Interrupted pulse electromagnetic expanding ring test for sheet metal

Abstract

This paper describes the development of an interrupted pulse electromagnetic (EM) expanding ring experiment to study the high rate properties of AA5182 aluminum commercial sheet alloys at strain rates in excess of 5,000 s−1. Experiments are performed to compare two commonly adopted methods of driving the expanding ring: EM expansion versus an exploding wire. After studying and testing both methods, it was determined that EM expansion had the greatest potential for being developed into a test that would result in free-flight of the samples. By interrupting the current pulse in the EM expanding ring test, the ring is allowed to achieve free-flight, thus eliminating the need to determine the induced EM forces and significantly reducing the uncertainty of the stress-strain behaviour determined from the test. Once the free-flight condition is established, the stress-strain behaviour of the material is determined from the free-flight deceleration of the sample, as calculated from the velocity measured using a Photon Doppler Velocimeter (PDV). Results are presented for AA5182 at strains rates between 1,000 to 5,500 s−1 and exhibit low strain rate sensitivity, are comparable to tensile split-Hopkinson bar results at strain rates of 1,000 s−1.