Research on crack initiation mechanism and fracture criterion of rock-type materials under compression–shear stress

Abstract

With the focus on the failure of single-cracked rocks under compression-shear stress, the form and the critical conditions of crack initiation by adopting theoretical derivation and numerical experiments methods are researched in this article. Maximum circumferential stress criterion and modified Griffith's criterion are utilized to derive the expressions for crack initiation angle and fracture criterion. Moreover, the PFC 3D , numerical simulation software, is used to verify the results of theoretical research and the research on the generation process of shear fracture zone and the number of microcracks and their distribution law. The results show that the crack initiation angle u 0 and critical conditions of crack initiation correlate with some factors, such as crack inclination angle b, coefficient of friction m, and the ratio of normal stress to shear stress s 1 /t x . When b is less than or equal to 90°, the deviation between the theoretical result of crack initiation angle and actual result is small; when the value of Mode I fracture toughness K IC is accurate, the crack criterion derived is reliable when b is less than or equal to 120°. The friction between cracks restricts the compression-shear failure on the surface of crack. The ratio of shear stress required for crack initiation to peak shear stress in the model decreases with the normal stress increased. At the crack initiation stage, when the increase in microcracks is relatively slow, the shear fracture zone is thin and when the increase in microcracks becomes rapid, shear fracture zone becomes thick at the peak stage. The shear strength is proportional to the number of microcracks in the model.

An overview on advances in computational fracture mechanics of rock

“…Despite of these weaknesses, this method was employed successfully by researches to investigate rock fracture and crack propagation (Fakhimi and Villegas, 2006;Hazzard et al, 2000;Konietzky et al, 2002;Lee and Jeon, 2011;Poulsen and Adhikary, 2013;Yue et al, 2017). based on relatively similar principles as PFC proposed by Frédéric and Magnier (1995) and Donzé and Magnier (1997).…”

Discrete numerical analyses of grain size influence on the fracture of notched rock beams

“…In any case, the obtained stress-strain curves are linear from the onset of loading and the estimated Young's modulus values correspond to the secant modulus at 50% of the peak strength (𝐸 50 ). In the case of uniaxial compression, crack initiation and peak load are very different (e.g., Yue et al 2017). This is due to the fact that, at low load level, a lot of microcracks start to develop in a diffuse manner, but later coalescence takes place and leads to a macroscopic crack and final failure.…”

Numerical Analysis of Crack Propagation Evolution of Specimens with Different Dip Angles of Cross Fractures

“…The crack propagation under uniaxial compression of a single fracture is taken as the research object. Cracks can be categorized as wing crack (Tw), anti-wing crack (To), coplanar shear crack (Sc) and oblique shear cracks (So) (Cao et al 2015;Yue et al 2017;Zhang et al 2014;Zhuang et al 2014), as shown in Fig. 3.…”