Specimen geometry effects on high-strain-rate testing of graphite/epoxy composites

Numerous papers have been published that include high-strain-rate experimental data obtained from Split Hopkinson Pressure Bar (SHPB) tests. There have been no standardized test specimens with differing dimensions and geometry. For this reason, it can be difficult to compare results of tests performed by other researchers. The SHPB facility was used in this study to determine if specimen geometry has an effect on the results of high-strain-rate compression tests. The material used in all of the tests is a unidirectional IM7/8551-7 graphite/epoxy composite. The experiments discussed herein show the effect of varying the length-to-diameter (L/D, or aspect) ratio of the specimen, as well as the effect of changing from the more typical cylindrical to a square/rectangular specimen geometry. The L/D study examined 84 cylindrical specimens with L/Ds from 0.5 to 2.0, with D=0.261 in., and tested in both the 1 and 2 directions. The geometry study used 42 square/rectangular specimens and tested in the 1, 2, and 3 directions. The results of both studies are compared, and no statistically significant effect of either L/D or geometry could be found.