Railgun Erosion Simulator

Abstract

resulting transient emfs tend to drive the current to the Abstract center of the armature. The U.S. Army Armament Research, Development, and II. MODEL Engineering Center's Benet Laboratories is currently developing a diagnostic launcher for use as an erosion A model of the launcher is being developed as an simulator to investigate issues associated with the bore life of rail guns. The launcher being developed at Benet gm g g predicting performance. It is also being used to estimate provides as b forvliti o f new erosion ioncet the location and energies associated with the dominant candidatere atfalIt for peliminar to of erosion mechanisms that result from the redistribution of cetadidsabute coematerinal thasboreenroptionmizedtohpvid currents in the rails and armature. The model is based on d retais labou th stedominan boeeoin ehnss transient circuit solutions of sequentially pulsed capacitive energy sources coupled with the Lorentz forces associated with the currents in a sliding contact on parallel 1. EROSIONconductive rails. The solution of the differential equations involving the state variables associated with the linear storage elements is solved using one step methods while There are significantly more reports in the literature the behavior of nonlinear circuit elements is modeled regarding damage to solid armatures than erosion on rail using an iterative linear companion solution. Figure 1 surfaces. This is presumably because of the severity of the shows the equivalent circuit of the launcher model for a damage typically observed in armatures. Aluminum series of switched parallel capacitor banks. Several armatures are usually employed, offering the advantage of capacitor banks are discharged in a sequence that melt lubrication which tends to produce a "zero friction" optimizes the current/force profile in an effort to condition. The low melting temperature of aluminum maximize the erosion effects we are trying to reproduce. leads to more thermal damage in the armature than in the The capacitance, resistance, and inductance are assumed rails which are usually made of Glidcop. Persad, et al [1] to be identical for each bank and are given by RI, R2, and studied armature-rail erosion phenomena using solid L1. L2 and R3 are common to all banks. The armature is aluminum armatures; armature-rail contact was accelerated by the current in the loop created by the linear maintained all along the rail in their experiments. They companion model of a diode (Geq, Ieq, and rs) and the observed that, upon firing, most of the rail surface became circuit inductance. In the equivalent circuit, R1 = Res, + coated with a protective layer of quenched aluminum Rbusbarl +Rfuse, R2 = RL, R3 = Rcable + Rbusbar2 + Rbreech + film, so no actual damage to the Glidcop rail surface was Rarmature + 2Rcontact + Rrails, LI = Lbank, and L2 = Lcable + detected. It is commonly observed in rails from firing Lbreech + Lrails The capacitor esr (Resr) and fusing (Rfuse), tests that erosion grooves initially form near the outer busbar resistance (Rb...

On the role of induced fields in railguns

“…A simple axisymmetric 3D model of an armature is also used to illustrate the basic time dependent effects of induced fields on the current distributions in armatures under pulsed current conditions. The model results are consistent with our data on the formation and convergence of concentrated currents at the armature-rail interface in our laboratory firing tests [1]. A number of our firing test results and conclusions are similar to those of Drobyshevski et al [2].…”

“…For large x A /h we can neglect the end effect contributions perpendicular to the rails along h at the breech and muzzle where the perpendicular fields are composed of E and E contributions. Away from the ends the Faraday rule expression, equation (1), is rewritten as: 2E x A = −d /dt = −LdI/dt = −L X x A dI/dt. Given the fact that E is uniformly distributed, we have the more general expression, 2E x = −L X xdI/dt for any x.…”

“…We show that the emf associated with armature motion is produced, instead, by flux creation. It is shown in standard texts [5] that with moving conducting loops in a distributed magnetic field, B, the emf generated in the loop is given by equation (1) where…”