Shale has remarkable bedding characteristics, and the key technology of shale gas extraction engineering is garnering great interest in the influence of bedding on the fracture mechanisms and fracture criteria of shale. Three-point bending tests combined with digital image correlation (DIC) were carried out on semicircular bend (SCB) specimens of shale with different bedding angles to investigate the influence of bedding on crack evolution. The results showed that the strain field of each bedding shale exhibited three stages during the three-point bending : uniform strain distribution, damage accumulation, and strain localization. In the stage of strain localization, each specimen first showed considerable tensile strain localization along a straight line extending from the tip of the prefabricated crack. With increasing loading, except for in the localized bands of the tensile strain, the maximum shear strain became aligned with the bedding orientation in the shale specimens, indicating that the original mode I cracks of the specimens were transformed into mixed-mode I/II cracks due to the influence of the bedding. A new fracture criterion (the generalized maximum circumferential stress criterion based on shale bedding, GMTS-SB) was deduced for predicting the propagation of a prefabricated mode I crack in bedding shale. The results calculated from the GMTS-SB were compared with the experimental results to evaluate the accuracy of the criterion. In the established GMTS-SB, the stress intensity factor is related to the specimen size, the load magnitude, and the bedding angle. This criterion also considers the influence of T-stress on the calculated result. For bedding shale, the GMTS-SB can effectively describe the crack angle and fracture resistance of a crack initiating along the bedding orientation.

页岩具有显着的层理特征，页岩气开采工程关键技术对层理对页岩断裂机理和断裂准则的影响正受到广泛关注。对不同层理角度的页岩半圆弯曲（SCB）试样进行三点弯曲试验结合数字图像相关（DIC）试验，研究层理对裂缝演化的影响。结果表明，各层理页岩应变场在三点弯曲过程中呈现出三个阶段：应变分布均匀、损伤积累和应变局部化。在应变局部化阶段，每个试样首先沿着从预制裂纹尖端延伸的直线出现相当大的拉伸应变局部化。随着负载的增加，除拉伸应变的局部带外，最大剪应变与页岩试样中的层理取向一致，表明试样的原始 I 型裂缝受到影响转变为混合型 I/II 裂缝的床上用品。推导了一种新的断裂准则（基于页岩层理的广义最大周向应力准则，GMTS-SB），用于预测层状页岩中预制 I 型裂缝的扩展。将 GMTS-SB 计算的结果与实验结果进行比较，以评估标准的准确性。在已建立的 GMTS-SB 中，应力强度因子与试样尺寸、载荷大小和层理角度有关。该标准还考虑了 T 应力对计算结果的影响。