Rock Stability Assessment Based on the Chronological Order of the Characteristic Acoustic Emission Phenomena

Sudden inelastic deformations in rock are associated with acoustic emission (AE). Therefore, AE monitoring technique can be used to study the fracture processes of rock. In this paper, AE tests were conducted on the granitic gneiss specimens under the uniaxial compressive loading conditions. The temporal changes in AE hit parameters and spatial-temporal evolution of AE events during the failure process of the granitic gneiss specimens were studied, and several characteristic AE phenomena (i.e., dramatic increase in dominant frequency, AE energy, and hit rate, the AE event with a high energy level, and the through-going distribution of the AE events with intermediate energy levels) were statistically analyzed before the failure occurred. It was found that the chronological order of the characteristic AE phenomena was relatively certain and correspondingly had a close relationship with the crack development stage. Because of the difference of the stress level at each crack development stage, the stability at different crack development stages is different. Therefore, a rock stability assessment approach was established based on the chronological order of the characteristic AE phenomena, and then the rock stability was assessed using the proposed approach.

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Кинетика процесса накопления повреждений и разрушения в зонах концентраторов при испытаниях образцов на разрыв

Дефектоскопия ◽

10.31857/s0130308221010048 ◽

2021 ◽

pp. 33-44

Author(s):

Н.А. Махутов ◽

И.Е. Васильев ◽

Д.В. Чернов ◽

В.И. Иванов ◽

Е.В. Терентьев

Keyword(s):

Acoustic Emission ◽

Damage Accumulation ◽

Welded Joint ◽

High Energy ◽

Uniaxial Tensile ◽

High Energy Level ◽

Weight Content ◽

Emission Testing ◽

Initiation And Propagation ◽

Acoustic Emission Testing

The paper considers the effect of various stress concentrators on processes of damage accumulation, initiation and propagation of crack in steel (steel 3) samples during uniaxial tensile. In the middle of the samples there was a transverse welded joint or a hole with a diameter of 5 mm. The acoustic-emission testing results showed that weight content of location impulses (Wi) in the clusters of low, middle and high energy level and criteria parameters value Wi at the stages of the samples destruction have similar pattern of change despite the various types of concentrators, stress-strain material diagrams, pattern of damage accumulation, number of registered acoustic emission (AE) events and its registration activity.

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Double-layered wrap-around sensor network for three-dimensional positioning of acoustic emission sources and its effect on monitoring crack propagation in rock samples

International Journal of Distributed Sensor Networks ◽

10.1177/1550147718803068 ◽

2018 ◽

Vol 14 (9) ◽

pp. 155014771880306 ◽

Cited By ~ 2

Author(s):

Jing Yang ◽

Zonglong Mu ◽

Guangjian Liu ◽

Shaokun Gong ◽

Atif Javed ◽

...

Keyword(s):

Acoustic Emission ◽

Crack Propagation ◽

Sensor Network ◽

High Energy ◽

Crack Development ◽

Emission Source ◽

Acoustic Emission Activity ◽

Rock Samples ◽

Acoustic Emission Source ◽

Emission Activity

The present sensor arrangement in a cubic way for monitoring crack propagation in rock samples exhibits shortfalls of blind monitoring zone and large deviation. This study proposes a double-layered wrap-around sensor network, which enhances the monitoring range and improves the location accuracy of acoustic emission source. Furthermore, based on the polar formation algorithm, acoustic emission source was positioned to explore the propagation of microscopic cracks in cylindrical rock samples and this was further validated by the acoustic emission activity index. The results show that: (1) The double-layered wrap-around sensor network exhibits considerably broader monitoring range and enhanced precision. The simulated fracture formed from cracks of high-energy release had a favorable consistency with the macro-failure surface of rock specimens; (2) During the loading process, acoustic emission activity had a significant positive correlation with signal amplitude and the number of events. In addition, acoustic emission activity of medium-grained sandstone showed a tendency of decreasing—remaining at a low value—increasing—remaining at a high value, which exactly corresponds to the four rock loading stages of compaction, elastic deformation, crack development, and crack connection; (3) rock samples experienced micro-cracking of low energy, micro-cracking of high energy, and crack connection in sequence in the failure process, which shows a high consistency between crack development and acoustic emission activity. Thus, acoustic emission activity could be used as an index for assessing the rock failure state.

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Assessment of Acoustic Emission and Triaxial Mechanical Properties of Rock-Cemented Tailings Matrix Composites

Advances in Materials Science and Engineering ◽

10.1155/2019/6742392 ◽

2019 ◽

Vol 2019 ◽

pp. 1-12 ◽

Cited By ~ 12

Author(s):

Shuai Cao ◽

Erol Yilmaz ◽

Weidong Song ◽

Gaili Xue

Keyword(s):

Acoustic Emission ◽

Mechanical Strength ◽

Failure Modes ◽

Failure Process ◽

Development Stage ◽

Test System ◽

Energy Reserve ◽

Strengthening Effect ◽

Matrix Composites ◽

Damage Development

Acoustic emission (AE) test is a powerful technique for examining the sounds of cracks growing, breaking, and other modes of damage in cementitious materials deforming under stress, such as rock-cemented tailings matrix composites (RCTMC). RCTMC, an engineered mixture of tailings, cement, rock, and water, is widely used to fulfill numerous important roles at underground mine sites as a construction material and a ground support tool. To study the mechanical strength and AE properties of RCTMC, compression testing was carried out using a triaxial compression test system (TAW-2000) and AE monitoring system (PCI-2), and the failure modes of samples were also examined. Results have shown that (1) the failure process of RCTMC samples can be divided into six main stages: compaction, linear elastic characteristic, crack growth, primary damage development, cemented tailings backfill withstand stress zone, and secondary damage development stage. CTB has the strengthening effect on mechanical strength of rock; (2) the AE process can be also divided into six main stages: the prepeak quiescence period, the elastic energy reserve period, the first destruction development AE area, the secondary energy reserve period, the second damage development stage, and the postpeak calm period; and (3) samples’ cumulative ring count is “stepped” distribution over time, and the ring count has entered the postpeak flat stage after many active periods. The process of RCTMC samples from tensile to shear failure mode is represented by numerical simulation. Finally, the obtained experimental results can offer a useful reference for the further study of the mechanism of the surrounding rock and cemented tailings backfill structure.

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Study on Acoustic Emission Evolution Characteristic of Plastic and Brittle Coal Failure Process

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.807-809.2398 ◽

2013 ◽

Vol 807-809 ◽

pp. 2398-2403 ◽

Cited By ~ 3

Author(s):

Hui Ming Yang

Keyword(s):

Acoustic Emission ◽

Theoretical Basis ◽

Main Crack ◽

Event Rate ◽

Failure Process ◽

Acoustic Emission Event ◽

Crack Plane ◽

Stability Monitoring ◽

Rock Stability ◽

Study Results

Under uniaxial compression loading, the failure experiments of plastic and brittle coal are carried out to study the acoustic emission evolution characteristic. The results show that the evolution of acoustic emission during the coal failure process corresponds with the process of coal crack initiation, propagation and coalescence. The acoustic emission event rate of the typical plastic coal displayed the variation of up-peak-down during the failure process. The event rate of acoustic emission increase sharply and then drop steadily is the precursor that the main crack plane of the plastic coal would coalescence and the coal will lose its stability. During the failure process of typical brittle coal, the event rate increased steadily with the increase of stress, showing the variation of up-peak; the down stage of acoustic emission is not obvious because the brittle coal suddenly fail after stress peak. The study results can provide a theoretical basis for explanations of the variation of acoustic emission and the establishment of instability criteria in coal and rock stability monitoring engineering by AE technology.

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Mechanical properties and acoustic emission characteristics of coal samples with different fissure angle

10.21203/rs.3.rs-870741/v1 ◽

2021 ◽

Author(s):

Xuebin Gu ◽

Tongbin Zhao ◽

Weiyao Guo ◽

Xufei Gong ◽

Yongqiang Zhao ◽

...

Keyword(s):

Mechanical Properties ◽

Acoustic Emission ◽

Elastic Modulus ◽

Crack Growth ◽

Failure Mechanism ◽

Strain Softening ◽

Failure Process ◽

High Energy ◽

Emission Characteristics ◽

Quiet Period

Abstract To study the influence of fissure angle on the failure mechanism of coal mass, uniaxial compression tests were conducted on coal specimens with different fissure angles. The failure process and acoustic emission characteristics during loading were obtained. The mechanical properties and failure mode were further analyzed. The results showed that (1) The stress-strain behavior of specimens with different fissure angles can be divided into four typical stages, compaction, elastic deformation, crack growth and propagation, and strain-softening. The existence of pre-existing fissures reduces the duration of the elastic stage with an obvious influence on the crack growth and propagation stage, and strain-softening stage. (2) The uniaxial compressive strength, elastic modulus of the specimens containing pre-existing fissure are all lower than those of the unfissured. The strength and elastic modulus do not change significantly with fissure angle, which is closely related to the primary fracture of the coal. (3) With the increase of the fissure angle, the crack initiation location moves from the center of the pre-existing fissure to the tip. While fissure angle has no obvious effect on the crack propagation direction, the cracks develop along the loading direction. (4) The AE characteristics can be divided into three typical periods, quiet period, active period, and remission period. With the increase of the fissure angle, the duration proportion of the quiet period increases, indicating that the energy storage time of coal increases. With the increase of the fissure angle, the occurrence time of low frequency and high energy signal is delayed, indicating that the large-size rupture gradually concentrates in the late loading period. (5) Compared with rock samples containing pre-existing fissure, coal specimens have more primary fractures, and the failure mechanism of coal is dominated by the non-uniform primary fractures.

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Modification of Coal Samples with Bursting Liability Subjected to Microwave Irradiation

Shock and Vibration ◽

10.1155/2021/1867771 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Yingyuan Wen ◽

Weiming Guan ◽

Hongchao Zhao ◽

Honglin Liu ◽

Huwei Li ◽

...

Keyword(s):

Acoustic Emission ◽

Microwave Irradiation ◽

Coal Seam ◽

Oil Recovery ◽

Failure Process ◽

Strain Curve ◽

High Energy ◽

Heating Time ◽

Coal Bed ◽

Stable Crack Propagation

This paper introduces the innovative technique to release the bursting liability of coal seam via microwave irradiation. To verify the feasibility of this environment-friendly technique, a series of laboratory tests incorporating acoustic emission (AE) investigation were carried out. Test results indicated that both the uniaxial compressive strength (UCS) and bursting energy index of raw and water-soaked coal samples were significantly reduced. In particular, the bursting liability was reduced by one level when the values of UCS were compared, the evidence of which is the variation of wave velocities of tested coal samples. It can also be found from the events and hits in the complete stress-strain curve and the cumulative curve of acoustic emission that the elastic modulus of the raw and water-soaked coal samples subjected to microwave irradiation decreased by 58.42% and 29.63%, respectively. This facilitates the entry into the stage of stable crack propagation more quickly, the growth rate and size of the cracks were slower and more uniform, and there were no smaller coal fragments ejecting during the failure process of the coal samples. Meanwhile, the proportion of high-energy events released in coal samples experienced a decline after the treatment of the microwave. Moreover, microwave heating principally promoted the initiation and expansion of microcracks in coal samples under the influence of microwave power of 1 kW and a heating time of 120s, which may cause the overall damage of large fractures to break into multiple small and medium cracks. Based on the experimental results, the conceptual process of using microwave in weakening the bursting liability of coal seam was then proposed, which will be the meaningful reference for microwave-assisted oil recovery and coal bed methane production.

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Deformation and Acoustic Emission Characteristics of Cracked Granite during Creep

Advances in Materials Science and Engineering ◽

10.1155/2020/7075287 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Chunping Wang ◽

Jingli Xie ◽

Jian Liu

Keyword(s):

Acoustic Emission ◽

Axial Strain ◽

Failure Process ◽

Deformation Characteristic ◽

Temporal Distribution ◽

Confining Pressure ◽

High Energy ◽

Lateral Strain ◽

Creep Tests ◽

Confining Pressures

A series of multistage creep tests under different confining pressures with acoustic emission monitoring have been performed to investigate the deformation characteristic and failure process of cracked granite during creep. The critical axial strain of cracked sample showed an increasing tendency with the increase of confining pressure. In contrast, critical lateral strain experienced a process of descending first at low confinement and then remaining nearly constant at high confinement. Compared with loading-cracked specimen, smaller critical axial strain, greater critical lateral strain, and higher lateral creep strain rate were found for unloading-cracked specimen. Based on the spatial and temporal distribution of acoustic emission events, the cracking process during creep was analysed. The AE events with high energy are mainly concentrated at the final fracture area of the specimen. The higher the confining pressure, the more the AE events with low energy. Compared with the loading-cracked specimen, the percentage of AE events with high energy is relatively small for the unloading-cracked specimen.

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Experimental Research on Brittleness and Rockburst Proneness of Three Kinds of Hard Rocks under Uniaxial Compression

Advances in Civil Engineering ◽

10.1155/2021/8891633 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Rongchao Xu ◽

Yiding Jin ◽

Yumin Zhang

Keyword(s):

Acoustic Emission ◽

Uniaxial Compression ◽

Fracture Mechanism ◽

Large Scale ◽

Rock Fracture ◽

Failure Process ◽

High Energy ◽

Brittle Rock ◽

Evaluation Index ◽

Unstable Crack

Rockburst is a highly destructive geological disaster caused by excavation and unloading of hard and brittle rock mass under high geostress environment. Quantitative evaluation of rock brittleness and rockburst proneness is one of the important tasks in potential rockburst assessment. In this study, uniaxial compression and acoustic emission tests were carried out for basalt, granite, and marble, and their brittleness and rockburst proneness were quantitatively evaluated. The acoustic emission evolution characteristics of the three rocks during uniaxial compression were analyzed, and the differences of fracture mechanism of the three rocks were compared. The results show that (1) based on the brittleness evaluation index, basalt is the most brittle rock, followed by granite, and marble is the weakest; (2) based on the rockburst proneness evaluation index, combined with the macroscopic failure phenomenon and morphology of the samples, the rockburst proneness of basalt is the strongest, followed by granite, and marble is the weakest; (3) there exists a positive correlation between rockburst proneness and brittleness, and the fitting results show that they are approximately exponential; and (4) brittleness has an important influence on the rock fracture mechanism. Unlike marble, basalt and granite with strong brittleness continuously present high-energy acoustic emission signals in the stage of unstable crack propagation, and large-scale fracture events continue to occur; from the calculation results of the acoustic emission b value, the stronger the brittleness of rock, the larger the proportion of large-scale fracture events in the failure process.

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The protein and energy nutrition of the pig. V. The effect of varying the protein and energy levels in the ‘finishing diets’ of heavy pigs

The Journal of Agricultural Science ◽

10.1017/s0021859600048978 ◽

1965 ◽

Vol 65 (3) ◽

pp. 405-409 ◽

Cited By ~ 3

Author(s):

D. W. Robinson

Keyword(s):

Crude Protein ◽

Energy Levels ◽

Live Weight ◽

High Energy ◽

Feeding Trial ◽

Large White ◽

High Energy Level ◽

Finishing Diets ◽

Main Effects ◽

Carcass Measurement

1. A feeding trial was carried out using fortyeight Large White pigs, individually fed in a Danish type piggery. Six different diets prepared at two levels of digestible energy and three levels of crude protein were fed to eight replicates consisting of four hogs and four gilts per replicate. A record was maintained of the weekly live-weight gain and food was given at a defined restricted level in relation to the live weight. Carcass quality was assessed by complete dissection into visible lean, fat and bone etc.2. Of the main effects, energy, supply was without significant effect upon growth, food conversion efficiency (FCE) or any carcass characteristics except body length which was increased with a high energy level. The protein level in the diet had a significant effect upon the percentage of carcass lean and the killing-out percentage, the higher levels of protein increasing both these measurements significantly. Gilts were significantly superior to hogs in every carcass measurement although hogs grew significantly faster.

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