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<p>Granite is a typical load-bearing rock in energy storage caverns. Due to the heterogeneity and widely existing joints, the mixed-mode crack propagation is likely to occur under high internal pressure. However, the mixed-mode fracture mechanisms of granite are still unclear. This paper designs a comprehensive experimental framework to investigate granite mixed-mode fracture. Three-Point Bending (TPB) tests on specimens with offset notches are carried out and the crack mouth opening displacement (CMOD) is controlled to obtain whole load-CMOD curves and stable cracks. The Acoustic emission (AE) and digital image correlation (DIC) techniques are employed to monitor the fracture process. Further, a random field model is developed to characterize the heterogeneity of granite based on the microscopic images. The heterogeneous random field model is implemented into the combined Finite and Discrete Element Method (FDEM) to simulate the mixed-mode fracture under offset TPB loads. The accuracy of the numerical method is verified through comparisons between numerical results and experimental results. The results show that: (1) As the offset increases (0–75&#xa0;mm), the specimen transitions from pure Mode I fracture to a mixed Mode I/II fracture. Compared with offset 0, the peak load increases by 20%, 48.9%, and 65.5%, and the fracture toughness improves by 13.59%, 20.42%, and 5.88% for offset 25&#xa0;mm, 50&#xa0;mm and 75&#xa0;mm, respectively. (2) The larger the offset is, the cumulative AE ringing counts and energies are larger while the duration time for AE growth and outbreak stages is longer. (3) The increase in offset lengthens the fracture process zone (FPZ) from 55.15&#xa0;mm to 73.21&#xa0;mm. (4) The larger the offset, the greater the contribution of shear to mixed-mode fracture. The shear ratio in the random field model increases from 0.09 to 0.17. The fracture of granite under offset TPB loads produces tension-dominated mixed-mode cracks, which are caused by the offset notch and rock heterogeneity.</p>

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Experimental and Numerical Investigations On the Mixed-Mode Fracture of Granite Under Offset Three-Point Bending Loads

  • 期刊论文

  • 发表日期：

    2025年9月6日

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  • Leiming Zhang,
  • Zegong Ning,
  • Shengjun Miao,
  • Zhiming Feng,
  • Jinglai Sun,
  • Meifeng Cai,
  • Xun Xi

摘要

Granite is a typical load-bearing rock in energy storage caverns. Due to the heterogeneity and widely existing joints, the mixed-mode crack propagation is likely to occur under high internal pressure. However, the mixed-mode fracture mechanisms of granite are still unclear. This paper designs a comprehensive experimental framework to investigate granite mixed-mode fracture. Three-Point Bending (TPB) tests on specimens with offset notches are carried out and the crack mouth opening displacement (CMOD) is controlled to obtain whole load-CMOD curves and stable cracks. The Acoustic emission (AE) and digital image correlation (DIC) techniques are employed to monitor the fracture process. Further, a random field model is developed to characterize the heterogeneity of granite based on the microscopic images. The heterogeneous random field model is implemented into the combined Finite and Discrete Element Method (FDEM) to simulate the mixed-mode fracture under offset TPB loads. The accuracy of the numerical method is verified through comparisons between numerical results and experimental results. The results show that: (1) As the offset increases (0–75 mm), the specimen transitions from pure Mode I fracture to a mixed Mode I/II fracture. Compared with offset 0, the peak load increases by 20%, 48.9%, and 65.5%, and the fracture toughness improves by 13.59%, 20.42%, and 5.88% for offset 25 mm, 50 mm and 75 mm, respectively. (2) The larger the offset is, the cumulative AE ringing counts and energies are larger while the duration time for AE growth and outbreak stages is longer. (3) The increase in offset lengthens the fracture process zone (FPZ) from 55.15 mm to 73.21 mm. (4) The larger the offset, the greater the contribution of shear to mixed-mode fracture. The shear ratio in the random field model increases from 0.09 to 0.17. The fracture of granite under offset TPB loads produces tension-dominated mixed-mode cracks, which are caused by the offset notch and rock heterogeneity.