Shengguo Xia

Simulations on Arc Surfaced C-Shaped Armatures for Round-Like Bore Railguns

Previous solid armature design studies have emphasized the effect of geometry change on armature performance. In order to acquire more uniform contact pressure and current density distributions at the armature–rail interface, the novel modified C-shaped armatures for round-like bore railguns are proposed and analyzed. By removing and adding two pieces of circular arch from the conventional C-shaped armature trailing arms, we construct two types of arc surfaced C-shaped armature (ASCA) for corresponding round-like bore railguns. They are called concave ASCA and convex ASCA. In this paper, both concave ASCA and convex ASCA are simulated with finite element method. The detailed description and construction of the model are presented. 3-D calculations of contact area, contact pressure, and current density distributions are performed and compared. Specially, current density simulations are modeled according to the results of elastic contact calculations. In addition, split-leg ASCAs are also simulated and discussed. The simulation results show that the performances of one split-leg concave ASCA are the best. Further electromagnetic launch experiments of concave ASCAs are in good agreement with the simulation results.

Studies on Interference Fit Between Armature and Rails in Railguns

There is an interference fit between the trailing arms of the monolithic C-shaped armature and the rails to provide good solid-on-solid contact during the early portion of a railgun launch. In this paper, the contact interference between the rail and armature in a railgun is calculated using a finite-element structural analysis code. The contact properties, including the contact pressure and contact area, are analyzed. It is found that a contact separation caused by the interference is inevitable in armatures with line-shaped contact interference. The reduction of the contact interference in an armature design cannot eliminate this kind of contact separation. A proper design of the armature structure can decrease the length of the separation effectively. A new design of the contact interference is proposed. Both the experiments and calculations show that the new design of the contact interference can effectively improve the performance of the armature.

Experimental Study of Armature Melt Wear in Solid Armature Railgun

Transition is an important issue in rail electromagnetic launches which limits the performance of electromagnetic launch systems. In the launch progress, wear on contact surface of armature significantly affects the morphology of contact surface and armature structure. Studying wear, contact resistance and sliding friction coefficient of the contact surface is important to understand principles of transition and suppress transitions in electromagnetic launches. In this paper, special designed armature, which makes the wear on armature contact surface all melt wear, is used in rail launch experiments to measure the wear rate of melt wear and the effects of loading on wear. Launch experiment results show that the wear rate is represented by the average thickness of the aluminum debris left on the rail. The average wear rate is about 0.6 to 2 mm/m and the average debris thickness is in a range of 3-10 um in the experiments. Based on the idea of melt wear is the main part, the heat balance of armature contact surface in launch process was analyzed. It is concluded that melt-wear absorbs mounts of heat generated on the surface, and the left heat goes into rails through the contact. The heat balance based equations was then derived, which established relationship among melt wear, launch parameters and material parameters. By the equations obtained, and using the data of launch experiments, the contact resistance of armatures with 80 mm2 contact area is 2.5564μΩ, the contact resistance of armatures with 50 mm2 contact area is 4.0902 μΩ and the sliding friction coefficient is 0.1131.

Recent Pseudo-Liquid Armature Experiments with Details of the Test Systems

The pseudo-liquid (PSL) armature with air-spring is a novel railgun armature, which has lower mass and more compliance than conventional C-shaped armature. The united research group leaded by Beijing Institute of Special Electromechanical Technology (BISET) has completed a lot of experiments of the PSL armatures with air-spring since 2004. The results of these experiments show this armature can prevent transition with some conditions. This paper presents an overview of PSL armature program including the pulsed power supply, two rail launchers (SRL1 and SRL3), projectiles and some experimental results. As the best result of SRL1 rail launcher tests, it is obtained that muzzle velocity of 1.1 km/s with a 52 g mass. The best performance of SRL3 launcher tests is muzzle velocity of 1.92 km/s with a 45 g mass operating at a stored energy of 1.39 MJ and a flat-top current of 400 kA with about 1.5 ms pulse duration. The further experimental studies are being continued.

Analysis of the Performance of C-Shaped Armature with Resistivity Gradient

The feasibility and the performance of the armature with resistivity gradient were studied. The current distribution and its improvement by resistance distribution adjustment in C-shaped armature were analyzed by finite-element method. The calculation was performed with a monolithic armature, in which we defined several layers arranged of two different types. With some adjustment of resistivity of the layers, the current density distribution was found more appropriate for EML. The armature of type-I seems more considerable than that of type-II, as it is more sensitive to resistance changes, and the maximum current density appears in head part of the armature instead of corner, which reduces the possibility of armature corner rupture in electromagnetic launch.

Study on the Tail Structure of a C-Type Armature in the Nonequal-Cross-Section Cantilever Model

It is necessary to maintain adequate contact pressure between the rail and armature for avoiding transition in solid armature railgun. At the current buildup stage, this contact pressure is often provided by deformation of solid armatures. In this paper, a nonequal-cross-section cantilever model of a monolithic C-type armatures tail is proposed firstly. Then an equation of the deflection curve associated with tail structural parameters is established. Based on the requirements of the mechanical interference pressure, the relation between structure of armature tail and deflection curve is established. Furthermore, the relation between interference pressure and structure of armature tail is discussed. The results show that reasonable design of armature tail structure can meet the requirement of mechanical interference pressure at the current ramp-up stage. Based on the nonequal-cross-section cantilever model, several kinds of armatures are designed. In certain circumstances, serious arcing is eliminated by using the designed armature in launch experiments with muzzle speed up to 2500 m/s.

Study on the Curve Shape of C-Shaped Armature's Trailing Arms in Rectangular Bore Railgun

During the electromagnetic launch process, there is a contact surface between the trailing arm of C-shaped armature and the rail. This contact is generally provided by the deformation of the trailing arm, from which it can keep a good metal-metal contact at the armature-rail interface, while providing sufficient contact force to ensure the launch without transition. Nowadays, C-shaped armatures with curved-surface trailing arms are used in rectangular bore railguns. In this paper, the effect of geometry change on the curve shape is investigated. Various kinds of reasonable curve shapes are explored and simulated by using finite element method. Contact pressure distributions and a series of contact characteristics variables of C-shaped armature with different curve shapes are calculated and compared respectively. Eventually, the variation laws of contact characteristics at the armature-rail interface with different kinds of curve shapes are acquired. 2-D and 3-D simulations are both carried out, and the simulation results are quite consistent with each other.

Simulations on arc surfaced C-shaped armatures for round-like bore railguns

Previous solid armature design studies have emphasized the effect of geometry change on armature performance. In order to acquire more uniform contact pressure and current density distributions at the armature-rail interface, the novel modified C-shaped armatures for round-like bore railguns are proposed and analyzed. By removing and adding two pieces of circular arch from the conventional C-shaped armatures trailing arms, we construct two types of arc surfaced C-shaped armature (ASCA) for corresponding round-like bore railguns. They are called concave ASCA and convex ASCA. In this paper, both concave ASCA and convex ASCA are simulated with finite element method. The detailed description and construction of the model are presented. Three dimensional calculations of contact area, contact pressure and current density distribution are performed and compared. Specially, current density simulations are modeled according to the results of elastic contact calculations. In addition, split-leg ASCAs are also simulated and discussed. The simulation results show that the performances of one split-leg concave ASCA are the best. Further electromagnetic launch experiments of concave ASCAs are in good agreement with the simulation results.

Study of Some Influencing Factors of Armature Current Distribution at Current Ramp-Up Stage in Railgun

Current ramp-up is an important stage for a railgun electromagnetic launch system. In lots of launching experiments, a big chunk of deposit aluminum can be found on the rail surface at the start-up position of the armature-rail contact area, sometimes, erosion is even emerged. The transition at current ramp-up is mainly related to local degradation of armature. The larger value of maximum current densities at the rail/armature (A/R) interface would lead to armature local temperature increasing rapidly, which deteriorates the material property of armature, degrades the static electrical contact performance, and reduces the railgun lifetime significantly. In this paper, for restraining start-up transition, several influencing factors of armature degradation and melt are studied based on current concentration. Rail resistivity, rail dimensions, armature resistivity, and the shape of current supply are considered and simulated. At current startup, skin effect and induced current are analyzed, which are considered as the direct factors of armatures current distribution. Armature current distribution and the maximum current density are obtained and compared for each factor. Finally, launching experiments are carried out as the same condition with simulation. On the rail surface at the start-up position of the A/R interface, the depositions reflect the current distribution on armature with different factors influence at the current ramp-up. The results of experiments are in reasonable agreement with simulation description.

Development of a Capacitive Pulsed Power Supply for High-Current High-Velocity Sliding Electrical Contact Studies

A pulsed power supply of a 1.5-MJ capacitor bank has been developed for high-current high-velocity sliding electrical contact studies in railgun launches. The system consists of 8 small modules, each with a capacitance of 15 mF, and one large module with a capacitance of 54 mF. All of nine modules use triggered spark gaps as the main switches. Various shapes of high-current pulse can be formed by controlling the charging voltage and firing time of each module. The small module has been designed for the maximum operating voltage of 5 kV, the peak current of 140 kA, the pulse rise time of 0.9 ms, in which semiconducting diode stack is used as crowbar switch. Since the large module has no crowbar switch and relatively small pulse forming inductance, it can supply high-amplitude oscillating current waveform. The effects of the large module are threefold. First, the large module provides a basic current on which the currents of small modules superimpose to form a nearly constant driving current of armature. Second, the oscillating nature of the current can drastically reduce the muzzle arc current; hence suppression of the muzzle arc can be obtained. Third, the crowbar switch can be removed and therefore the cost of the system can be reduced. The experiments were performed to verify the operation performances of the two kinds of modules, where the modules were discharged simultaneously and/or sequentially. The feasibility of large module on the muzzle arc control is also examined. The results of the experiments show that a total current of 400 kA with a 1.5 ms flat-top time can be obtained and all the modules show good performance during the railgun firing.