The expanding tube experiment consists of discharging a large alternating current through a copper coil encased in epoxy resin. A cylindrical aluminum tube sample is placed over the coil. The aluminum sample has a circular pattern etched on its surface. The tube can be coated with a polymer.
The coil is connected to a capacitor bank. During the test, the capacitor bank is discharged through the coil, inducing a current in the aluminum specimen. The Lorentz force interaction causes the specimen to expand radially outward at very high speeds.
A high-speed camera and a flash system are used to record the expansion of the specimen. A conical mirror is placed behind the specimen such that the surface of the specimen is reflected in the mirror and captured in the high-speed camera footage.
This image shows an example of the specimen as it expands. The expansion follows a uni-axial tension stress state.
The reflection of the sample in the conical mirror is unwrapped through mapping of pixels in image post processing.
The unwrapped images allow for local strain measurements of the surface of the specimen to be performed, as well as track localization and fragmentation of the sample.
Local and global (from sample diameter evolution) strain measurements can then me compared to better understand the dynamic behavior of the material.
Variations to the experiment described were performed. The first deviation aimed at creating a plane-strain loading condition on longer tube specimens.
This sequence shows the expansion of the longer tube.
Post-mortem image of the plane-strain condition test specimen.
The second variation of the experiment looked at using a flat coil to accelerate a flat plate.
This image shows the of the flat plate specimen being accelerated by the flat coil.
Post-mortem image of flat plate specimen.
gLike
High-strain rate deformation research
This research was performed during my time as Graduate Research Assistant at The University of Texas at Austin, under Dr. Krishnaswamy Ravi-Chandar.
The goal of this research was to utilize electromagnetic loading to study the high-strain rate behavior of aluminum samples.
The expanding tube experiment was used to study the effects of polymer coatings on cylindrical specimens. Modifications to this experiment were carried out to allow for testing of tubes under plane-strain conditions and unrestrained flat plates under rapid acceleration.
