页岩II型断裂韧性的各向异性特征研究

doi:10.3724/1000-6915.jrme.2025.0182

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摘要为深入认识页岩抵抗剪切断裂能力的各向异性特征，在裂纹剪切起裂理论分析的基础上，采用双边切口巴西圆盘（DNBD）法，测定不同层理方位页岩的II型断裂韧性，明确DNBD试样裂缝的起裂与扩展演化规律，揭示DNBD法测试岩石II型断裂韧性的机制。结果表明：（1）较大的压缩T应力显著降低了DNBD试样预制裂缝尖端的周向应力，抑制了张拉裂缝的竞争起裂，促使自相似剪切断裂发生。（2）随层理角度增加，页岩II型断裂韧性近似线性增加，表现出明显的各向异性特征；层理方向的II型断裂韧性最小，基质体的最大，而垂直层理方向与基质体几乎相等；作为材料固有性质，无法向压力真II型断裂韧性明显小于试验值，且不随翼型张拉裂缝的竞争起裂而改变。（3）不同层理方位页岩断裂时形成了相似的裂缝扩展形态，即岩桥剪切断裂前已优先发生了翼型张拉裂缝和雁列状裂缝的竞争起裂与亚临界扩展等复杂断裂过程。（4）翼型张拉裂缝竞争起裂后的亚临界扩展是DNBD试样仍能沿预制裂缝发生自相似剪切断裂的主要原因，也是DNBD法测试岩石II型断裂韧性的机制。

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	衡帅1
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	曹端伟1
	陈宇1
	李贤忠1
	董卓1

关键词 ：岩石力学, 页岩, II型断裂韧性, 双切口巴西圆盘（DNBD）法, 剪切断裂, 各向异性

Abstract：To enhance our understanding of the anisotropy in shear fracture resistance of shale, the mode-II fracture toughness of shale with different bedding orientations was measured using the double-edge notched Brazilian disc (DNBD) method. These tests were conducted based on theoretical analyses of shear crack initiation. The initiation and propagation of fractures generated in DNBD specimens were determined, and the mechanism for testing the mode-II fracture toughness of rocks using the DNBD method was investigated. The results indicated that: (1) the high compressive T-stress in DNBD specimens significantly reduces the circumferential stress at the tips of pre-cut notches, thereby inhibiting the competitive initiation of tensile cracks and facilitating self-similar shear fractures. (2) The mode-II fracture toughness of shale increases approximately linearly with the bedding angle, displaying marked anisotropy. The fracture toughness is minimal at the bedding plane, maximal in the matrix, and nearly equal in the direction normal to the bedding compared to the matrix. As an intrinsic material property, the true mode-II fracture toughness, in the absence of normal compressive stress, is considerably lower than the apparent (experimental) value. Moreover, the true mode-II fracture toughness remains relatively constant even when wing-shaped tensile cracks initiate competitively. (3) Similar fracture propagation patterns were observed in DNBD specimens with varying bedding orientations. The findings revealed that complex fracture processes, including the competitive initiation and subcritical propagation of wing-shaped and en-echelon fractures, occurred prior to the shear fracture of the rock bridge. (4) The subcritical propagation of wing-shaped tensile cracks following competitive initiation has been identified as the primary mechanism driving self-similar shear fractures along pre-cut notches in DNBD specimens. This understanding elucidates the mechanism for measuring mode-II fracture toughness in rocks using the DNBD method.

Key words： rock mechanics shale mode-II fracture toughness double-edge notched Brazilian disk (DNBD) method shear fracture anisotropy

引用本文:

衡帅1，2，曹端伟1，陈宇1，李贤忠1，董卓1. 页岩II型断裂韧性的各向异性特征研究[J]. 岩石力学与工程学报, 2025, 44(10): 2622-2637.
HENG Shuai1, 2, CAO Duanwei1, CHEN Yu1, LI Xianzhong1, DONG Zhuo1. Anisotropy in mode-II fracture toughness of shale. , 2025, 44(10): 2622-2637.

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https://rockmech.whrsm.ac.cn/CN/10.3724/1000-6915.jrme.2025.0182 或 https://rockmech.whrsm.ac.cn/CN/Y2025/V44/I10/2622

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