Study on the influence of length-diameter ratio on the mechanical characteristics of cracks at the end of linear charges

Dynamic caustic experimental method and numerical simulation method were used to study the crack propagation rules and the tension/compression damage zone at the end of boreholes in the planar model.The results show that the effect of different length-diameter ratios on the crack propagation was significant. As the length-diameter ratio increasing , the crack propagation lengths increased and the expansion angles decreased.When the length-diameter ratio was 5/5 ,the crack propagation angle was about 90°.When the length-diameter ratio increased to be 20(30/1.5) , the crack propagation angles decreased to be 40°.As the length-diameter ratios increased again , the crack propagation angled didn 't change any more.The numerical results are in good agreement with the experimental results , and Numerical simulation shows that small area of compression damage area formed in the area of the column hole , and“X"type tensile damage zone formed at the end of the hole , which lead to the formation of explosive crack easily at the end of the borehole.The radius of the tensile damage zone was approximately 5 times the radius of the compression zone around the borehole.