Electrothermal behavior of railgun solid armatures

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Watt, Trevor James

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Understanding the behavior of solid armatures has been at the forefront of railgun research in the U.S. for over a decade. Computational models have matured in parallel with experimental techniques, but experiments resulting in good data on armature behavior have not existed until recently. As a result, there has been little correlation between what models predict and how solid armatures actually behave. A recent technique for recovering armatures was used to provide a collection of armatures launched with currents from 848 kA to 1256 kA, at speeds around 300 m/s. The recovered armatures showed a progressive amount of melting and cracking in the throat region. Optical microscopy revealed microstructural changes of the armatures due to heating, as well as characteristics of the observed cracks. State of the art computational models were used to estimate the electromagnetic, thermal, and structural response of the armatures. Historical modeling assumptions were tested to see whether they held true when compared with experimental evidence. Thermal diffusion, temperature-dependent material properties, and heating rate effects must all be used for an accurate comparison. Finite element models accurately predicted the thermal behavior of armatures, with the largest stresses coming from thermal expansion. Crack formation is likely due to cooling of the armature surface


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