Combined effect mechanism of linear loading and disturbance with different amplitudes on sandstone

To comprehend the stress state and response characteristics of materials under complex conditions, researchers have decomposed stress states into fundamental paths and investigated diverse path combinations. To ensure comparability, four identical samples were carefully selected from a pool of 100 samples using ultrasonic tests based on the wave speed and waveform characteristics. These samples underwent specially designed stress paths to analyze the combined effects of linear loading and perturbation. Our result analysis centred on the perturbation amplitude and stress levels during composite action, revealing intricate relationships between the stress levels, strain, and nonlinear/linear energy evolution under complex stress paths. Simultaneously, 3D surface fractures were precisely reconstructed using the YOLOv5 and FAST feature point detection algorithms, elucidating the evolving patterns of the fractures. As a result of our study, the rotation trend of the main fracture was validated by integrating mechanics and P-wave reflection rules. Notably, our experimental results closely aligned with the theoretical predictions, showing the reliability of our study. These findings can significantly contribute to guiding safety protocols in the field of underground engineering. The combined effects of the stress paths under linear loading and perturbation conditions were investigated via a comprehensive analysis of the experimental results integrating mechanical theory and prior research findings.The YOLOV5 and FAST feature point detection algorithms were used for three-dimensional crack reconstruction, providing insights into the fracture morphology of the experimental specimens and showing the crack propagation patterns on the specimen surfaces.The energy evolution trend was explored, revealing a notable linear trend in the cumulative values. The stiffness evolution trend under compound paths was examined, elucidating the change mechanism through integration with established laws.