Abstract:This study investigates the effect of length-to-diameter ratios (L/D) on dynamic mechanical properties of coal samples using Split Hopkinson Pressure Bar (SHPB) experimental device, using rectangular bullets in different impact velocity within 3.107-7.108m per-second to load and break the cylinder of raw coal specimen, the draw ratio of that in 0.5, 1, 1.5, 2 Researching the impact of the length of raw coal sample with on the dynamic mechanical properties. The results indicate that: ①due to the combination of the uneven distribution of the coal specimen self-contained bedding and strain rate effect, in the condition with relatively high impact velocity, strain-rate time-history curves showed two typical forms: the one is constant strain rate platform change gently, the other is the posterior part of constant strain-rate platform has obvious fluctuation; ② The samples with different draw-ratio show obvious strain rate effect, the shapes of the stress-strain curve of that range from 0.5 to 2 change in peaks , hills and polymorphism, showing different process of effects of elastic and plastic deformation; ③ With regard to the bedding structure of coal and the theory of SHPB test, whatever which are too long or too short , the samples are not suitable for studying the breakage features of the impact dynamic strain of coal. The sample with L=50mm is the best, that of 75mm is inferior.
