A Novel Torsional Kolsky Bar for Testing Materials at Constant-Shear-Strain Rates

Abstract

Kolsky bars, also known as split-Hopkinson bars, have been widely used in the dynamic characterization of engineering materials for over 50 years. Kolsky bars can be made to test materials in compression, tension, or torsion, and until recently, have been generally employed in the testing of high-impedance ductile materials to collect rate-dependent stress-strain data during large-strain inelastic flow. The advancement of “pulse-shaping” techniques in the last decade has allowed Kolsky bars to be utilized for testing low-impedance and brittle materials as well. Pulse-shaping is a processes of tailoring the dynamic loading during a test, with consideration given to the material being tested, in order ensure that the sample achieves a state of dynamic stress equilibrium and constant strain-rate if desired. The most common design of torsional Kolsky bars currently in widespread use offer no way to incorporate pulse-shaping. This limits their use mostly to high-impedance, large-strain applications. A novel torsional Kolsky bar design is presented in this work, which allows for straightforward pulse-shaping, similar to the method employed in compression testing, that can be used to test brittle and low-impedance materials as well as to design experiments that ensure the sample is undergoing a constant-shear-strain-rate deformation. Details of the design as well as some preliminary data demonstrating the pulse shaping capabilities collected during tests are presented.