Abstract In this experimental study, behavior of rock-like specimens with smooth and rough cracks has been investigated in closed and open condition under uniaxial loading. To study the behavior, physical models made up cement, gypsum and water with 10 20 5 cm of dimensions were used. Open and closed joints with smooth and rough surfaces were located at the center of specimens. The length and inclination angle of cracks are selected 6, 5and 4 cm and 30, 45 and 60 degree, respectively. Results shows depend on crack length and crack inclination angle two types of cracks (wing and secondary) propagation from the pre-existing cracks tips. Inclination angle, length and closed or open condition of cracks effects on crack initiation stress. Crack initiation stress for specimens with rough joints is higher than smooth ones. The criterion is presented for diagnosis of secondary crack propagation for samples with one crack.

Keywords: Crack propagation, Wing crack, Secondary crack, Open Crack, closed crack

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