Mechanical Properties and Acoustic Emission Characteristics of Water-Bearing Coal Specimens under a Coupled Compression–Shear Load
Abstract
:1. Introduction
2. Materials and Methods
2.1. Specimen Preparation
2.2. Test Equipment and Methods
2.3. AE Techniques
3. Results and Discussion
3.1. Variation Law of Mechanical Characteristic Parameters
- (1)
- Peak stress σc
- (2)
- Elastic modulus E
- (3)
- Peak shear stress τc
3.2. Macroscopic Failure Characteristics
4. Analysis of AE Behavior
4.1. Crack Evolution Law
4.2. Evolution Law of CC Threshold, CI Threshold, and CD Threshold
5. Conclusions
- (1)
- When the moisture content was less than 7.55%, the peak shear stress increased according to the inclination angle. Still, when the moisture content was 10.08%, the peak shear stress first increased and then decreased according to the inclination angle. The stress showed an obvious moisture content weakening effect; the peak stress and elastic modulus of coal specimens showed significant moisture content and inclination angle weakening effects. The progressive decrease in the peak stress and elastic modulus was especially susceptible to a high moisture content and a considerable inclination angle.
- (2)
- Microcrack expansion and penetration in the coal specimens were controlled by shear cracks. Under a low moisture content (ω = 0%, 2.42%), the macroscopic fracture mode of the coal specimens progressively shifted from tensile to shear failure as the loading inclination increased. At a medium moisture content (ω = 5.53%), the coal specimen mostly showed a combination of tension and shear failures. At a high moisture content (ω = 7.55%, 10.08%), the coal specimen mostly showed a shear-based failure. The higher the ratio, the better the integrity of the coal specimen when it is damaged. The crack mode indicated by the AE characteristic parameters was consistent with the coal specimen’s macroscopic damage characteristics.
- (3)
- When the moisture content was 7.55%, the CC threshold, CI threshold, and CD threshold decreased as the angle of inclination increased, but their ratio to the peak stress stayed in the range of 0.22~0.24, 0.35~0.41, and 0.71~0.83, respectively. This means that they did not change with the angle of inclination. At a 10° inclination angle, the CC threshold, CI threshold, and CD threshold all decreased with increasing moisture content, but their ratios to the peak stress remained constant in the range of 0.23~0.24, 0.36~0.41, and 0.78~0.85, respectively.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Inclination Angle (°) | 0 | 5 | 10 | 15 | |
---|---|---|---|---|---|
σCC (MPa)/Ratio(1) | Cumulative AE count | 3.52/0.24 | 2.67/0.22 | 2.29/0.22 | 1.69/0.24 |
Cumulative AE energy | 3.52/0.24 | 2.67/0.22 | 2.29/0.22 | 1.69/0.24 | |
Average value | 3.52/0.24 | 2.67/0.22 | 2.29/0.22 | 1.69/0.24 | |
σCI (MPa)/Ratio(1) | Cumulative AE count | 5.97/0.41 | 4.41/0.36 | 3.59/0.35 | 2.88/0.41 |
Cumulative AE energy | 5.97/0.41 | 4.52/0.37 | 3.62/0.35 | 2.85/0.41 | |
Average value | 5.97/0.41 | 4.47/0.36 | 3.61/0.35 | 2.87/0.41 | |
σCD(MPa)/Ratio(1) | Cumulative AE count | 11.91/0.82 | 8.96/0.73 | 7.28/0.71 | 5.84/0.83 |
Cumulative AE energy | 11.90/0.82 | 9.01/0.74 | 7.28/0.71 | 5.75/0.82 | |
Average value | 11.91/0.82 | 8.99/0.73 | 7.28/0.71 | 5.80/0.83 |
Moisture Content (%) | 0 | 2.42 | 5.53 | 7.55 | 10.08 | |
---|---|---|---|---|---|---|
σCC (MPa)/Ratio(1) | Cumulative AE count | 4.33/0.24 | 3.48/0.23 | 2.52/0.24 | 1.69/0.24 | 0.64/0.23 |
Cumulative AE energy | 4.33/0.24 | 3.48/0.23 | 2.52/0.24 | 1.69/0.24 | 0.64/0.23 | |
Average value | 4.33/0.24 | 3.48/0.23 | 2.52/0.24 | 1.69/0.24 | 0.64/0.23 | |
σCI (MPa)/Ratio(1) | Cumulative AE count | 7.08/0.39 | 5.58/0.36 | 4.08/0.39 | 2.88/0.41 | 1.07/0.38 |
Cumulative AE energy | 7.01/0.38 | 5.55/0.36 | 3.96/0.38 | 2.85/0.41 | 1.11/0.39 | |
Average value | 7.05/0.38 | 5.57/0.36 | 4.02/0.39 | 2.87/0.41 | 1.09/0.39 | |
σCD(MPa)/Ratio(1) | Cumulative AE count | 14.49/0.79 | 12.12/0.79 | 8.83/0.85 | 5.84/0.83 | 2.20/0.78 |
Cumulative AE energy | 14.27/0.78 | 12.21/0.79 | 8.76/0.85 | 5.75/0.82 | 2.22/0.78 | |
Average value | 14.38/0.78 | 12.17/0.79 | 8.80/0.85 | 5.80/0.83 | 2.21/0.78 |
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Wang, L.; Wu, P.; Li, M.; Mao, X.; Chen, L. Mechanical Properties and Acoustic Emission Characteristics of Water-Bearing Coal Specimens under a Coupled Compression–Shear Load. Minerals 2022, 12, 704. https://doi.org/10.3390/min12060704
Wang L, Wu P, Li M, Mao X, Chen L. Mechanical Properties and Acoustic Emission Characteristics of Water-Bearing Coal Specimens under a Coupled Compression–Shear Load. Minerals. 2022; 12(6):704. https://doi.org/10.3390/min12060704
Chicago/Turabian StyleWang, Lan, Peng Wu, Ming Li, Xianbiao Mao, and Liang Chen. 2022. "Mechanical Properties and Acoustic Emission Characteristics of Water-Bearing Coal Specimens under a Coupled Compression–Shear Load" Minerals 12, no. 6: 704. https://doi.org/10.3390/min12060704