Measurement of ejection velocity of rock fragments under dynamic compression and insight into energy partitioning

High-speed three-dimensional digital image correlation (3D-DIC) technique was utilised to examine the ejection velocity characteristics of rock fragment in dynamic compression tests. The fragment velocity components of fragment were extracted from velocity fields distributed within the fragment area. By identifying the peak resultant velocity, the initial fragment ejection velocity was determined. The kinetic energy of fragments was evaluated with the initial ejection velocity and the mass of the fragments in each size group. Results show that the fragment movement is successively accelerated by stress-wave propagation, crack opening and Poisson's effect which contribute to the axial, circumferential and radial velocity component of fragment, respectively. The variance in circumferential velocity of two neighbouring fragment areas indicates the formation of fragments. The peak value of radial velocity, which is the chief component in ejection velocity reveals the time when ejection taking place. The initial ejection velocity of fragment gradually decreases with increasing size, but increases significantly as strain rate increases. The kinetic energy of fragments ejection comprises 12%-24% of absorbed energy at strain rate of 69-100 s-1, and the percentage further increases with increasing strain rates. Ignoring the kinetic energy of fragments will lead to overestimation of dissipated energy consumed by rock fragmentation in dynamic compression.

Automated summary

The study utilized the high-speed three-dimensional digital image correlation (3D-DIC) technique to investigate the ejection velocity characteristics of rock fragments in dynamic compression tests. It was found that the fragment movement is successively accelerated by various factors, and the ejection velocity varies with size and strain rate.