Abstract: Fracture of rocks under dynamic loading is very common in rock engineering. To study the crack response of dynamic fracture of mode I cracks under impact loading, the dynamic fracture test of single cleavage triangle (SCT) granite specimens with lateral opening was carried out using a split Hopkinson pressure bar test system. The Hough transform method was used to quantitatively describe the length and angle distribution of the surface crack morphology, and the relationship between crack morphology and the energy absorbed was analyzed. The 3D point cloud data of the section was obtained by using the 3D surface topography instrument, and the section reconstruction method based on the fitting surface threshold detection was proposed, which effectively eliminates the error of the 3D point cloud data of the section. The relationship between section roughness and energy dissipation was discussed. The results show that the exponential distribution of crack length  tends to increase with the increase of absorbed energy; the angles of cracks are evenly distributed, with few cracks appearing in the horizontal direction; when the energy dissipation of the specimen is low, the cracks present obvious directivity, while the cracks bend more violently and the connectivity is better when the energy dissipation is high; the proposed section reconstruction method performs well at 0.03～0.08 of the points in x and y directions, and the threshold value is 0.25. The roughness statistical parameters of specimens A and B sections decrease with the increase of energy dissipation.

Key words: SCT specimen, rock fracturing, Hough transform, section roughness, mode I crack