Dynamic tensile mechanical properties and energy dissipation characteristics of sandstone with varying degrees of initial damage

To elucidate the influence of pre-existing damage on the dynamic tensile behavior and energy dissipation mechanisms of sandstone, cyclic loading-unloading followed by dynamic Brazilian splitting tests were conducted using a split Hopkinson pressure bar (SHPB) system. X-ray computed tomography (CT) was utilized to quantify the internal microstructural evolution under varying degrees of initial damage. The results reveal a clear intrinsic coupling relationship among initial damage, dynamic tension, and energy evolution: First, cyclic loading exacerbates internal fracture coalescence, significantly increasing the pre-existing damage degree. Second, this initial damage fundamentally deteriorates the rock's dynamic tensile properties; the dynamic tensile strength decreases markedly as damage intensifies, with highly damaged samples retaining only 54% of the intact strength. Under impact, crack propagation in pre-damaged sandstone remains predominantly tensile, while macroscopic deformations (shear strain and vertical displacement) are significantly amplified. Finally, from an energy perspective, pre-existing internal cracks act as localized energy absorption zones. Consequently, an increase in initial damage drives a higher damage-dissipated energy density and a corresponding reduction in transmitted energy during dynamic failure. This study highlights the failure mechanisms of damaged rock driven by energy dissipation, providing essential theoretical support for the stability evaluation and dynamic disaster early-warning of surrounding rock in deep mining engineering.