Abstract: Rock breaking by high voltage pulse has the characteristics of environmental protection and energy controllable,which is an emergent rock fragmentation technology with broad application prospect.The fracture mechanism of red sandstone specimens under high voltage pulse was analyzed by electric breakdown experiment,and the fracture modes and fracture degrees of red sandstone specimen under different size and discharge voltages were studied.The results show that high temperature and shock wave are the internal mechanisms leading to the fracture of the specimen.Under the action of high voltage pulse,a breakdown zone near the electrodes is formed in the sandstone specimen due to the rapid expansion of plasma channel,and the damage is the most serious.Radial cracks appear on the outside of the breakdown zone under the action of shock wave.When the shock wave is strong enough,it can induce spalling cracks near the boundary.The formation of breakdown zone,radial cracks and spalling cracks is closely related to the specimen size and discharge voltage.The crack density and fractal dimension are selected to quantitatively analyze the fracture degree of the specimen after high voltage pulse.With the increase of specimen size,the failure mode of specimen changes from fragmentations to perforation failure,the fracture density,the complexity and the fractal dimension of the specimen decrease continuously.With the increase of discharge voltage,the failure mode of specimen changes from perforation failure to fragmentations,the fracture density,the complexity of crack and the fractal dimension of the specimen are increased.

Key words: high voltage electric pulse,rock fragmentation,fracture mode,fracture density,fractal dimension