Pore evolution, mechanical response, and energy dissipation mechanisms of coal ranks under impact loading

China's coal resources—lignite, bituminous coal, and anthracite—exhibit distinct pore structures and mechanical properties, influencing mining safety and stability. Using the split Hopkinson pressure bar system and a specific surface area analyzer, this study found that kaolinite content increases with coal rank, while calcite and quartz content decrease. Scanning electron microscope analysis shows lignite has a rough surface, bituminous coal a moderate texture, and anthracite a smooth surface with minimal pores. Specific surface areas are 2.30 m2/g (lignite), 3.17 m2/g (bituminous), and 1.37 m2/g (anthracite), with pore volumes from 0.0076 to 0.012 cm3/g and average pore sizes of 7.43–14.28 nm. Dynamic tests reveal that increasing impact velocity (2.50–5.00 m/s) increases dynamic strength by 22.47% (lignite), 83.09% (bituminous), and 73.85% (anthracite), with bituminous coal being the most sensitive. Fractal dimensions of debris and pores also increase with impact velocity, ranging from 1.86 to 2.34 and 3.21 to 3.54, respectively. Energy analysis indicates lignite consumes the least energy, anthracite the most, and bituminous coal is intermediate. The image captured by the high-speed camera shows that the greater the impact velocity, the more cracks will appear at the moment of rupture; lignite and bituminous coal have lower brittleness compared to anthracite, resulting in fewer cracks at the moment of rupture. These findings enhance understanding of coal behavior, offering insights for improved mining safety and coalbed methane extraction.