Fracturing evolutionary law and energy utilization efficiency of green sandstones under different loading rates

Objective This study aims to explore the fracturing evolutionary laws and energy utilization efficiency of rocks under different loading rates is a pressing issue in the field of rock fragmentation and processing. Methods To this end, the microscopic parameters of green sandstones were calibrated based on laboratory tests, followed by the identification of relationships between the macro- and microscopic mechanical responses of the sandstones. Using Particle Flow Code (PFC), this study investigated the stress-strain curves and stress chain distribution of green sandstones under different loading rates. Then, based on the fracturing and crack characteristics, this study analyzed the fracturing evolutionary laws, and analyzed the energy utilization efficiency during the fracturing process of green sandstones. Results and Conclusions The results indicate that: (1) The stress-strain curves obtained during the fracturing of green sandstones exhibited the stages of pre-peak linear elasticity, pre-peak plastic deformations, and post-peak progressive destabilization. The tensile chains lead to crack propagation in green sandstones, and the eventual failure of the sandstones was caused by the interactions between pressure and tensile chains. (2) Under varying loading rates, green sandstones experienced the stages of shear fracturing, penetrating fracturing, and mixed multistage fracturing. The fracturing in the former stages was primarily caused by shear force, while tensile force predominated in the last stage. Tensile cracks were primarily found throughout the rock fracturing. These cracks exhibited a formation rate significantly higher than shear cracks, with an overall crack generation rate reaching up to 2400.81 m/s. (3) The failure energy of green sandstones evolved from slow increase to rapid increase and then to stabilization. The energy utilization efficiency peaked at 0.088% when the loading rate was 0.05 m/s. This study conducted a preliminary exploration into the fracturing evolutionary laws and energy utilization efficiency of rocks microscopically, and the results serve as a guidance for selecting rational process parameters for rock fracturing.