Down-Slope Contact Transition in Railguns

Abstract

Most railgun experiments exhibit transition to high-voltage contact after the applied current starts to decrease from its peak value. A statistical examination of existing data revealed that such contact transitions occur at approximately 80% of peak current during down-slope. While several plausible explanations exist for the cause of such transition, we demonstrate through numerical simulation that a likely cause of this transition mechanism is a diffusion-controlled process that reduces the contact pressure below the threshold value necessary to carry the applied current. The current down-slope was found to result in a nonuniform body-force-density distribution in the armature such that the contact pressure at the armature-rail interface decreases (eventually becoming zero) even though the total electromagnetic force resulting from the applied current is still compressive. This event's diffusive nature suggests that transition can be delayed by controlling the diffusion time, either by judicious material grading or increasing the diffusion depth