An interrupted pulse electromagnetic (EM) expanding ring test is being developed at the University of Waterloo to study the high rate behaviour of sheet metals. In a classic EM expanding ring test, a ring is expanded radially using the forces induced on the ring by a high frequency high intensity current flowing in a nearby coil. If the driving force and the acceleration of the ring are known, then the stress-strain history of the ring can be determined. Coil currents are typically generated by

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... large capacitor banks that produce a current discharge in the shape of a damped sinusoid. To properly determine the stress of the ring, the forces induced on the ring by the current pulse must be known, which is difficult to do in practice. The approach taken in this work is to interrupt the current by means of an exploding wire switch to eliminate the Lorentz forces and achieve a free flight condition, where the stress can be determined using only the measured velocity and density of the ring. The velocity of the rings was measured using a photon Doppler velocimeter (PDV). With this technique significant periods of free-flight were obtained, with the corresponding stressstrain data. Results for 1.5 mm sheet of AA 5182-O are presented.