Investigation of Rail Deformation and Stress Wave Propagation in the ISL-NGL60 Railgun

Abstract

Railgun performance requires a low-resistance electric gliding contact between the rails and the armature. The electromagnetic forces, which accelerate the launch package (0.7 to 3 kg mass) up to more than 2000 m/s, are acting on the rails as repulsive forces. Therefore, the rails of the NGL60 electromagnetic gun, with caliber 60 $\times$ 60 mm2, are held in their position by an arrangement of discrete steel bolts, further by beams and plates made of glass fiber reinforced plastic, as well as by stiffening metal plates. The highly dynamic electromagnetic forces generate stress waves and elastic rail deformation that might contribute to contact transition between the rails and the armature. If the rail deformation enters the plastic domain, the rail geometry may be altered in an unfavorable way for subsequent shots. For our numerical investigation, we used the multiphysics finite-element computation code LS-DYNA to simulate a railgun projectile launch with a moving armature by injecting an electric current into the rails. It is therefore possible to study the dynamic deformations during the launch and get insight in the dynamic stress states. The material models for the rails and for the armature take into account elastic-plastic stress-strain behavior as well as strain rate sensitivity. We expect to simulate launch dynamics with higher accuracy than previously presented models with a nonmoving armature. The principal objective of the study is to show that this procedure is capable of effectively optimizing the structural behavior of the rails inside the barrel.