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.

Sliding electrical contact between rail and armature in rail launchers is characterized by high speed and large current. Melt erosion is caused by the current concentration on the contact surface of armature. This current melt erosion (CME) has been experimentally studied in the current range of 10-20 kA/mm with a 20-mm caliber lab-scale rail launcher, and payload separated method was used to keep the recovered armatures intact. Thus, the onset behavior and erosion patterns of CME can be successfully observed in such relatively low current densities. In this paper, we will further our study to analyze the patterns of CME with the increasing current densities under the effect of different initial mechanical contact force. Results show that CME all start at the side edge, and then spreading longitudinally and transversely with the increase of current. It is found that the starting position of CME appears near the trailing edge at small mechanical contact force and moves to the leading edge with larger mechanical contact force. At the same current magnitude, erosion amounts are much more under small mechanical contact force. Stationary mechanical contact pressures and current distribution of armature surface are simulated to investigate the effect of initial mechanical contact force on starting position of CME. Current distributes at the edges of actual contact zone and the maximum of current density appears at the side edges of armature. As the initial mechanical contact force increases, actual contact zone and current density move toward to the leading edge from trailing edge. It can be confirmed that the erosion starting position is at the side edge along actual contact zone and will move toward to the leading edge from trailing edge with the increase of initial mechanical contact force. Smaller initial mechanical contact force will cause more erosion at the same current magnitude because of larger current density. Furthermore, an average friction coefficient calculation method is proposed to evaluate the melt lubrication effect of CME. The result shows that the lubrication effect becomes better with larger current densities.

In the process of electromagnetic launch, the nonuniform contact pressure distribution on the armature-rail interface kept changing with the armature moving forward. At first, the contact pressure was mainly provided by the deformation of the trailing arm, from which it could keep a good metal-metal contact at the armature-rail interface. After the pulse current was constructed, the magnetic pressure would dominate the contact pressure because it was much larger than the mechanical interference pressure. In this paper, the 3-D modeling of contact pressure distribution was carried out with the finite-element method. In the simulation of 3-D contact calculations, the current entered the armature from the trailing edge. The electromagnetic force perpendicular to the armature trailing arm was equivalent to the uniform load on the inner surface of the trailing arm. A typical contour pattern of nonuniform contact pressure distribution was acquired. Some nonuniform coefficients of contact pressure distribution were proposed and analyzed to evaluate the contact performances between the armature and rails. A series of simulations was conducted at different magnitudes of magnetic pressure, and with different armature structure parameters. The characteristics of the nonuniform coefficients were investigated and discussed. The dependences of the nonuniform coefficients on the equivalent uniform load and armature structure parameters were obtained.

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.

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.