Experimental study on blasting crack initiation and propagation behaviorin compression stress field

The digital-laser dynamic caustics system in combination with a static-dynamic loading device was utilized in the blasting fracturing test, in which the PMMA specimens underwent four kinds of vertical static stresses (0, 3, 6 and 9 MPa, respectively) with the strictly same total charge. By using the fracture mechanics theory, the mechanism of the fracture and propagation behaviors of the cracks along the static principle stresses was analyzed. The result indicates that the stress concentration is first created under the pre-applied vertical stress field around the borehole, where the maximum tensile stress is located on the borehole wall corresponding to the far-field maximum principle stress direction. Then, when disturbed by the dynamic loads induced by blasting, the crack is precociously initiated from the maximum tensile stress point and extends along the maximum principle stress direction. Furthermore, the crack velocity increases accordingly with higher vertical pre-static stresses; the greater the crack velocity increases, the higher the stress intensity factor of the crack tip.