Acoustic Emission Method Research Articles

Core Orientation Technology Based on Drilling Trajectory Projection and Its Application in In Situ Stress Measurement of the Deepest Shaft in China

Deep borehole cores are an important material basis for understanding deep stress conditions and rockburst risk; however, the complex environment of deep boreholes poses many challenges to traditional core orientation techniques, thus limiting the application of cores in fields such as in situ stress measurement. A technical method of restoring the original spatial attitude of nonoriented geological cores on the ground was proposed based on the inherent “trajectory projection consistency” relationship between the borehole and the corresponding core. A prototype machine of core ground reorientation was developed. Using this method and machine, ground reorientation was performed on cores drilled from the deepest shaft in China. Subsequently, the reoriented core acoustic emission (AE) method was conducted to identify the in situ stress within the project area. Meanwhile, measurement accuracy was verified by the stress relief method. The results show that the in situ stress distributions, including the azimuth and the trends in principal stresses by the two methods, are in good agreement and indicate that the historical maximum principal stress in the case of the mine has little abrupt variability with that of the present day. The research results can be used as the design basis for the safe construction of the deepest shaft.

Damage mechanism characterization of ±35° and ±55° FW composite tubes using acoustic emission method

The focus of this study is to investigate the mechanical properties, of ±35° and ±55° filament wound (FW) composite tubes under axial compression loading using the acoustic emission technique. For this purpose, material failure, crashworthiness characteristics, and the effect of each mechanism on the energy absorption capacity were studied using numerical and experimental approaches. Also, to identify and estimate the contribution percentage of damage mechanisms as well as how the damage grows in the specimens, the analysis of acoustic emission signals recorded during loading was performed. Digital image correlation was additionally used to capture displacement/strain contour maps. Finally, to analyze the effect of the winding pattern in the experimental test, the tubes were simulated using finite element analysis (FEA). For modeling of damage mechanisms, a 3D continuum damage model was used. The results of signal processing showed that by increasing the weaving angle of fibers from ±35° to ±55°, the separation of fibers from the matrix decreases, and the percentage of matrix crushing and fiber failure increases. The assessment of damage percentages showed that the reason for the large drop in force at ±55° compared to ±35° is the increase in matrix crushing. Furthermore, the failure behavior of FW tubes appeared to be dominated by local buckling, and the FEA effectively predicted the linear behavior and maximum load value of the composite tubes.

Assessment of the Destruction of a Fibre Cement Board Subjected to Fire in a Large-Scale Study.

This article presents the results of a study involving the assessment of the structural destruction of fibre cement boards taken from a large-scale model subjected to fire. These were subjected to a three-point bending test using the acoustic emission method. The analysis of the obtained results took into account the course of bending stresses σm, the modulus of rupture (MOR), the number of acoustic emission events Nzd and the sum of EA events ∑Nzd. The conducted tests showed that the samples subjected to fire exhibited a clear decrease, up to 72%, in the recorded sum of EA events compared to a reference board (not subjected to fire). The analysis of the obtained modulus of rupture (MOR) values showed a similar trend—the reduction of the modulus of rupture for the degraded samples was in the range of 66–96%. In order to illustrate the changes taking place in the structure of the tested plates more precisely, analyses were carried out using the optical method and a digital microscope. This method may be sufficient for the final evaluation of degraded samples.

Damage analysis of a SiCf/SiC ceramic matrix composite under stepwise fatigue loading with acoustic emission

Continuous fiber-reinforced ceramic matrix composites (CMCs) exhibit different damage mechanisms at multiple scales under cyclic loading. In this paper, the tension-tension fatigue behavior of a plain woven SiCf/SiC CMC was investigated, and damage accumulation and evolution process were studied in detail via acoustic emission (AE) method. With the increase of cycles, the material exhibits obvious hysteresis behavior affected by interfacial slip and wear mechanisms. Most of the fibers with radial fracture characteristic have relatively high strength, showing excellent toughening property. In the stepwise cyclic loading process, the Kaiser effect of AE determines the initiation of AE activities at each initial loading moment, which shows obvious nonlinear damage accumulation behavior of the material. High-energy events are related to significant matrix cracking and fiber fracture, and the evolution process of material damage initiation and propagation is monitored in real time.

Influence of weak ac electric field on the temperature of dielectric maximum of (1-x)PbMg1/3Nb2/3O3-xPbTiO3 relaxor ferroelectric single crystals based on acoustic emission data studies

(1-x)PbMg1/3Nb2/3O3-xPbTiO3, [100]-oriented relaxor ferroelectric crystals were studied by means of dielectric and acoustic emission methods in dependence on temperature and under ac measuring electric field with several values and frequencies. The dependence of temperature of dielectric constant maximum on and without ac field value and frequency was plotted. Also a scatter of the temperature of dielectric constant maximum was calculated in dependence on ac field frequency. Such the phenomenon was discussed from a point of view of growth of the polar nanoregions on cooling.

A novel in-situ stress measurement method incorporating non-oriented core ground re-orientation and acoustic emission: A case study of a deep borehole

The measurement of in-situ stress is a critical prerequisite for the mining design and the stability analysis of surrounding rock in deep mining engineering. In this study, a novel re-oriented core acoustic emission (RCAE) method incorporating the non-oriented core ground re-orientation and AE techniques was proposed for in-situ stress measurement. First, the principle of non-oriented core ground re-orientation is established according to the spatial coupling relationship between the drilling trajectory and the core surface characteristics. Then, an innovative apparatus was designed for recovering the original spatial orientation of non-oriented cores. Furthermore, the measurement procedures of RCAE method are described in detail, involving suitability analysis, outdoor operations, core re-orientation, specimen preparation, AE test and stress calculation. Using this method, a case study for in-situ stress measurement was performed in an ultra-deep borehole (2360 m) of the Sanshandao gold mine, China. Meanwhile, the verifications of measurement accuracy were conducted based on the tectonic stress inversion and the underground overcoring method. The results show that the measurement accuracy of RCAE method is acceptable, especially the horizontal maximum principal stress and its azimuth measured are well matched with those measured by other methods. In addition, the field applications indicate that the in-borehole procedure of RCAE method only requires drilling trajectory measurement without excessive complex operations, and the adequate measuring depth of this method in the case area is up to 3841 ± 521 m according to the damage stress threshold analysis. Therefore, the RCAE method could break through the challenges caused by the restricted measuring space and large measuring depth when no deep underground access exists. Moreover, the non-oriented cores can be rapidly re-oriented on the ground, which could expand the application value of ordinary geological boreholes in the field of deep geostress and tectonic measurement.

Detection of bolt head corrosion under external vibration using a novel entropy-enhanced acoustic emission method

Detection of bolt head corrosion under external vibration using a novel entropy-enhanced acoustic emission method

Detection and Analysis of Partial Discharges in Oil-Immersed Power Transformers Using Low-Cost Acoustic Sensors

Partial Discharge (PD) is one of the symptoms of an electrical insulation problem, and its permanence can lead to the complete deterioration of the electrical insulation in high-voltage equipment such as power transformers. The acoustic emission (AE) method is a well-known technique used to detect and localize PD activity inside oil-filled transformers. However, the commercially available monitoring systems based on acoustic sensors still have a high cost. This paper analyses the ability of low-cost piezoelectric sensors to identify PDs within oil-filled power transformers. To this end, two types of low-cost piezoelectric sensors were fully investigated using time-domain, frequency-domain, and time-frequency analysis, separately. Thereafter, the effectiveness of these sensors for PD detection and monitoring was studied. A three-phase distribution transformer filled with oil was examined. PDs were produced inside an oil-immersed transformer by applying a high voltage over two copper electrodes, and the AE sensors were coupled to the housing of the transformer. By extracting typical features from the AE signals, the PD signals were differentiated from on-site noise and interference. The AE signals were analyzed using acoustic signal metrics such as peak value, energy criterion, and other statistical parameters. The obtained results indicated that the used low-cost piezoelectric sensors have the capability of PD monitoring within power transformers.

Application of Forward Error Correction (FEC) Codes in Wireless Acoustic Emission Structural Health Monitoring on Railway Infrastructures

Structural health monitoring (SHM) has been extensively used in the railway industry, with applications ranging from railway infrastructures to carbody shells. An SHM method that dominates monitoring procedures is Acoustic Emissions (AE). The utilisation of the AE method could use a significantly large amount of data, collected and forwarded to terminal computers using wireless communications. Nowadays, the use of 5G is taking over traditional wireless such as Wi-Fi and 4G telecommunications. However, errors in the transmission due to noisy channels may be experienced. The SHM system may result in the wrong detection of a potential defect in a railway infrastructure with dangerous consequences, such as derailment. Hence, methods for adequately dealing with these errors need to be established, such as Forward Error Correction (FEC) codes. In this paper, we suggest the use of the wireless FEC codes applied to a number of deployed AE devices, in order to perform correction at the transmissions. We investigate the new POLAR codes and compare this method with the Reed-Solomon (RS) codes. We present simulations that the POLAR codes are more efficient with trials using the AFF3CT simulator.

Experimental Francis Turbine Cavitation Performances of a Hydro-Energy Plant

An investigation is conducted on the Francis turbine’s cavitation characteristics and its influence on system hydraulic stability using two experimental methods, namely the flow visualization and acoustic emission methods. The investigated turbine is of Francis type with a 15-blade runner and has a specific speed of 202 rpm and a rated head of 30 m. Having tested the machine under a wide range of cavitation conditions, the gap cavitation is the earliest to develop as the cavitation coefficient gradually decreases and has no obvious effect on the machine’s external performance characteristics. The airfoil cavitation follows and causes the increase and decrease in machine flow rate and head, respectively, showing its drag reduction effect, where, at the same time, the pressure pulsation amplitude gets to its peak value. There is also the formation of constant cavitation zones and the involvement of an unsteady surge close to the wall of the draft tube’s cone. Pushing the cavitation coefficient to even lower values, there is the formation of an annular cavitation zone, accompanied by a sharp drop in cone pressure pulsation amplitudes while the former drag reduction effect disappears. The trend of noise is basically the same as that of pressure fluctuation, which confirms its trustworthiness when it comes to cavitation occurrence detection within Francis turbines.

СОВРЕМЕННЫЕ ТЕНДЕНЦИИ В РАЗВИТИИ МЕТОДОВ И СРЕДСТВ ЭКСПЕРИМЕНТАЛЬНОЙ МЕХАНИКИ. ЧАСТЬ 2

The article considers a number of new directions in the development of methods and means of experimental mechanics. They are: the unification of test and calculation methods; the development of equipment and test methods in extreme conditions; the widespread use of acoustic emission methods and video recording during testing; the creation and development of equipment and methods for complex testing (for example, wear-fatigue) of materials and products. The achievements of Belarusian scientists are also noted in the field of experimental mechanics of contact interaction, including: an adhesiometer for measuring the molecular interaction of technical surfaces; a millitribometer for measuring friction forces under loads which are characteristic of a precision contact; an onboard tribometer for testing materials for friction and wear in extreme conditions of the action of space factors.

Bending damage evolution from micro to macro level in CFRP laminates studied by high-frequency acoustic microscopy and acoustic emission

This work presents the results of the experimental investigation of the bending damage evolution in the volume of laminate with a stacking sequence of [0°/90°]4S and thickness of 4.32 mm. Damage formation under the step-by-step loading (three iterations) was detected by acoustic emission (AE) and was visualized by high-frequency acoustic microscopy. The acoustic emission method revealed the moments of the fiber breakage, formation of cracks and delaminations in the process of bending. AE activity and the energy of AE pulses were related to drops and slope of the loading curves, which corresponded to the damage in the composite volume. The layer-by-layer ultrasound imaging revealed the location of matrix cracking, fiber fracture and interlayer delaminations. We presented the scheme of the step-by-step damage development in the laminate volume, based on experimental data.

Implementasi Keamanan Citra Menggunakan Algoritma AES-128 Dengan Aplikasi Client-Server

Digital images that are private and confidential are very vulnerable to eavesdropping by irresponsible parties. Especially when distributed over the internet, such as chat-based applications such as Facebook, WhatsApp and e-mail media. Image sent via the internet. Because digital images are still recognizable images and can be used by eavesdroppers for personal gain, to the detriment of those who have access to image data. The act of tapping the image data can be minimized by the application of cryptographic encryption techniques. This research will secure digital images with 128 bit AES method for encryption and decryption of digital images in client-server based applications. The results of the AES algorithm encryption produce a cipherimage with pixel values that are much different from the plainimage pixel values.

Combined in-oil PD sensor with AE and UHF methods for PD detection in transformer

In the present study, a combined in-oil partial discharge (PD) sensor based on oil valve with acoustical emission and ultra high frequency (AE/UHF) methods for PD measurement in transformer is proposed. The combined PD sensor is designed by placing an AE sensor in front of a UHF antenna, and resorting to be fixed on an oil valve to invade inside the transformer to simultaneously couple the AE/UHF signals from PD source. Besides the AE/UHF signals coupling, construction design of the combined PD sensor with oil sealing are shown in particular. And considering the phenomenon of air entering the transformer box due to the improper installation to the oil valve, an installation method using air extraction for the combined PD sensor based on the oil valve is also shown with a discussion on safety and detection sensitivity caused by the sensor insertion depth. Discharge tests in air and insulation defects prove that the combined PD sensor with AE/UHF methods proposed and processed can simultaneously measure or detect the AE/UHF signals produced by PD source effectively with an obvious time difference value Δt, which presents a innovative mixed AE/UHF method of PD measurement for transformer.

Influence of temperature on deformation failure and acoustic emission characterisation of asphalt concrete under uniaxial compression

ABSTRACT The deformation behaviour of the asphalt concrete (AC) depends on the loading state and the temperature, accompanied by a large number of microcracks. In this study, the deformation and failure behaviour of the AC under uniaxial compression were investigated by the acoustic emission (AE). Both the stress–strain relationship and the energy dissipation were employed to analyse the macroscopic deformation of the specimen at low and medium temperatures. The AE parameters including count, energy and amplitude were measured in real-time during the loading process. The damage morphology of specimens was characterised by the failure location with the AE technology. Results show that with the rise of the temperature, the strength of AC specimens gradually decreased, which leads to a lower capacity in storing strain energy. The dissipative energy is greatly affected by the damage degree of the specimen. Both the event count and amplitude increased rapidly when the specimen failure occurred. The AE parameters are relatively sensitive to the deformation failure of asphalt mixtures influenced by the temperature. Furthermore, the results also imply that the AE method used in the present study to characterise the deformation failure in pavement engineering is more scientific and precise.

Application of wavelet transform in evaluating the Kaiser effect of rocks in acoustic emission test

The Kaiser Effect is amongst the phenomena that can be detected through the so-called acoustic emission method. This effect can be used to evaluate in-situ stress of the rock. Identification of the point at which the Kaiser Effect is applied is problematic in particular cases where the acoustic parameters increase gradually, and this is where signal analysis methods come into play. In this research, Brazilian test was performed on Phyllite samples and acoustic data was recorded simultaneously. Following an energy-based and count-based parametric approach, the occurrence time and the Kaiser Effect stress were obtained for the test specimens. Then, wavelet transform method was used to estimate the occurrence time of the Kaiser Effect. Continuous wavelet transform analysis was undertaken to analyze the signals. The signal analysis was performed by considering the peak frequency as desired parameter and db5 wavelet as the mother wavelet. In continuous wavelet analysis method, the results were classified into five cluster using the K-means clustering algorithm. Considering the mechanism of the Kaiser Effect, the fifth category was considered for further investigations. The results showed that the Phyllite specimens exhibited good capabilities for recovering the stress memory and evaluating the Kaiser Effect-driven stress, the results further showed a good agreement between the occurrence times obtained from the parametric method and those resulted from continuous wavelet transform technique, so that the corresponding differences in the Kaiser Effect-driven stress are negligible. The level of Kaiser Effect-driven stress obtained from the proposed method were acceptably in agreement with the preloading stress levels.

Effect of Velocity Anisotropy in Shale on the Acoustic Emission Events Matching and Location

Accurate source event location is important in fracturing monitoring and characterization. Velocity anisotropy has a great influence on both events matching and events location. Failure to take into account the velocity anisotropy can lead to huge errors in locating events. In this article, we have presented an experimental study on lower Silurian shale from the Sichuan Basin. The experimental observations include ultrasonic measurements, acoustic emissions (AEs) in a three-point bend experiment, and CT scanning of the original sample and the fractured sample. The ultrasonic measurements show that the shale sample has strong velocity anisotropy. Initially, AEs are analyzed using the conventional event-matching method and event location method (Geiger’s method), and the detected events are compared to the X-ray image of the fracture. Event-matching aims to obtain AE signals from the same source event and thus assists in selecting valid AE signals that come from the same source and are received by at least four sensors, to determine the location of the source. Although many reliable signals are obtained by isotropic event-matching, fewer sources were located than expected, and the event location results did not match the fracture distribution. To address this problem, an improved event-matching method is proposed using a stricter matching threshold based on directional velocity rather than a single threshold same for all directions. In addition, we propose an improved Geiger’s method using the anisotropic velocity model. The new methods located more sources that better match fracture distribution than the results of the isotropic method. We have concluded that both event-matching and the source location of the fracturing are largely influenced by velocity anisotropy, and thus in practice, the velocity anisotropy information obtained from various measurements (e.g., laboratory measurements, well logs, VSP, and velocity analysis of reflected seismic surveys) should be involved in both processing procedures. This study can be useful to provide some background for monitoring and predicting dynamic geo-hazards in relation to the AE method.

Modeling and Analysis of Acoustic Emission Generated by Fatigue Cracking

The acoustic emission (AE) method is a popular and well-developed method for passive structural health monitoring of metallic and composite structures. The current study focuses on the analysis of one of its processes, sound source or signal propagation. This paper discusses the principle of plate wave signal sensing using piezoelectric transducers, and derives an analytical expression for the response of piezoelectric transducers under the action of stress waves, to obtain an overall mathematical model of the acoustic emission signal from generation to reception. The acoustic emission caused by fatigue crack extension is simulated by a finite element method, and the actual acoustic emission signal is simulated by a pencil lead break experiment. The results predicted by the mathematical model are compared with the experimental results and the simulation results, respectively, and show good agreement. In addition, the presence of obvious S0 mode Lamb waves is observed in the simulation results and experimental results, which further verifies the correctness of the analytical model prediction.

Damage and failure analysis of a SiCf/SiC ceramic matrix composite using digital image correlation and acoustic emission

The analysis of failure behaviors of continuous fiber-reinforced ceramic matrix composites (CMCs) requires the characterization of the damage evolution process. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso architecture, inherent defects, and loading conditions. In this paper, the in-plane tensile mechanical behavior of a plain woven SiC f /SiC CMC was investigated, and damage evolution and failure process were studied in detail by digital image correlation (DIC) and acoustic emission (AE) methods. The results show that: the initiation of macro-matrix cracks have obvious local characteristic, and the propagation paths are periodically distributed on the material surface; different damage modes (matrix cracking and fiber fracture) would affect the AE energy signal and can be observed in real-time; the significant increase of AE accumulated energy indicates that serious damage occurs inside the material, and the macroscopic mechanical behavior exhibits nonlinear characteristic, which corresponds to the proportional limit stress (PLS) of the material.

Experimental Study on Strength Enhancement of Expansive Grout.

Adding an expansive agent to ordinary grout can cause an expansion in volume, but also reduces its strength. In order to improve the strength of expansive grout, quartz sand is used as the strength enhancement additive. In this study, the expansion behavior and mechanical properties of the expansive grout with quartz sand are explored, through expansion development monitoring, uniaxial compression strength (UCS), acoustic emission (AE), SEM and XRD test methods. The results showed that: (1) The final expansion ratio and expansion development of the samples are related to the use of an expansive agent, but not affected by quartz sand. With the increase in expansion agent content, the average expansion ratios of the samples are 0.03%, 0.16%, 0.67%, 1.06% and 1.48%; (2) The UCS of the samples decreases with the increase in expansive agent content but increases with the increase in quartz sand content. Compared with no quartz sand, and with the increase in quartz sand content, the average strength of the samples increased by 10.51%, 29.88%, and 37.92%; (3) Quartz sand does not effectively participate in the hydration reaction, but it can effectively enhance the strength of the expansive grout without affecting its volume expansion, which makes it an ideal expansive grout strength enhancement additive.