AE Source Location Research Articles

Acoustic emission characteristics and damage evolution of basalt by microwave irradiation

The microwave-assisted rock breaking technology has been proven to be feasible, and has received considerable attention in the field of civil and mining engineering. A copper foil was used to wrap basalt to simulate rock excavation of practical application scenario in this paper. To this end, a multi-mode cavity with an operating frequency of 2.45 GHz was used to conduct microwave irradiation experiments on basalts with different irradiation times and different power. The thermal properties, AE characteristics, and damage evolution process of basalt were studied. The results show that the high heat generated by microwave leads to the development of cracks in the upper part of basalt. The higher the power level, the higher the degree of crack propagation in the sample, the lower the basalt strength, and the more active the AE activity. The fluctuation rule of the b value indicates that the basalt is dominated by small-scale microfractures before failure. High power levels or long irradiation time lead to more microwave-induced cracks participating in the failure process during loading. Compared with unheated basalt, microwave-heating basalt detects the characteristics of the precursor of failure in advance. The AE source location and the nephogram of the maximum principal stress of microwave-treated basalt reflected that the fracture path begins in the upper part of the rock. In addition, the combination of high power level and short irradiation time can achieve the purpose of energy saving.

A computational study of AE signal due to fiber break and fiber matrix debonding in model composite

Acoustic emission monitoring is a useful method to deal with detection and identification of damage in composite materials during mechanical tests. From an experimental point of view, it is not straightforward to establish a quantitative link between the damage sources and AE signals. Modeling and numerical simulations appear as a promising way to reach this objective. In this study, Finite Elements Modeling (FEM) was used to simulate AE signals due to fiber break and fiber/matrix debonding in a model carbon fiber composite. A specimen made of a single carbon fiber and epoxy matrix was used to experimentally validate the simulated fiber break AE signals. The objective was to compare the AE signals from a validated fiber break simulation (Fig. 1a) to the AE signals obtained from fiber/matrix debonding (with several models) and fiber break obtained in several media and to discuss the capability to detect and identify each source (Fig. 1b). The influence of the type of sensor, specimen geometry and AE source location were also studied. The proposed model was extended to identify the main parameters that influence the acoustic emission signatures. These validated results open the way to combine the experimental and the simulated data to generate a library in order to identify real-time damage mechanisms. Fig. 1: (a) Amplitude and roll-off frequency vs. source/sensor distance for experimental signals and numerical signals. (b)Evolution of Partial Power PP1 [0–125 kHz] as a function of amplitude obtained with a nano 30 sensor for several sources. Fiber break and debonding (L = 20 μm or 100 μm). EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

Evaluation of experience from long-term ae monitoring

A working group within the Committee on Acoustic Emission Testing of the German Society for Nondestructive Testing (FA-SEP of DGZfP) has collected published data on the long-term behavior of the AE or the Guided Ultrasonic Wave (GUW) measurement chain (sensor, sensor coupling and mounting, signal transmission, data acquisition and storage). Since only scant data is publicly available, the working group drafted a questionnaire for collecting respective information from the committee members. The returned questionnaires indicate that data acquisition and storage likely pose problems more frequently than other parts of the measurement chain. The only exception noted was for one case of integrity monitoring at elevated temperatures. In this case, sensor sensitivity was observed to decrease compared to the performance at room temperature, requiring the mounting of additional sensors for achieving AE source location with the same resolution. Based on the empirical information, recommendations for long-term monitoring with AE and GUW are discussed. These comprise, e.g., periodic checks of sensors and measurement chain, periodic data back-up, and planning of maintenance and repair.

Research on macroscopic mechanical properties and microscopic evolution characteristic of sandstone in thermal environment

To study macro and micro characteristics of rock and their correlation in high temperature environment, uniaxial compression experiment is conducted to analyze macroscopic mechanical properties of sandstone samples after different temperature treatment, and AE source location technology is used to study corresponding microscopic evolution characteristics. Then, the correlation between macroscopic mechanical properties and microscopic evolution characteristics is discussed qualitatively, and their quantitative relationship is revealed further. The research results show that the brittleness of the sandstone sample experiences transform process of “first increasing and then decreasing” as treatment temperature increases from room temperature to 1000 °C and turning point is 400 °C, according to the change trend in peak stress, peak strain and fracture characteristics. Based on the variations of fractal dimension and microfracture type of AE events, it is evident that the microcrack system of the sandstone sample experiences the change process of “first simple and then complex” with an increase of treatment temperature. The reason for these variations is that treatment temperature can change microcrack system through the game process of thermal healing effect and thermal fracture effect, resulting in the difference of macroscopic mechanical properties. As treatment temperature increases from room temperature to 400 °C, thermal healing effect is always stronger than thermal fracture effect and the difference enlarges continuously. The microcrack system shrinks gradually, and the sandstone sample presents less properties of the microcrack system and its brittleness increase. As treatment temperature is above 400 °C, a continued increase in treatment temperature makes the difference between the two effects start to decreases until thermal fracture effect exceeds thermal healing effect, then their difference enlarges again. The microcrack system develops gradually, and the sandstone sample presents more properties of the microcrack system and its brittleness decrease. Further, according to data fitting analysis, it can be considered that thermal healing effect presents a linear correlation with treatment temperature during the game process and thermal fracture effect shows an nonlinear correlation with treatment temperature. The difference in the increase rate of these two effects results in nonlinear relationship between the microcrack system and treatment temperature. Then, the linear relationship between the microcrack system and macroscopic mechanical properties is reveal and quantitative relationship model between macroscopic mechanical properties and treatment temperature is established, which has good agreement with the experimental data. This research is helpful to know the correlation of macro and micro variations of the sandstone sample in high temperature environment. It possesses important guiding significance and reference value for ensuring stability of the surrounding rock in deep underground engineering.

A time-field search method for AE source location with a regional velocity model

A time-field search method was proposed for AE event source location, combining the grid search method and the database technique. Theoretical process was given, and laboratory hydraulic fracture stimulation experiments under true-triaxial confining stresses were performed to prove the practicability of the method. A regional velocity model with variable wave velocities and directionality was required to fit observations. The location results showed that time-field location method obtains the global optimal source location solution with a relatively high efficiency and accuracy.

Performance Investigation of Two AE Source Location Techniques on a Planar Multilayer Structure

The comparisons of an AE source location performance of two widely used methods, time of arrival (TOA) and difference of arrival time (DOAT) have been analyzed in a complex planar multilayered surface. The complex surface has been prepared by covering a steel plate (SM400A) with a multilayered rubber material (Natural Rubber). The purpose of using this structure has been defined to get the comparable AE source location performance in a complicated signal propagation pathway. Both source location techniques have been conducted in a simulated AE wave propagating plane (300 mm * 200 mm in size) under Hsu-Nielsen method. Investigations reveal that the TOA technique gives several erroneous results along with good results. However, the DOAT method has produced all excellent results, even when using a complex surface. It was found since the TOA method is sensitive to constant velocity continuity, the present complex pathway leads to the velocity discontinuity, and thus, several incorrect results have been found. On the other hand, the DOAT method is dependent on the arrival time difference only, and therefore, it shows a higher performance in the source location, even in the presence of a complex structure.

Detection of cracking and damage mechanisms in brittle granites by moment tensor analysis of acoustic emission signals

An acoustic emission (AE) testing of rock cracking was performed under uniaxial loading conditions by precut varisized circular holes in selected brittle granites. Based on AE-source location technique and AE-theory for moment tensor analysis, rules of the temporal–spatial evolution of micro-cracks in different failure mechanisms were explored and types of micro-cracks were analyzed as well. The results revealed that the micro-cracks are uniquely easy to generate in the positions where stress are concentrated. Tensile fractures are easy to form on the roof and floor of a circular hole, while shear fractures are easy to be found on both sides. The locations of initial cracks generated around the holes in the loading process are the direction or vertical direction of maximum principle stress. Macroscopic crack orientation agrees with the direction of maximum principle stress approximately. As the size of circular opening increases and the relative size of pillar decreases, shear cracks are dominant with the percentage more than 45%, tension cracks are fewer, accounted for less than 40% of the total events, and mixed-mode cracks represent a minimum proportion, despite the decrease of percentage of shear cracks. The findings of this work can serve for supporting design of tunnel or roadway to avoid collapse.

AEセンサ間距離による鋼平面上の損傷源位置への影響

AEセンサ間距離による鋼平面上の損傷源位置への影響

シリカ粒子充てんエポキシ樹脂の曲げ試験における微視破壊過程のAE法による評価

Four-point bending tests were carried out for silica-particle-filled epoxy composites. Resin-rich (Type R) and cut (Type C) surfaces were taken as the tensile surfaces in order to investigate the effect of volume fraction of silica particle on microfracture process. AE measurement was performed during the test using the two AE sensors attached to both the ends of the specimen. Rapid increasing point of cumulative AE energy was observed before final fracture in both specimens. AE source location at this point corresponded to the location of final fracture. It was then suggested that the maincrack is formed at this point. The critical stress for maincrack formation and the final fracture strength were defined as σC and σB, respectively. The average value of σC of Type R was higher than of Type C. It was suggested that the maincrack is formed from silica particle. Furthermore, the average value of σB-σC of Type C was higher than of Type R. It was suggested that crack growth resistance increases with increasing volume fraction. Consequently, the critical stress, σC, would be available as the conservative design parameter than the final fracture strength.

104 構造物の欠陥源位置診断についてAE二次元アルゴリズムの挑戦(セッション1 損傷検知・信号処理)

Source location of damage initiation is often considered as the main goal of acoustic emission non-destructive testing. Principally, AE technique has been applying for finding the damage source by getting the time delay information of AE signal propagations. Two dimensional AE source location is considerably applied for determining the defect area in an applied structural material. In the present research a plate type structural steel specimen has been considered for monitoring the challenges of two-dimensional AE source location algorithm based on random pencil lead breaking tests. The classical two-dimensional source location technique has been applied for monitoring the defect-source evaluation artifacts based on acoustic phase velocity measurement technique and sensor to sensor distance ratio technique. In both cases results have been evaluated in depicting the considerable contour values which make the AE source location techniques more challenging in some successful applications.

The use of acoustic emission for bearing condition monitoring

This paper reports research currently in progress at Swansea University in collaboration with SKF Engineering & Research Centre as part of a continuing investigation into high frequency Acoustic Emission. The primary concerns are experimentally producing subsurface cracks, the type of which would occur in a service failure of a ball bearing, within a steel ball and to closely monitor the properties of this AE from crack initiation to the formation of a ball on the ball surface. It is worth noting that there is evidence that the frequency content of the AE changes during this period, although this has yet to be proved consistent or even fully explained. Conclusive evidence could lead to a system which detects such cracks in a bearing operating in real life conditions, advantageous for many reasons including safety, downtime and maintenance and associated costs.The results from two experimental procedures are presented, one of which loads a single ball held stationary in a test rig to induce subsurface cracks, which are in turn detected by a pair of broadband AE sensors and recorded via a Labview based software system. This approach not only allows detailed analysis of the AE waveforms but also approximate AE source location from the time difference between two sensors.The second experimental procedure details an adaptation of a four-ball lubricant tester in an attempt to produce naturally occurring subsurface cracks from rolling contact whilst minimising the AE arising from surface wear. This thought behind this experiment is reinforced with 3D computational modelling of the rotating system.

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.

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.

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.

21113 人工関節用アルミナのAE法による微視損傷検出とハイブリッド保証試験法の開発(バイオエンジニアリング(3),OS3 バイオエンジニアリング)

Microdamages during proof tests were monitored by AE technique, and residual strength of specimens which survived proof tests were investigated. Two AE behaviors, with and without increasing point of AE energy, were observed in proof tests. Specimens without increasing point of AE energy had higher residual strength than specimens with increasing point of AE energy. AE source location during proof tests and residual strength measurement demonstrated that the microcrack formed during proof tests were propagated to final unstable fracture during residual strength tests. Consequently, it was understood that proof test with AE technique which could detect microdamages during proof test insured higher reliability than proof test without AE technique.

2831 ニューラルネットワークを用いた屋外石油タンクの擬似AE源位置標定(S37-2 非破壊評価とモニタリング(2),S37 非破壊評価とモニタリング)

The development of the technique to monitor the acceleration of corrosion in outdoor oil tank is desired to prevent environmental pollution accident. Present study utilized the acoustic emission technique to monitor the corrosion. Artificial AE signals were generated by breaking pencil leads on 73 locations of the bottom of the real tank (300kl) to investigate an accuracy of predicted location. AE source location was carried out using a neural network. Arrival time intervals of each sensor were used for input units of the NN. Two methods, visual observation and threshold technique for normalized AE wave, were examined to detect arrival time. The result suggested that accurate location is possible for both methods.

1833 スラッジを内蔵した屋外石油タンクのニューラルネットワークによる擬似AE源位置標定(G03-5 ニューラルネットワーク・非破壊検査,G03 材料力学)

1833 スラッジを内蔵した屋外石油タンクのニューラルネットワークによる擬似AE源位置標定(G03-5 ニューラルネットワーク・非破壊検査,G03 材料力学)

228 マッハ・ツェンダ干渉計型光ファイバAEセンサの指向性評価とAE源位置標定への適用(OS4-3 新しい測定法,OS4 実験力学手法の新展開3)

228 マッハ・ツェンダ干渉計型光ファイバAEセンサの指向性評価とAE源位置標定への適用(OS4-3 新しい測定法,OS4 実験力学手法の新展開3)