scholarly journals Characteristic strength and acoustic emission properties of weakly cemented sandstone at different depths under uniaxial compression

2021 ◽  
Author(s):  
Bin Liu ◽  
Yixin Zhao ◽  
Cun Zhang ◽  
Jinlong Zhou ◽  
Yutao Li ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Failure Modes ◽  
Shear Failure ◽  
Underground Mining ◽  
Peak Strength ◽  
Dissipated Energy ◽  
Burial Depth ◽  
Characteristic Strength ◽  
Different Depths

AbstractAs coal mining is extended from shallow to deep areas along the western coalfield, it is of great significance to study weakly cemented sandstone at different depths for underground mining engineering. Sandstones from depths of 101.5, 203.2, 317.3, 406.9, 509.9 and 589.8 m at the Buertai Coal Mine were collected. The characteristic strength, acoustic emission (AE), and energy evolution of sandstone during uniaxial compression tests were analyzed. The results show that the intermediate frequency (125–275 kHz) of shallow rock mainly occurs in the postpeak stage, while deep rock occurs in the prepeak stage. The initiation strength and damage strength of the sandstone at different depths range from 0.23 to 0.50 and 0.63 to 0.84 of peak strength (σc), respectively, decrease exponentially and are a power function with depth. The precursor strength ranges from 0.88σc to 0.99σc, increases with depth before reaching a depth of 300 m, and tends to stabilize after 300 m. The ratio of the initiation strength to the damage strength (k) ranges from 0.25 to 0.62 and decreases exponentially with depth. The failure modes of sandstone at different depths are tension-dominated mixed tensile-shear failure. Shear failure mainly occurs at the unstable crack propagation stage. The count of the shear failure bands before the peak strength increases gradually, and increases first and then decreases after the peak strength with burial depth. The cumulative input energy, released elastic energy and dissipated energy increase with depth. The elastic release rate ranges from 0.46 × 10–3 to 198.57 × 10–3 J/(cm3 s) and increases exponentially with depth.

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 Energy Dissipation-Based Method for Strength Determination of Rock under Uniaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
M. M. He ◽  
F. Pang ◽  
H. T. Wang ◽  
J. W. Zhu ◽  
Y. S. Chen
Keyword(s):  
Yield Strength ◽  
Uniaxial Compression ◽  
Peak Strength ◽  
Dissipated Energy ◽  
Compression Tests ◽  
Dissipation Energy ◽  
Evolution Characteristics ◽  
Deformation Properties ◽  
Energy Coefficient ◽  
The Stability

The energy conversion in rocks has an important significance for evaluation of the stability and safety of rock engineering. In this paper, some uniaxial compression tests for fifteen different rocks were performed. The evolution characteristics of the total energy, elastic energy, and dissipated energy for the fifteen rocks were studied. The dissipation energy coefficient was introduced to study the evolution characteristics of rock. The evolution of the dissipation energy coefficient for different rocks was investigated. The linear interrelations of the dissipation energy coefficients and the yield strength and peak strength were explored. The method was proposed to determine the strength of rock using the dissipation energy coefficients. The results show that the evolution of the dissipation energy coefficient exhibits significant deformation properties of rock. The dissipation energy coefficients linearly increase with the compaction strength, but decrease with the yield strength and peak strength. Moreover, the dissipation energy coefficient can be used to determine the rock burst proneness and crack propagation in rocks.

scholarly journals Mechanical Properties and Acoustic Emission Characteristics of Karst Limestone under Uniaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Jianxun Chen ◽  
Qingsong Wang ◽  
Jiaqi Guo ◽  
Yanbin Luo ◽  
Yao Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Water Content ◽  
Uniaxial Compression ◽  
Wave Velocity ◽  
Brittle Failure ◽  
Shear Failure ◽  
Testing Machine ◽  
Natural State ◽  
Saturated State

Firstly, I-RPT ultrasonic detector was used to test the wave velocity of karst limestone with different initial microstructure and water content. Then, RMT-150B rock testing machine and DS2-16B acoustic emission system were used to test the acoustic emission (AE) under uniaxial compression. Mechanical properties and AE characteristics were obtained during rock failure. The detailed relationship between stress-strain and AE characteristics was studied in this paper. Research results indicated the following: (1) For samples with many primary fissures and defects, wave velocity in dry state was larger than that in its natural state. From natural state to saturated state, the wave velocity tended to increase. For samples with good integrity, wave velocity increased with increasing of water content. (2) In the dry state, the samples presented tension failure. In saturated state, the samples presented tension-shear failure. For samples with cracks and good integrity, samples showed brittle failure. For samples with many corrosion pores which showed ductile damage under natural and saturated state, the spalling phenomenon was enhanced under saturated state. (3) With increasing of water content, the peak stress and AE peak reduced dramatically. In brittle failure, AE peak could be considered a sign of failure. In ductile failure, AE activity decreased gradually with the decrease of stress. (4) The mechanical properties and AE characteristics corresponding to four main fracture propagation types were also discussed.

scholarly journals Experimental and Numerical Investigation of Failure Characteristics and Mechanism of Granites with Different Joint Angles

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhenhua Wang ◽  
Jun Fang ◽  
Gang Wang ◽  
Yifan Jiang ◽  
Dongwei Li
Keyword(s):  
Elastic Modulus ◽  
Uniaxial Compression ◽  
Elastic Strain Energy ◽  
Peak Stress ◽  
Peak Strength ◽  
Particle Flow Code ◽  
Dissipated Energy ◽  
Shear Cracks ◽  
Compression Tests ◽  
Dip Angle

The uniaxial compression tests were conducted on granite samples with different joint dip angles to more favorably explore the influences of the nonconsecutive joint on mechanical properties and deformation characteristics of the rock mass. The stress-strain curves, deformation and strength characteristics, and energy evolution process of the samples were analyzed. Numerical simulation using particle flow code (PFC) is employed to study the crack propagation process. The mode of jointed and fractured rock was investigated. The research results showed a significant reduction in both the peak strength and elastic modulus of jointed samples compared with intact ones: the peak strength and elastic modulus drop to the minimum at the joint dip angle of about 45°, especially for the peak strength, which takes up about 55% of the intact samples. The fractured samples’ total energy, elastic strain energy, and dissipated energy during the uniaxial compression drop significantly relative to intact samples. The proportion of the fracture modes varies with different joint dip angles, in which the ratio of shear cracks grows at first and then declines, with the highest balance at the dip angle of 45°. The damage stress’s sensitivity to the dip angle change is greater than that of the peak stress, with reduction amplitude more extensive than the latter.

Mechanical and energy release characteristics of different water-bearing sandstones under uniaxial compression

2017 ◽  
Vol 27 (5) ◽  
pp. 640-656 ◽  
Author(s):  
Yongchuan Zhao ◽  
Tianhong Yang ◽  
Tao Xu ◽  
Penghai Zhang ◽  
Wenhao Shi
Keyword(s):  
Acoustic Emission ◽  
Water Content ◽  
Energy Release ◽  
Peak Strength ◽  
Experimental Results ◽  
Dissipated Energy ◽  
Normal Density ◽  
Acoustic Emission Energy ◽  
High Tendency ◽  
Emission Energy

This paper presents the experimental results of calcium argillaceous cemented sandstones with different water contents under uniaxial and cyclic loading conditions. The effects of the water content status on peak strength, deformation, and dissipated energy are discussed. Meanwhile, the acoustic emission energy is also studied based on the accelerating energy release theory and energy distribution density function. The experimental results show that the water content has remarkable effects on the peak strength and elastic modulus by a decrease of 37–58% and 15.7–21% after being saturated, respectively. Both the accumulated dissipated energy and dissipated energy generating ratio of dry specimens are higher than those of the saturated specimens. The acoustic emission energy release rate of dry specimens is higher than those of the saturated specimens, which means a high tendency of sudden failure for dry specimens. Moreover, the distributions of acoustic emission absolute energy are consistent with the normal density distribution function, and the AE energy expectations of dry specimens are higher than those of the saturated ones in the loading process and they show an obvious increasing trend on approaching failure. These conclusions will be helpful for the illumination of water-weakening effects on the mechanics parameters and failure mechanism analysis in view of the releasing energy.

scholarly journals Analysis of Mechanical and Acoustic Emission Characteristics of Rock Materials with Double-Hole Defects Based on Particle Flow Code

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Qi Zhang ◽  
Xiao Wang ◽  
Long-gang Tian ◽  
Dong-mei Huang
Keyword(s):  
Acoustic Emission ◽  
Damage Evolution ◽  
Failure Modes ◽  
Numerical Models ◽  
Strain Range ◽  
Peak Strength ◽  
Particle Flow Code ◽  
Stress Strain ◽  
Rock Materials ◽  
Connection Line

There are a lot of fissures, holes, and other defects in the formation of natural rocks. Under the influence of the external loads, these defects may cause engineering problems. Therefore, it is of great significance to analyze the characteristics of damage evolution of the defective rocks. In the study, the double-hole defective rocks with different angles of the center connection line are considered and the numerical models are established firstly. Then the mechanical behavior and acoustic emission (AE) characteristics are analyzed systematically. Finally the laws of damage evolution of the defective rock materials are investigated based on the AE characteristics. The research results show that the stress-strain behavior of the defective rocks can be divided into elastic stage, plastic stage and failure stages. The characteristics of acoustic emission evolution and laws of damage evolution are closely related to the stress-strain relationship. The elastic modulus of the double-hole defective rocks is similar with different angles of the center connection line, but the peak strength is different. The shape of the peak strength of these defective rocks is a W type owing to the different failure modes. The influences of different angles of the center connection line on the characteristics of AE evolution include the maximum events number, the strain value of the initial AE events and the maximum AE events, and the strain range of the serious AE events. Different angles of the center connection line have different influences on the laws of damage evolution of the double-hole defective rocks.

scholarly journals An Assessment of the Effect of Progressive Water Absorption on the Interlaminar Strength of Unidirectional Carbon/Epoxy Composites Using Acoustic Emission

Sensors ◽  
2021 ◽  
Vol 21 (13) ◽  
pp. 4351
Author(s):  
Faisel Almudaihesh ◽  
Stephen Grigg ◽  
Karen Holford ◽  
Rhys Pullin ◽  
Mark Eaton
Keyword(s):  
Acoustic Emission ◽  
Water Absorption ◽  
Asset Management ◽  
Failure Modes ◽  
Shear Failure ◽  
Pure Shear ◽  
Degradation Process ◽  
Optical Measurements ◽  
Gradual Change ◽  
Aerospace Applications

Carbon Fibre-Reinforced Polymers (CFRPs) in aerospace applications are expected to operate in moist environments where carbon fibres have high resistance to water absorption; however, polymers do not. To develop a truly optimised structure, it is important to understand this degradation process. This study aims to expand the understanding of the role of water absorption on fibrous/polymeric structures, particularly in a matrix-dominant property, namely interlaminar strength. This work used Acoustic Emission (AE), which could be integrated into any Structural Health Monitoring System for aerospace applications, optical strain measurements, and microscopy to provide an assessment of the gradual change in failure mechanisms due to the degradation of a polymer’s structure with increasing water absorption. CFRP specimens were immersed in purified water and kept at a constant temperature of 90 °C for 3, 9, 24 and 43 days. The resulting interlaminar strength was investigated through short-beam strength (SBS) testing. The SBS values decreased as immersion times were increased; the decrease was significant at longer immersion times (up to 24.47%). Failures evolved with increased immersion times, leading to a greater number of delaminations and more intralaminar cracking. Failure modes, such as crushing and multiple delaminations, were observed at longer immersion times, particularly after 24 and 43 days, where a pure interlaminar shear failure did not occur. The observed transition in failure mechanism showed that failure of aged specimens was triggered by a crushing of the upper surface plies leading to progressive delamination at multiple ply interfaces in the upper half of the specimen. The crushing occurred at a load below that required to initiate a pure shear failure and hence represents an under prediction of the true SBS of the sample. This is a common test used to assess environmental degradation of composites and these results show that conservative knockdown factors may be used in design. AE was able to distinguish different material behaviours prior to final fracture for unaged and aged specimens suggesting that it can be integrated into an aerospace asset management system. AE results were validated using optical measurements and microscopy.

scholarly journals Shear Failure Mechanism and Acoustic Emission Characteristics of Jointed Rock-Like Specimens

2021 ◽  
Vol 50 (2) ◽  
pp. 287-300
Author(s):  
Yuxin Ban ◽  
Qiang Xie ◽  
Xiang Fu ◽  
Rini Asnida Abdullah ◽  
Jingjing Wang
Keyword(s):  
Acoustic Emission ◽  
Normal Stress ◽  
Failure Mechanism ◽  
Failure Modes ◽  
Shear Failure ◽  
Jointed Rock ◽  
Failure Behavior ◽  
Direct Shear ◽  
Physical Test ◽  
Dilation Angle

Evidence indicate that the stability of rock mass is highly associated with the shear behaviours of jointed surfaces under the effect of in situ stress conditions. Understanding the shear failure mechanism of jointed surface has great significance for tunneling and drilling engineering. Direct shear tests were conducted on jointed rock-like specimens to investigate the influence of joint roughness and normal stress on shear failure characteristics. In the present study, regular triangular sawtooth was produced to simulate different asperities. Based on the direct shear test, the specimens exhibited four types of failure modes: damage tend to occur on the sawtooth tips under low normal stress; whereas damage occurred on a large scale under high normal stress; a localized region of the sawtooth was worn when the dilation angle was small; meanwhile the sawtooth tips or base were cut off when the dilation angle was large. In addition, Acoustic Emission (AE) technology was adopted to synchronously monitor the development of cracks during testing. Further attempt has been carried out to simulate the crack initiation, propagation and coalescence using Particle Flow Code (PFC). The numerical model has successfully verified and explained the crack behaviors determined by the shear failure mechanism in the physical test. Additionally, the irregular profile was introduced in the PFC, it was found that the failure behavior in sawtooth profile has established a good conclusion to fully understand the failure mechanism in the irregular profile. This work can provide some reference for evaluating the behavior of underground engineering composed of jointed rock masses during the shearing.

Study on Acoustic Emission and Failure Modes of Rock in Uniaxial Compression Test

2011 ◽  
Vol 261-263 ◽  
pp. 1393-1400
Author(s):  
Ji Liang Zhang ◽  
Chang Hong Li
Keyword(s):  
Compressive Strength ◽  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Compression Test ◽  
Failure Modes ◽  
Soft Rock ◽  
Development Stage ◽  
Uniaxial Compression Test ◽  
Whole Process ◽  
Shear Rupture

Based on uniaxial compression test, the mechanical properties and acoustic emission characteristics of rock had been obtained, including the relationship between AE and time, AE and stress level, and so on, in the whole process of rock failure. Research shows AE rate of rock has the subparagraph features obviously. There are three obvious AE sections for the higher strength elastic-brittle rock: First section is compaction stage, corresponding stress is 10% of compressive strength of rock; Second section is crack-development stage, corresponding stress is 80% of compressive strength; Third section is rupture stage, corresponding stress is the compressive strength. Furthermore, AE signals for the rupture stage is strongest. The law is still correct in cycle loading conditions. However, the subparagraph phenomenon isn’t clear for elastic-plastic rock, and the AE peak is lagging behind the ultimate strength of rock, the AE signal in the decline stage of strength is the most intensive and strong. The lagging phenomenon is due to X-shear rupture model of soft rock. The significant stress concentration in cone tip between the two relative extrusion cones leads to local rock broken seriously. Then, many acoustic signals have been observed.

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