Dynamic impact experimental and global cohesive element method to shale fracture characterization.

• The crack propagation process and its strain evolution were captured using the split Hopkinson pressure bar (SHPB) device combined with high-speed digital image processing. • The relationship between dynamic mode Ⅰ fracture toughness and crack propagation velocity of bedding shale with bedding and loading rate was analyzed qualitatively and quantitatively. • Based on the Traction-Separation Law, the method of global cohesive element was used to simulate the dynamic crack propagation and calculate the fracture toughness of bedding shale. The fracture behavior and various of mechanical mechanisms of shale are greatly influenced by the bedding surface. To study the effects of bedding angles on the crack propagation patterns and dynamic fracture properties, the shale notched semi-circular bend (NSCB) specimens were studied by the modified split Hopkinson pressure bar (SHPB) device, three-dimensional digital image correlation (3D-DIC) system with the high-speed (HS) photography and ABAQUS finite element software. The research results showed that at the same impact velocity, the 30°, 45° and 60° beddings played an obvious deflexion effect on the shale crack propagation. However, the 0° and 90° bedding did not deflect the crack propagation. The dynamic fracture toughness of shale NSCB specimens increased with the increase of impact loading rate but the increase magnitude decreased with the higher impact rate. The kinetic energy during specimen fracture was calculated by the extracting displacement data from the 3D-DIC, and it was found that the kinetic energy accounted for less than 6% of the absorbed energy during the dynamic compression of the shale. The crack propagation characteristics of ABAQUS simulation was approximately consistent with the experimental results. It is conducive to the study of shale gas fracturing and the formation of complex seam networks in shale and it is of great research significance for the efficient extraction of shale gas. [ABSTRACT FROM AUTHOR]