Analysis of the dynamic impact behavior and fracture mechanism of coal samples at various temperatures

A thorough understanding of the mechanical properties and fracture mechanisms of coal under high-temperature conditions is crucial for preventing deep coal and rock dynamic disasters. Utilizing the Hopkinson pressure bar experimental system, this study conducts an in-depth analysis of the strength characteristics, failure modes, microscopic properties, and energy consumption effects of coal between 0 and 250 degrees C. The findings reveal that during the heating process, coal's mass loss increases with temperature, but at a decreasing rate. Significant changes in the coal samples' dynamic strength, fragmentation, microscopic features, energy evolution, and fracture mechanisms occur at 100 degrees C, marking a turning point in their dynamic behavior. Both dynamic strength and elastic modulus experience a transient increase at 100 degrees C, while the fractal dimension experiences a brief decrease. At 100 degrees C, the thermal expansion of coal particles predominates over the thermal damage from high temperatures, resulting in an increase in the coal samples' dynamic strength. As the temperature further rises, thermal damage to the coal samples intensifies, leading to a decrease in dynamic strength. Similarly, the absorption and dissipation energy index K of the coal samples experiences a brief increase at 100 degrees C, signifying a sudden change in the energy evolution pattern. Observations of the coal samples' failure modes upon impact reveal a transition from tensile failure to a combined shear-tensile failure with increasing temperature.