Fracking is widely applied to enhance shale gas mining, and insight into the fracture behaviors of shale rocks is important. To characterize the fracture properties of Lower Silurian Longmaxi shale, a chevron-notched deep beam specimen, which inherits the advantages of notched deep beam and chevron-notched specimens, is introduced, and several three-point bend tests were conducted on the Longmaxi shale specimens in three principal fracture orientations: the divider, short-transverse, and arrester orientations; the anisotropy in the critical shape coefficient, fracture toughness and fracture energy were then examined and highlighted. The results demonstrate that the critical shape coefficient depends on the anisotropic elasticity of the investigated shale, and a maximum error in the calculated fracture toughness of 9.2% could occur if a critical shape coefficient for isotropic rock is adopted. For the tested shale, the mode I fracture toughness in the divider orientation is close to that in the arrester orientation, with both values being approximately 1.5 times that in the short-transverse orientation; in addition, a progressive decrease in fracture energy from the arrester orientation to the short-transverse orientation is apparent. The fracture surface morphology was observed by scanning electron microscopy, and obvious material deterioration was found near the fracture surfaces for the arrester and divider samples.

中文翻译：

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志留系龙马溪页岩各向异性断裂性质表征

压裂技术被广泛应用于加强页岩气开采，深入了解页岩的破裂行为很重要。为表征下志留统龙马溪页岩的断裂特性，介绍了一种继承了缺口深梁和人字形缺口试样优点的人字形缺口深梁试样，并对龙马溪页岩试样进行了多次三点弯曲试验。在三个主要裂缝方向：分隔器、短横向和避雷器方向；然后检查并突出显示临界形状系数、断裂韧性和断裂能的各向异性。结果表明，临界形状系数取决于所研究页岩的各向异性弹性，计算的断裂韧度的最大误差为 9。如果采用各向同性岩石的临界形状系数，则可能会出现 2%。对于被测页岩，分隔器方向的 I 型断裂韧度与避雷器方向的接近，均约为短横向方向的 1.5 倍；此外，断裂能从避雷器方向到短横向方向逐渐降低是显而易见的。通过扫描电镜观察断口形貌，避雷器和分压器样品在断口附近发现明显的材料劣化。短横方向的5倍；此外，断裂能从避雷器方向到短横向方向逐渐降低是显而易见的。通过扫描电镜观察断口形貌，避雷器和分压器样品在断口附近发现明显的材料劣化。短横方向的5倍；此外，断裂能从避雷器方向到短横向方向逐渐降低是显而易见的。通过扫描电镜观察断口形貌，避雷器和分压器样品在断口附近发现明显的材料劣化。