Experimental study on the influence of loading rate on the directional propagation law of rock mode-I cracks

•This study is conducted to investigate the influence of the loading rate on the propagation behavior of rock mode-I cracks.•The rock mode-I crack propagation changes from a low-energy-efficiency fracture mode with high energy consumption to a high-energy-efficiency fracture mode with low energy consumption with the loading rate increases.•This research can provide a reference for studying the fracture mechanism and designing the control method of fractured rock or coal mass. To investigate the influence of the loading rate on the propagation behavior of rock mode-I cracks, a simple device for simulating rock-crack directional propagation was developed. Subsequently, loading tests were performed for rock mode-I crack propagation at different loading rates. The entire crack propagation process was monitored by applying acoustic emission (AE) and digital image correlation (DIC), and the influence of the loading rate on the mode-I crack propagation mechanism was investigated. The results showed that the peak load increased as the loading rate increased; however, the crack initiation angle and crack initiation time both tended to decrease. According to the evolution law of the deformation field, the crack propagation process can be divided into four stages: local strain band initiation, local strain band development, main control crack initiation, and main control crack coalescence. The deformation separation degree of the main control crack increased with an increase in the loading rate. The evolution process of AE can be divided into four stages: quiet, slowly increasing, booming, and decreasing periods. When the loading rate increased, the intensity of the released AE energy increased. The energy evolution law of the crack propagation process was closely related to the loading rate. The energy dissipated before the peak load decreased with an increasing loading rate, whereas the releasable elastic energy increased after the peak load increased. Scanning electron microscopy analysis revealed that when the loading rate increased, the crack propagation changed from a low-energy-efficiency fracture mode with high energy consumption to a high-energy-efficiency fracture mode with low energy consumption.