The objective of this paper is to investigate the complete process of dynamic crack propagation in brittle materials under different loading rates. By using Improved Single Cleavage Semi-Circle (ISCSC) specimens and Split Hopkinson Pressure Bar equipment, experiments were conducted, with the fracture phenomenon and crack propagation of tight sandstone investigated. Meanwhile, the process of crack propagation behaviour was simulated. Moreover, with the experimental–numerical method, the crack propagation dynamic stress intensity factor (DSIF) was also calculated. Then, the crack propagation toughness of tight sandstone under different loading rates was investigated and illustrated elaborately. Investigation results demonstrate that ISCSC specimens can achieve the crack arrest position unchanged, and the numerical simulation could effectively deduce the actual crack propagation, as their results were well matched. During crack propagation, the crack propagation DSIF in the whole process increases with the rising loading rate, and so does the crack propagation velocity. Several significant dynamic material parameters of tight sandstone are also given, for engineering reference.

Water contents in rocks vary with local hydrogeological conditions and may significantly affect the stability of rock mass engineering. For example, geological disasters are usually occurring after rainfall, such as landslides, karst collapse. In this paper, drop plate impact (DPI) tests were performed on single cleavage triangle (SCT) red sandstone specimens with dry, natural, absorbed and saturated conditions, which has a great guiding significance for deep understanding of dynamic failure of rock materials. The crack initiation time was obtained by crack propagation gauges (CPGs), and crack propagation speeds were computed by fractal method. The dynamic stress intensity factors (DSIFs) were calculated by ABAQUS code. Meanwhile, the microstructure of the fracture surface was scanned and was analyzed. The results show that the average critical DSIFs and crack propagation speeds vary with water content significantly. For the dry sandstone, the average critical DSIF is the highest, whereas the average crack speed is the lowest. For the natural sandstone, the average critical DSIF is the lowest, whereas the average crack speed is the highest. For the water-bearing sandstone, i.e., the natural, absorbed and saturated sandstone, the average critical DSIF increases with water content, whereas the crack speed decreases with increasing water content.

In civil, geotechnical, and mining engineering, the investigation of the holes’ effect on dynamic crack propagation is essential because it can be used to predict possible fracture and protect cracked structures being further damaged. In this paper, a specimen made from polymethyl methacrylate (PMMA) with a pre-crack and two holes was proposed, and the Split-Hopkinson pressure bar was employed to investigate the effect of holes on dynamic crack propagation under impact loading. Notably, the locations of the holes were well designed with different two-hole spacing (12 mm, 16 mm, and 20 mm) and crack-hole distance (15 mm, 30 mm, and 45 mm). Crack propagation gauges were applied to monitor the fracturing time and crack extending velocity. The interaction characteristic between the crack and two holes was studied numerically using the AUTODYN code. In the numerical models, the failure criteria of maximum tensile stress and softening damage were employed for brittle material. The crack path, the propagating velocity, the particle velocity vector, and the stress state between the holes were analyzed. The calculation results indicate that compressive stresses between the two holes induced by the deformation of the holes play a crucial role in confining the vertical crack propagation. Both experimental and numerical results demonstrate that the holes have a suppressing action on the moving crack; as the two-hole spacing decreases, the suppressing action intensifies.