Investigation of high strain rate behavior of metallic specimens using electromagnetic inductive loading

Aerospace Engineering

The aim of this thesis is to explore the high strain rate behavior of metallic specimens using electromagnetic inductive loading as the means to inflict the required high strain rate deformation on laboratory scale specimens, allowing for controlled, repeatable experiments to be performed. Three separate experiments were designed and performed, using helical and spiral coils as the sources of radial and unidirectional loading.

The first experiment evaluated the effect of applying a polymer coating on 30.5 mm diameter, Al 6061- O tube samples, in two lengths, 18 and 36 mm. The expanding tube experiment was used to apply a radial loading on the specimens and record the event. Several optical techniques were then used to evaluate the behavior of the samples. Coatings of polyurea and polycarbonate were used. It was observed that the polycarbonate coating seemed to have a more profound effect on the behavior of the metal, by applying a larger restraining pressure on the tube surface during the expansion process, and thereby modifying the stress state of the specimen.

The second experiment looked to design an experimental arrangement to test the plane strain, high strain rate behavior of Al 6061-O tubes of different lengths. A 112 mm long solenoid was designed and manufactured, and testing was performed on 30.5 mm diameter Al 6061-O tubes in lengths of 50, 70 and 90 mm. It was observed that the coil behaved similar to shorter ones at low voltages and that the longer the specimen used, the more its deformation path approached a plane strain condition.

Finally, a third experiment was performed to develop an experiment to accelerate a plate to high linear velocities, as a means to evaluate the use of a flat spiral coil as the driver for future experiments based upon electromagnetic inductive loading. A prototype coil was manufactured and installed into a converted expanding tube experimental setup. Three samples were tested in several sizes, and materials: aluminum and steel. Speeds in the range of 45 to 251 m/s were obtained, validating the apparatus as a viable method to provide a unidirectional loading.