Study on the evolution of coal fracture behavior and stress energy consumption model: Experimental study and implications for in situ coal seam cracking

The extent of coal fracturing directly affects the efficacy of coalbed methane extraction. Therefore, we performed an examination of the mechanical properties, energy dynamics, and damage characteristics of coal under varying strain rates (30–120 s−1) using the Split Hopkinson Pressure Bar. The findings reveal that peak strength, strain, average rate of stress increase, energy dissipation, and damage severity in coal specimens exhibits a positive correlation with the strain rate. Conversely, the duration of stress escalation and the average size of fragments demonstrate a negative correlation with strain rate. As the strain rate increases, the cumulative curve of fragments transitions from a concave to a convex configuration, and the degree of coal sample fracturing gradually progresses from type I to II and III. Based on these findings, stress and energy models for coal samples subjected to varied strain rate conditions were developed and validated with experimental data, providing significant insights into the stress and energy dissipation mechanisms critical for coal mining safety. The study introduces an innovative evaluation index, q (0–1, 1–5, >5), for assessing the degree of coal sample fragmentation, which increases with increasing strain rate, reflecting the transition from initial to complete fracturing of coal samples. This discovery holds substantial engineering value for refining new dry ice fracturing techniques in coal mining safety and enhancing the efficiency of gas extraction.