Abstract
The cracks in a rock tend to initiate, propagate, and coalesce under loading. Based on the digital image correlation (DIC) method, uniaxial compression tests are carried out on rock-like specimens with various arrangements of two parallel cracks. The full-field strain and failure features of the rock-like materials are observed and analysis by a self-developed code. Two process zones are defined according to the differences between the shear strain field and the tensile strain field: a shear process zone and a tensile process zone. The following results are obtained in this study. (1) Three coalescence modes can be observed using the DIC method: a shear coalescence mode, a tensile coalescence mode, and a mixed coalescence mode. (2) At the microscopic level, the bridge angle and crack arrangement affect the formation of the process zone; at the macroscopic level, they determine the crack propagation path and the failure mode. (3) The peak strength of the rock-like specimen is related to the crack inclination angle and the bridge angle. (4) Numerical modeling by the expanded distinct element method and the strain strength criterion simulates the different coalescence modes of the experimental study efficiently.
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Abbreviations
- α :
-
Crack inclination angle
- β :
-
Bridge angle
- \({\varepsilon _t}\) :
-
Critical tensile strain
- \({\gamma _{xy{\text{cri}}}}\) :
-
Critical shear strain
- \({\sigma _t}\) :
-
Critical tensile strength
- \({\sigma _{\text{c}}}\) :
-
Critical compressive strength
- \({\sigma _1},{\sigma _3}\) :
-
Maximum and minimum principal stresses, respectively
- \(\nu\) :
-
Poisson’s ratio
- \(\varphi\) :
-
Internal friction angle
- c :
-
Cohesion
- C :
-
Correlation coefficient
- E :
-
Young’s modulus
- G :
-
Shear modulus
- \({f_{1m}},{f_{2m}}\) :
-
Average gray values of the reference and deformed images, respectively
- \({f_1}(x,y),{f_2}(x',y')\) :
-
Gray-level values for the reference and deformed images, respectively
- \({f_{\text{t}}},{f_{\text{s}}}\) :
-
Judgement factors of the tensile and shear cracks, respectively
- BPM:
-
Bonded-particle model
- DDM:
-
Displacement discontinuity method
- DEM:
-
Discrete element method
- DIC:
-
Digital image correlation
- EDEM:
-
Expanded distinct element method
- LEFM:
-
Linear elastic fracture mechanics
- PFC:
-
Particle flow code
- SIF:
-
Stress intensity factor
- SPZ:
-
Shear process zone
- TPZ:
-
Tensile process zone
- UDEC:
-
Universal distinct element code
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Acknowledgements
The authors would like to acknowledge the financial support of the National Key R&D Program of China (no. 2017YFC0806000), the National Natural Science Foundation of China (nos. 41202193 and 41572262), the Innovation Program of the Shanghai Municipal Education Commission (no. 15ZZ016), and the Shanghai Rising-Star Program (no. 17QC1400600).
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Zhao, C., Zhou, Y.m., Zhao, C.f. et al. Cracking Processes and Coalescence Modes in Rock-Like Specimens with Two Parallel Pre-existing Cracks. Rock Mech Rock Eng 51, 3377–3393 (2018). https://doi.org/10.1007/s00603-018-1525-y
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DOI: https://doi.org/10.1007/s00603-018-1525-y