In a railgun, the velocity of the armature has an important effect on the magnetic field distribution and current density distribution of the launch system. However, the calculation models established by scholars were mostly models under static conditions. They could not effectively reflect the velocity skin effect (VSE). This article uses the finite-element softwares COMSOL and LS-DYNA to establish a calculation model that considers the influence of the armature movement velocity on the magnetic field distribution and current density distribution. The calculation results show that when considering the armature movement, the magnetic field distribution of the rail side is very different from the static calculation result. Under the influence of the VSE, the current of the armature/rail (A/R) interface is mainly concentrated on the end of the armature's tail. When considering the armature movement, the values of maximum current density of the rail side doubled. Also, as the armature velocity increases, its range of influence also increases. However, it tends to saturate after reaching a certain velocity. Considering the influence of the armature velocity on the magnetic field distribution and current density distribution can make our results closer to the actual launch situation.

In the process of electromagnetic launch, the initial contact pressure distribution of armature/rail (A/R) contacts interface is uneven, and the actual contact area is obviously different from the perfect contact. The uneven contact pressure leads to uneven contact resistance distribution, affecting the magnetic diffusion process and changing the A/R interface current distribution. Therefore, it is necessary to consider the influence of contact pressure on the current distribution. In the past, the simulation studies usually considered the contact between rails and armature as the perfect contact, and the result obtained may be different from the actual situation. This paper uses the finite element software COMSOL to perform coupling simulation analysis on the electromagnetic module and solid mechanics module in the initial stage of electromagnetic launch. At the initial stage of electromagnetic launch, the contact pressure is mainly provided by the prepressure generated by the interference fit. In this paper, the influence of contact pressure on current distribution and the influence of magnitude of interference on contact position, contact pressure, and current distribution are analyzed.

In railgun, the melting erosion and deposition at the interface between the armature and rail have severe influences on the bore life and the launch performance. In this article, using a payload-separated method, experiments at a small-caliber rail launcher were performed to study the melting erosion and deposition on the convex rails. The erosion pattern of the armature surface, the mass loss of the armature, and the distribution of the deposition were measured. The results show that central erosion occurs, and edge erosion is significantly mitigated on armatures for convex rails, whereas flat rail presents an obvious edge erosion pattern. Moreover, convex rails reduce material losses of armatures and homogenize depositions. It is found that the initial contact pressure on the contact interface of the convex rail is less concentrated on edges, contributing to the mitigation of edge erosion, which not only allows the molten aluminum to be deposited more evenly but also prevents it from ejecting and damaging the bore insulator.

In an electromagnetic rail launcher, a metal liquid film is created at the armature/rail (A/R) contact interface. It has a significant impact on electromagnetic launch performance. In this paper, an electromagnetic-elastic mechanics-hydrodynamics multi physics coupling model is established in consideration of the metal liquid film’s own acceleration, magnetic pressure and dynamic changes in film thickness. Based on this model, the lubricating characteristics of magnetic pressure and fluid pressure distribution, film thickness distribution and velocity distribution of the metal liquid film were studied. When the velocity of the metal liquid film is very fast, and the magnetic pressure is reduced, it may fail to maintain stability and rupture, which may be an important reason for the transition. Finally, this paper analyzes the lubrication effect of the metal liquid film, and points out that when we want strictly to control the muzzle velocity, the lubrication effect of the metal liquid film must be considered.

Keeping good electrical contact between armature and rails is an important issue in the electromagnetic launch process. At the start of railgun launching with driving current ramp-up, the appearance of aluminum coating tends to be concentrated on the outsides of rails, which indicates current concentration on the edge of armature resulting in the armature edge erosion. The current distribution in the railgun determines its efficiency and contact performance of armature/rail sliding. To improve the electromechanical performance, one type of armature with concave arc surface and saddle structure is designed by removing arch forms from the conventional flat armature and adopts saddle structure. Using a finite-element software to establish a 3-D perfect electric contact simulation models on static condition, the current density distribution of armature, inductance gradient of railgun, and erosion area of armature with various central angles φ was numerically simulated. The results show that: 1) in the nonaugmented railgun system, the increase in the central angle φ is beneficial to reduce the maximum current density value of contact interface and the erosion area of armature, but it is not conducive to the improvement on the electromagnetic launch system's inductance gradient and 2) in the augmented railgun system, the change of the central angle φ has little effect on the maximum current density value of contact interface and the electromagnetic emission system's inductance gradient, but the influence on the erosion area is obvious. Based on the above-mentioned work, the improved armature structures are proposed.

Electromagnetic launcher relies primarily on initial mechanical interference to provide contact pressure on the initial launch phase to maintain good electrical contact performance at the rail/armature (A/R) contact interface. Reasonable design of the bore and armature's structure can provide good contact pressure and improve the current density distribution at the A/R interface, reducing the melting deposition of the aluminum armature, avoiding the transition phenomenon, and inhibiting the rail grooving. It also has a significant impact on the inductance gradient of the launch system. In this article, we have considered the influence of the caliber width of the electromagnetic launcher on the contact pressure distribution, current density distribution, and acceleration of the payload. It is found that the increase in the caliber width is more favorable for the contact pressure distribution; however, the effect on the current distribution is less. At the same time, as the caliber width increases, the inductance gradient of the electromagnetic launcher system first increases and then decreases. Based on these studies, the optimal caliber width of a rectangular electromagnetic launcher with a caliber height of 20 mm is proposed.