Dynamic caustics experiment on crack propagation of defective medium under the effect of explosive stress waves of double holes

The dynamic behavior of blast-induced cracks propagation between two notched boreholes in PMMA materi- al with prefabricated crack under blasting load was studied by a new digital laser experimental system of dynamic caus- tics. The experimental results show that ① in the simultaneous blasting process for the double notched boreholes,the interaction between the prefabricated crack and the blast-induced main crack interdicts the propagation of blast-in- duced main crack and the coalescence of two blast-induced main cracks,which indicates that the prefabricated crack has great influence on the directional fracture controlled blasting;② the blast-induced secondary cracks generated at the tips of horizontal prefabricated crack and the blast-induced main cracks do not meet directly in the propagating process,but move to the near blast-induced main crack surface,which leads to blast-induced secondary cracks growth in a curved way. Compared with the horizontal prefabricated cracks,the vertical one has even greater influence on the propagation of the blast-induced main crack. The blast-induced secondary cracks are mainly affected in tension stress field and expand with mode I;③ the values of propagating speed and dynamic stress intensity factor are reduced by the interaction between the frontal compression wave of P wave in explosive stress wave and propagating crack.