Effect of Specimen Diameter in Compression at High Strain Rates

The split Hopkinson pressure bar (SHPB) is one of the most widely used experimental techniques to study the behavior of materials at medium to high strain rates. This paper deals with the use of the SHPB to investigate the effect of the specimen diameter on the mechanical properties of materials. Specimens made of aluminum alloy 6061-T6, with length 5?mm and varying diameters of 5, 6, 8, 10, and 12?mm, are tested. For same strain rate, higher stresses are observed for the smaller-diameter specimens. The smaller-diameter specimens give rise to higher and more uniform strain rates but oscillating stress-strain curves. They result in a low transmission coefficient that affects the output signals; therefore, smaller diameters should be selected carefully with the transmission coefficient of 0.5 or better. With some compromise on oscillating stress-strain behavior, the specimens with smaller diameters can be used successfully to achieve high strain rates.