Acoustic Emission Monitoring Research Articles

Deep learning-assisted structural health monitoring: acoustic emission analysis and domain adaptation with intelligent fiber optic signal processing

Structural health monitoring aims to detect damage progression in materials. This study focuses on categorizing crack stages, a critical aspect of monitoring structural integrity. By leveraging acoustic emission (AE) monitoring, cracks can be analyzed in a data-driven manner. However, applying AE analysis poses several challenges, including discrepancies between simulated AE data from models and experimental data from the field, as well as class imbalance in crack progression data, with a scarcity of late-stage data. To bridge the gap between theory and experiments, our approach employs domain adaptation to synchronize simulated and actual AE data. The model learns robust domain-invariant features through meticulous experimentation across training epochs. Quantitative analysis of the model’s performance provides key insights. F1 scores vary with feature counts, and domain adaptation outperforms by 20% on highly imbalanced datasets. This emphasizes the model’s adaptability for precise crack classification, even with underrepresented damage classes. In summary, this study advances structural health monitoring by offering a solid AE analysis approach. Core contributions include reconciling simulated and experimental data discrepancies, tackling class imbalance, optimizing feature extraction, and demonstrating robust crack stage categorization. The insights gained highlight the merits of domain adaptation and data-driven AE analysis for predicting crack progression.

Study on the Law of True Triaxial Hydraulic Fracturing by Acoustic Emission Monitoring.

Hydraulic fracturing generates fractures in a coal seam, which has been extensively used in coal mining and disaster management. To study the influences of water injection pressure and time on the propagation of hydraulic fracture, we conducted true triaxial hydraulic fracturing experiments under acoustic emission monitoring. Five briquette specimens were prepared by molding the mixture of coal powder, cement, river sand, and distilled water under 60 MPa to simulate the properties of coal seam. True triaxial loading was used to simulate the in situ stress environment of the coal seam. Hydraulic fracturing experiments on the test specimens were conducted under different water injection pressures and times. The following conclusions have been drawn. At the fixed injection time, increasing water injection pressure promotes the propagation of hydraulic fracture and the migration of water in the coal seam after the fractures are connected. The number of fractures increases from 3 to 8 as the water injected pressure increased from 3 to 9 MPa. Under the constant water injection pressure, the increase in longitudinal wave velocity in the test specimen decreases with the prolongation of water injection time. When the water reaches the action boundary of the water injection pressure, the water stops moving. At this moment, the water injection time has no effect on the longitudinal wave velocity anymore. The fracturing influence range can be increased by increasing the water injection pressure to produce a fracture network of a large radius with many fractures. Appropriately prolonging hydraulic fracturing time can ensure that the fracturing fluid fully moistens the coal seam and thus effectively reduces dust pollution.

Macro-micro mechanical behavior of saturated cemented sands during drained triaxial shearing

To enhance the understanding of the macro-micro mechanical behavior of cemented sands, a series of drained triaxial shearing tests were conducted on saturated cemented sands with varying cement contents and confining stresses. These tests incorporated high-performance acoustic emission (AE) monitoring and an environmental scanning electron microscope (ESEM) technique. The results yielded quantitative interpretations of macro-mechanical response, microstructural variation, and AE behaviors. Specifically, increasing cement content led to an exponential reduction in porosity (or pore area ratio) and a power increase in pore number, possibly due to the production of hydration products that segment large pores. Relationships were established among peak strength (or AE hits), cement content, and confining stress. However, AE trends diverged from those observed in peak strength due to microstructural modifications under different cement contents and their resulting differences in micromechanical behavior during shearing. General relationships between AE rate and mechanical parameters were established during the initial shearing stage, regardless of cement content and confining stress. Moreover, AE evolution efficiently characterized subtle variations in failure patterns due to its high sensitivity to failure-induced structural modifications. These contributions have the potential to establish a non-destructive field evaluation framework and provide guidelines for the efficient utilization of cemented soils in geological and geotechnical engineering applications.

Evolution of Crack Source Mechanisms in Laboratory Hydraulic Fracturing on Harcourt Granite

Hydraulic fracturing has gained escalating significance in recovering unconventional reservoirs. However, the failure mechanism and its evolution with progressive fluid injection are not fully understood for granitic materials. To investigate, triaxial hydraulic fracturing on Harcourt granite and acoustic emission (AE) monitoring was performed by the self-developed multi-physical rock testing platform (MRTP). Source mechanism analysis suggests that tensile cracks account for the majority (62%) of all cracks throughout the hydraulic fracturing process. Tensile cracks with large energy are induced mainly around the borehole bottom, but their average energy is smaller than shear cracks. The entire hydraulic fracturing process is divided into three stages by injection measurements. In Stage 1, AE events are recorded with low energy emissions but high signal-to-noise ratios, revealing the initiation of hydraulic fractures before peak injection pressure. Tensile cracks are more dominant (78%) than other stages. In Stage 2, the number and magnitude of AE events increase exponentially along the trace formed in Stage 1. In Stage 3, hydraulic fractures have the largest magnitude among all stages. Shear cracks are nearly the same proportion as Stage 2, but more shear cracks with large magnitudes are observed following the trace formed by tensile cracks. A dense population of shear cracks can be found at the borehole bottom, and their distribution follows the average slip plunge of individual shear cracks induced by the injection fluid.

Acoustic emission analysis for crack initiation in AA7075-T6 alloy under mixed tensile and bending cyclic loading

In most critical components, fatigue occurs under mixed loadings, such as bending and tensile cyclic loading. Furthermore, in the realm of fatigue loading conditions, scant information has been documented regarding the combination of bending and tensile cyclic loading. Therefore, in this paper, Acoustic Emission (AE) as a non-destructive method was used to investigate crack initiation in AA7075-T6 specimens subjected to fatigue conditions involving bending and tensile cyclic loading. The results showed that generated AE signals had the same trend in all tests, and there was a reasonable correlation between AE and mechanical characteristics. By correlating mechanical data and AE data using the sentry function, the failure process, which includes dislocation movement, plastic deformation, work hardening, micro-crack formation, and crack initiation, respectively, was identified. The S-N curve was plotted by using AE monitoring. This curve was depicted as non-destructive and based on the crack initiation cycle. Obtaining the S-N curve through AE monitoring will greatly assist designers in the design of structures under mixed fatigue loading conditions. This will result in a reduced Safety Factor and, consequently, decreased weight and cost for structures while still ensuring that the structure meets the necessary safety requirements.

Effect of Chemical Corrosion on Rock Fracture Behavior in Coastal Deep Mines: Insights from Mechanical and Acoustic Characteristics

The demand for critical minerals has increased extraction activities in coastal deep mines where challenges such as high stresses, chemical corrosion, and mining disturbance impacts are present. This study investigated the effects of chemical corrosion and confining pressure on the mechanical and fracture behaviors of granite specimens, which are crucial for ensuring the stability of surrounding rock in coastal deep mines. Triaxial compression tests were conducted on uncorroded specimens and corroded specimens immersed in acid and alkali solutions under varying confining pressures, with real-time acoustic emission (AE) monitoring. Based on the test results, the strength and deformation properties, progressive fracture, and failure processes, as well as the AE response characteristics of the specimens under chemical corrosion and confining pressure were analyzed. Additionally, the influence of confining pressure on the chemical damage and brittle–ductile transition behavior of specimens was discussed, and the mechanism of chemical corrosion on the physical and mechanical behavior of specimens was revealed based on mineralogical analysis. These findings underscore the importance of understanding the interplay between chemical corrosion, confining pressure, and rock fracture behavior in coastal deep mining and contribute to evaluating the stability of underground surrounding rocks under corrosion environments.

Comprehensive assessment and monitoring of bond deterioration in GFRP-reinforced concrete beams using guided wave and acoustic emission techniques

The debonding between glass fiber-reinforced polymer (GFRP) rebars and concrete significantly reduces the bond strength and jeopardizes the safety and durability of GFRP-reinforced concrete (GFRP-RC) structures. As a result, it is imperative to monitor the structural integrity of infrastructures being built using these composite materials in structural elements during their service lives. Previous studies have primarily focused on artificially induced debonding scenarios for guided wave (GW)-based monitoring, which has resulted in an inability to capture debonding events that arise naturally due to external loads. Furthermore, flexural bond test investigations simulating real loading scenarios in GFRP-RC structures have not been linked with acoustic emission (AE) and GW monitoring. The present study addresses these research gaps by comprehensively examining the flexural bond integrity in GFRP-RC structural elements subjected to realistic loading conditions using a hybrid approach combining GW and AE as active and passive structural health monitoring techniques, respectively. A series of bond tests, conforming to RILEM specifications, have been performed to investigate various parameters (including rebar surface characteristics, embedment length, and confinement conditions) that affect the flexural bond degradation response of GFRP-RC members. Damage indices based on GW and AE signal parameters have been developed to evaluate the characteristics of confined and unconfined specimens distinctly. It has been observed from the test results that the L (0,3) GW mode is more sensitive to debonding than other modes and that a threshold of 25% has been established for the GW damage index to denote significant bond damage. Furthermore, AE damage indices have provided valuable insights into concrete damage, including splitting and damage at the rebar-concrete interface. Thus, a thorough understanding of bond deterioration in GFRP-RC structures has been developed by combining GW and AE health monitoring techniques, with implications for enhancing structural safety and durability.

Monitoring warning criterion of acoustic emission active waveguide system based on loess deformation and failure.

The construction of acoustic emission criterion system is crucial for monitoring and providing early warning of geological hazards. In the current soil acoustic emission monitoring methods, the signal generated by soil deformation and failure is weak and experiences high attenuation, resulting in a low level of the monitored signal. One approach to enhance the quality of monitoring data is by utilizing the active waveguide model. However, the current research on the active waveguide model system is not extensive. To address these issues, a set of active waveguide system was designed to improve the data quality of acoustic emission monitoring and early warning. The deformation and failure process of loess monitored by acoustic emission was divided into stages, and the precursor information of acoustic emission for geological disasters in loess areas was comprehensively deconstructed. The data quality advantage of the active waveguide model was verified through comparative experiments of with the passive waveguide model. This study investigates the AE signal characteristics of the active waveguide model. It explores various aspects such as the AE waveform parameter characteristics, the discrimination method for failure mode based on RA-AF value, the AE r-value characteristics, the AE b-value characteristics, and the frequency-amplitude characteristics. The study reveals the evolution law of AE signals in the active waveguide model, including early warning signs and failure morphological characteristics. Furthermore, it constructs a warning criterion for the active waveguide system. The development of this criterion system is of great importance in guiding the monitoring and early warning of geological disasters in loess areas.

Mechanical and acoustic characteristics of sandstone failure at different immersion heights under tailings water erosion conditions

To investigate the influence of tailings water immersion height on the failure process of rocks, intact yellow sandstone samples and yellow sandstone samples with prefabricated fissures were prepared. Uniaxial compression tests were conducted on these sandstone samples with varying immersion heights, and the failure processes were simultaneously monitored using a camera and an acoustic emission monitoring system. Based on the test results, the crack propagation and failure characteristics of the yellow sandstone samples under uniaxial loading at different immersion heights were determined. The relationships between the immersion height and peak strength and between the immersion height and elastic modulus were characterized. Additionally, the intrinsic connection between sandstone damage and acoustic emission signal parameters was revealed. The experimental results indicate that the uniaxial compressive strength and elastic modulus of the sandstone samples decrease continuously with increasing immersion height, but the rate of decrease gradually slows. The presence of water is the primary reason for the deterioration of mechanical properties, and the chemical components in the tailings water are significant factors that cannot be ignored. The initiation location and propagation of cracks in intact samples depend on the immersion height, while the fracture behaviour of fissured samples after immersion is mainly influenced by the prefabricated fissures. As the immersion height increases, the longitudinal wave velocity increases, while the number of acoustic emission events, peak frequency, and amplitude exhibit a decreasing trend that is initially rapid and then slows. A damage evolution model based on acoustic emission ringing counts at different immersion heights was established. It was also found that the acoustic emission signals of these yellow sandstone samples mainly show the characteristics of abrupt signals under any immersion water height.

Tension and Shear Behaviour of Basalt Fiber Bio-Composites with Digital Image Correlation and Acoustic Emission Monitoring.

This research investigates the mechanical behavior and damage evolution in cross-ply basalt fiber composites subjected to different loading modes. A modified Arcan rig for simultaneous acoustic emission (AE) monitoring was designed and manufactured to apply quasi-isotropic shear, combined tensile and shear loading, and pure tensile loading on specimens with a central notch. Digital image correlation (DIC) was applied for high-resolution strain measurements. The measured failure strengths of the bio-composite specimens under different loading angles are presented. The different competing failure mechanisms that contribute to the local reduction in stress concentration are described. Different damage mechanisms trigger elastic waves in the composite, with distinct AE signatures that closely follow the sequence of fracture mechanisms. AE monitoring is employed to capture signals associated with structural damage initiation and progression. The characteristic parameters of AE signals are correlated with crack modes and damage mechanisms. The evolution of AE parameters during the peak load transition is presented, which enables the timely AE detection of the maximum load transition. The combination of DIC and AE monitoring improves understanding of the mechanical response and failure mechanisms in cross-ply basalt fiber composites, offering valuable insights for possible performance monitoring and structural reliability in diverse engineering applications.

Optimizing tool life in SiCp/Al composites milling with acoustic emission analysis: A comprehensive monitoring and implementation strategy

The machining of SiCp/Al composites is hampered by tool wear monitoring challenges. SiCp/Al composites are used in industries like aerospace where tool wear can lead to workpiece loss, necessitating real-time monitoring. Acoustic emission (AE) sources during machining are complex due to SiC particles. This paper attempts to isolate AE frequencies for plastic deformation and silicon carbide particle behavior through scratch experiments at different depths. The relationship between signal energy distribution and tool wear during milling is analyzed using the wavelet packet method. The frequency band correlating best to tool wear is identified outside the scratch experiment's frequency range. A monitoring strategy is proposed based on this, and the effect of machining parameters on AE monitoring is analyzed, with refinements to the monitoring model. The proposed strategy's effectiveness has been validated through experimental trials, resulting in an average tool utilization rate of 85 % during milling.

Fracture characteristics and damage evolution of manufactured sand-based ultra-high performance concrete using tensile testing and acoustic emission monitoring

To address the challenges posed by the excessive exploitation of natural river sand, manufactured sand (MS) was used as a substitute material for natural sand to produce manufactured sand-based ultra-high performance concrete (UHPMC). This study aims to investigate the effects of MS replacement ratio, stone powder content, steel fiber content, and steel fiber shape on the fracture characteristics and damage evolution of UHPMC under tensile load through tensile tests combined with acoustic emission (AE) technology. The research results indicated that the stress-strain behavior of UHPMC could be divided into low strain hardening, low strain softening, and high strain softening. The tensile strength and energy absorption of the UHPMC were less correlated with MS replacement ratio. The tensile strength showed a trend of first increasing and then decreasing with the increase of stone powder content, and UHPMC with a 4% stone powder content presented the better tensile strength. The tensile damage process of UHPMC was mainly concentrated in the range of tensile strain from 0.0002 to 0.0025. The microstructure analysis of the UHPMC matrix revealed that an optimal amount of stone powder enhances the bond property between MS and mortar, thereby improving tensile performance. AE monitoring indicated that AE amplitude and AE energy provide sensitive identification capabilities for classifying the elastic state, strain hardening, and strain softening stages of UHPMC. The findings of this study contribute to understanding the fracture characteristics and damage evolution of UHPMC, promoting the engineering application of MS in ultra-high-performance concrete.

Acoustic Emission Monitoring for Damage Assessment of a Magnetite Ultra-High-Performance Concrete (MUHPC) Block in a Bending Test

Ultra-high-performance concrete (UHPC) is widely used because of its exceptional properties, such as high compressive and flexural strength, low permeability, and resistance to abrasion and chemical attack. It is commonly employed for intricate constructions like skyscrapers, precast concrete components, and infrastructure. Nevertheless, the incorporation of appropriate fibers into UHPC is carried out in order to accomplish objectives such as augmenting strength, enhancing toughness, and regulating cracking. This study employed magnetite as an additive to a UHPC block in order to examine the mechanical characteristics of a newly cast UHPC block. Acoustic emission was employed to evaluate the damage to the UHPC block for tracking purposes. Acoustic emission is a non-invasive testing technique that does not cause harm to the specimen when it is exposed to a load. On the basis of this, many critical locations that indicated the propagation of cracks were analyzed, as well as various loading stages across the specimen. The b-value is a method that can evaluate the extent of damage by analyzing the amplitude distribution. Distinct paths of b-values were noted for each loading stage, indicating major damage scenarios based on their slopes.

Effect of moisture content on the rockburst intensity of sandstones

Rockburst is a common geological hazard in deep underground engineering, and it often occurs in strata consisting of brittle rocks. In this study, the moisture content effect on the rockburst intensity of sandstones is systematically studied. A series of triaxial unloading compression tests along with the acoustic emission monitoring are performed for sandstone specimens with different moisture content levels. The mechanical properties, failure characteristics, and dilatancy behaviors of sandstone specimens are then properly compared. Comparative results reveal that the triaxial compressive strength and total strain energy of the saturated specimen decrease by about 30% and 35%, respectively, as compared to those of the dry specimen. Moreover, the magnitude of elastic strain energy tends to decrease with the increasing water content. The effect of moisture content on the rockburst intensity of sandstones is, therefore, significant. Besides, it is also found that the onset of dilatancy is generally unaffected by the water content, whereas the extent of dilatancy significantly decreases with the increasing water content. Numerical simulations for a tunnel excavation model confirm that injecting water into the surrounding rock is an effective way of reducing the rockburst intensity during tunnel excavations. These results have a guiding significance for the prevention and control of rockbursts in underground engineering.

Detection of early fatigue damage during ultrasonic fatigue testing of steel by acoustic emission monitoring

Ultrasonic fatigue testing (USFT) is a time-efficient method for evaluation of the fatigue limit of metallic alloys in a high and very high cycle range. Propagation of a final crack at the very end of the fatigue life can be clearly detected by USFT parameters and monitoring techniques. In contrast, initiation of fatigue damage during USFT remains unclear. Despite its excellent sensitivity, the implementation of acoustic emission (AE) for damage monitoring is hindered by severe noisiness of acoustic signals from USFT. In addition to resonance-related quasi-stationary noises, USFT in a pulse-pause mode is accompanied by non-stationary ones, which makes recognition of material-related AE signals even more difficult. A special AE processing algorithm was developed to overcome this issue and get useful insights from USFT monitoring. Consistent cropping, Fourier transformation, adaptive filtration and thresholding allowed to calculate noise-free AE activity during USFT of 42CrMo4 steel. Remarkably, most of this activity was located in the very beginning of fatigue loading. In comparison to non-failed runout samples, AE activity of samples with fatigue cracks was significantly higher, indicating its relation to fatigue damage. The proposed AE processing principle can be helpful for monitoring of USFT samples and other parts, operating in resonance conditions.

INVESTIGATING FIRE-INDUCED DAMAGE ON FIBER-REINFORCED CONCRETE SAMPLES USING NONDESTRUCTIVE EVALUATION METHODS

This research article investigates the effect of severe thermal exposure on the mechanical behavior of fiber-reinforced concrete specimens. Having been exposed to direct fire, the specimens undergo the fracture experiment to determine their mechanical properties. Fire-damage examination is performed with nondestructive techniques such as acoustic emissions (AE) and ultrasonic pulse velocity (UPV). The main purpose is to demonstrate that AE parameters, such as amplitude, cumulative hits, and energy, have a strong correlation with mechanical parameters and temperature. Besides that, acoustic emission monitoring is also an assessment tool of the structural integrity throughout the entire loading process. The distribution of AE events and the variation of key AE parameters across the load process give very useful hints to differentiate between intact and fired-damaged specimens. The fact that the AE can be used on-site to determine cracks means that it may be used as an alternative method to describe concrete's mechanical properties after fire exposures.

Applicability of a new composite amusement ride safety device based on acoustic emission monitoring technology

Under the premise of ensuring safety, it is of great significance to realize the lightweight of the non-main load-bearing parts of amusement facilities. The purpose of this study is to study the failure process of a newly designed carbon fiber bumper by using acoustic emission technology. First of all, the design of carbon fiber anti-collision bar can effectively restrain passengers, and its weight is reduced by nearly two-thirds compared to traditional metal materials. Subsequently, the load-bearing capacity of the bumper was tested and acoustic emission monitoring was carried out. The test results show that this new type of combined structure of amusement facility has high reliability, which exceeds the safety factor of 3.5 required by the steel structure of amusement facility. In addition, Renyi entropy was used to select the best window function of short-time Fourier transform, and the frequency domain characteristics of acoustic emission signals of typical damage modes were discussed through appropriately selected windows function. A classifier based on supervised machine learning is established by combining frequency features and acoustic emission feature parameters. Furthermore, the use of classifiers helps to understand the damage behaviour of composite structures.

INVESTIGATING FIRE-INDUCED DAMAGE ON FIBER-REINFORCED CONCRETE SAMPLES USING NONDESTRUCTIVE EVALUATION METHODS

This research article investigates the effect of severe thermal exposure on the mechanical behavior of fiber-reinforced concrete specimens. Having been exposed to direct fire, the specimens undergo the fracture experiment to determine their mechanical properties. Fire-damage examination is performed with nondestructive techniques such as acoustic emissions (AE) and ultrasonic pulse velocity (UPV). The main purpose is to demonstrate that AE parameters, such as amplitude, cumulative hits, and energy, have a strong correlation with mechanical parameters and temperature. Besides that, acoustic emission monitoring is also an assessment tool of the structural integrity throughout the entire loading process. The distribution of AE events and the variation of key AE parameters across the load process give very useful hints to differentiate between intact and fired-damaged specimens. The fact that the AE can be used on-site to determine cracks means that it may be used as an alternative method to describe concrete's mechanical properties after fire exposures.

Method for rock fracture prediction and early warning: Insight from fusion of multi-physics field information

Understanding the precursors leading to rock fracture is crucial for ensuring safety in mining and geotechnical engineering projects. To effectively discern these precursors, a collaborative monitoring approach that integrates multiple sources of information is imperative. This paper considered a rock multi-parameter monitoring loading system, incorporating infrared radiation and acoustic emission monitoring technologies to simultaneously track the rock fracture process. The study delves into the spatiotemporal evolution patterns of infrared radiation and acoustic emission in rock under loading. Utilizing stress, cumulative acoustic emission count, and average infrared radiation temperature (AIRT), the paper establishes a comprehensive evaluation model termed “acoustic-thermal-stress” fusion information, employing principal component analysis (PCA). The research reveals that the sensitivity to rock sample damage response follows the sequence of cumulative acoustic emission count, AIRT, and stress. Furthermore, a novel method for identifying rock fracture precursors is proposed, based on the first derivative of the comprehensive evaluation model. This method addresses the limitations of single physical field information, enhancing the robustness of monitoring data. It determines the average stress level of fracture precursors to be 0.77σmax. Subsequently, the study defines the probability function of rock damage during loading and fracture, enabling the realization of probability-based warnings for rock fracture. This approach introduces a new perspective on rock fracture prediction, significantly contributing to safety monitoring and warning systems in mine safety and geotechnical engineering. The findings of this research hold paramount engineering significance, offering valuable insights for enhancing safety measures in such projects.

Simulation of Shear and Tensile Fractures Using Ductile Phase Field Modelling with the Calibration of P Wave Velocity Measurement and Moment Tensor Inversion

The appropriate understanding and formulation of rock discontinuities via FEM is still challenging for rock engineering, as continuous algorithms cannot handle the discontinuities in rock mass. Also, different failure modes of rock samples, containing tensile and shear failure, need to be computed separately. In this study, a novel double-phase field damage model was introduced with two independent phase field damage variables. The construction of the proposed model follows the thermodynamics framework from the overall Helmholtz free energy, with elastic, plastic and surface damage components. The proposed model is calibrated via traditional damage variables, based on ultrasonic wave velocity measurement and acoustic emission monitoring, and both show great consistency between simulation results and laboratory observations. Then the double-phase field damage model is applied to COMSOL software to simulate microcrack propagation in a pre-fractured rock sample. Both lateral and wing cracks are observed in this study, manifested as shear- and tensile-dominated cracks. We also observed different microcracking mechanisms in the proposed numerical models, such as tensile and shear cracking, the influence of plastic strain and the percolation between tensile and shear microcracks. Overall, this study provides valuable insights into the mechanics of microcracking in rocks, and the proposed model shows promising results in simulating crack propagation.