Experimental and theoretical study on cyclic fatigue damage evolution of sandstone based on acoustic emission monitoring and resistivity measuring

The fatigue damage induced by cyclic loading can significantly reduce the strength of rock, highlighting the critical need to investigate its evolution process. This study dynamically monitored the damage evolution of saturated sandstone under cyclic loading using acoustic emission and resistivity techniques. The results indicate that the peak fatigue strength of the rock at a frequency of 1 Hz follows the order: Path II (57.2 MPa) > Path III (53.8 MPa) > Path I (51.9 MPa). In contrast, the peak strength at a frequency of 0.5 Hz shows the order: Path II (55.9 MPa) > Path III (52.2 MPa) > Path I (41.7 MPa). Damage variables established based on acoustic emission and resistivity parameters offer micro- and macro-perspectives on rock damage, respectively. Coupling these variables produces an equation effectively reflecting sandstone's fatigue damage evolution, validated against damage variables established by strain energy. Additionally, a damage constitutive equation constructed from these variables aligns well with the experimental results. The coefficient of determination exceeds 0.95 (R2 > 0.95), emphasizing the practical value of the proposed equations for studying sandstone damage evolution.