Response characteristics of acoustic emission signal and judgment criteria for different fracture modes.

• ·The differential characterization of AE signals from various fractures and the precursor law were investigated. • ·Proposed a novel approach to decompose the P- and S- waves of AE signals. • ·The criterion value of Es/Ep for laboratory differentiation between tensile and shear fracture is determined. Coal mining is going deeper into the ground, resulting in more intense and frequent mine dynamic disasters. To ensure the early warning of dynamic disasters, it is significant to accurately reveal the differences of acoustic emission (AE) signals generated by rock fractures. This paper focuses on studying how AEs average frequency (AF) and rise angle (RA) change in sandstone during loading, and examines the characteristics of waveform amplitude, energy, and frequency distribution of AE signals from different types of fractures. The findings reveal that the percentage of shear fracture gradually increases with increasing load, and the energy activity of the AE signal is significantly enhanced in the high stress stage. The occurrence of the main fracture was preceded by a large number of low-frequency tensile fracture AE signals, accompanied by a small decrease in RA and a small increase in AF. The spectra of different fracture signals were characterized as "low anomalous F" for shear fractures, "vertical F" for low-frequency tensile fractures, and "high anomalous F" for high-frequency tensile fractures. Their energy distribution in the frequency domain was respectively described as "peak-centered distribution", "pillar-shaped distribution" and "peak-skewed distribution". The outcomes of the decomposition and reconstruction from the P- and S-waves reveal that the P wave energy (Ep) dominates in the high-frequency tensile fracture AE signal, while the S wave energy (Es) is greater in the low-frequency tensile fracture and the shear fracture AE signals. The E S /E P threshold value for laboratory discrimination of tensile and shear fracture is 3, as the fracture extends and penetrates, the E S /E P value rises rapidly at the appearance of macroscopic fracture. The findings offer theoretical guidance for monitoring and early warning of coal and rock dynamic hazards as well as revealing the morphology of fracture source. [ABSTRACT FROM AUTHOR]