Estimation of the dynamic fracture process of rock material utilizing high speed photography

The experimental study is conducted to estimate fracture process of the cylindrical rock specimen. In this experiment, an explosive is used as the explosion source, and a pipe filled with water is arranged between the explosive and the cylindrical rock specimen. The main purpose of this fracture test is to collect the experimental data on the behaviors of the dynamic fracture of the rock. In addition, one of the aims of this test is to estimate the dynamic tensile strength of the rock in wide range of strain rate utilizing Hopkinson's effect. Therefore, During the fracture process of the rock, the free surface velocity and the fracture part near the free surface were observed by a laser vibration meter and high speed camera. The precise detonator was used to control the initiation time of the explosive by using an accurately controlled blasting machine. The results of the fracture test for Kimachi sandstone and the validity of this test are discussed. In order to understand the relationship above fracture condition and the incident underwater shock wave into the rock specimen, the numerical simulation is carried out. The 2D hydrodynamic code based on ALE finite difference scheme is employed. In the case of the fracture test with 50mm water pipe, the incident underwater shock wave into the cylindrical rock specimen has irregular pressure distribution near the shock front.