Investigating strength of materials at very high strain rates using magnetically driven expanding cylinders

¹ Rafael- Advanced defence systems, Haifa, Israel
² Faculty of Mechanical Engineering, Technion – Israel Institute of Technology
³ Solid State Institute and Physics Department, Technion – Israel Institute of Technology

^a Corresponding author: cvloving@gmail.com

Published online: 7 September 2015

Abstract

Dynamic characterization of strength properties is done, in common practice by the means of a Split-Hopkinson Pressure Bar (also named Kolsky-Bar) apparatus. In such systems, strain rates are limited up to ∼ 5 ⋅ 10³ sec⁻¹. For higher strain rates, the strain rate hardening is assumed to be the same as that measured at lower rates, with no direct measurement to validate the assumptions used for this extrapolation. In this work we are using a pulsed current generator (PCG) to create electro-magnetic (EM) driving forces on expanding cylinders. Most standard techniques for creating EM driving forces on cylinders or rings, as reported in the literature, reach strain rates of 1e3-1e4. Using our PCG, characterized by a fast rise time, we reach strain rates of ∼1e5, thus paving the way to a standard technique to measure strength at very high strain rates. To establish the experimental technique, we conducted a numerical study of the expanding cylinder set up using 2D hydrodynamic simulations to reach the desired high strain rates.