Development of an Interrupted Pulse Expanding Ring Test
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Date
2016-04-27
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Abstract
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 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.
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Keywords
high rate testing, interrupted pulse, expanding ring test