Influence of impact velocities of hammer crusher on crushing effect and utilization efficiency of fracture energy in green sandstone

The impact velocities of hammer crusher directly affect the crushing effect of rock. In order to study influence of impact velocities of hammer head on the crushing effect and utilization efficiency of fracture energy in green sandstone, macroscopic and microscopic mechanical response relationship of green sandstone was established by combining with physical experiments and microscopic parameter calibration. The characteristics of stress chain, characteristics of damage and degradation, acoustic emission and changes of crack in green sandstone under different impact velocities of hammer crusher were analyzed using particle flow code, and the utilization efficiency of fracture energy was studied. The results show that: ① During the crushing process of green sandstone, the internal part of destructive micro-unit is mainly composed of tension chain, and the edge of failure is mainly composed of pressure chain. In the undamaged micro-unit, the pressure chain and tension chain cross each other to form network. The tension chain cause extension of crack, and the final failure is the result of the combined action of pressure chain and tension chain. ② The failure pattern of green sandstone is divided into the stage of local failure, extended failure, and intensified failure. The number of destructive micro-unit is divided into the stage of rapid increase, gradual slowing, and stabilization. The larger the impact velocities, the greater the stable increase in the number of destructive micro-unit, and the number of destructive micro-unit approximately follows linear distribution with the impact velocities. ③ With the increase of impact velocities, the cumulative number of crack in green sandstone is divided into the stage of rapid increase and stabilization. In the stage of crack initiation, shear crack are the main type, and the initial input energy is mainly used for the generation of shear crack, while the proportion of tensile crack gradually increases, and eventually tensile crack are the main type. ④ During the failure process of green sandstone, the fracture energy can be divided into the stage of rapid increase, gradual slowing, and stabilization. The utilization efficiency of fracture energy can be divided into the stage of rapid increase, slow increase, and slow decrease, with the maximum value of 10.851%, and the quantitative relationship between utilization efficiency of fracture energy and impact velocities is established. The result of the study not only provide preliminary exploration of the crushing effect and utilization efficiency of fracture energy in green sandstone from microscopic perspective, but also provide reference for the reasonable selection of process parameters in the crushing process of hammer crusher.