Damage effect and progressive failure mechanism of sandstone considering different flaw angles under dynamic loading

In many engineering applications, it is essential to have information about rocks that inherently contain preexisting flaws under dynamic loading conditions. Dynamic impact tests are conducted on samples with varying flaw angles using the split Hopkinson pressure bar (SHPB) test system and the Digital Image Correlation system (DIC). The characteristics of the samples after dynamic loading, including dynamic strength, energy dissipation, and fractal fracture, are compared and analyzed. As the flaw angle increases, the peak stress and strain exhibit a typical V-shaped pattern, reaching the minimum value at 30 degrees, and the initial initiation position shifts from the flaw tips to the middle of the flaw. Failure modes can be divided into three modes depending on the flaw angle. The progressive failure process, taking into account the heterogeneity of the rock, is demonstrated by developing an elastic damage constitutive model that uses dynamic compression and tensile tests to parameterize it. As the flaw angle increases, the initial damage zone also moves from the flaw tips to the middle of the flaw. Failures around the hole with redistributed stress are observed, and the failure mechanisms can be explained with the aid of strain energy density (SED). Using fracture mechanics, the analytical solution of stress around the flaw is provided, and the variation of crack initiation angle, stress distribution, and energy dissipation under different flaw angles is theoretically explained, which is in good agreement with the experimental and simulated results.