Time-frequency characteristics of acoustic emission during brittle-ductile fracture of coal under impact loading and damage extraction based on the Stockwell transform

Based on the Split Hopkinson Pressure Bar (SHPB) and acoustic emission (AE) techniques, stress–strain curves, energy evolution and AE amplitude during coal failure were monitored to reveal the dynamic failure mechanism of coal under different impact pressures, explore the effect of impact pressure on AE characteristics during the brittle-ductile transition, and achieve accurate identification of major damage points. Crack propagation under loading and the particle size distribution of fragmented coal after failure were analyzed. The macroscopic characteristics of brittle-ductile failure were clarified, the temporal evolution of ringing counts and energy with stress–strain response was investigated, and the staged crack evolution characteristics were revealed based on the proportion of RA/AF classified cracks. Fast Fourier Transform (FFT) was adopted for the frequency-domain analysis of AE waveforms, and the differences in spectral characteristics between brittle-dominated and ductile-dominated coal failure were clarified. Based on the Stockwell Transform, time–frequency feature fusion analysis was performed to identify key damage points, and their identification accuracy was verified through b-value time-series analysis. This study clarifies the AE time–frequency response mechanism of coal brittle-ductile failure, identifies key damage points via the Stockwell Transform, and provides support for the precise early warning and mitigation of coal mine rockbursts.