Showing papers on "Acoustic emission published in 2018"
TL;DR: In this article, the authors investigated the effect of water content on quasi-static fracture behavior of sandstone and found that both the fracture toughness and crack propagation velocity observably decreased with the increase of water contents.
154 citations
TL;DR: In this article, uniaxial compression experiments were performed for sandstone specimens with different flaw inclinations varying from 0° to 90°, and four kinds of infilling conditions, including no filler, gypsum filler, cement filler, and resin filler were considered.
151 citations
TL;DR: In this article, a uniaxial cyclic loading and unloading compression experiment was conducted based on an MTS 815 rock mechanics test system and an AE21C acoustic emissions test system.
Abstract: To explore the acoustic emission (AE) characteristics of rock materials during the deformation and failure process under periodic loads, a uniaxial cyclic loading and unloading compression experiment was conducted based on an MTS 815 rock mechanics test system and an AE21C acoustic emissions test system. The relationships among stress, strain, AE activity, accumulated AE activity and duration for 180 rock specimens under 36 loading and unloading rates were established. The cyclic AE evolutionary laws with rock stress–strain variation at loading and unloading stages were analyzed. The Kaiser and Felicity effects of rock AE activity were disclosed, and the impact of the significant increase in the scale of AE events on the Felicity effect was discussed. It was observed that the AE characteristics are closely related to the stress–strain properties of rock materials and that they are affected by the developmental state and degree of internal microcracks. AE events occur in either the loading or unloading stages if the strain is greater than zero. Evolutionary laws of AE activity agree with changes in rock strain. Strain deformation is accompanied by AE activity, and the density and intensity of AE events directly reflect the damage degree of the rock mass. The Kaiser effect exists in the linear elastic stage of rock material, and the Felicity effect is effective in the plastic yield and post-peak failure stages, which are divided by the elastic yield strength. This study suggests that the stress level needed to determine a significant increase in AE activity was 70% of the i + 1 peak stress. The Felicity ratio of rock specimens decreases with the growth of loading–unloading cycles. The cycle magnitude and variation of the Felicity effect, in which loading and unloading rates play a weak role, are almost consistent.
136 citations
TL;DR: In this article, a series of uniaxial compressive strength (UCS) variable-time experiments were performed on low-clay shale samples saturated in sub-/supercritical CO2.
125 citations
TL;DR: In this paper, a self-developed mining-induced stress testing system and acoustic emission monitoring system was used to investigate the mechanical and acoustic properties of rock-like materials under non-uniform loads.
Abstract: The mechanical and acoustic emission characteristics of rock-like materials under non-uniform loads were investigated by means of a self-developed mining-induced stress testing system and acoustic emission monitoring system. In the experiments, the specimens were divided into three regions and different initial vertical stresses and stress loading rates were used to simulate different mining conditions. The mechanical and acoustic emission characteristics between regions were compared, and the effects of different initial vertical stresses and different stress loading rates were analysed. The results showed that the mechanical properties and acoustic emission characteristics of rock-like materials can be notably localized. When the initial vertical stress and stress loading rate are fixed, the peak strength of region B is approximately two times that of region A, and the maximum acoustic emission hit value of region A is approximately 1–2 times that of region B. The effects of the initial vertical stress and stress loading rate on the peck strain, maximum hit value, and occurrence time of the maximum hit are similar in that when either of the former increase, the latter all decrease. However, peck strength will increase with the increase in loading rate and decrease with the increase in initial vertical stress. The acoustic emission hits can be used to analyse the damage in rock material, but the number of acoustic emission hits cannot be used alone to determine the degree of rock damage directly.
121 citations
TL;DR: In this paper, the effects of fiber type, volume fraction and aspect ratio on the flexural and acoustic emission (AE) behaviors of steel fiber reinforced concrete (SFRC) using four-point bending tests were investigated.
108 citations
01 May 2018
TL;DR: Two deep learning approaches to localize acoustic emissions (AE) sources within metallic plates with geometric features, such as rivet-connected stiffeners and a stack of autoencoders and a convolutional neural network are introduced.
Abstract: This paper introduces two deep learning approaches to localize acoustic emissions (AE) sources within metallic plates with geometric features, such as rivet-connected stiffeners. In particular, a stack of autoencoders and a convolutional neural network are used. The idea is to leverage the reflection and reverberation patterns of AE waveforms as well as their dispersive and multimodal characteristics to localize their sources with only one sensor. Specifically, this paper divides the structure into multiple zones and finds the zone in which each source occurs. To train, validate, and test the deep learning networks, fatigue cracks were experimentally simulated by Hsu–Nielsen pencil lead break tests. The pencil lead breaks were carried out on the surface and at the edges of the plate. The results show that both deep learning networks can learn to map AE signals to their sources. These results demonstrate that the reverberation patterns of AE sources contain pertinent information to the location of their sources.
102 citations
TL;DR: In this article, the particle size distribution of aggregate effects on the mechanical and structural properties of cemented rockfill was analyzed and the particle failure model was constructed in the numerical software of PFC3D to reproduce the crack evolution and particle failure of a sample.
100 citations
TL;DR: In this article, a method combining acoustic emission (AE) signals with digital image correlation (DIC) was used to monitor compressive buckling behaviors of delamination composites.
98 citations
TL;DR: A new energy-dissipation method to identify crack initiation and propagation thresholds is introduced in this article, which demonstrates that the crack initiation threshold was proportional to the peak stress (σ p) for ratios that ranged from 0.4351 to 0.4753σ p.
Abstract: A new energy-dissipation method to identify crack initiation and propagation thresholds is introduced. Conventional and cyclic loading–unloading triaxial compression tests and acoustic emission experiments were performed for coal specimens from a 980-m deep mine with different confining pressures of 10, 15, 20, 25, 30, and 35 MPa. Stress–strain relations, acoustic emission patterns, and energy evolution characteristics obtained during the triaxial compression tests were analyzed. The majority of the input energy stored in the coal specimens took the form of elastic strain energy. After the elastic-deformation stage, part of the input energy was consumed by stable crack propagation. However, with an increase in stress levels, unstable crack propagation commenced, and the energy dissipation and coal damage were accelerated. The variation in the pre-peak energy-dissipation ratio was consistent with the coal damage. This new method demonstrates that the crack initiation threshold was proportional to the peak stress (σ
p) for ratios that ranged from 0.4351 to 0.4753σ
p, and the crack damage threshold ranged from 0.8087 to 0.8677σ
p.
95 citations
TL;DR: In this article, the authors presented an experimental study on leak detection of a water distribution system subject to failure of a socket joint, where the acoustic characteristics of leak signals in the socket and spigot pipe segments were investigated.
TL;DR: In this paper, the authors focused on the clustering of the indentation-induced interlaminar and intralaminar damages in carbon/epoxy laminated composites using Acoustic Emission (AE) technique.
Abstract: This study focuses on the clustering of the indentation-induced interlaminar and intralaminar damages in carbon/epoxy laminated composites using Acoustic Emission (AE) technique. Two quasi-isotropic specimens with layups of [60/0/-60]4S (is named dispersed specimen) and [604/04/-604]S (is named blocked specimen) were fabricated and subjected to a quasi-static indentation loading. The mechanical data, digital camera and ultrasonic C-scan images of the damaged specimens showed different damage evolution behaviors for the blocked and dispersed specimens. Then, the AE signals of the specimens were clustered for tracking the evolution behavior of different damage mechanisms. In order to select a reliable clustering method, the performance of six different clustering methods consisting of k-Means, Genetic k-Means, Fuzzy C-Means, Self-Organizing Map (SOM), Gaussian Mixture Model (GMM), and hierarchical model were compared. The results illustrated that hierarchical model has the best performance in clustering of AE signals. Finally, the evolution behavior of each damage mechanism was investigated by the clustered AE signals with hierarchical model. The results of this study show that using AE technique with an appropriate clustering method such as hierarchical model could be an applicable tool for structural health monitoring of composite structures.
TL;DR: In this paper, the authors explored the growth behavior of supercritical CO2 (SC-CO2)-induced fractures in layered tight sandstones through a series of laboratory fracturing experiments under triaxial stress states.
TL;DR: In this paper, the evolutionary features of the acoustic emissions and sound signals were investigated to improve the accuracy of rockburst prediction, and a quiescent period was observed in both the evolutionary process of the AE hits and the sound waveform on the eve of a rockburst.
Abstract: Rockbursts are markedly characterized by the ejection of rock fragments from host rocks at certain speeds. The rockburst process is always accompanied by acoustic signals that include acoustic emissions (AE) and sounds. A deep insight into the evolutionary features of AE and sound signals is important to improve the accuracy of rockburst prediction. To investigate the evolutionary features of AE and sound signals, rockburst tests on granite rock specimens under true-triaxial loading conditions were performed using an improved rockburst testing system, and the AE and sounds during rockburst development were recorded and analyzed. The results show that the evolutionary features of the AE and sound signals were obvious and similar. On the eve of a rockburst, a ‘quiescent period’ could be observed in both the evolutionary process of the AE hits and the sound waveform. Furthermore, the time-dependent fractal dimensions of the AE hits and sound amplitude both showed a tendency to continuously decrease on the eve of the rockbursts. In addition, on the eve of the rockbursts, the main frequency of the AE and sound signals both showed decreasing trends, and the frequency spectrum distributions were both characterized by low amplitudes, wide frequency bands and multiple peak shapes. Thus, the evolutionary features of sound signals on the eve of rockbursts, as well as that of AE signals, can be used as beneficial information for rockburst prediction.
TL;DR: In this article, the quenching effect on mechanical and flow behavior of Australian Strathbogie granite was investigated by conducting a series of micro and macro-experiments, profiling the micro-structure of rock with CT scanning, microscopic imaging and quantifying the thermally induced damage due to quenched treatment.
TL;DR: In this paper, a new qualitative AE parameter based on Shannon's entropy was proposed for damage monitoring, which is independent of the threshold and other time-driven parameters and can characterize the original micro-structural deformations.
TL;DR: In this article, a new index for evaluating coal brittleness was established from the perspective of energy evolution during coal failure, and the applicability of the new index and the influence of the confining pressure and cleat orientation on the coal brittleness were analyzed.
Abstract: Evaluating the ability of coal seams to form fracture networks by hydraulic fracturing is important for the development of coalbed methane (CBM) reservoirs. In this paper, a new index for evaluating coal brittleness was established from the perspective of energy evolution during coal failure. Uniaxial and triaxial compression tests of coal monitored by an acoustic emission (AE) system were carried out and the applicability of the new index and the influence of the confining pressure and cleat orientation on the coal brittleness were analyzed. The pre-peak and post-peak dissipated energies were the essential factors in determining the coal brittleness. The new index can characterize the influence of the external stress and cleat orientation on coal brittleness, and can also comprehensively reflect the mechanical properties of the coal during the pre-peak and post-peak stages. The corresponding AE energy curves can be divided into Rapid Fracture Type, Stable Fracture Type and Plastic Fracture Type. For the Rapid Fracture Type, the accumulation rate of AE energy showed sudden changes when reaching the yield stress and peak strength, which represented high brittleness. The Plastic Fracture Type represented low brittleness, and the accumulated AE energy curves were smooth—first concave and then convex. The brittleness index of coal studied in this paper can provide a new method for selecting the optimal CBM reservoir and optimizing the fracturing scheme.
TL;DR: A micro-cracking monitoring and fracture evaluation method for crumb rubber concrete based on the acoustic emission technique was developed in this paper, where the precursory microcracking activity and fracture was investigated.
Abstract: A micro-cracking monitoring and fracture evaluation method for crumb rubber concrete based on the acoustic emission technique was developed. The precursory micro-cracking activity and fracture beha...
TL;DR: In this article, the authors investigated the evolution of the frequency-magnitude b-value during stable and unstable frictional sliding experiments using a biaxial shear configuration.
TL;DR: In this paper, microscopic observation and uniaxial compression tests with acoustic emission (AE) monitoring were conducted on two bedrocks (i.e., marble and granite) after treatment with different thermal cycles at high temperature.
TL;DR: In this article, the effects of thermal damage on the strain burst characteristics of brittle rocks under true-triaxial loading-unloading conditions using the acoustic emission (AE) and kinetic energy analyses were investigated.
Abstract: Strain burst is a common problem encountered in brittle rocks in deep, high-stress mining applications. Limited research focuses on the effects of temperature on the strain burst mechanism and the kinetic energies of rocks. This study aims to investigate the effects of thermal damage on the strain burst characteristics of brittle rocks under true-triaxial loading-unloading conditions using the acoustic emission (AE) and kinetic energy analyses. The time-domain and frequency-domain responses related to strain burst were studied, and the damage evolution was quantified by b-values, cumulative AE energy and events rates. The ejection velocities of the rock fragments from the free face of the granite specimens were used to calculate kinetic energies. The experimental results showed that thermal damage resulted in a delay in bursting but increased the bursting rate at ~ 95% of normalised stress level. This is believed to be due to the micro-cracks induced by temperature exposure, and thus the accumulated AE energy (also supported by cumulative AE counts) at the initial loading stage was reduced, causing a delay in bursting. The strain burst stress, initial rock fragment ejection velocity, and kinetic energy decreased from room temperature (25 °C) to 100 °C, whereas they resulted in a gradual rise from 100 to 150 °C demonstrating more intense strain burst behaviour.
TL;DR: In this paper, the acoustic signals collected during the tests were analyzed by a classification method which consists of the k-means method and principal component analysis (PCA) to assess and evaluate the intensity of these activities for each stacking sequence.
TL;DR: In this paper, the authors investigated heat transfer and fracture propagation behaviors under in situ geological condition with LN2 injections, and the experimental results can provide evidences for the proposed crack propagation model for the coal masses.
TL;DR: In this article, the tensile strength and acoustic emission of shale were investigated at various orientations of the laminations with respect to the loading direction, and the results showed that fractal dimension values fluctuate with increase of the stress, signifying the initiation of complex microcracks within the shale.
TL;DR: In this article, the effect of loading and unloading behavior on the elastic properties of Harcourt granite was evaluated at two locations prior to failure: (1) crack initiation and (2) crack damage.
Abstract: The aim of this study is to characterise the changes in mechanical properties and to provide a comprehensive micro-structural analysis of Harcourt granite over different pre-heating temperatures under two cooling treatments (1) rapid and (2) slow cooling. A series of uniaxial compression tests was conducted to evaluate the mechanical properties of granite specimens subjected to pre-heating to temperatures ranging from 25–1000 °C under both cooling conditions. An acoustic emission (AE) system was incorporated to identify the fracture propagation stress thresholds. Furthermore, the effect of loading and unloading behaviour on the elastic properties of Harcourt granite was evaluated at two locations prior to failure: (1) crack initiation and (2) crack damage. Scanning electron microscopy (SEM) analyses were conducted on heat-treated thin rock slices to observe the crack/fracture patterns and to quantify the extent of micro-cracking during intense heating followed by cooling. The results revealed that the thermal field induced in the Harcourt granite pore structure during heating up to 100 °C followed by cooling causes cracks to close, resulting in increased mechanical characteristics, in particular, material stiffness and strength. Thereafter, a decline in mechanical properties occurs with the increase of pre-heating temperatures from 100 °C to 800 °C. However, the thermal deterioration under rapid cooling is much higher than that under slow cooling, because rapid cooling appears to produce a significant amount of micro-cracking due to the irreversible thermal shock induced. Multiple stages of loading and unloading prior to failure degrade the elastic properties of Harcourt granite due to the damage accumulated through the coalescence of micro-cracks induced during compression loading. However, this degradation is insignificant for pre-heating temperatures over 400 °C, since the specimens are already damaged due to excessive thermal deterioration. Moreover, unloading after crack initiation tends to cause insignificant irreversible strains, whereas significant permanent strains occur during unloading after crack damage, and this appears to increase with the increase of pre-heating temperature over 400 °C.
TL;DR: In this article, acoustic emission (AE) analysis method was applied to monitor the damage evolution process of ultra high performance concrete (UHPC) under direct tensile test, and the crack width developments of UHPCs were measured.
Abstract: In this study, acoustic emission (AE) analysis method was applied to monitor the damage evolution process of ultra high performance concrete (UHPC) under direct tensile test. Three types of UHPCs, including high strain-hardening UHPC, low strain-hardening UHPC and strain-softening UHPC were investigated. Meanwhile, the crack width developments of UHPCs during the tensile test were measured. Test results show that high strain-hardening UHPC exhibited high ductility by forming multiple microcracks invisible to naked eyes (typically below 0.05 mm) in the strain-hardening stage. The crack width-strain curves indicate that increasing the ultimate tensile strain of UHPC can improve its crack width control ability effectively. The AE analysis method could effectively detect the internal damages of the high strain-hardening UHPC at a strain of 600μe. At that time, the crack width was smaller than 0.01 mm that could not be detected by crack width measuring instrument in this study. For three types of UHPCs, damages were generated around the localized crack during the strain-softening stage. In a word, the AE analysis method provides strong evidence to the multiple cracking behavior of UHPC during the strain-hardening stage, and provides a clear explanation to the identical damage evolution mechanism for three types of UHPCs during the strain-softening stage.
TL;DR: In this article, a modification of the original b-value (Gutenberg-Richter parameter) is proposed to evaluate local damage of reinforced concrete structures subjected to dynamical loads via the acoustic emission (AE) method.
TL;DR: In this paper, the authors investigated BVID in two quasi-isotropic carbon/epoxy laminates under quasi-static indentation and low-Velocity impact (LVI) loadings using Acoustic Emission (AE).
Abstract: Despite the key advantages of Fiber Reinforced Polymer (FRP) composites, they are susceptible to Barely Visible Impact Damage (BVID) under transverse loadings This study investigates BVID in two quasi-isotropic carbon/epoxy laminates under quasi-static indentation and Low-Velocity Impact (LVI) loadings using Acoustic Emission (AE) First, the evolution of interlaminar and intralaminar damages is studied by analyzing the AE signals of the indentation test using b-value and sentry function methods Then, the specimens are subjected to the LVI loading and the induced damages are compared with the indentation test and the percentage of each damage mechanism is calculated using Wavelet Packet Transform (WPT) In consistent with the mechanical data, ultrasonic C-scan and digital camera images of the specimens, the AE results show a considerable similarity between the induced BVID under quasi-static indentation and LVI tests Finally, the obtained results show that AE is a powerful tool to study BVID in laminated composites under quasi-static and dynamic transverse loadings
TL;DR: In this article, the authors used uniaxial compression to measure the strength of a given rock mass under different stress levels and temperatures, and found that once the mass is subjected to higher thermal stresses, strength characteristics are significantly reduced, mainly due to thermal damage of mineral particles.
TL;DR: In this article, the effect of the orientation of non-recrystallized grains (non-DRX) and the LPSO phase on plasticity in extruded MgY2Zn1 alloy with a bimodal grain structure was studied in-situ using the combination of synchrotron diffraction and acoustic emission techniques during compression tests.