Experimental Study on Coal Specimens Subjected to Uniaxial Cyclic Loading and Unloading
Abstract
:1. Introduction
2. Experiment Design
2.1. Specimen
2.2. Experimental Devices
2.3. Test Scheme
3. Testing Results
3.1. Deformation and Elastic Modulus
3.1.1. Stress versus Strain Curves
3.1.2. Relation between Strain and Loading–Unloading Cycle Number
3.1.3. Elastic Modulus
3.2. AE Characteristics
3.2.1. AE Ring Count
3.2.2. AE Energy Count
3.2.3. AE Hit Count
3.2.4. AE Kaiser Effect
3.3. Damage Evolution Characteristics
3.4. AE b Value
3.4.1. Calculation of AE b Value
3.4.2. Evolution of AE b Value
3.4.3. Prediction of AE Maximum Magnitude
4. Conclusions
- (1)
- The axial strain is very well linear with the loading–unloading cycle number, and the circumferential and volumetric strains are approximately quadratic functions with the loading–unloading cycle number;
- (2)
- Under the same loading stress interval, the elastic modulus firstly increases and then keeps basically stable with the loading–unloading cycle number. In addition, the higher the maximum stress of a loading–unloading cycle, the more significant the plastic strengthening effect produced by this cycle;
- (3)
- The damage calculated by the cumulative AE hit count can better reflect the fact that the damage has been increasing in the loading phase and keeps basically unchanged in the unloading phase. So, the AE hit count as a damage variable can better describe the damage development of coal specimens;
- (4)
- The significant fluctuation of the AE b value can be used as the precursor of coal specimen failure. In addition, it decreases rapidly at coal specimen failure;
- (5)
- The closer to the loading–unloading cycle of coal specimen failure, the more accurate the predicted “maximum magnitude” at coal specimen failure.
Author Contributions
Funding
Conflicts of Interest
References
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Specimen Number | Diameter/mm | Height/mm | Density/g·cm−3 | Mass/g |
---|---|---|---|---|
1 | 50.3 | 101.2 | 1.157 | 232.6 |
2 | 49.5 | 99.1 | 1.158 | 220.8 |
3 | 49.4 | 98.2 | 1.161 | 218.4 |
4 | 49.5 | 99.6 | 1.158 | 221.8 |
Cycle Number | Cumulative AE Hit Count in Several Key Stress Points | |||||
---|---|---|---|---|---|---|
3.5 MPa | 4.0 MPa | 4.5 MPa | 5.0 MPa | 5.5 MPa | 5.826 MPa | |
1 | 104 | — | — | — | — | — |
2 | 9 | 164 | — | — | — | — |
3 | 2 | 49 | 423 | — | — | — |
4 | 0 | 0 | 267 | 774 | — | — |
5 | 0 | 0 | 1 | 35 | 785 | — |
6 | 0 | 0 | 0 | 2 | 27 | 1277 |
Cycle Number | 1 | 2 | 3 | 4 | 5 | 6 |
---|---|---|---|---|---|---|
Cyclic loading maximum stress/MPa | 3.5 | 4 | 4.5 | 5 | 5.5 | 5.826 |
Kaiser point/MPa | — | 3.886 | 4.166 | 4.708 | 5.501 | 5.819 |
Fr | — | 1.110 | 1.042 | 1.046 | 1.100 | 1.058 |
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Gao, M.; Yan, H.; Duan, H.; Xiong, S. Experimental Study on Coal Specimens Subjected to Uniaxial Cyclic Loading and Unloading. Appl. Sci. 2022, 12, 11810. https://doi.org/10.3390/app122211810
Gao M, Yan H, Duan H, Xiong S. Experimental Study on Coal Specimens Subjected to Uniaxial Cyclic Loading and Unloading. Applied Sciences. 2022; 12(22):11810. https://doi.org/10.3390/app122211810
Chicago/Turabian StyleGao, Mingtao, Hongyu Yan, Huiqiang Duan, and Si Xiong. 2022. "Experimental Study on Coal Specimens Subjected to Uniaxial Cyclic Loading and Unloading" Applied Sciences 12, no. 22: 11810. https://doi.org/10.3390/app122211810
APA StyleGao, M., Yan, H., Duan, H., & Xiong, S. (2022). Experimental Study on Coal Specimens Subjected to Uniaxial Cyclic Loading and Unloading. Applied Sciences, 12(22), 11810. https://doi.org/10.3390/app122211810