Experimental study on the evolution characteristics of one-dimensional stress spallation in gray sandstone

This study investigates the tensile mechanical properties of gray sandstone under dynamic impact. Drawing on the one-dimensional stress wave theory, we conducted a one-dimensional spallation experiment using a 50 mm diameter Hopkinson pressure bar, an ultra-high speed camera and a long rod specimen of gray sandstone rock. Specifically, we probed into the spallation evolution of gray sandstone specimens under impact loading and the influence of loading rate on the spallation mechanical properties of gray sandstone by digital image correlation method (DIC). Results show that: ① When spallation occurred, the axial strain on the surface of the gray sandstone specimen exhibited a sudden jump at the spallation position, where particle velocities exhibited opposite trends on either side.② As impact velocity increased, fracture strain at the spallation position increased, the spallation position gradually approached the free end and the first spallation occurred earlier.③ By comparing with the wave superposition method and the free surface velocity method, the accuracy of the DIC method in the spall strength test is verified. ④ Further analysis reveals that the fracture strength of the gray sandstone has a significant strain rate effect, and the subsequent spall strength in the same specimen is higher than the first spall due to the superposition of stress waves. This study provides evidences for exploring the dynamic fracture behavior of rock, strain rate effect and optimizing rock dynamic constitutive equation.