Study on the Progressive Failure Characteristics of Coal in Uniaxial and Triaxial Compression Conditions Using 3D-Digital Image Correlation
Abstract
:1. Introduction
2. Materials and Methods
2.1. Specimens and Test Method
2.2. Loading System and Transparent Pressure Cell
2.3. Instrumentation of 3D-DIC System
2.4. Calibration of Cameras
3. Results
3.1. Progressive Failure Characteristics and Energy Evolution
3.2. Field Strain Patterns and Crack Propagation
4. Discussion
5. Conclusions
- The average stress level of crack initiation and crack damage of coal in uniaxial compression are 43.75% and 63.03%, while that in triaxial compression are 74.53% and 89.84%, respectively. The dissipation energy evolution corresponds to the crack volumetric strain, while the elastic energy release leads to flake ejection and coal failure.
- Through the analysis of digital images, the apparent field strain and crack propagation of coal were obtained under a confining pressure for the first time. Localization takes place progressively in the pre-peak region, which indicates coal failure in uniaxial compression; localization mainly occurs in the post-failure region in triaxial compression, which indicates shear sliding.
- In uniaxial compression, the original cracks and defects have a large influence on damage evolution. New cracks extend from the end of original cracks and are parallel to the loading direction. Flake ejection with sound occurred near the peak strength of coal. Thus, the coal sample undergoes failure in tension. In the triaxial compression, the original cracks were compacted by the confining pressure and the inclined cracks extended and combined with each other; further, there were also tension cracks, which reduced the coal strength. Thus, coal samples undergo tension-shear failure.
- By analyzing the full-field strain and crack evolution, we can correctly understand the progressive failure process and mechanism of coal. This study is an important contribution toward the safety and stability of mining engineering.
Author Contributions
Acknowledgments
Conflicts of Interest
References
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Proximate Analysis (%) | Ro,max (%) | Coal Rank | |||
---|---|---|---|---|---|
Mad | Aad | Vad | FCad | ||
1.44 | 12.69 | 7.62 | 78.25 | 2.7 | anthracite |
Test | E (GPa) | v | σci (MPa) | σcd (MPa) | σc (MPa) | σci/σc | σcd/σc |
---|---|---|---|---|---|---|---|
UC | 5.66 | 0.23 | 14.80 | 21.31 | 33.82 | 43.75% | 63.03% |
TC | 6.14 | 0.36 | 49.38 | 59.51 | 66.25 | 74.53% | 89.84% |
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Tang, Y.; Okubo, S.; Xu, J.; Peng, S. Study on the Progressive Failure Characteristics of Coal in Uniaxial and Triaxial Compression Conditions Using 3D-Digital Image Correlation. Energies 2018, 11, 1215. https://doi.org/10.3390/en11051215
Tang Y, Okubo S, Xu J, Peng S. Study on the Progressive Failure Characteristics of Coal in Uniaxial and Triaxial Compression Conditions Using 3D-Digital Image Correlation. Energies. 2018; 11(5):1215. https://doi.org/10.3390/en11051215
Chicago/Turabian StyleTang, Yang, Seisuke Okubo, Jiang Xu, and Shoujian Peng. 2018. "Study on the Progressive Failure Characteristics of Coal in Uniaxial and Triaxial Compression Conditions Using 3D-Digital Image Correlation" Energies 11, no. 5: 1215. https://doi.org/10.3390/en11051215