Simple Thermal Model to Select Electromagnetic Launcher Tribomaterials

Lab-scale electromagnetic launcher (EML) tests for the baseline case of an aluminum armature spanning a pair of copper rails reproduced excessive aluminum melt wear depth leading to loss of conductive contact and resultant electrical transition before completion of launch. A simple thermal model partitioning interfacial Joule heat input between conduction into the rails and melting of the armature provided compact expressions describing armature wear behavior. A quantity from this expression, termed the armature melt resistance (AMR), predicts a decrease of armature wear and the likelihood for resultant electrical transition with increasing rail thermal conductivity and heat capacity, as well as armature heat capacity, latent heat, and melt point. With this AMR metric to guide materials' selection, in subsequent tests, a slight increase in wear indeed occurred upon substitution of stainless steel rails, with more dramatic order of magnitude decreases in wear and avoidance of electrical transition instead realized upon substitution of solid molybdenum armatures.