Experimental investigation of rock mechanics behavior under multistage pulsating load based on digital image correlation and acoustic emission technology

Pulsating loading effectively reduces rock strength and improves rock-breaking efficiency. To reveal the influence mechanism of pulsating parameters on rock mechanical properties, this study conducted a series of pulsating loading tests on sandstone specimens with varying frequencies and stress amplitudes. Results show that low frequency and medium stress amplitude are most favorable for strength and deformation resistance reduction. Pulsating load weakens rock strength primarily by reducing inter-particle cohesion and friction. Lower frequencies correlate with higher acoustic emission (AE) counts and greater rock damage. Under medium stress amplitude, AE b-value fluctuations last longest, with earliest failure precursors. As pulsating frequency and stress amplitude increase, damage transitions from overall to localized, and from gradual to instantaneous. Dissipated energy reflecting crack propagation resistance decreases with lower frequencies, while elastic energy driving crack extension increases with higher amplitudes. When pulsating frequency and stress amplitude are elevated, one-dimensional damage indices fail to accurately reflect local damage concentration in the rock. However, two-dimensional and threedimensional damage indexes from digital image correlation and AE cumulative counting effectively characterize rock damage progression. This study elucidates the mechanisms by which pulsating loads influence the mechanical behavior of rocks, providing insights for the optimization of rock-breaking techniques in various applications.