Experimental and computational investigation of root-radius melting in C-shaped solid armatures

Heating at the root or throat position in C-shaped armatures is a concern because it can lead to cracking, melting, and premature failure. This paper presents results from experiments in which railgun armatures made of 7075 aluminum alloy were recovered after being launched at various levels of electrical action. Inspection of the recovered armatures showed reproducible patterns of damage at the root position that correlated with the severity of the launch conditions. Damage ranged from deformation and cracking at low levels of electrical action to melting to ejection of material and magnetic sawing at higher levels of action. There appears to be a threshold beyond which damage begins to propagate rapidly into the armature. The temperature rise in the armature was modeled with the three-dimensional (3-D) finite-element analysis (FEA) program EMAP3D. Our results show that it is possible to predict the onset of severe damage without modeling the complex phase-change behavior of the materials.