Dynamic Behavior and Damage Failure Mechanisms of Coal Samples Subjected to Single Impact Loading

This study investigated the effect of varying strain rates on the dynamic behavior and damage mechanisms in coal. We employed the split Hopkinson pressure bar to conduct dynamic unconfined compression tests on coal samples. This involved obtaining the coal samples dynamic mechanical properties and failure characteristics. We performed analyses on the extent of impact damage before and after testing, leading to the development of a dynamic damage constitutive model based on strain rates. The findings demonstrated the clear nonlinearities in the dynamic stress–strain curve, segmented into three phases: linear elasticity, plastic yield, and post-peak softening. In both low and high strain rate scenarios, the observed peak stress, strain, kinetic and dissipation energy exhibited a phased linear growth. The coal sample exhibited two macroscopic fracture modes: axial splitting under low strain rates and pulverization under high strain rates. The degree of coal fragmentation rose, and the size of the shattered pieces decreased as the strain rate increased. Based on wave velocity tests, the damage to coal samples at lower strain rates rose exponentially. Combined with fractal dimension analysis, it was evident that the damage dimension of coal samples under high strain rates rose linearly. A constitutive model for coal samples was built, adjusted, and validated against experimental findings, establishing a connection between parameters F₀, m, and strain rate. It was confirmed that the model’s fitting degree may reach 0.9. This study helps to elucidate the damage mechanisms in coal samples under strain rate change from low to high.