Down-Slope Contact Transition in Railguns

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