Fracture mechanism due to blast-imposed loading under high static stress conditions

Using a dynamic-static experimental loading device and a digital laser dynamic caustic system, the effect rules for blasting induced main cracks responding to an initial static stress field are studied. The propagation rules of a 45 degrees oblique crack subjected to different initial static stress fields and of cracks with different angles and initial static stress fields are also studied. The experiment results show that (1) Under an initial static stress load, different stress concentrations are generated around boreholes, and the maximum tensile stresses are generated in the direction of the maximum principle stress of the borehole. The combined action of the initial static stress field and dynamic blasting stress field causes the longest crack to propagate in the direction of initial static stress preferentially. The initial static stress field changes the distribution characteristics of the blasting-induced cracks. (2) The level of the stress concentration increases, the propagation direction of the main crack is deflected along the direction of the principle stress, the propagation time of the main crack becomes shorter, the mode II fractures of specimens are more severe, and the maximum deflection angle of the main crack increases as initial static stress load increases. (3) As the angle between crack and initial static stress load direction increases, the propagation times of the main cracks decrease, and the occurrence of an obvious shear fracture occurs in the main crack more quickly. Also, with the increased angle between crack and initial static stress load direction, the peak values of the reflecting angles gradually increase, and the displacement along the pre-existing crack direction decreases showing the crack path becomes more flexural.