In this paper, the propagation mechanism of an oblique straight crack has been studied theoretically, which reveals its mechanical characteristics under in-plane biaxial compression. Firstly, the stress components away from the boundary are derived based on the superposition principle. The normal stress components are strengthened and shear stress component is restrained compared to the uniaxial condition. Then the relationship between stresses and stress intensity factors is analyzed, and the effect of stresses on the strength of cracked rocks is discussed. The analysis of wing crack growth shows that the reliable experimental results are very demanding for sample preparation. Based on Mohr-Coulomb criterion and Mohr’s stress circles, the failure mechanism of cracked rocks is analyzed, and the physical meaning of some formulas is vividly displayed. Moreover, we study the relationship between friction angle θ₀ and angle β, which determines the minimum compressive strength of cracked rocks. There are evidences that the increase of crack opening width leads to β₀ (a value of β) away from the theoretical value determined by sliding crack model, so that the role of stress σ_x can no longer be ignored. Theoretically speaking, for an initially closed crack, we find that, for the first time, both wing crack growth and shear compression failure are more likely to occur when the angle β between 22.5 and 45 degrees combining the statistical results of Barton and Choubey (Rock Mech Rock Eng 10:1–54, 1977). As for an initially open crack, the characteristics of stress intensity factors and circumferential stresses are also discussed, especially when σ₁ equals σ₃. Finally, we study the effect of osmotic pressure on stresses and stress intensity factors, the weakening of the properties of crack surfaces by water is also considered, and the mechanical behavior of a rock sample with an oblique straight crack changes dramatically.

中文翻译：

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岩石样品中斜直裂纹的扩展机理及面内双轴压缩下的渗透压效应

本文对斜直裂纹的扩展机理进行了理论研究，揭示了斜双裂纹在面内双轴压缩下的力学特性。首先，基于叠加原理推导了远离边界的应力分量。与单轴状态相比，法向应力分量得到加强，剪应力分量得到抑制。然后分析了应力与应力强度因子之间的关系，并讨论了应力对裂隙岩石强度的影响。对机翼裂纹扩展的分析表明，可靠的实验结果对样品的制备要求很高。基于Mohr-Coulomb准则和Mohr应力场，分析了裂隙岩石的破坏机理，并生动地显示了某些公式的物理含义。此外，我们研究了摩擦角之间的关系θ ₀和角度β，其确定岩石破裂的最小抗压强度。有证据表明裂缝开口宽度引线的增加β ₀（的值β）从通过滑动裂缝模型确定的理论值远，从而使应力的作用σ _X不能再被忽略。从理论上讲，对于最初闭合的裂纹，我们发现，当角度β较大时，机翼裂纹扩展和剪切压缩破坏都更容易发生结合Barton和Choubey的统计结果在22.5至45度之间进行比较（Rock Mech Rock Eng 10：1-54，1977）。至于最初张口裂纹，还讨论的应力强度因子和周向应力的特性，特别是当σ _1个平等σ ₃。最后，我们研究了渗透压对应力和应力强度因子的影响，还考虑了水对裂缝表面特性的削弱，并且具有斜直裂缝的岩石样品的力学行为发生了巨大变化。