Computer modeling and prediction of solid armature contact wear and transitioning in electromagnetic guns

Abstract

A 30 mm round bore solid armature development and test program has been completed at the Electric Armaments Research Center at Picatinny Arsenal, New Jersey. The program has furthered the understanding of solid armature contact wear and how it relates to the subsequent loss of the solid armature to rail contact. The Army Railgun Modular Simulator (ARMS) computer code has been improved to provide a 1D model of the parasitic effects of the contact ohmic and the melt layer viscous shear heating on contact wear at the rail to armature Interface. The theoretical premise for the simulator asserts that contact wear is a result of the loss of contact material from a sliding melt layer which forms between the armature and the rail. The melt layer interface Is sustained by the heat inputs to the armature from both ohmic and viscous shear heating. The net contact force at any time is a resultant of both the mechanical force arising from the contact interference and stiffness product and the induced magnetic force. As the contact wear progresses, the resulting loss of interference between the armature and rail reduces the net contact force in proportion to the armature stiffness to the point where the mechanical contact force component ceases to assist the induced magnetic force. Transition of the contact from a low voltage/efficient sliding interface is shown to occur when the mechanical contact force is equal and opposite to the magnetic force, resulting in near zero contact force. This paper describes the 30 mm armature test plan, the computer model theoretical premise, the thermodynamic and electromechanical modelling techniques utilized and compares the simulation results to the 30 mm armature test cases.