Abstract This paper presents the results of 124 pure Mode I fracture toughness tests on two types of anisotropic rocks, the metamorphic Grimsel Granite and the sedimentary Mont Terri Opalinus Clay. The results show that Mode I cracks in anisotropic rocks tend to kink towards the foliation or bedding planes that are weaker in strength. The experiment data for kink angle and apparent fracture toughness are compared to the predictions of three well-known crack growth criteria: the maximum tangential stress (MTS), the maximum energy release rate (MERR), and the minimum (maximum in anisotropic materials) strain energy density (MSED). All these criteria overestimate the kink angle, while underestimating the apparent fracture toughness. The MTS yields predictions that are closest to the experiment data, while the MSED predictions are the furthest. We also show that the inclusion of the T-stress into the MTS criterion improves the predictions of the fracture growth. This indicates that the T-stress can play a significant role in the Mode I fracture growth of anisotropic rocks.

中文翻译：

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各向异性岩石中的 I 型裂缝扩展：理论与实验

摘要 本文介绍了对两种类型的各向异性岩石，变质的 Grimsel 花岗岩和沉积的 Mont Terri Opalinus Clay 进行 124 次纯 I 型断裂韧性试验的结果。结果表明，各向异性岩石中的模式 I 裂缝倾向于向强度较弱的叶理或层理平面扭结。将扭结角和表观断裂韧性的实验数据与三个众所周知的裂纹扩展标准的预测进行比较：最大切向应力 (MTS)、最大能量释放率 (MERR) 和最小值（各向异性材料中的最大值）应变能密度 (MSED)。所有这些标准都高估了扭结角，而低估了表观断裂韧性。MTS 产生最接近实验数据的预测，而 MSED 预测最远。我们还表明，将 T 应力纳入 MTS 标准可以提高对裂缝生长的预测。这表明 T 应力在各向异性岩石的 I 型裂缝生长中起重要作用。