It was found that the sensor can detect the longitudinal wave in the water and the sensitivity depends on the length of the sensing region.

Subsurface AE Source Location with Simplified Velocity Model in Multi-Point Triaxial Measurement

Subsurface AE Source Location with Simplified Velocity Model in Multi-Point Triaxial Measurement

음향방출법을 응용한 복합재 날개 구조물의 정적구조 건전성 평가

복합재 날개 구조물에 대한 구조 건전성 및 손상을 평가하기 위하여 정적 구조강도시험에 음향방출(AE)법이 응용되었다. 시험중 스트레인과 변위측정기법을 통하여 정적구조강도를 확인하였고, 음향방출요소 분석과 위치표정기법을 통하여 구조물의 내부 손상을 평가하고 손상위치를 찾을 수 있었다. 시험은 설계제한하중시험, 2차에 걸친 설계극한 하중시험, 파단시험이 수행되었다. 주요한 AE신호는 front lug근처의 표면에 부착된 센서에 의하여 감지되었다. 특히 1차 설계극한하중시험에서 스트레인 및 변위결과는 내부 손상을 보이지 않았으나 AE신호는 내부 손상이 이미 형성된 현상을 나타내었다. 파단시험에서는 AE활성도가 매우 활발하였고, 스트레인 및 변위의 결과는 심한 손상에 의하여 하중경로가 바뀌는 경향을 나타내었다. 음향방출법을 적용하여 정적 구조시험이 진행되는 동안 내부손상이 발생되는 하중과 위치를 정확하게 평가할 수 있었다. 본 연구로부터 음향방출법은 정적 구조강도시험에 있어 내부 손상을 평가하는데 유용한 기법임이 확인되었다. AE technique was applied to the static structural test of the composite wing structure to evaluate the structural integrity and damage. During the test, strain and displacements measurement technique were used to figure out for static structural strength. AE parameter analysis and source location technique were used to evaluate the internal damage and find out damage source location. Design limit load test, the 1st and 2nd design ultimate load tests and fracture test were performed. Main AE source was detected by an sensor attached on skin near by front lug. Especially, at the 1st design ultimate test, strain and displacements results didn't show internal damage but AE signal presented a phenomenon that the internal damage was formed. At the fracture test, AE activities were very lively, and strain and displacements results showed a tendency that the load path was changed by severe damage. The internal damage initiation load and location were accurately evaluated during the static structural test using AE technique. It is certified from this paper that AE technique is useful technique for evaluation of internal damage at static structural strength test.

Fracture Analysis Based on Quantitative Evaluation of Microcracking in Ceramics Using AE Source Characterization

Quantitative detection of microcracks during fracture process of alumina was carried out by AE source characterization, which enables the quantitative characterization of the size, nucleation velocity and fracture mode, as well as nucleation time and location of individual microcracks. Fracture toughness tests of SENB specimens of two types of alumina with different grain size and purity were carried out in air and water. AE signals emitted from microcrackings were detected by piezoelectric transducers. The combined response function of the specimen and measurement system was experimentally determined using a pencil lead breaking as a simulated source. Then AE source function which describes the nature of microcrack nucleation was determined by the inverse calculation using obtained response function and detected signal. Consequently, it was clarified that the size of microcrack in water was larger than that in air for both alumina and larger microcracks nucleated in water resulted in the degradation of fracture resistance.

21312 セラミックスの微視破壊過程における微視割れのAE原波形解析による定量検出(材料強度と構造設(1),OS.5 材料強度と構造設計)

Quantitative detection of microcracks during fracture process of alumina was carried out by AE source characterization which yields the quantitative characterization of the size, nucleation velocity and fracture mode, as well as nucleation time and location of individual microcracks. The fracture tests of two types were carried out. The 4-point bending test was carried out to understand the maincrack formulation process in the ceramics. The fracture toughness tests of SENB specimens were carried out in the air and the water to understand the maincrack propagation process. Then AE source function which describes the nature of microcrack nucleation was also determined by inverse calculation using detected signal. Consequently, in the maincrack formulation process, intergranular microcracking with the size of about 12 gm became the fracture origin. Furthermore, in the maincrack propagation process, it was clarified that the size of microcrack in the water was larger than that in the air and larger microcracks nucleated in the water resulted in the degradation of fracture resistance.

Using wavelet transform to locate acoustic emission source in composite plate with one sensor

In this paper a new method for locating the AE source with one sensor is presented. When acoustic emission signals propagate in wave-guided, they have multi-mode and dispersion characteristics. The separation of the modes at the sensors could make it possible to extract the exact information about the source that produced the waves. Based on the modal nature of AE, it can be understood that a good location would have two methods to determine the arrival times. One is determined on the same part of the waves (not only the same mode, but also the same frequency) at all sensors. The other is determined on the different modes at one sensor, which makes it possible to reduce the number of sensors needed. First, through modal analysis of the propagation of elastic waves in a thin plate, the dispersion characteristics of the modes are predicted. Second, the wavelet transform theory is briefly outlined and its application in elastic waves is explained. It is shown that by using the peak of the magnitude of the wavelet transform, the arrival times of the different modes can be determined. Additionally, experiments were undertaken using a lead break on the edge of the plate. These demonstrated the feasibility of the one sensor linear location scheme.

1443 AE原波形解析を用いたセラミックスの微視破壊過程の解明(S07-1 セラミックスおよびセラミックス系複合材料I,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Fracture toughness tests of notched bending specimens of alumina ceramics were carried out in air and water. During the test, stable crack propagation was observed, and AE signals emitted from microcracking were detected by piezoelectric transducers. Then AE source function which describes the nature of microcrack nucleation was also determined by inverse calculation using detected signal. Sizes and nucleation velocities of individual microcracks could be determined from the source functions. For tests in air, radius was 7.1-42.6μm, while it was 8.1-43.5μm in water. Cumulative AE event was less in water than in air. Fracture resistance was also lower in water than in air. In addition, The size of coalescing cracks observed on fracture surface by SEM was in good agreement with the result of AE source characterization.

AE Evaluation of Relationship between AE Signals and Fracture Mechanisms for the Weldment of Pressure Vessel Steel

The purpose of this study is to find out the AE characteristics and fracture mechanisms through AE signal analysis for the weldment, PWHT specimen and basemetal of the pressure vessel steel. Charpy sized specimens were taken from the multi-passed weld block. Specimens were given to four point bend and AE tests. Lots of AE signals were emitted from the weldment compared with the basemetal and PWHT specimen. Besides, amplitude for the weldment was the largest, followed by PWHT specimen and basemetal and more AE counts for the weldment were emitted in the process of deformation. Lots of microcracks around the notch for the weldment were formed so that more AE signals were produced. In addition, second phase particle such as MgO for the basemetal acts as AE source. However, in case of weldment, debonding mechanisms between matrix and hard oxides which are formed during welding in air attributed to the emission of AE signals and softened particles for the PWHT specimen cause to produce the low level AE signals.

An Experimental Study of Excavation Damaged Zone in Anisotropic Rock

When a tunnel or an underground structure is excavated in rock mass, rock disturbed or damaged zone (EDZ) is formed around the excavation due to the stress concentration resulting from stress redistribution. Recent studies on the rock EDZ revealed it’s important to structural stability around underground opening. In this study, the fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by AE tests. The results of the experiments showed that tensile failure was the major microscopic failure mechanism of rock in excavation damaged and disturbed zone. The expression of the damage magnitudes in each AE source leads to accurate prediction of macroscopic failure mechanisms. In addition, the orientation of the macroscopic failure plane could be estimated by the orientational distribution of microcracks.

AE Source Location Using Neural Network on AE Evaluation of Floor Conditions in Above-Ground Tank

AE Source Location Using Neural Network on AE Evaluation of Floor Conditions in Above-Ground Tank

20711 人工関節用バイオセラミックスのAE法による微視損傷モニタリングと保証試験(バイオエンジニアリングI,OS.7 バイオエンジニアリング)

AE monitoring was conducted during proof tests of the high-purity alumina ceramics in order to detect microdamages which might degradate the strength of surviving components. The tested material in this study is the bioceramics used in artificial joints for total hip replacement (THR). Surviving specimens showed two types of AE behaviors, with or without increasing point of AE energy. Specimens without increasing point of AE energy showed higher residual strength than specimens with the AE increasing point. In addition, the average strength of specimens without increasing point of AE energy was higher than specimens which survived the conventional proof test. The AE source location during measured residual strength demonstrated that the maincrack formed during proof tests were propagated to final unstable fracture during residual strength tests. Furthermore, time to the maincrack formation was investigated. Consequently, it was understood that the proof test with AE monitoring of microdamage enhances significantly the reliability of bioceramics.

Laboratory measurements of acoustic emissions and wave velocities associated with the formation of fractures in sandstones

Abstract Acoustic emission (AE), ultrasonic velocity and petrophysical property measurements are increasingly being used as tools to investigate mechanical, thermal and hydraulic changes in rock masses around underground excavations and in the exploration of oil and gas. In order to develop these measurements into an effective tool it is necessary to understand how they relate to changes in the fracture and fluid content under controlled laboratory conditions. A polyaxial (true triaxial) test system has been developed to perform high-resolution measurements of AE, ultrasonic velocities and fluid permeability characteristics in a cubic specimen under true-triaxial stress. The polyaxial system also allows the measurement of AEs using an array of small-diameter, high-frequency transducers. The measurements allow the AE source locations and mechanisms to be calculated, thus providing an analysis of the distribution, orientation and type of fracture growth in the specimens. Example results are given from an experiment, showing that AE mechanisms during crack initiation describe a dominant failure mode with a significant tensile component.

510 セラミックスの微視割れ生成に及ぼす水分の影響のAE原波形解析による定量評価(セラミック/セラミック基複合材料2)

510 セラミックスの微視割れ生成に及ぼす水分の影響のAE原波形解析による定量評価(セラミック/セラミック基複合材料2)

Failure Process of Rock Sample Observed by AE Source Locating Technique under Uniaxial Compression

A series of uniaxial-compression tests were conducted on some representative brittle rock specimens, such as granite, marble and dolerite. A multi-channel, high-speed AE signal acquiring and analyzing system was employed to acquire and record the characteristics of AE events and demonstrate the temporal and spatial distribution of these events during the rupture-brewing process. The test result showed that in the primary stage, many low amplitude AE events were developed rapidly and distributed randomly throughout the entire specimens. In the second stage, the number of AE increased much slower than that in the first stage, while the amplitude of most AE events became greater. Contrarily to the primary stage, AE events clustered in the middle area of the specimen and distributed vertically conformed to the orientation of compression. The most distinct characteristic of this stage was a vacant gap formed approximately in the central part of the specimen. In the last stage, the number of AE events increased sharply and their magnitude increased accordingly. The final failure location coincidently inhabited the aforementioned gap. The main conclusion is that most macrocracks are developed from the surrounding microcracks existed earlier and their positions occupy the earlier formed gaps, and the AE activity usually becomes quite acute before the main rupture occurs.

Dependence of the number of acoustic-emission pulses on the mechanical testing load of bearing races in an axle unit

Acoustic-emission tests of flawless bearing races in axle units are performed on a special loading stand. Dependences of the number of AE pulses on the loading force are established for objects with and without flaws. The spatial distribution of AE sources in the flawless bearing races and a change in activity during reloading of the races are studied. Numerical parameters of the local-dynamic rejection criterion are determined on the basis of the analysis of the experimental data on races containing fatigue cracks.

Modern acoustic emission technique and its application in aviation industry

This paper proposes the concept of modern acoustic emission (MAE) technique and describes its application in aviation industry. Modern AE is characterized by the combination of AE parameter and waveform analysis based on the understanding of AE source mechanism, the property of sound wave propagation and the interaction between sound wave and the medium in which the sound wave is propagating. Another feature of MAE is characterized by the application of so-called fully digital AE apparatus with low noise, high speed of data transmission and accurate AE source locating capability. MAE is merely an imagination without the realization of the advanced fully digital AE instrument. The application of MAE in monitoring the conditions of aircraft structures during a fatigue test was taken as an example for showing the important role played by AE. Roles of AE in the evaluation of (environment-related) corrosion damage of aircraft were also presented.

Acoustic Emission Monitoring during Solidification Processes

The paper summarizes the experiences acquired from on-line acoustic emission monitoring (herafter AE) of heavy castings during their manufacturing (solidification and following cooling in the mould). They are usually monitored elastic waves generated above all by stress changes in the solid state. In order to exactly determine plastic-elastic transition state the investigation was focused on raising the sensitivity of detection. The suitable experimental technique is discussed in the first part of this article. The main problem of the measurement by high temperatures was solved by using waveguides. It is very important in this case to select useful signal sources from mechanical and electromagnetical disturbances. Some laboratory experiments were done for studying the signal origin in the first state of solidification. The results from on-line monitoring of two types cast rolls during manufacturing were compared. Each type of casting has its typical AE histogram. For the quality evaluation ( in our case) is significant the time period of approximate 5 days after pouring . The time delayed stress induced cracking generates high level AE signal in this time period and the presence of such signal indicates defective product. The study of high temperature tensile tests, structural phase transformation and solidification processes using AE is very important for analysis of AE sources. The use of the laboratory results for the AE source analysis on real products will be subject to futher research.

Monitoring of Rail-Wheel Interaction Using Acoustic Emission (AE)

This work presents the results of field measurements and laboratory studies carried out with a view to developing ways to monitor rail-wheel interaction using Acoustic Emission. It is known that impact, wear and cracking generate AE and it is therefore expected that axle loads, wheel out-of-roundness, speed and traction will influence the AE generated by an interaction. It is hoped that the extent of the effect might be sufficient to permit a measure of “interaction intensity” that could be used to quantify cumulative damage by wear and contact fatigue. In the field measurements, AE was acquired as a train with 20 moving sources of AE (20 wheels) passed a single sensor position and a laboratory rig has been devised which uses a single wheel whose condition, speed and loading can conveniently be modified. Simulated source tests have indicated that the AE wave characteristics on real rails are similar to those in the laboratory rig. A simplified analytical model, devised for AE waves propagating from a moving source(s), based on a ‘vehicle’ speed and wave damping coefficients, has been compared to measured results. As a wheel rolls towards a sensor and then away from the sensor the measured AE generally rises and falls in a predictable way. The effects of wheel and rail surface features appear to complicate the results by introducing sharp spikes in the signals. The numerical model for AE wave propagation from the moving sources (wheels) shows good agreement with the more slowly changing envelope of the signals.