Signal response and energy evolution of separated sandstone

This study aims to establish a precise prediction system for strong rockbursts and mine earthquakes caused by high-hard roof fractures. A three-point bending test was conducted on separated sandstone (SS) to analyze deformation field changes under the influence of digital image correlation (DIC) and acoustic emission (AE) signals during rock fracture. Microscopic fracture modes and energy evolution patterns of SS are investigated using scanning electron microscopy and Particle Flow Code in 2 Dimension, revealing the internal mechanisms linking fracture modes, crack classifications, and energy evolution. The results show that the AE signals and DIC deformation fields are highly correlated. Tensile cracks are the primary indicator of damage to SS during the strong contact phase. Complete failure occurs at peak load, driven by a combination of tensile and shear cracks. Increasing the precast crack length (b) or the upper-to-lower rock layer thickness ratio (U/L) enhances tensile failure sensitivity, whereas simultaneous increases reduce it. Macroscopically, this is reflected in variations of AE peak frequency and the primary fracture's peak frequency. Microscopically, it appears as changes in fracture surface roughness and grain fracture morphology. Energetically, this is evident in changes to the ratios of strain energy and slip energy relative to total energy. Additionally, as b and U/L increase, the primary crack location and AE energy density concentration shift progressively from the lower to the upper rock layers. Meanwhile, total input energy decreases with increasing b or as U/L deviates from 1.