Rocks often show an anisotropic behavior due to microcracks, mineral-based structure, and unequal in-situ stresses. The crack tip's stress intensity factors (SIFs) that control rock failure heavily depend on anisotropy. Given the significance of extensive research to identify the effects of anisotropy on the mechanical behavior and strength of rocks, numerical modeling is considered an essential method in designing structures and analyzing their stability. This study experimentally and numerically evaluated the effects of the bedding angle, initial crack angle with the loading axis, crack length, and anisotropy ratio on the stress intensity factor of transversely isotropic rocks via the extended finite element method (XFEM). Cracked chevron-notched Brazilian disks (CCNBDs) were fabricated from phyllite under the International Society for Rock Mechanics (ISRM) standards and tested at different initial crack lengths and angles for validation. The XFEM approach was then used to predict toughness and crack propagation path in the tested and new specimens with varying ratios of anisotropy and bedding angles ( = 0, 30, 45, 60, and 90°). The results demonstrated that with the increase of the anisotropy ratio, in equal crack length and initial angle, the absolute value of the SIFs have larger values. In addition, with the increase of crack length, the first and second modes of SIF increased, which indicates the failure of the specimen at lower loads. Also, bedding angle is effective on the stress intensity factors and this effect becomes more intense as the crack length increases. Finally, the anisotropy properties not only affect the values of SIFs, but also can change the angle at which the specimen experiences pure mode I or mode II.

中文翻译：

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使用扩展有限元法评估各向异性岩石的实验和数值破坏机制

由于微裂纹、矿物结构和不均匀的地应力，岩石常常表现出各向异性行为。控制岩石破坏的裂纹尖端应力强度因子 (SIF) 在很大程度上取决于各向异性。鉴于广泛研究确定各向异性对岩石力学行为和强度影响的重要性，数值建模被认为是设计结构和分析其稳定性的重要方法。本研究通过扩展有限元法（XFEM）通过实验和数值方法评估了层理角度、初始裂纹与加载轴的角度、裂纹长度和各向异性比对横观各向同性岩石应力强度因子的影响。裂纹 V 形缺口巴西圆盘 (CCNBD) 采用千枚岩根据国际岩石力学学会 (ISRM) 标准制造，并在不同的初始裂纹长度和角度下进行测试以进行验证。然后，使用 XFEM 方法来预测具有不同各向异性比率和层理角度（= 0、30、45、60 和 90°）的测试样本和新样本的韧性和裂纹扩展路径。结果表明，随着各向异性比的增大，在裂纹长度和初始角度相同的情况下，SIF的绝对值较大。此外，随着裂纹长度的增加，SIF的第一和第二模式增加，这表明试件在较低载荷下发生破坏。此外，层理角对应力强度因子也有影响，并且随着裂纹长度的增加，这种影响变得更加强烈。最后，各向异性特性不仅影响 SIF 的值，而且还可以改变样本经历纯模式 I 或模式 II 的角度。