Acoustic Emission Source Location Research Articles

Acoustic Emission Source Location Monitoring of Laboratory-Scale Hydraulic Fracturing of Coal Under True Triaxial Stress

Crack monitoring is an important issue in coal and rock hydraulic fracturing (HF). In this study, we conducted experimental coal HF acoustic emission (AE) monitoring tests under true triaxial stress by using a self-developed experiment system. The results showed that the AE signal statistical parameters had a good positive correlation with the water pressure curve. Based on the STA/LTA, improved AIC and simplex algorithm, we developed a new method for AE event automatic identification and source location for coal HF. By using this new method, we were able to detect and locate more accurately the AE events induced by HF. Hydraulic crack propagation and temporal-spatial AE event distribution were located with high accuracy. According to the AE event temporal-spatial distribution of AE events, coal hydraulic crack propagation was not uniform. In the middle and late HF stages, especially when hydraulic cracks approach the coal sample boundary, the hydraulic crack propagation speed was accelerated significantly. The important factors that affected hydraulic crack initiation, propagation, steering, and acceleration included the triaxial stress state, original joints and cracks, and local stress disturbance caused by hydraulic cracks. These results offer a reference for designing optimized, safe and effective HF programs, which are important in preventing coal/rock dynamic disasters and ensuring safe and efficient mining.

AE source location of debonding steel-rod inserted and adhered inside rubber

Rubber bearings have been applied worldwide to bridge and building components. However, it comes out a critical issue, since significant amounts of damage and deterioration of the bearings have been reported. Therefore, the authors attempted an experimental study on damage evaluation of rubber bearings, by using acoustic emission (AE) method. In the case, it was found that the velocity of the elastic-wave propagating inside the rubber was slower than those of concrete, steel, and other rigid materials. As a result, one question remains on the location accuracy, where AE sources are generated inside the rubber.In order to clarify an applicability of AE method to damage evaluation of rubber bearings, experimental research was conducted. A steel rod was inserted in a rubber specimen and the tip of the rod was adhered. Then, debonding of the rod was measured with a pull-out test. Even distances from the tip of the steel rod to the rubber surface were investigated. Two types of AE sensors were used, with resonances at 60 kHz and 150 kHz. A three-dimensional location analysis was performed by AE method to identify debonded locations. Thus, both applicability and accuracy of AE method in the rubber bearings are verified, and a good promise to evaluate the damage in the rubber bearings is confirmed.

Experimental study of crack evolution in prefabricated double-fissure red sandstone based on acoustic emission location

The development of micro-cracks during damage to rocks affects the propagation of macroscopic cracks on the surface. To explore the crack evolution among pre-existing flaws in rocks, based on the acoustic emission (AE) source location results, the paper analysed the influences of micro-crack development on failure mode. By analyzing AE characteristic parameters, the main controlling factors affecting the development of micro-fractures are determined. The results show that: (1) the development of micro-cracks in rock samples presents a trend of having a high-energy fracture point, the low-energy and small fracture region, the extensive fracture region, and a macroscopic fracture zone. (2) The difference in rock failure mode arises from the influence of rock bridge on the number, location, and extension direction of high-energy fractures, which results in the difference in the formation of main damage zone in rock samples. (3) The total number of micro-cracks, the proportion of shear cracks, and mixed-mode cracks gradually increase with the increase of the rock bridge inclination angle, leading to the gradual evolution of rock samples from simple tensile failure mode to complex crack penetration mode. The variation of the rock bridge inclination angle affects the stress direction of the rock particles at a microscopic level, while it affects the direction of macroscopic crack propagation at a macroscopic level.

Reveal of Internal, Early-Load Interfacial Debonding on Cement Textile-Reinforced Sandwich Insulated Panels

Internal interfacial debonding (IID) phenomena on sandwich façade insulated panels are detected and tracked by acoustic emission (AE). The panels are made of a thin and lightweight cementitious composite skin. In the lab, the panels are tested under incremental bending simulating service loads (i.e., wind). Local (up to 150 mm wide) skin-core detachments are reported in the early loading stage (at 5% of ultimate load) and are extensively investigated in this study, since IID can detrimentally affect the long-term durability of the structural element. A sudden rise in the AE hits rate and a shift in the wave features (i.e., absolute energy, amplitude, rise time) trends indicate the debonding onset. AE source localization, validated by digital image correlation (DIC) principal strains and out-of-plane full-field displacement mapping, proves that early debonding occurs instantly and leads to the onset of cracks in the cementitious skin. At higher load levels, cracking is accompanied by local debonding phenomena, as proven by RA value increases and average frequency drops, a result that extends the state-of-the-art in the fracture assessment of concrete structures (Rilem Technical Committee 212-ACD). Point (LVDT) and full-field (AE/DIC) measurements highlight the need for a continuous and full-field monitoring methodology in order to pinpoint the debonded zones, with the DIC technique accurately reporting surface phenomena while AE offers in-volume damage tracking.

A New Algebraic Solution for Acoustic Emission Source Localization without Premeasuring Wave Velocity.

The technique of acoustic emission (AE) source localization is critical for studying material failure mechanism and predicting the position of potential hazards. Most existing positioning methods heavily depend on the premeasured wave velocity and are not suitable for complex engineering practices where the wave velocity changes dynamically. To reduce the influence of measurement error of wave velocity on location accuracy, this paper proposes a new algebraic solution for AE source localization without premeasuring wave velocity. In this method, the nonlinear TDOA equations are established and linearized by introducing two intermediate variables. Then, by minimizing the sum of squared residuals of the linear TDOA equations with respect to the AE source coordinate and two intermediate variables separately, the optimal algebraic solution of the AE source coordinate in the least squares sense is obtained. A pencil-lead breaks experiment is performed to validate the positioning effectiveness of the proposed method. The results show that the new method improves the positioning accuracy by more than 40% compared with two pre-existing methods, and the minimum positioning accuracy of the proposed method can reach 1.12 mm. Moreover, simulation tests are conducted to further verify the location performance of the proposed method under different TDOA errors and the number of sensors.

Acoustic Emission Source Location in Composite-Honeycomb Sandwich Panel

Acoustic emission is a promising technique for damage detection and location in composite structures. It refers to the process of using a sensor array to detect the elastic waves generated by a damage source within a structure. However, it is challenging to propose suitable and reliable damage location strategies when applying this technique on composite-honeycomb sandwich panels due to their complex nature which affects the acoustic wave propagation. Further, composite-honeycomb sandwich panels are susceptible to damage on either one of their surfaces, yet acoustic emission sensors are likely to be bonded to just one of these surface and the ability of acoustic emission to locate events occurring on the opposite surface from which they are bonded has yet to be explored. This paper seeks to shed light on this phenomenon with an investigation into the ability of acoustic emission to locate sources in a glass fibre aluminium honeycomb sandwich panel, for sources originating from both the front and back surfaces. An array of four sensors was bonded to the front surface of a 820 x 820 mm sandwich panel. Artificial emission sources were generated on both front and back surfaces of sandwich panel. Two location techniques were used to locate the sources; difference in time of arrival, and Delta-T Mapping. For sources generated on the front surface, difference in time of arrival technique located all sources with an average error of 20.2 mm, while Delta-T Mapping located all sources with average error 11.1 mm. For the sources generated on the back surface, opposite to the sensors, difference in time of arrival technique located all sources with average error 42.8 mm, while Delta-T Mapping located them with an average error of 20.78 mm. Overall, Delta-T Mapping technique consistently demonstrates its potential and credibility for source location in complex structures when inspecting the sandwich panel in 2D and 3D, as well.

Advanced Acoustic Emission Source Location in Aircraft Structural Testing

Acoustic emission (AE) is an in situ Structural Health Monitoring (SHM) technique, where a structure is monitored for the ultrasonic waves produced due to crack growth. A major challenge with AE when applied to aircraft, and other complex structures, is that wave propagation is significantly affected by stiffeners, holes, thickness changes and other complexity. This reduces the accuracy of traditional source location techniques, that are based on a singular propagating wave speed. The Delta-T method enables higher levels of accuracy by mapping the structure and accounting for these changes. In this work AE monitoring equipment was installed on a section of an aluminium Airbus A320 wing. Location trials showed the Delta-T technique improved the average error from 85mm to 23mm, for artificial Hsu-Nielson sources, compared to the commercial standard technique. Testing under fatigue however demonstrated the challenges encountered when inspecting 3D structures (due to multiple signal paths) with significant levels of background noise. Of two cracks identified in the structure, the first of these was successfully detected and located, whilst the other was missed due to high machine noise and unrepresentative loading.

Acoustic Emission Test of Changlongshan Pumped Storage Power Station Steel Bifurcation Pipe

The maximum test load of Changlongshan pumped storage power station steel bifurcation pipe is 10MPa. To ensure the safety of the water pressure test, acoustic emission is used to monitor the main welds of the crescent rib steel bifurcation and main cone. Taking NO.3 pipe’s data as an example, acoustic emission source location system was used to find the possible position of harmful defects, through the activity and intensity of the acoustic emission sources to confirm the defect significance. After analysis, the acoustic emission integrated level of the steel bifurcation pipe is in level II, the pipe’s data comply with the design requirements.

State-of-the-Art Review on the Acoustic Emission Source Localization Techniques

he acoustic emission technique has been applied successfully for the identification, characterization, and localization of deformations in civil engineering structures. Numerous localization techniques, such as Modal Acoustic Emission, Neural Networks, Beamforming, and Triangulation methods with or without prior knowledge of wave velocity, have been presented. Several authors have conducted in-depth research in the localization of AE sources. However, existing review papers do not focus on the performance evaluation of existing source localization techniques. This paper discusses these techniques based on the number of sensors used and the geometry of the structures of interest. Furthermore, it evaluates them on the basis of their performance. At the end of this paper, a comparative analysis of existing methods has been presented based on their basic principles, key strengths, and limitations. A deep learning circular sensor cluster-based solution has the potential to provide a low-cost reliable localization solution for acoustic emission sources.

An Integrated Approach to Real-Time Acoustic Emission Damage Source Localization in Piled Raft Foundations

Acoustic emission (AE) has garnered significant interest as a promising way to detect the early-stage development of internal cracks and damage in underground and geotechnical structures, associated with natural disasters. Meanwhile, AE source localization techniques that can identify the damage location in a piled-raft foundation (PRF) are premature because of its complex geometry, although the PRF is a widely used deep foundation type for high-rise buildings. In this study, we propose an integrated approach to localize AE sources in the PRF by using the modified Akaike information criterion (AIC) method and examine its accuracy to mark with pile zones. We performed a series of experiments on a scaled PRF model at a ratio of 1:50, composed of one raft and 25 piles. The results demonstrate that the combined approach with the modified AIC method and the Simplex method can localize the AE source zones with good accuracy, greater than 95% on average. The suggested two-stage AIC picker shows accurate onset time determination, and hence, it significantly improves the accuracy, particularly effective for the signals with low signal-to-noise ratios. The approach exploiting the two-stage AIC picker can be readily used for automated real-time AE monitoring to detect crack generation and its location in buried foundations that cannot be inspected visually.

Acoustic emission source location using Lamb wave propagation simulation and artificial neural network for I-shaped steel girder

Acoustic emission (AE) is often used for structural health monitoring (SHM) in the wide field of engineering structures and one of its most beneficial attributes is the ability to localize the damage/crack based on the AE events. The vast majority of ongoing work on AE monitoring focues on geometrically simple structures or a confined area, but the AE source location strategies are rather complicated for real engineering structures. In this paper, an effective method for source localization in realistic structures is presented based on the application of artificial neural networks (ANN), using finite element (FE) simulation results of Lamb waves as the modelling basis. Pencil lead break experiments and related FE simulations on a steel-concrete composite girder are conducted to evaluate the performance of the method. The identification of different wave modes is carried by comparing alternative onset time detection methods. Numerical results are found to be matching closely with the experimental results. To get a reliable ANN model, the validated FE model is used to create a comprehensive database with five different sensor arrangements. It is found that the proposed method is superior to the classical Time of Arrival (TOA) method with the same input data. The results indicate that using trained neural networks based on numerical data is a viable option for AE source location in the case of the I-shaped girder, increasing the likelihood of design and optimization of the AE technique in monitoring realistic structures.

Comparative study on fracture characteristics of coal and rock samples based on acoustic emission technology

Monitoring on the damage evolution process of the coal and rock mass in coal resource mining play a vital role in safe production and avoiding economic losses. This study aims at further improving effectiveness and accuracy of acoustic monitoring method in the process of coal resource mining. For this purpose, a rock mechanics testing system and an acoustic emission (AE) test system are employed to conduct AE event location experiments on the coal and rock samples under uniaxial loading. According to the basic theory of b-value and single-link cluster (SLC) method, changing trend of related parameters with stress is studied, including b-value, spatial correlation length ξ and information entropy H. Then, the reason for variation of these three parameters is revealed. The analysis results show that b-value has not obvious change at the initial stage of loading, but spatial correlation length ξ presents upward trend during this period. Compared with b-value and spatial correlation length ξ, information entropy H is not sensitive to damage state of the coal and rock sample during the most time of loading process. However, it is worth noting that that these three parameters show significant change trend before the buckling failure of the coal and rock samples. Based on three-dimensional crack growth theory and criterion of microcrack density, the research results show that the change of the parameters are the macro characterization of transformation process from small-scale microfracture to large-scale microfracture and from local damage to overall damage for the coal and rock samples subjected to uniaxial loading. This research provides a new method to evaluate the damage state of the coal and rock mass under high stress using AE source location technology, and it has important guiding significance and reference value for ensuring the safety of life and property in the process of coal resource mining.

A Novel Joint Localization Method for Acoustic Emission Source Based on Time Difference of Arrival and Beamforming

Time difference of arrival (TDOA) method and beamforming method are often individually utilized in the localization of acoustic emission source of a plate. Based on the performances of the two methods, a novel joint localization method for acoustic emission source is proposed in this paper. Firstly, the performances of TDOA method and beamforming method are studied based on the simulation signals. Then, aiming at the advantages and disadvantages of these two methods, a joint localization method is proposed. Finally, the performances of joint localization method are verified by simulation and experiment. Both simulation and experimental results show that the accuracy of the joint localization method is improved, and the calculation amount is greatly reduced in comparison to the TDOA method and the beamforming method.

Damage mechanism of ultra-high performance fibre reinforced concrete at different stages of direct tensile test based on acoustic emission analysis

The two strain-hardening stages for ultra-high performance fibre reinforced concrete (UHPFRC) under direct tensile loading are the swift strain-hardening (stage II) and widely held strain-hardening (stage III) stages. A direct tensile test with acoustic emission (AE) registration and air permeability measurement was conducted on three UHPFRC types. StageII displays more superior crack-width control, higher tensile stiffness, and better impermeability compared to stage III. Based on the analysis of three AE parameters, the damage mechanism of UHPFRC at different tensile stages was identified. The AE source location provides strong evidence of multiple randomly distributed micro-defects (<0.01 mm) at stage II. The AE average frequency and energy can distinguish three UHPFRC damage patterns (matrix cracking, fibre–matrix debonding, and fibre pullout) and evaluate their contributions at different tensile stages. Matrix cracking is dominant at stage II. Matrix cracking and fibre–matrix debonding is roughly balanced at stage III. The large-scale fibre–matrix debonding is generated accompanied by marginal fibre pullout at the strain-softening stage. The stress state of steel fibres at UHPFRC crack sections at stagesII and III was also analysed. The configuration of the strain-hardening stage is determined by the relationship between the fibre–matrix bond strength and the tensile stress of the steel fibres at the crack sections.

Research on AE Source Location of Linear and Plane Rock Mass

The occurrence of rockburst dynamic disaster is a process from the microdamage to macroinstability of coal and rock mass, which is accompanied by the acoustic emission (AE) phenomenon. The application of AE technology can reliably help to judge and predict the damage evolution of coal and rock mass, as the most basic problem in the study of AE is the location of the AE source. In this work, the AE source localization experiments of rod-shaped rocks and plate-shaped rocks were carried out. The influence of calibration wave velocity of linear and plane positioning on the location of the AE source was studied. The feasibility analysis of the AE source localization of a plate-shaped rock with different sensor arrays was conducted. The result of the plane location was optimized by wavelet packet analysis combined with cross correlations. The results show that the homogeneity of marble members in this work is suitable, and the positioning error is least affected by wave velocity. In the positioning of the plane AE source, it is suitable to choose a diamond sensor array. The positioning source should be located near the center of the array network. The positioning effect of the rod-shaped rock is generally better than that of the plate-shaped rock. In the actual source positioning work, it should be simplified as much as possible as a linear positioning problem. A more accurate AE signal delay could be obtained using wavelet packet analysis combined with cross-correlation technology, which can greatly reduce the positioning error caused by the accuracy of time difference. The purpose of this work is to provide a basis for determining a more accurate location of the fracture source of rock materials, which is of great significance and application value on the prediction and control of rockburst dynamic disaster.

In-situ fatigue life analysis by modal acoustic emission, direct current potential drop and digital image correlation for steel

Optimizing acoustic emission (AE) is useful to understand fatigue crack growth of metal structures. Experimental investigation of fatigue in steel with an edge notch was performed using AE to understand source and location of crack formation and growth. Non-Destructive Techniques like Direct Current Potential Drop (DCPD) and Digital Image Correlation (DIC) are useful in assisting to interpret the AE. The cumulation of AE correlated well with the initiation and propagation similar to potential drop values and DIC strain field. 2D AE source location technique was successfully implemented to monitor crack growth. Frequency content correlate with the mode of crack growth.

Acoustic emission source localization in composite stiffened plate using triangulation method with signal magnitudes and arrival times

This paper introduced the triangulation method using the relations of the signal magnitudes and distances between each sensor and impact location. In order to extract the useful feature having good correlation with these distances, the time of arrival (TOA) data of sensor signal was applied. Using the signal magnitudes and TOA data, the effective features could be derived for estimating the distances between each sensor and impact location. For investigating this suggested algorithm, low-velocity impact experiments were carried out on the composite stiffened plate as a target structure. The acoustic emission signals were captured by the commercial high-speed optical fiber sensing system. From the impact signals on the baseline locations (30 points), the regression model was constructed for estimating the distances of impact location from each sensor on the target area. Then, through the non-baseline signals (20 points), the validations of constructed regression model were performed. As a result, this regression model is able to accurately predict the AE source locations on the non-baseline cases.

Research on Acoustic Emission Source Location Imaging in Aluminum Alloy Plate-type Structure

Abstract The time reversal focusing and imaging technique is often used to locate the acoustic emission (AE) source on a plate-type structure. Because of the computational error caused by the dispersive modes of the raw AE signal, the AE source is sometimes located in the adjacent region of its real position and the pseudo-AE source will be focused in the location image of the AE source. This study is interested in how to effectively avoid the focusing of the pseudo-AE source. Thus, in this article, a Shannon wavelet transform with “Morlet” mother wavelet was used to isolate S0 modes from raw AE signals. The modulus value curves of the isolated S0 modes were treated by time reversal, time delay, and superposition at every grid point in the monitoring area, based on the time reversal focusing principle. The AE source was located at a certain grid point where the peak of the superposition curve is maximal. The monitoring area imaging was realized by defining every grid point’s pixel value with the peak of the superposition curves. The validating experiment was done in a 600 mm by 600 mm monitoring area which is on a 5052 aluminum alloy plate with dimensions of 1,200 mm by 1,200 mm by 3 mm. Comparing with the traditional square location method based on time difference of arrival (TDOA) calculation, the localization accuracy was improved and the maximal radial error is lower than 30 mm. Furthermore, the proposed localization method has a certain ability to overcome the effect of the plate size and local curvature.

Online acoustic emission source localization in concrete structures using iterative and evolutionary algorithms

This study is motivated by the need to develop an efficient online structural health monitoring (SHM) framework to accurately localize damage induced acoustic emission (AE) sources in concrete structures. Experimental studies are carried out in concrete slabs considering pencil lead break (PLB) as artificial damage source to initialize acoustic emission (AE) waves. A simplified yet robust Iterative Planar Source (IPS) localization algorithm based on arrival time (ToA) is proposed first to identify arbitrarily selected several damage source locations for (1) rectangular (2)circular, and (3) zig-zag distributed AE sensor network arrangements. The results of the proposed localization algorithm are then compared with those obtained from an evolutionary particle-swarm optimization (PSO) algorithm for each sensor network arrangement to assess the performance of the AE source monitoring strategy. It is found that the zig-zag arrangement of the distributed AE sensors is the most efficient sensor network arrangement for damage source localization. The obtained results clearly represent the accuracy and robustness of the proposed online monitoring framework for localizing damage induced acoustic emission sources in concrete structures without extensive manual intervention.

Evaluation of acoustic emission source localization accuracy in concrete structures

Acoustic emission source localization is a promising monitoring technique for concrete structures. However, the accuracy of acoustic emission source localization is influenced by many factors, such as the presence of cracks, which are commonly observed in existing reinforced concrete structures. In this article, the acoustic emission source localization is evaluated using a numerical model with a total number of 11,827,200 independent simulated tests. In this work, the investigated influential factors include the presence of cracks, arrival time picking error, and senor layout. The accuracy of source localization is quantified by the characteristic error defined in this article. Using the proposed wave propagation properties, a relatively stable characteristic error of 150 mm is estimated in the detection zone with the maximum sensor spacing less than 1 m. The evaluation approach and simulated characteristic error are validated experimentally by comparing the 200 manually generated signals using hammer hits on a cracked concrete beam.