scholarly journals Laboratory Study of Deformational Characteristics and Acoustic Emission Properties of Coal with Different Strengths under Uniaxial Compression

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1070
Author(s):  
Shuangwen Ma ◽  
Han Liang ◽  
Chen Cao
Keyword(s):  
Plastic Deformation ◽  
Acoustic Emission ◽  
Bearing Capacity ◽  
Uniaxial Compression ◽  
Coal Sample ◽  
Hard Coal ◽  
Dissipation Energy ◽  
Deformation Stage ◽  
Soft Coal ◽  
Ae Counts

Acoustic emission (AE) can reflect the dynamic changes in a material’s structure, and it has been widely used in studies regarding coal mechanics, such as those focusing on the influence of loading rate or water content change on the mechanical properties of coal. However, the deformational behavior of coals with various strengths differs due to the variation in microstructure. Hard coal presents brittleness, which is closely related to certain kinds of geological disasters such as coal bursts; soft coal exhibits soft rock properties and large deformation mechanical characteristics. Therefore, conclusions drawn from AE characteristics of a single coal sample have application limitations. This paper studies the deformation patterns and AE characteristics of coals with different strengths. A uniaxial compression experiment was carried out using coal samples with average uniaxial compressive strengths of 30 MPa and 10 MPa; the SAEU2S digital AE system was used to measure the AE counts, dissipation energy, and fracturing point distributions at each deformation stage of the different coals. The results show that the bearing capacity of hard coal is similar to that of the elastic stage and plastic deformation stage, but it may lose its bearing capacity immediately after failure. Soft coal has a relatively distinct stress-softening deformation stage and retains a certain bearing capacity after the peak. The AE counts and dissipation energy of hard coal are significantly higher than those of soft media, with average increases of 49% and 26%, respectively. Via comparative analysis of the distribution and development of internal rupture points within soft coal and hard coal at 15%, 70%, and 80% peak loads, it was observed that hard coal has fewer rupture points in the elastic deformation stage, allowing it to maintain good integrity; however, its rupture points increase rapidly under high stress. Soft coal produces more plastic deformation under low loading conditions, but the development of the fracture is relatively slow in the stress-softening stage. We extracted and summarized the AE characteristics discussed in the literature using one single coal sample, and the results support the conclusions presented in this paper. This study subdivided the deformation process and AE characteristics of soft and hard coals, providing a theoretical guidance and technical support for the application of AE technology in coal with different strengths.

scholarly journals Uniaxial Experimental Study of the Deformation Behavior and Energy Evolution of Conjugate Jointed Rock Based on AE and DIC Methods

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Jiliang Pan ◽  
Xu Wu ◽  
Qifeng Guo ◽  
Xun Xi ◽  
Meifeng Cai
Keyword(s):  
Stress Field ◽  
Uniaxial Compression ◽  
Testing Machine ◽  
Peak Strength ◽  
Image Correlation ◽  
Compression Tests ◽  
Dissipation Energy ◽  
Included Angle ◽  
Natural Rock ◽  
Ae Counts

Conjugate joint is one of the most common joint forms in natural rock mass, which is produced by different tectonic movements. To better understand the preexisting flaws, it is necessary to investigate joint development and its effect on the deformation and strength of the rock. In this study, uniaxial compression tests of granite specimens with different conjugate joints distribution were performed using the GAW-2000 compression-testing machine system. The PCI-2 acoustic emission (AE) testing system was used to monitor the acoustic signal characteristics of the jointed specimens during the entire loading process. At the same time, a 3D digital image correlation (DIC) technique was used to study the evolution of stress field before the peak strength at different loading times. Based on the experimental results, the deformation and strength characteristics, AE parameters, damage evolution processes, and energy accumulation and dissipation properties of the conjugate jointed specimens were analyzed. It is considered that these changes were closely related to the angle between the primary and secondary joints. The results show that the AE counts can be used to characterize the damage and failure of the specimen during uniaxial compression. The local stress field evolution process obtained by the DIC can be used to analyze the crack initiation and propagation in the specimen. As the included angle increases from 0° to 90°, the elastic modulus first decreases and then increases, and the accumulative AE counts of the peak first increase and then decrease, while the peak strength does not change distinctly. The cumulative AE counts of the specimen with an included angle of 45° rise in a ladder-like manner, and the granite retains a certain degree of brittle failure characteristics under the axial loading. The total energy, elastic energy, and dissipation energy of the jointed specimens under uniaxial compression failure were significantly reduced. These findings can be regarded as a reference for future studies on the failure mechanism of granite with conjugate joints.

scholarly journals Failure behaviour and acoustic emission characteristics of different rocks under uniaxial compression

2019 ◽  
Author(s):  
Zhaohui Wang ◽  
Jiachen Wang ◽  
Shengli Yang ◽  
Lianghui Li ◽  
Meng Li
Keyword(s):  
Acoustic Emission ◽  
Bearing Capacity ◽  
Strain Hardening ◽  
Uniaxial Compression ◽  
Strength Increase ◽  
Evolutionary Trend ◽  
Sudden Increase ◽  
Load Bearing Capacity ◽  
Load Bearing ◽  
Ae Energy

Abstract In the present study, mechanical behaviour of three types of rocks has been investigated under uniaxial compression. The stress–strain responses of the tested rocks are composed of four regions: the compaction stage; elastic stage; strain hardening stage and strain softening stage. The elastic modulus and uniaxial compressive strength increase in order from the result of the coal to the mudstone and then to the sandstone, while the Poisson ratio shows a reverse order. In coal and mudstone, volumetric dilation behaviour vanishes gradually with an increase in damage degree, while it remains stable in the sandstone where the strain hardening behaviour is less obvious. Regarding acoustic emission (AE) characteristics, AE hit and AE energy show a similar evolutionary trend in the loading process. A sudden increase in AE energy is accompanied with drastic drop or local fluctuation in the load-bearing capacity of the rock while AE hit fails in predicting such variation in the load-bearing capacity. A quiet stage of AE signal prior to the peak stress is captured, which can be taken as a precursor for rock failure. Failure pattern of the coal, mudstone and sandstone varies from shear faulting to tension-shear mixed fracturing and then to axial splitting, which is in good accordance with that deduced from AE location analysis.

Rock’s Acoustic Emission and Damage Deformation Characteristic in Uniaxial Compression Condition

2012 ◽  
Vol 170-173 ◽  
pp. 486-491 ◽  
Author(s):  
Zi Hong Guo ◽  
Qian Tao ◽  
Bao Xian Liu ◽  
Chao Luo ◽  
Li Meng ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Deformation Characteristic ◽  
Constitutive Models ◽  
Emission Characteristic ◽  
Uniaxial Compression Test ◽  
Strength Based ◽  
Damage Constitutive Model ◽  
Set Up ◽  
Ae Counts

Rock’s uniaxial compression test is completed and the datum is analyzed, then relationship between loading time and AE amplitude, AE counts sum, AE total energy’s released rate come out. Rock’s critical damage is defined which equal result of one minus ratios of residual strength to critical strength. Based on strain equivalence discipline, damage constitutive models related with acoustic emission characteristic are set up. With damage constitutive models established with AE counts sum and AE total energy serving as damage variables respectively and testing datum, the relationship between rock’s damage and stress and strain is described. Then conclusions come out: 1) damage constitutive model with AE counts sum serving as damage variable manifest rock’s damage increasing process and accords with testing result better; 2) theoretical curve is well consistent with testing curve at rock’s peak strength zone.

scholarly journals Acoustic Emission Response Characteristics of Anthracitic Coal under Uniaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Haiyan Wang ◽  
Gongda Wang ◽  
Guojun Zhang ◽  
Feng Du ◽  
Ji Ma
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Wave Velocity ◽  
Coal Sample ◽  
Compression Process ◽  
Deformation And Failure ◽  
Response Characteristics ◽  
Fracture Evolution ◽  
Anthracite Coal ◽  
Coal Deformation

The damage evolution of coal is accompanied by the generation of acoustic emission (AE) signal. Through the analysis and research of the AE response characteristics of coal deformation and failure, it is helpful to reveal the initiation, propagation, and fracture evolution of microcracks in coal. In this work, taking the anthracite coal as research object, the basic mechanical parameters of the coal samples were obtained by ultrasonic tests and uniaxial compression experiments. Meanwhile, the AE response characteristics of coal samples during uniaxial compression were obtained through AE experiments. The results show that when the density is low, the wave velocity of the coal sample decreases with the increase of density. When the density is higher than a certain value, the wave velocity of the coal sample increases with the increase of density. Through the measurement of ultrasonic wave velocity, it is found that there is some nonuniformity and anisotropy in raw coal samples. The ring counts, energy counts, and AE events with time in uniaxial compression process have approximately normal distribution. The AE events are concentrated in the elastic stage and yield stage, and the energy amplitude of AE events is higher in the plastic stage. Compared with the ring counts and energy counts, the AE events have a good positioning function, which can better reflect the evolution of internal cracks of coal samples during uniaxial compression.

scholarly journals Acoustic emission response characteristics of anthracitic coal under uniaxial compression

2020 ◽  
Author(s):  
Feng Du ◽  
Kai Wang ◽  
Guojun Zhang ◽  
Gongda Wang ◽  
Qian Zhang ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Wave Velocity ◽  
Coal Sample ◽  
Compression Process ◽  
Deformation And Failure ◽  
Response Characteristics ◽  
Fracture Evolution ◽  
Anthracite Coal ◽  
Coal Deformation

Abstract The damage evolution of coal is accompanied by the generation of acoustic emission (AE) signal. Through the analysis and research of AE response characteristics of coal deformation and failure, it is helpful to reveal the initiation, propagation and fracture evolution of micro cracks in coal. In this work, taking the anthracite coal as research object, the basic mechanical parameters of coal samples were obtained by ultrasonic tests and uniaxial compression experiments. Meanwhile, the AE response characteristics of coal samples during uniaxial compression were obtained through AE experiments. The results show that when the density is low, the wave velocity of coal sample decreases with the increase of density. When the density is higher than a certain value, the wave velocity of coal sample increases with the increase of density. Through the measurement of ultrasonic wave velocity, it is found that there are some non-uniformity and anisotropy in raw coal samples. The distribution of ring count, energy count and AE events with time in uniaxial compression process is approximately normal distribution. The AE events are concentrated in the elastic stage and yield stage, and the energy amplitude of AE events is higher in the plastic stage. Compared with the ring count and energy count, the AE events have good positioning function, which can better reflect the evolution of internal cracks in coal samples during uniaxial compression.

scholarly journals Damage characterization of red sandstones using uniaxial compression experiments

RSC Advances ◽  
2018 ◽  
Vol 8 (70) ◽  
pp. 40267-40278
Author(s):  
Kui Zhao ◽  
Zhen Huang ◽  
Bin Yu
Keyword(s):  
Acoustic Emission ◽  
Constitutive Model ◽  
Uniaxial Compression ◽  
Volume Strain ◽  
Dissipation Energy ◽  
Damage Characterization ◽  
Crack Volume

This paper proposes calculation formulae for damage variables that are characterized by four methods based on acoustic emission (AE), crack volume strain, a damage statistic constitutive model, and dissipation energy.

scholarly journals Experimental Investigation of Progressive Failure Processes Using 3D Acoustic Emission Tomography

2021 ◽  
Vol 9 ◽  
Author(s):  
Yan Cheng ◽  
Paul Hagan ◽  
Rudrajit Mitra ◽  
Shuren Wang ◽  
Hong-Wei Yang
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Failure Modes ◽  
Progressive Failure ◽  
Three Dimensional ◽  
Stress Conditions ◽  
Compression Tests ◽  
Tomographic Images ◽  
Fracture Development ◽  
Ae Counts

In this paper, the potential of 3D acoustic emission (AE) tomography technique in demonstrating fracture development and delineating stress conditions was examined. Brazilian tests and uniaxial compression tests were monitored by 3D AE tomography. AE counts, AE source locations and 3D tomographic images of locally varying velocity distributions were analyzed along with stress and strain measurements. Experimental results revealed two distinct failure processes between Brazilian tests and uniaxial compression tests indicated by differences in AE counts, source locations and the temporal variation of velocity. Furthermore, the development of micro-cracks showed by the results correlated well with theoretical analysis and experimental observations. Additionally, stress patterns, failure modes and final failure planes were indicated by AE locations and velocity tomography. Three-dimensional velocity tomographic images indicated the anisotropy of samples caused by stresses as well. These results confirm the usefulness of AE tomography as a method to monitor stress induced failure and the potential of AE tomography for delineating stress conditions and predicting rock failure.

scholarly journals Study on Acoustic Emission Characteristics and Mechanical Behavior of Water-Saturated Coal

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Muhammad Ali ◽  
Enyuan Wang ◽  
Zhonghui Li ◽  
Haishan Jia ◽  
Dexing Li ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Mechanical Behavior ◽  
Uniaxial Compression ◽  
Engineering Practice ◽  
Slow Increase ◽  
Soaking Time ◽  
Emission Signal ◽  
Secondary Cracks ◽  
Water Saturated ◽  
Ae Counts

In terms of coal’s stability and failure, soaking time and water content play a significant role in geotechnical engineering practice. To determine the soaking time effect on the mechanical behavior of coal samples and the response of AE (acoustic emission) signal throughout loading, the samples with different soaking times (0–120 hours (h)) were prepared and tested under uniaxial compression. AE signals were continuously monitored during loading to examine the AE characteristic response via the AEwin Express-8.0 system. The results revealed that the mechanical characteristics of the coal samples decreased with an increase in soaking time. When coal samples were subjected to uniaxial compression, AE events occurred due to the formation of the cracks, which further propagated to cause coal fracture. AE counts and the accumulative counts fluctuated with time and corresponded very well to the load. Therefore, AE counts and the trend of the accumulative counts of AE qualitatively explained the rupture of the coal under stress. In addition, the variation in trends of AE counts, AE accumulative counts, and load with time at various phases of all samples were obtained. It is concluded that AE counts increase suddenly during a slow increase phase and peak at the active increase phase. During the attenuation phase, the AE counts first decrease significantly with stress drop, but also a slight increase was observed due to the initiation of secondary cracks. These research results are of great significance as a precursor in coal and rock failure.

scholarly journals Acoustic Emission Characteristics and Joint Nonlinear Mechanical Response of Rock Masses under Uniaxial Compression

Energies ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 200
Author(s):  
Zhongliang Feng ◽  
Xin Chen ◽  
Yu Fu ◽  
Shaoshuai Qing ◽  
Tongguan Xie
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Modes ◽  
Strain Curve ◽  
Particle Flow Code ◽  
Rock Masses ◽  
Physical Experiments ◽  
Inclination Angles ◽  
Joint Inclination

The joint arrangement in rock masses is the critical factor controlling the stability of rock structures in underground geotechnical engineering. In this study, the influence of the joint inclination angle on the mechanical behavior of jointed rock masses under uniaxial compression was investigated. Physical model laboratory experiments were conducted on jointed specimens with a single pre-existing flaw inclined at 0°, 30°, 45°, 60°, and 90° and on intact specimens. The acoustic emission (AE) signals were monitored during the loading process, which revealed that there is a correlation between the AE characteristics and the failure modes of the jointed specimens with different inclination angles. In addition, particle flow code (PFC) modeling was carried out to reproduce the phenomena observed in the physical experiments. According to the numerical results, the AE phenomenon was basically the same as that observed in the physical experiments. The response of the pre-existing joint mainly involved three stages: (I) the closing of the joint; (II) the strength mobilization of the joint; and (III) the reopening of the joint. Moreover, the response of the pre-existing joint was closely related to the joint’s inclination. As the joint inclination angle increased, the strength mobilization stage of the joint gradually shifted from the pre-peak stage of the stress–strain curve to the post-peak stage. In addition, the instantaneous drop in the average joint system aperture (aave) in the specimens with medium and high inclination angles corresponded to a rapid increase in the form of the pulse of the AE activity during the strength mobilization stage.

scholarly journals In Situ Shear Test for Revealing the Mechanical Properties of the Gravelly Slip Zone Soil

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6531 ◽  
Author(s):  
Zongxing Zou ◽  
Qi Zhang ◽  
Chengren Xiong ◽  
Huiming Tang ◽  
Lei Fan ◽  
...  
Keyword(s):  
Mechanical Property ◽  
Plastic Deformation ◽  
Shear Test ◽  
Slip Zone ◽  
Three Gorges Reservoir Area ◽  
Silty Clay ◽  
Sigmoid Function ◽  
In Situ Test ◽  
Deformation Stage

Slip zone soil is usually composed of clay or silty clay; in some special geological environments, it contains gravels, which make the properties of the slip zone soil more complex. Unfortunately, in many indoor shear tests, gravels are removed to meet the demands of apparatus size, and the in situ mechanical property of the gravelly slip zone soil is rarely studied. In this study, the shear mechanical property of the gravelly slip zone soil of Huangtupo landslide in the Three Gorges Reservoir area of China was investigated by the in situ shear test. The test results show that the shear deformation process of the gravelly slip zone soil includes an elastic deformation stage, elastic–plastic deformation stage, and plastic deformation stage. Four functions were introduced to express the shear constitutive model of the gravelly slip zone soil, and the asymmetric sigmoid function was demonstrated to be the optimum one to describe the relationship of the shear stress and shear displacement with a correlation coefficient of 0.986. The comparison between the in situ test and indoor direct shear test indicates that gravels increase the strength of the slip zone soil. Therefore, the shear strength parameters of the gravelly slip zone soil obtained by the in situ test are more preferable for evaluating the stability of the landslide and designing the anti-slide structures.

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