Effect of the shape of metal solids on the rate of their joule heating in electromagnetic rail launchers

Abstract

IN ELECTROMAGNETIC RAIL LAUNCHERSUDC 537.311.5 S. V. Stankevich and G. A. ShvetsovThis paper presents a method and results of numerical simulations of current-density, magnetic-field, and temperature distributions in rail launchers of conducting solids for armatures of various shapes. A comparison is made of the results of calculations using two-dimensional and three-dimensional models. It is shown that for cylindrical and saddle-shaped armatures, Joule heating calculations performed by two-dimensional simulation of electromagnetic and thermal phenomena are in good agreement with calculations for the three-dimensional model. Introduction.To reach high velocities in electromagnetic rail launchers (ERL) with a metal armature and to increase the service life of the launcher, it is necessary, as a rule, to maintain metal contact between the rails and armature throughout the acceleration process. Transition to arc contact is extremely undesirable since it reduces the acceleration, and leads to degradation of the launcher barrel and fracture of the projectiles.The main mechanisms involved in the transition to arc contact are the loss of contact force, velocity skin effect (VSE), mechanical wear of the armature, armature fracture under the action of magnetic forces and magnetic cutting of the central part of the armature, electrodynamic unloading of the contact, etc.[1]. However, an analysis of papers (see, for example, [2]) shows that, in many cases, crisis processes leading to disruption of metal contact develop when the armature is heated to temperatures at which melting and (or) vaporization of the material begins.To limit the heating of the launcher and projectile throughout the acceleration process, it is necessary to impose restrictions on the maximum magnetic field strength in the channel and, hence, on the maximum linear current density in the electromagnetic launcher. Obviously, if these conditions are satisfied, the velocity to which a solid of given mass can be accelerated on a given distance is also limited, and for homogeneous materials, its is, as a rule, of the order of 1 km/sec. Previous calculations [2,3] have shown that the ultimate (for heating conditions) characteristics of launchers depend largely on the electrothermal properties of the structural materials used, the kinematic parameters of the launcher, projectile mass, the acceleration dynamics determined by the shape of the current pulse, and the acceleration distance; these characteristics can be increased severalfold by using structural and composite conductors in the current-carrying units of launchers and by optimizing the current pulse shape. However, the results presented in [2,3] and in a number of other papers have been obtained by numerical simulations of launchers in a twodimensional formulation. The question of how much the maximum current density on the armature-rail interface, the armature heating rate, and the ultimate (for heating conditions) kinematic characteristics in real launchers differ from those obtained in two-dimensional...