Development of “Dropkinson” Bar for Intermediate Strain-rate Testing

Abstract

A new apparatus – “Dropkinson Bar” – has been successfully developed for material property characterization at intermediate strain rates. This Dropkinson bar combines a drop table and a Hopkinson bar. The drop table is used to generate a relatively long and stable low-speed impact to the tensile specimen, whereas the Hopkinson bar principle is applied to measure the load history with accounting for inertia effects in the system. In addition, pulse shaping techniques were applied to the Dropkinson bar to facilitate uniform stress and strain as well as constant strain rate in the specimen. The Dropkinson bar was used to characterize 304L stainless steel and 6061-T6 aluminum at a strain rate of ~600 s−1. The experimental data obtained from the Dropkinson bar tests were compared with the data obtained from conventional Kolsky tensile bar tests of the same material at similar strain rates. Both sets of experimental results were consistent, showing the newly developed Dropkinson bar apparatus is reliable and repeatable.