Transient process of mechanical response and energy conversion of rocks with different lithologies under impact loading

Abstract

The mechanical response and energy utilization efficiency of rocks with different lithologies during percussion drilling are highly significant for optimizing engineering and tool parameters improving the efficiency of percussion drilling. In this study, dynamics tests were conducted on rocks of different lithologies, considering the impact compression and tensile process versus the strain rate effect of the rock. A high-speed camera was used to observe the generation and development of cracks during the transient fracture of the rock and analyze the time-varying effect of strain during fracture. A model of fracture energy changing with time was established, and the relationship between the strain rate and dynamic strength, failure time, and fracture energy was developed and verified. The results of this study revealed that, the higher the impact velocity and the harder the rock, the shorter the time required for the rock to break. This means that under the same impact conditions, it takes longer to break a soft rock. Moreover, the fracture energy conversion rate of a rock is greatly affected by the impact velocity, and the fracture energy of the rock increases as the strain rate increases. There was an optimal impact velocity for each type of rock and the fracture energy conversion rate was the highest at that velocity. When the strain rate was 50–150 s−1, the specimen strength and fracture energy showed similar trends: strength and fracture energy of granite were the highest, followed by that of tuff and sandstone. The specimen failure time displayed an opposite trend: sandstone had the longest failure time, followed by tuff and granite. The findings could form the basis for the further analysis of dynamic failure characteristics to improve the energy utilization rate and rock-breaking efficiency of different lithology rocks.