EFFECTS OF ELECTROMAGNETIC BLOW OFF OF MATERIALS SUBJECT TO HIGH CURRENTS

LT Paul Cross, USN

The phenomenon of electromagnetic (EM) blow off, a repulsive force at the contact interface of two conducting materials due to the passage high electrical current, is studied. Material strength, electrical conductivity, hardness and surface roughness are important parameters to consider in the EM blow off. Avoiding this phenomenon is of particular importance to the EM railgun, where electrical joints, such as the pulsed power module output, breech bus plate connection, an armature/rail interface are especially susceptible to catastrophic damage from mega-amp electrical arcing resulting from EM blow off. A series of experiments were performed using a High Current Test Fixture (HiCTF), which is based upon a pioneering design by Naval Surface Warfare Center Dahlgren Division with improvements made by Naval Postgraduate School. Simulations were performed by 2-D Finite Element Magnetic Modeling and 3-D COMSOL Multi-Physics modelling to determine HiCTF design limits and magnetic fields strengths. The EM blow off theory requires empirical constants that can only be determined through experiments. In particular this thesis investigated current thresholds for EM blow off on C182 annealed copper and C182 copper coated with carbon nano tubes, the later as a potential candidate to reduce EM blow off events in an EM railgun.