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

We present here a new methodology to measure the strength of materials at very high strain rates, up to 7.5⋅104 s−1, using magnetically driven expanding cylinder experiments. We use a pulse current generator (PCG) to apply magnetic forces on hollow cylindrical specimens and measure the expanding motion using velocity interferometery. To investigate the dynamic behavior of the specimens and their strength, we use numerical simulations. 2D hydrodynamic simulations were conducted for the design of the specimens, and 1D MHD simulations for simulating the actual tests. In this work, we present results for nine EM driven OFHC cylinders, reaching strain rates up to 7.5⋅104 s−1. We report a significant strain rate hardening for the OFHC copper and provide a calibrated Modified Johnson Cook (MJC) constitutive model for our data in the regime ranging from 103 s−1 (Kolsky bar tests) up to 105 s−1, from the PCG tests. It is believed that the methodology that is presented here will open the way for very high strain-rate characterization of metallic materials.