scholarly journals Study on the Mechanical Behavior and Acoustic Emission Properties of Granite under Triaxial Compression

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Jiaqi Guo ◽  
Pengfei Liu ◽  
Junqi Fan ◽  
Hengyuan Zhang
Keyword(s):  
Acoustic Emission ◽  
Crack Initiation ◽  
Triaxial Compression ◽  
Testing Machine ◽  
Confining Pressure ◽  
High Energy ◽  
Granite Sample ◽  
Initiation Point ◽  
Granite Samples ◽  
Ae Signals

To study the rock mechanical behaviors and damage process mechanism of granite samples under triaxial stress, conventional triaxial compression tests were carried out on an RMT-150B rock mechanics testing machine and acoustic emission detector. The test results show that the strength of the granite sample has a good linear relationship with the confining pressure, the cohesion force c of the granite samples is 29.37 MPa, and the internal friction angle is 54.23° by calculation based on the Mohr-Coulomb strength criterion. The larger the initial confining pressure of the rock sample is, the larger the crack initiation stress ( σ ci ) and dilatancy stress ( σ cd ) of the granite specimen are, the larger the energy values at the crack initiation point and dilatancy point are, and the larger the peak energy storage and energy release rate at the failure are. In the case of a small initial confining pressure, the AE ringdowning counts and the cumulative AE ringing counts increase to their maximum instantaneously at the peak stress point, and the damage of the sample develops rapidly. While the initial confining pressure is high, the AE ringing counts and the cumulative AE ringing counts of the granite specimens increase evenly, and the deformation damage of the granite specimens is slow. Before the crack initiation point, AE signals are mainly low-energy and low-frequency friction-type AE events, while after the dilatation point, AE signals of samples are mainly high-frequency and high-energy fracture-type AE events. The failure mode of granite samples judged by acoustic emission parameters according to the distribution of characteristic values of AE parameters RA and AF is consistent with the reality. The AE b value of the granite sample is large when the confining pressure is low, and there will be a sudden drop, the decrease time is late, and the decrease rate is large. Under the same stress level, the larger the confining pressure is, the larger the damage variable D is.

scholarly journals Method Improvement and Effect Analysis of Triaxial Compression Acoustic Emission Test for Coal and Rock

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Yan Zhou ◽  
Chuanxiao Liu ◽  
Depeng Ma
Keyword(s):  
Acoustic Emission ◽  
Rock Mechanics ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Outer Wall ◽  
Test System ◽  
Test Method ◽  
Effect Analysis ◽  
High Confining Pressure ◽  
Ae Signals

In the study of the acoustic emission (AE) characteristics of rock samples or coal samples under triaxial compression conditions, most scholars carry out relevant experiments by placing the AE detector on the outer wall of the triaxial chamber of the rock mechanics test system. Owing to the continuous obstruction of AE signals by hydraulic oil in the triaxial chamber and the frequent interference of external noises, the final experimental data cannot objectively and truly reflect the essential characteristics of AE of rock or coal under triaxial compression conditions. It is difficult to scientifically guide and accurately predict precursory information of rock’s or coal’s rupture and instability. Based on this, a series of improvements and optimizations were made to the original triaxial compression AE test method, which is based on the modification of the communication interface of the rock mechanics test system, a test head which can put the AE detector into the triaxial chamber and withstands high confining pressure, in order to obtain the true, comprehensive, and reliable AE signals. It is of considerable significance to the scientific determination of the precursory characteristics of rock’s or coal’s rupture and instability.

scholarly journals Effect of Multistage Thermal Cracking on Permeability of Granite

2020 ◽  
Vol 2020 ◽  
pp. 1-8 ◽  
Author(s):  
Zi-jun Feng ◽  
Yang-sheng Zhao ◽  
Peng Zhao ◽  
Zhi-jun Wan
Keyword(s):  
Acoustic Emission ◽  
Ambient Pressure ◽  
Testing Machine ◽  
Thermal Cracking ◽  
Granite Sample ◽  
Term Evaluation ◽  
Reservoir Construction ◽  
Granite Samples ◽  
Ae Counts

Experiments on thermal cracking in granite sample were conducted through acoustic emission monitoring, and changes in permeability were concomitantly studied using 600°C 20 MN servo-controlled triaxial rock mechanics testing machine. Two granite samples, 200 mm in diameter and 400 mm long, from Shandong, China, were selected for these experiments. Both samples were heated up to 500°C at ambient pressure. We find that thermal cracking of large-scaled granite is discontinuous and exhibits multiple stages with temperature. In addition, the permeability exhibits the following characteristics: (a) it neither increases nor decreases monotonously with the temperature rising and it exhibits multipeak due to the multistage thermal cracking; (b) the temperature of permeability peak lags behind that of the drastic acoustic emission activities. Both AE counts and permeability dramatically increased after 300°C, which indicated serious thermal cracking occurred after 300°C. Permeability ratio is approximately linear with the ratio of AE cumulative counts. The results will be helpful for understanding the mechanism of geothermal reservoir construction and long-term evaluation of safety for nuclear waste geological disposal.

Study on mechanical properties and damage evolution of carbonaceous shale under triaxial compression with acoustic emission

2021 ◽  
pp. 105678952199119
Author(s):  
Kai Yang ◽  
Qixiang Yan ◽  
Chuan Zhang ◽  
Wang Wu ◽  
Fei Wan
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Water Content ◽  
Damage Evolution ◽  
Damage Assessment ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Damage Variable ◽  
Natural State ◽  
Carbonaceous Shale

To explore the mechanical properties and damage evolution characteristics of carbonaceous shale with different confining pressures and water-bearing conditions, triaxial compression tests accompanied by simultaneous acoustic emission (AE) monitoring were conducted on carbonaceous shale rock specimens. The AE characteristics of carbonaceous shale were investigated, a damage assessment method based on Shannon entropy of AE was further proposed. The results suggest that the mechanical properties of carbonaceous shale intensify with increasing confining pressure and degrade with increasing water content. Moisture in rocks does not only weaken the cohesion but also reduce the internal friction angle of carbonaceous shale. It is observed that AE activities mainly occur in the post-peak stage and the strong AE activities of saturated carbonaceous shale specimens appear at a lower normalized stress level than that of natural-state specimens. The maximum AE counts and AE energy increase with water content while decrease with confining pressure. Both confining pressure and water content induce changes in the proportions of AE dominant frequency bands, but the changes caused by confining pressure are more significant than those caused by water content. The results also indicate that AE entropy can serve as an applicable index for rock damage assessment. The damage evolution process of carbonaceous shale can be divided into two main stages, including the stable damage development stage and the damage acceleration stage. The damage variable increases slowly accompanied by a few AE activities at the first stage, which is followed by a rapid growth along with intense acoustic emission activities at the damage acceleration stage. Moreover, there is a sharp rise in the damage evolution curve for the natural-state specimen at the damage acceleration stage, while the damage variable develops slowly for the saturated-state specimen.

scholarly journals Identification of Deformation Stage and Crack Initiation in TC11 Alloys Using Acoustic Emission

2020 ◽  
Vol 10 (11) ◽  
pp. 3674
Author(s):  
Jiaoyan Huang ◽  
Zhiheng Zhang ◽  
Cong Han ◽  
Guoan Yang
Keyword(s):  
Acoustic Emission ◽  
Titanium Alloy ◽  
Crack Initiation ◽  
Peak Frequency ◽  
Identification Accuracy ◽  
Energy Ratio ◽  
Frequency Bands ◽  
Mode Decomposition ◽  
Tc11 Titanium Alloy ◽  
Ae Signals

The Acoustic Emission (AE) is a widely used real-time monitoring technique for the deformation damage and crack initiation of areo-engine blades. In this work, a tensile test for TC11 titanium alloy, one of the main materials of aero-engine, was performed. The AE signals from different stages of this test were collected. Then, the AE signals were decomposed by the Variational Mode Decomposition (VMD) method, in which the signals were divided into two different frequency bands. We calculated the engery ratio by dividing the two different frequency bands to characterize TC11′s degree of deformation. The results showed that when the energy ratio was −0.5 dB, four stages of deformation damage of the TC11 titanium alloy could be clearly identified. We further combined the calculated Partial Energy Ratio (PER) and Weighted Peak Frequency (WPF) to identify the crack initiation of the TC11 titanium alloy. The results showed that the identification accuracy was 96.33%.

scholarly journals Comparative analysis of the strength of restoration polymers of light polymerization for dental restoration using the acoustic emission method: part one

2021 ◽  
Vol 107 (3) ◽  
pp. 26-32
Author(s):  
V. Kukhta ◽  
◽  
V. Makeev ◽  
O. Kyrmanov ◽  
V. Skalsky ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Comparative Analysis ◽  
High Energy ◽  
Dental Restoration ◽  
Acoustic Emission Method ◽  
Local Loading ◽  
Emission Method ◽  
Composite Failure ◽  
Initial Stage ◽  
Ae Signals

Purpose. Comparative analysis of the strength of hybrid restoration composites of light polymerization during their local loading using the phenomenon of acoustic emission. The following restoration composites were studied: Latelux, Tetric N-Ceram, Charisma Classic. Results. It was determined that the nature of the destruction of all composites is the same: elastic-plastic at the initial stage of the load with a transition to brittle as its further growth. Three types of composite failure are observed: correct, incorrect and mixed. The first predominated during fracture under the action of local loading of the Latelux composite, for Tetric N-Ceram and Charisma Classic materials a mixed type of fracture is characteristic. Conclusions. Analysis of the parameters of the AE signals showed that the signals had the highest amplitude and energy when the Tetric N-Ceram composite was destroyed, and the lowest – Latelux. All dental composites are dominated by high-energy ductile-brittle and brittle fracture, which indicates the spread of micro- and macrocracks of various sizes in materials. Key words: polymer composites, strength, acoustic emission method.

scholarly journals Influence of Freeze-Thaw Cycles on Acoustic Emission Characteristics of Granite Samples under Triaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhandong Su ◽  
Ke Geng ◽  
Fubiao Zhou ◽  
Jinzhong Sun ◽  
Huayan Yu
Keyword(s):  
Acoustic Emission ◽  
Triaxial Compression ◽  
Peak Frequency ◽  
Dominant Frequency ◽  
P Wave ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Ae Signal ◽  
The Stability ◽  
Granite Samples

Understanding the acoustic emission (AE) characteristics of rocks that have undergone freeze-thaw cycling is of great significance for the use of AE technology to monitor the stability of rock masses in cold regions. A series of freeze-thaw cycling experiments and triaxial compression AE tests of granite samples were performed. The results show that, with an increasing number of freeze-thaw cycles, the P-wave velocity and peak AE intensity of granite show a substantial downward trend. The AE ringing counts during triaxial compression can be divided into three stages: abrupt period, calm period, and failure period. The overall change of the characteristic AE signal of granite samples that underwent different freeze-thaw cycles is the same. The AE signal during the destruction of granite occurs in clear dual dominant frequency bands. The peak frequency increases with increasing load time, and this trend becomes less clear as the number of freeze-thaw cycles increases. Overall, the peak frequency distribution tends to change from high to low with an increasing number of freeze-thaw cycles. The results provide basic data for rock mass stability monitoring and prediction, which is of great significance for engineering construction and management in cold regions.

scholarly journals Investigation of Energy Mechanism and Acoustic Emission Characteristics of Mudstone with Different Moisture Contents

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Jingdong Jiang ◽  
Jie Xu
Keyword(s):  
Acoustic Emission ◽  
Moisture Content ◽  
Total Energy ◽  
Failure Time ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Development Stage ◽  
Dissipated Energy ◽  
Deformation And Failure ◽  
Moisture Contents

Characteristics of energy accumulation, evolution, and dissipation in conventional triaxial compression of mudstones with different moisture contents were explored. Stress-strain relations and acoustic emission (AE) characteristics of the deformation and failure of rock specimens were analyzed. The densities and rates of stored energy, elastic energy, and dissipated energy under different confining pressures were confirmed. The results demonstrated that the growth rate of absorbed total energy decreases with the increase of moisture content, indicating that the higher the moisture content is, the less the total energy mudstone samples absorb. The dissipated energy of the soaking sample, by contrast, has the first increase speed, and natural sample comes second at the beginning. When entering the crack stable development stage, the dry sample has the fastest growing rate of dissipated energy, meaning that dissipated energy used for crack propagation gradually decreases with the increase of moisture content. The AE signals significantly enhance at the initial compression stage and plastic deformation stage with the moisture content decreasing. The AE location events at the failure moment decrease as the moisture content increasing. The time that the maximum AE even rate appears is slightly lagged behind the macroscopic failure time, and the AE even rates increase with the decrease of confining pressure. The above results indicate that the water erosion process on rock reduces the cohesive energy and cohesive force, destroys the micromechanical structure, and minimizes the energy states of rock.

Acoustic Emission Characteristics of Sericite Schist Coarse Aggregates under Consolidated Undrained Triaxial Tests

2013 ◽  
Vol 423-426 ◽  
pp. 909-913
Author(s):  
Lan Qiang Yang ◽  
Shang Lin Qin ◽  
Hui Gao ◽  
Shan Xiong Chen
Keyword(s):  
Acoustic Emission ◽  
Large Scale ◽  
Sliding Friction ◽  
Axial Strain ◽  
Confining Pressure ◽  
Rolling Friction ◽  
Triaxial Tests ◽  
Emission Characteristics ◽  
Coarse Aggregates ◽  
Ae Signals

In order to study the acoustic emission characteristics of coarse aggregates, improved of large-scale triaxial apparatus is used to do the consolidated undrained triaxial tests of sericite schist coarse aggregates, with the acoustic emission signals monitoring. The test results show that a large number of AE signals of sericite schist coarse aggregates are generated in the initial stage. Before the axial strain reach 10%, AE counts are relatively quiet. But after 10%, they become anomalous and emerge obvious leap values. When the confining pressure up to 200kPa, AE signals are mainly generated by sliding friction. With confining pressure increasing, the proporation of rolling friction and particle breakage is more and more obvious.

scholarly journals An Evaluation Method of Rock Brittleness Based on the Prepeak Crack Initiation and Postpeak Stress Drop Characteristics

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Meiben Gao ◽  
Tianbin Li ◽  
Lubo Meng
Keyword(s):  
Crack Initiation ◽  
Stress Drop ◽  
Evaluation Method ◽  
Triaxial Compression ◽  
Experimental Tests ◽  
Confining Pressure ◽  
Brittleness Index ◽  
Comparison Results ◽  
Confining Pressures ◽  
Rock Brittleness

Recent research shows that the brittleness of rock is closely related to the initiation and propagation of internal microcracks, but there are few brittleness evaluation indices considering the characteristics of rock initiation. Based on the theoretical analysis of brittleness and the characteristics of rock initiation, this study proposes an evaluation method of rock brittleness based on the prepeak crack initiation and postpeak stress drop characteristics. First, based on the description and definition of brittleness by George Tarasov and Potvin et al., the feasibility of an evaluation method based on the prepeak crack initiation and postpeak stress drop is theoretically analyzed. Second, the component Bi representing the prepeak brittleness of rock and component Bii representing the prepeak brittleness of rock are constructed, and the product of the two is the brittleness index BI, representing the prepeak crack initiation and postpeak stress drop. Finally, experimental tests of granite and marble were conducted to evaluate the new index, and the brittleness indices of different methods are calculated and compared. The results show that, like other brittleness indices (B1∼B5), the brittleness index BI can effectively reflect the effects of different confining pressures and loading modes on rock brittleness. The brittleness of marble decreases with increasing confining pressure from 5 MPa to 35 MPa. At a confining pressure of 5 MPa, the brittleness of granite during a triaxial unloading test is greater than that during a triaxial compression test. The calculated results are consistent with the experimental results. By tests and comparison results, the reliability of this evaluation method was verified, which provides a way to evaluate rock brittleness from the perspective of crack initiation and is helpful to enrich the analysis and evaluation of rock brittleness in the laboratory.

scholarly journals Experimental Research into the Evolution of Permeability of Sandstone under Triaxial Compression

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5065
Author(s):  
Liming Zhang ◽  
Shengqun Jiang ◽  
Jin Yu
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Testing Machine ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Rate Of Change ◽  
Peak Strength ◽  
Sudden Increase ◽  
Seepage Pressure ◽  
Confining Pressures

Failure tests on sandstone specimens were conducted under different confining pressures and seepage pressures by using an MTS triaxial rock testing machine to elucidate the corresponding correlations of permeability and characteristic stress with confining pressure and pore pressure during deformation. The results indicate that permeability first decreases and presents two trends, i.e., a V-shaped increase and an S-shaped trend during the non-linear deformation stage. The greater the seepage pressure, the greater the initial permeability and the more obvious the V-shaped trend in the permeability. As the confining pressure was increased, the trend in the permeability gradually changed from V- to S-shaped. Compared with the case at a high confining pressure, the decrease of permeability occurred more quickly, the rate of change becomes greater, and the sudden increase observed in the permeability happened earlier under lower confining pressures. Within the range tested, confining pressure exerted a greater effect on the permeability than the seepage pressure. In comparison with the axial strain, volumetric strain better reflected changes in permeability during compaction and dilation of sandstone. The ratio of crack initiation stress to peak strength ranged from 0.37 to 0.50, while the ratio of dilation stress to peak strength changed from 0.58 to 0.72. Permeabilities calculated based on Darcy and non-Darcy flow changed within the same interval, while the change in permeability was different.

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