Fracture behavior of an empty hole using the digital laser dynamic caustic method under directional controlled blasting

A systematic approach for using a new digital laser dynamic caustic (DLDC) method to provide useful insights for blasting crack propagation is illustrated. Under blast loading conditions, the dynamic behavior of blasting crack propagation and stress distribution around the empty hole between two boreholes were investigated. The results show that the crack tips were gradually deflected towards the empty hole. Then, it was eventually perforated under the guiding role of empty holes. By the interaction between the blast stress waves and the empty hole, the reflected tensile waves were generated. Moreover, these waves changed the stress field and reduced the velocity of the crack tip with a greater diameter for the empty hole. It was also found that the size of the empty holes had a slight influence on the direction of the principal stress. The larger the size of the empty hole was, the smaller was the speed of the crack propagation. In general, the crack propagation velocity of the circular empty hole was the highest, followed by that of the square hole and the notched circular hole. As the blast crack extended to the vicinity of the empty hole, the stress intensity factor of the crack tip started to show an upward trend again.