In this study, a uniaxial impact compression test was performed on coal samples with length-to-diameter
L
/
D
ratios of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 using a
Φ
50 mm split Hopkinson pressure bar (SHPB) test system. This study researched the stress uniformity and deformation behavior of coal samples with different
L
/
D
ratios during dynamic compression, defined the stress equilibrium coefficient
ξ
, proposed a new method for determining whether a sample meets the stress uniformity hypothesis, and obtained the critical
L
/
D
ratio of 0.6 and the optimal
L
/
D
ratio of 0.3 or 0.4 for coal samples to obtain the stress equilibrium. The experimental results showed that the dynamic stress-strain curve of coal had an elastic stage, a plastic stage, and a failure stage. As the
L
/
D
ratio increased, the proportion of the elastic stage to the prepeak curve of the samples declined progressively; with an increase in the
L
/
D
ratio, the peak part of the curve also changed from “sharp” to “stagnated,” while an increase in the plasticity led to strain softening. As the
L
/
D
ratio of the samples increased, the average strain rate decreased approximately as a power function, and the decreasing trend was gradually reduced from 296.49 s−1 (
L
/
D
=0.3) to 102.85 s−1 (
L
/
D
=1), with a reduction of approximately 65.31%. With an increase in the
L
/
D
ratio, the peak strain gradually decreased exponentially. This study concluded that the SHPB test protocol design is of a certain reference value for low-density, low-strength, heterogeneous brittle materials, such as coal.
Experimental Study on Stress Uniformity and Deformation Behavior of Coals with Different Length-to-Diameter Ratios under Dynamic Compression
