Fragmentation characteristics and energy components of cylindrical rock specimens in a novel collision system

Abstract

Abstract

By means of a novel experimental method for rock collision reported recently, a total of 27 cylindrical rock specimens from three rocks were tested. The collision process was filmed by a camera, the velocity of each specimen was measured by a laser instrument, the stress wave energy transferred to the transmitted bar was measured by the strain gauges, and all fragments of each specimen were collected, weighed, and sieved after collision tests. The results showed that: (1) all rock specimens were successfully released from the incident bar of the new collision system, confirming that the new collision method is successful for collision tests using cylindrical specimens flying with a velocity of 13–39 m/s. (2) All rock specimens were fragmented into numerous particles. (3) Specific input energy, defined as the input energy per unit volume of rock, varied from 0.48 to 4.4 MJ/m3. (4) The energy transferred to the transmitted bar was 0.4–1.8 % of the total input energy. (5) The translational kinetic energy and the rotational kinetic energy carried by the flying fragments were equal to or less than 7.7 % and 6.9 % of the total input energy respectively. (6) The energy used in fragmentation was up to 83.6 % of the input energy if only the kinetic and transmitted energies were considered while other unknown energies neglected. (7) Specific input energy was one of most important factors influencing rock fragmentation, and larger specific input energy resulted in better (finer) fragmentation, and vice versa. (8) Rock impedance was another important factor effecting rock fragmentation. At an approximately constant specific input energy, a rock specimen having smaller impedance yielded better fragmentation, and vice versa. (9) The wavelength measured in the transmitted bar during the collision tests was on average 13 times of the calculated wavelength based on elastic theory.