Experimental study on mechanical properties and failure characteristics of sandstone containing a pre-existing surface flaw under dynamic loading

Dynamic loading tests were conducted on sandstone specimens containing a three-dimensional surface flaw with different angles and depths using a modified split Hopkinson pressure bar (SHPB) device. A high-speed camera with digital image correlation method was used to record the crack initiation, propagation and failure process of specimens and to monitor the surface strain field. The test results show that both the angle and depth of the surface flaw have an important influence on the dynamic mechanical properties and energy dissipation of the specimens. The specimen is least weakened at a surface flaw angle of 90°, with the angle having a greater effect on dynamic strength and energy absorption at greater depths. Analysis of the x-axis direction strain, shear strain and y-axis direction strain fields by DIC shows that the crack initiation is due to a combination of tensile and shear stresses. Both the angle and depth of the surface flaw have a significant effect on the failure patterns. Specimens show shear failure at surface flaw angles less than or equal to 60° and tensile failure at surface flaw angles of 75° and 90°. When the angle of surface flaw is less than or equal to 60°, there are more shear cracks at greater depths. The complexity of three-dimensional crack propagation under dynamic loading was confirmed by the observation of traces of internal shell-like crack growth in a partial fragmentation of specimen after failure.