Numerical modeling of crack propagation from open and closed flaws in rock.

• Positive and negative oscillations of K II under compression are the reason for zigzag crack propagation paths modeled by the traditional fracture criterion. • GMTS criterion considering T -stress can effectively eliminate K II oscillations but requires complicated parameter calculations. • SLMS criterion proposed in this study can conveniently and efficiently model the propagation of both tensile and shear cracks. • The effects of flaw inclination, friction coefficient, loading level, and flaw surface contact status on the crack propagation paths were studied. The traditional fracture criterion performs well when calculating crack propagation under tensile conditions, but a zigzag crack propagation path was obtained under compression, which is inconsistent with experimental results. This study indicates that the positive and negative oscillations of the mode-II stress intensity factor (K II) under compressive loading during crack propagation is the reason for the zigzag trajectory of crack propagation. Such oscillation of K II can be effectively eliminated when the non-singular stress (T -stress) at the flaw tips is considered, and thus, the path of crack propagation can also be smoothed. However, due to the complicated calculations of the stress intensity factors and T -stress at each step of crack propagation, it is not suitable for simulation in fast, complex environments and multi-flaws. Also, the lack of a shear fracture criterion in traditional fracture methods leads to difficulty in studying shear crack propagation in rock. Therefore, a strength-based localized maximum stress (SLMS) criterion was proposed in this study to model both tensile and shear crack propagations in rock more efficiently, conveniently, and accurately. Then, the crack propagation processes in both plate and Brazilian disc specimens with a single flaw under uniaxial and biaxial compression were modeled to investigate the effects of the flaw inclination angle, friction coefficient, and loading level on the crack propagation path. The influence of the contact friction between the flaw surfaces on the contact status and the crack propagation path during the crack propagation process was also analyzed. Also, the crack propagation in a plate with a single flaw under biaxial tension was modeled, which shows bifurcation crack propagation when the lateral tension is several times larger than the axial tension. All the modeled results indicated that the proposed SLMS criterion can get better results when modeling crack propagations for open or closed flaws under tension or compression conditions. [ABSTRACT FROM AUTHOR]