Structural Mechanics of Railguns in the Case of Discrete Supports

In this paper, numerical calculations concerning the dynamic behavior of a railgun are presented. At the first stage, the structural problem can be decoupled from electromagnetic phenomena as well as from the local projectile behavior. The magnetic pressure repelling the rails from each other and expanding with the speed of the projectile serves as a boundary condition for purely mechanical calculations. The particularity of the investigation is represented by the type of railgun housing. For some years, the ISL has been using laboratory housings of an open design allowing, for instance, to take flash radiographs during launch. The repelling forces are mainly taken by discrete supports in the form of steel bolts. These bolts are connected to bars made of glass fiber-reinforced plastics, while the rails are mounted on these bars. A 2-D finite-element model of a complex housing was developed in this paper. Bars, including rails, are described by plane-stress elements, while bolts, playing the role of discrete elastic supports, are presented by truss elements. The model is implemented using the ANSYS code. Deformation properties of the rail section and elastic supports are examined by considering a static solution, assuming constant loading. Differences between 2-D and conventional beam models being of importance for this kind of problem are briefly discussed. Transient analysis was performed for a set of constant loading velocities (600-1600 m/s) and for the experimentally derived transient-loading profile. The latter was obtained in the railgun experiments performed using the ISL-railgun EMA3 with a caliber of 15times30 mm² and typical muzzle velocities up to 1600 m/s as well as peak currents of about 600 kA.