BORE LIFETIME EXPERIMENT

Although the need for a railgun bore lifetime metric has been establis hed for some time, to date there have been no serious attempts to quan tify the anticipated lifetime of a railgun bore surface. The Air Force (AF) is meeting this challenge with an in-house bore lifetime experim ent that compares four different bore insulator materials and lay-ups in a controlled test environment. Initial testing has established a G- 9 material as a baseline for comparison. Each of the four insulator te st series consists of a low current checkout shot followed by a ten sh ot series of plasma armature firings with peak pressures of about 30 k si and currents on the order of 750 kA. The test sequence produces ero sion that is easily measured both as bore growth during the test serie s and as post-test component mass loss. Typically, the rails lost almo st twice as much mass as the insulators, but volumetrically, about thr ee times more volume of insulator material was removed compared to ero ded volume of copper from the rails. The loss of copper from the rails is highly non-uniform, as might be expected in a round bore railgun. Mass loss and bore growth data from all four insulator test series are compiled as a gauge of bore lifetime. The railgun performance on a ty pical shot is given along with a tabulation of the coarse shot paramet ers for each test in all four series,