Experimental investigation on dynamic mechanical behavior and fracture evolution of fissure-filled red sandstone after thermal treatment

Natural or artificially disturbed rocks containing massive fillings are frequently subjected to various sophisticated temperature and stress perturbations. To investigate the effects of temperature and filling angle on the dynamic mechanical characteristics and fracture patterns of red sandstone, thermal treatments at 25 degrees C, 200 degrees C, 400 degrees C, 600 degrees C, and 800 degrees C were conducted on red sandstone samples containing single fracture filling angles at 0 degrees, 30 degrees, 60 degrees, and 90 degrees. Subsequently, the dynamic mechanical information and crack evolution of specimens after thermal treatment were tested and recorded utilizing a modified split Hopkinson pressure bar (SHPB) test system integrated with a high-speed camera, and the crack expansion modes were identified and analyzed. Meanwhile, X-ray diffraction (XRD), scanning electron microscopy (SEM), simulation and one-dimensional stress wave theory were employed to analyze and discuss the thermal damage and failure mechanism of the specimens in detail. The results demonstrate that temperature and filling angle have conspicuous effects on the elastic modulus, thermal expansion, mineral composition, dynamic compressive strength, strain rate effects, and crack expansion modes of the specimens. Tensile cracks dominate the fracture of the specimen during dynamic loading, while shear cracks tend to appear in thermal stress concentration area. Moreover, thermal damage, wave impedance and stress wave propagation path are the critical factors controlling the fracture evolution and dynamic mechanical properties of the specimens.