Failure Characteristics and Failure Process Investigation of Fine-Grained Sandstone under Impact Load by Ultrahigh Speed DIC and SEM Techniques

The dynamic failure characteristics and fracture process of brittle materials such as rock involves a complex crack propagation process, the underlying mechanics of which is not yet fully understood. At present, the combination of high-speed photography and Digital Image Correlation (DIC) technology is considered to be the most promising and ideal means to observe crack growth and analyze the failure mechanism of rock-like materials. In this work, ultra-high-speed photography is used to investigate the dynamic failure characteristics of fine-grained sandstone, and scanning electron microscope (SEM) is used to investigate the relationship between the mechanical properties and failure law of fine sandstone and strain rate from the micro perspective. Finally, the failure mechanism of the rock is analyzed by combining the DIC technology. It is found that the fine-grained sandstone undergoes five critical moments under impact load, namely, initiation of the first crack, initiation of the second crack, crack penetration, local crushing, and thorough breaking. With the increase of strain rate, the whole failure process of rock specimen is shortened, and the time between two critical moments is shorter and shorter, indicating that the more severe the failure of the rock specimen in a time interval between the critical moments, the shorter the time required for the process, and the less obvious the strain rate effect. The first crack on the rock surface initiates from the direction of the transmission rod. With the increase of the strain rate, the angle between the crack on the rock surface and the axial direction is larger, and the second crack will penetrate the specimen first.