Thermal analysis of fiber armatures

A detailed time-dependent thermal model using temperature-dependent material properties has been developed and implemented in the Westinghouse railgun simulation code to estimate interface temperature for fiber armatures. Fiber and rail materials are selected to protect the rails by confining deformation and melting to the armature. Heat generation at the interface, composed of electrical contact and friction heating, is calculated with a novel friction model using static and hydrodynamic terms. Projectile injection velocity and starting current waveform guidelines are given to protect the breech end of the gun, where the armature is moving slowly. Results are presented for typical railgun conditions as a parametric study which includes precooled armatures. Computer runs were performed for both copper and aluminum fiber armatures on copper, tungsten, and molybdenum rail surfaces. The results indicate that full film lubrication of fibers is unlikely for the typical railgun systems currently in use. However, melting of the fiber ends of actual armatures is common and is probably due to bouncing arc contact of the fibers with the rails