Dynamic impact characteristics of coal specimens with different structural defects based on SHPB tests

• Different dynamic responses of dense, porous, and fissure coal were investigated. • DIC analysis revealed real-time dynamic strain fields and crack evolution. • Failure mechanisms were cross-verified by SHPB experiments and LS-DYNA. • Internal defects significantly affected wave propagation and breakage patterns. To investigate the dynamic response and energy dissipation mechanism of coal with different structural defects, this study selected three representative coal types: intact coal specimens, porous coal specimens, and fractured coal specimens. Split Hopkinson pressure bar (SHPB) impact tests were conducted under an incident gas pressure of 0.1 MPa to acquire stress waveforms and dynamic stress–strain curves. The mechanical response characteristics associated with distinct defect configurations were analyzed using a high-speed camera and a synchronized multi-sensor data acquisition system. Combining sieve-based fragment size distribution analysis with fractal dimension characterization, the impact failure modes and fragmentation patterns of the three coal types were systematically characterized. A three-dimensional numerical model was subsequently developed, incorporating a coupled analysis framework of plastic strain localization and evolving damage fields—to simulate stress wave propagation, micro-damage nucleation, and macroscopic failure evolution—and thereby elucidating the mesoscale energy dissipation mechanisms. Results indicate that Dense coal undergoes predominantly global brittle splitting, exhibiting highly localized energy deposition and relatively low dissipation efficiency; porous coal displays diffuse, multi-scale fragmentation and yields a higher fractal dimension; and fractured coal specimen develops complex, stress-concentrated fracture networks governed by crack-tip fields. Numerical simulations demonstrate strong phenomenological agreement with physical experiments in terms of failure morphology, fragment size statistics, and spatiotemporal energy evolution. This work validates the mechanistic principle that macroscopic failure modes are governed by how structural defects steer mesoscale plasticity and damage evolution pathways.