Rock dynamic fragmentation is essentially a process of energy consumption, and energy dissipation analysis is essential to elucidate the mechanism of rock dynamic crushing. In this paper, the split Hopkinson pressure bar (SHPB) shock compression tests on sandstone and cement mortar under five different impact velocities are carried out. The fracture surface area of rock fragments and surface energy of the two kinds of rock have been studied based on the fractal principle and fracture mechanics theory. Furthermore, the fragment-size distribution of broken rock is obtained by sieving and the relationship among average size of rock fragments, fractal dimension and energy dissipation has been analyzed. Results from the SHPB tests show that along with the increase of fractal dimension, the size of rock fragments decreases linearly, the larger the fractal dimension is, the higher the degree of rock fragmentation is; the fracture energy performs remarkable power function correlation with average size of rock fragments, with the increasing of fracture energy, the average size decreases significantly. Besides, with the increasing of impact velocities, both the fracture energy and fracture surface area increase, but the energy required for producing new unit surface area is basically constant, and the fracture surface energy of testing sandstone and cement mortar are obtained respectively.

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