MACRO AND MICRO QUANTITATIVE STUDY ON IMPACT BEHAVIOR OF GLASS BEADSBY SHPB TESTS AND FEM-DEM COUPLING ANALYSIS

In order to study the macro and micro impact behavior of glass beads, one-dimensional SHPB impact tests on glass balls with different relative densities were carried out. The coupled numerical model of SHPB impact test was established by discrete element and finite difference methods. The experimental and numerical results indicate that the glass ball experiences four specific phases under one-dimensional load, i.e., initial elastic response, yielding, lock-up and particle crushing. The average coordination of particles increases with the applied impact load but the increasing rate decreases gradually. This is because the coordination number is determined by both pore compression and particle redistribution which is caused by particle rotation and relative movement. Particle rotation and relative movement become more than more difficult with the compression of granular sample. The porosity of sample remains almost constant in initial elastic response, but decreases approximately linearly in the yielding and lock-up phases (grain redistribution). This is because the porosity is mainly determined by the bulk movement of particles, which causes compression in pores. The bulk movement of particles has not been developed at the initial loading, but after yielding the pore compression caused by the bulk movement of the particles develops linearly with the load history. The particle displacement is dominated by bulk movement; thus it is not sensitive to initial density. The particle rotation and relative movement need to overcome the lock-up effects which are closely related to the particle size distribution, thus they are very sensitive to the relative density.