Electromagnetically Driven Expanding Ring Experiments for Strength Studies

Most high-temperature mechanical properties of metals are available for isothermal conditions obtained after heating the specimen for several hours. However, in pulsed-power applications, materials are adiabatically heated by rapid deposition of energy. Experimental evidence from electron beam heating indicates that high- temperature mechanical properties significantly depend on the rapidity and duration of heat deposition. We have designed an experimental apparatus to apply heat using a short-duration electric pulse in an expanding ring experiment originally developed by Gourdin et al. [1], [2]. While earlier experiments were primarily concerned with obtaining high-strain-rate strength and fragmentation data, our primary goal is to obtain high-temperature data under pulsed heating conditions. The experiment uses a primary coil powered by an RC circuit designed to be critically damped to induce a current pulse in a thin ring of specimen that expands and fragments due to electromagnetic forces. The induced current heats the sample prior to significant expansion of the ring. Current in the primary and secondary are measured using Pearson and Rogowski coils. We used a VISAR to measure the ring's expansion speed and a high-speed camera to capture its dynamic fragmentation. Data generated will quantify the rate of heating sensitivity of material properties in commonly used materials for development and validation of appropriate constitutive equations.