The effects of specimen size and strain rate up to nearly ε = 10
3/s on the compressive properties of isotropic nuclear-grade graphite IG-11 were investigated experimentally at room temperature. Solid cylindrical specimens with two different slenderness (length/diameter) ratios of 0.5 and 1.0 were used in the impact and static compression tests, respectively. The specimen's diameter was varied from 6 to 15 mm, keeping the slenderness ratio constant. The high strain-rate compressive stress-strain curves up to failure were determined using the conventional split Hopkinson pressure bar (SHPB). The corresponding static and intermediate strain-rate stress-strain curves up to failure were measured with an Instron testing machine. The two parameters of Weibull distribution were used to evaluate the ultimate compressive strength (nominal maximum compressive stress) at three different strain rates. It was found that the ultimate compressive strength and corresponding strain (or failure strain), and the absorbed energy up to failure increased substantially at strain rates of over 10
−1/s, and were independent of the specimen size tested over a strain rate range from 10
−3/s to 10
3/s. Macro- and micro-scopic examinations revealed that there was a marked difference in the failure modes between the static and impact compression specimens.
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