Abstract:The maximum Mode I and Mode II stress intensity factors (SIFs), K_I,kmax(θ) and K_II,kmax(θ) (0°<θ<360°), of inclined parallel multi-crack varying with relative positions (including horizontal and vertical spacings) are calculated by the complex function and integration method to analyze their interacting mechanism and determine the strengthening and weakening zone of SIFs. The multi-crack initiation criterion is established based on the ratio of maximum tension-shear SIF to predict crack initiation angle, load, and mechanism. The results show that multi-crack always initiates in Mode I and the vertical spacing is better not to be times of half crack-length for crack-arrest, which is in good agreement with test results of the red-sandstone cube specimens with three parallel cracks under uniaxial compression. This can prove the validity of the multi-crack initiation criterion.

Key words: interaction mechanism; multi-crack initiation criterion; initiation prediction; multiple cracks; stress intensity factor