Railgun Research Articles

Ammunition Reliability Against the Harsh Environments During the Launch of an Electromagnetic Gun: A Review

Electromagnetic railguns have an advantage over traditional chemical propulsion weapons, in that the projectile can be accelerated to extremely high speeds and effective damage can be achieved. However, during the launch from an electromagnetic railgun, the ammunition will be subject to a harsh environment, including very strong and violently changing electromagnetic fields, high-g acceleration impact, high temperatures, and so on; and thus, the reliability of the fuze is threatened, and the safety and damage effectiveness of the ammunition will be seriously degraded. In this paper, the harsh environment during the launch process is first reviewed, including the experimental data, the modeling, and simulation of the multiphysics fields. In particular, the coupling effect of these multiphysics fields are revealed, which aggravates the extreme environment. Furthermore, this paper reviews the protection of fuzes against strong magnetic fields and high-g impacts from three aspects, namely, materials, devices, and systems, and presents prospects for future research. This review will guide studies on the protection of fuzes and the stability of ammunition, as well as promote the effectiveness of electromagnetic railguns.

Analysis of Magnetic Field Waveforms of Different Launching Stages of Rail Gun Based on Wavelet Transform

Electromagnetic disturbance in the course of rail-gun launching has great influence on the launching process and staff. Based on the magnetic force measured at the startup acceleration and separation stages, the corresponding magnetic field can be calculated. The magnetic field at different positions and heights near the rail gun is analyzed and compared. The results show that the position of the armature has great influence on the magnetic field. The maximum value of the instantaneous magnetic field should be located in the middle of the rail gun. At the same position, the magnetic field decays rapidly with the increase of height. The electromotive force waveforms are analyzed by using the wavelet transform; the analysis shows that the wavelet transform can reveal the time-frequency energy distribution of the electromotive force more accurately and clearly. The research of this paper has a guiding significance to the shielding design of magnetic field of the electromagnetic rail gun, and will promote the development of rail guns.

Theoretical Model and Analysis on the Locally Concentrated Current and Heat During Electromagnetic Propulsion

Electromagnetic propulsion technology has important applications in military equipment such as electromagnetic rail guns. The extremely harsh multiphysics environment during electromagnetic propulsion is the key problem that now restricts its practical application. Most previous modeling studies have neglected or set overidealized approximations for the coupling effects between different physics fields, resulting in large deviations between simulated and actual results. In this paper, the multi-field coupling dynamic model of the electromagnetic propulsion process is established. Based on this model, the dynamic changes of the armature’s speed, current distribution and temperature distribution during the electromagnetic propulsion process are effectively simulated, and some characteristics of these distributions are different from the previous uncoupled model. Furthermore, the physical mechanism behind these special distribution features is revealed, and the significance of the nonideal factors such as the piezoresistive effect of contact resistance and friction effect of the contact interface on the electromagnetic propulsion are analyzed. Therefore, a feasible path for the simplification of the multiphysics model and the relief of the extreme environment is revealed, which will greatly promote the practical application of electromagnetic propulsion technology.

Modeling for the Calculation of Interior Ballistic Velocity of Electromagnetic Rail Launch Projectile

Interior ballistics is of great importance to the study of gun barrels and projectiles. One of its important characteristics is velocity, which determines the firing capability of projectiles. Aiming at the interior ballistic velocity (IBV) of projectiles launched from electromagnetic (EM) rail, this paper has analyzed the differences in the mechanism between the EM rail gun and the traditional cannon. Based on some assumptions, the calculation formula of projectile EM force was gained with the time-frequency analysis method. Then, it built a simulation calculation model of IBV of the projectile. In addition, the use of the positioned data of the magnetic probe (B-dot probe), to obtain the displacement fitting matrix, leads to the establishment of an experimental fitting model of IBV of the projectile. With the plane EM rail launcher in our laboratory as an example, the above-mentioned two models are applied to analyzing the accelerated motion of the projectile in the chamber. The experimental fitting results are compared with the measured data and simulation results of the B-dot probe, which are basically consistent. Thus, it shows that the IBV's simulation model and the experimental fitting model have high reliability.

Modeling of an Air-Core Compulsator and the Pulse Shaping Using Optimization Algorithm

Compensated pulsed alternator (compulsator) plays a significant role in the field of pulsed power supply. Different kinds of compulsators have been used to drive high-energy weapons. In this paper, the mathematical model of a two-phase four-pole air-core compulsator is established, taking the current coupling, the change of rotor speed and changing load characteristics into account. Both the self-excitation process and the discharge process are modeled. Simulation results indicate that our model has high accuracy in comparison with the results of the co-simulation method using finite-element method and circuit principle. Moreover, the usage of the mathematical model can improve the simulation efficiency and flexibility. The current pulse requirements of electromagnetic rail gun (EMRG), flash lamp, and electro-thermal-chemical gun (ETCG) are analyzed, respectively, and the pulse shape optimization problem is studied based on the intelligent optimization algorithm. For EMRG and flash lamp, the term “acceleration ratio” is introduced to identify whether a pulse is flat or spiked. For ETCG, the conception of “shape variance” is proposed to evaluate the fitness of its pulse shape. With the help of suitable objection function and intelligent optimization algorithm, the optimal discharge pulse for specific load can be obtained easily.

Peculiarities of Milligram Mass Acceleration in Electromagnetic Railguns with an External Pulsed Magnetic Field

Solid polycarbonate impactors were accelerated in a channel of electromagnetic railgun to which an external pulsed magnetic field was applied. The channel was filled with air at atmospheric pressure. The dynamics of impactor acceleration in the railgun was calculated. The impactor velocities in the railgun muzzle were measured in two cases. In the first case the railgun and external field system were powered from independent energy sources (scheme 1) and in the second case the railgun and external field circuits were connected in series to a common energy source (scheme 2). It was established that the effective coefficient of rail erosion in a 2-mm caliber channel that takes into account only the eroded mass captured by the plasma piston was 1.5–1.7 mg/C, and the eroded mass involved in the motion was comparable with the impactor mass. It was shown that in scheme 1, when the external field system was switched earlier, the impactor was accelerated at a maximum magnetic induction, and the impactor velocity in the channel muzzle exceeded 6 km/s.

Simulations, Experiments, and Launch Characteristics of a Multiturn Series–Parallel Rail Launcher

In order to markedly improve the inductance gradient of electromagnetic (EM) railgun and current-carrying capacity of the armature, and enhance the ability to launch large mass projectiles, a system simulation analysis and preliminary experiments were carried out for the multiturn series-parallel rail launcher (MSPRL). First, the Simulink simulation model of the rail launcher system based on the circuit model was established, and the changing rules of current waveforms and armature velocities under different contact resistances were obtained. Then, an EM-structural multiphysics fields coupling model is constructed, with the supplied currents obtained earlier, the EM propelling force on the armature as well as contact force between the armature and rails were analyzed. In view of those analyses, the inductance gradient and armature velocity in bore were calculated. Finally, the test platform of the MSPRL was built to carry out preliminary verification experiments of relevant parameters. During the test, the muzzle impedance and muzzle velocity were measured, and the validities of the simulation models were verified.

Performance Analysis of Electromagnetic Railgun Launch System Based on Multiple Experimental Data

As an emerging kinetic damage weapon system, railgun has attracted much attention due to its remarkable advantages such as high initial speed, high kinetic energy, high shooting speed, high emission density, low cost, and antijamming. However, there are currently degradations of electromagnetic railgun launch performance and reliability, the limited service life as well, resulting from rail damage such as the transition erosion and grooving damage. Based on 24 consecutive shots, this paper presents the statistical analysis of B-dot probe data, aiming to show the working stability and reliability of the electromagnetic rail launch system when consecutive firing. On the basis of current data and B-dot probe data, the speed-displacement curve was obtained by simulation, through which it is easy to get the movement state of the armature in the launch track. Finally, by checking the disassembly of the launch rail, this paper analyses the damage states of launching rail after the 24 consecutive launch experiments. Through the above three aspects of research and analysis, this paper could be the reference for the further research and analysis on the performance and lifetime of railgun.

Особенности ускорения тел миллиграммовой массы в рельсовых электромагнитных ускорителях с внешним импульсным магнитным полем

AbstractSolid polycarbonate impactors were accelerated in a channel of electromagnetic railgun to which an external pulsed magnetic field was applied. The channel was filled with air at atmospheric pressure. The dynamics of impactor acceleration in the railgun was calculated. The impactor velocities in the railgun muzzle were measured in two cases. In the first case the railgun and external field system were powered from independent energy sources (scheme 1) and in the second case the railgun and external field circuits were connected in series to a common energy source (scheme 2). It was established that the effective coefficient of rail erosion in a 2-mm caliber channel that takes into account only the eroded mass captured by the plasma piston was 1.5–1.7 mg/C, and the eroded mass involved in the motion was comparable with the impactor mass. It was shown that in scheme 1, when the external field system was switched earlier, the impactor was accelerated at a maximum magnetic induction, and the impactor velocity in the channel muzzle exceeded 6 km/s.

Development of a three-stage gas gun launcher for ultrahigh-pressure Hugoniot measurements.

A three-stage gas gun, composed of a two-stage gas gun and the add-on part, has been developed to launch high-Z (tantalum, for example) flyer plates up to 10 km/s for ultrahigh-pressure Hugoniot measurements. Great care has been taken to optimize the add-on part in which a specially designed graded density impactor is employed to quasi-isentropically accelerate the high-Z flyer plate for maximizing its impact velocity. The shock wave in the target generated by the flyer plate is characterized with the flatness of the shock-front better than 1 ns in the concerned area and the uncertainty of the shock-wave velocity less than 2%, thus satisfying the requirements for high-precision Hugoniot measurements. As a demonstration, we measured the ultrahigh-pressure Hugoniot equation of state of tantalum ranging from 0.45 TPa to 0.85 TPa with a symmetric impacting geometry in which the shock-wave velocity and the particle velocity are simultaneously determined. The results obtained are well consistent with data available in the literature, indicating the extended capability of the gas-gun launcher technique.

Relating a Small-Scale Experiment to a Full-Scale Railgun Using Simulation and Similarity Theory

In this paper, a small-scale experimental method for the study of the dynamic performance of an electromagnetic railgun is proposed. A silicon-based microbeam under electrostatic force was used to simulate the electromagnetic railgun. An experimental model was developed for a set of railgun parameters. On the basis of similarity theory, the natural frequency similarity ratio between the railgun and the experimental model was determined. The excitation and detection circuits of the experimental model were designed and fabricated. Using the experimental model, the natural frequency for the railgun was obtained and compared with the real full-scale one. Results revealed that the small-scale experimental results agreed well with the experimental result of the full-scale railgun. The proposed method can be used to predict the dynamic performance of the full-scale railgun system.

Design of overload test system for electromagnetic rail gun

Design of overload test system for electromagnetic rail gun

Design and Launching Performance of Armature Coating with Low Melting Point Alloy

Hydrodynamic lubrication is an effective method to improve the sliding electrical contact performance for electromagnetic railguns. A kind of U-shaped aluminum armatures coated with low melting point alloy was designed, and the solid coating could melt and form a fluid dynamic lubrication film during initial launching process. A series launching experiments were comparatively conducted about armatures with and without coating, the current waveform, the muzzle velocity, and the contact resistance were collected. The experiments results reached three aspects. First, the variation of the sliding electrical contact resistance of the armature/rail can be divided into three stages: rapid reduction stage, stabilization stage, and oscillation and rising stage. And the coating works mainly in the first stage. Second, with the increasing number of repeated launching, the amplitude of oscillations in the last stage gradually decreases, and the muzzle velocity tends to be stable. And in the last stage, with the increase of rail depositions, contact resistance gradually tends to stability. Third, compared with common armature, the armature coating with low melting point alloy occupies a shorter launching time interval and gets a higher muzzle speed. That work has some reference significance to the sliding electrical contact of the electromagnetic railgun.

Refining FE Structural Mechanics Simulations of a Railgun by Taking Into Account Electromagnetic Effects

Modeling of the structural behavior of the housing of an electromagnetic railgun is usually carried out without considering the electromagnetic origin of the forces; the magnetic pressure acting on the rails is assumed to act at the rail surfaces only. This approximation proves to be a great challenge, as moving pressure profiles at speeds of a railgun projectile are very rare in purely mechanical investigations. In the past, we have published several papers on the structural mechanics of railgun housings characterized by discrete supports. We could show that the displacement of rail surfaces at the position of the armature can reach amplitudes that are not negligible. In fact, in the case of metal brush armatures, the increase in distance between the rail surfaces of only tenths of a millimeter can make the difference between the solid contact and arcing to increase. We also matched our findings to experimental data that were, however, so far only gained in static tests. In this paper, we analyze the foundations of our mechanical modeling using electromagnetic calculations. We calculate a 3-D distribution of the $J \times B$ volume force density in the rails and use them as input for our structural mechanics model. A second point to be addressed concerns the parts made from conducting materials, such as our discrete supports made from steel bolts, which are situated in rapidly changing magnetic fields during the experiments. Again, the influence on our structural mechanics modeling is discussed.

Dynamic Stress Analysis of a Composite Electromagnetic Track

The firing of an electromagnetic gun is shown to result in the armature moving along the guide rail, which can cause extrusion, wear, planing and other problems, which set limits on its application. The track properties can be adjusted by changing its composition, so as to obtain good electrical conductivity, corrosive resistance, and strength. For simplicity, the composite track is presented as an elastic foundation beam, and the general solution of composite track deflection at dynamic load is obtained by using the two-dimensional Fourier integral transformation, on this basis, the bending moment distribution and expression for dynamic stress are obtained. The characteristics of dynamic stress distribution and factors that influence them are analyzed, the effect of the proportion of the composite layer and its parameters on the dynamic stress of the track is discussed.

The process of surface carburization and high temperature wear behavior of infiltrated W-Cu composites

Tungsten-copper (W-Cu) composites are used as high temperature frictional materials under special service conditions for electromagnetic gun rail and precision guide for rolled pieces due to their good ablation resistance and electrical conductivity. However, they have poor wear resistance at elevated temperatures. In this paper, surface carburization method was applied on the W-20 wt%Cu composite to investigate the mechanisms of carburization and its effects on the high temperature friction behavior of composite. Carburization process has been done at a temperature of 1100 °C for 30 h. The obtained results showed that carburizing at 1100 °C with a dwelling time of 30 h resulted into formation of a carburized layer and a dense intermediate sub-layer on the substrate. Also, the surface carburized layer with a thickness of about 70 μm composed of mixed phases of graphite, WC and W2C. The hardness of carburized layer (~HV454) was significantly higher than that of substrate (HV223). Also, bending strength of the carburized W-Cu composites has been significantly improved, although their electrical conductivity and tensile strength was decreased slightly. The carburization mechanism of the W-Cu composites was found to be dominant by carbon atom diffusion through reaction with W atoms and formation of surface liquid copper, which promoted migration and diffusion of tungsten and carbon at high temperatures. Average coefficients of friction and wear rate of carburized W-Cu composites are all lower than these of un-carburized W-Cu composites owing to the presence of surface carburized layer. Also, formation of CuWO4 at high temperatures reduced the friction and wear resistance of the W-Cu composites.

Research on Melting Erosion Law of a Multiturn Series–Parallel Railgun During Launching Period

The melting erosion law of the contact interface between armature and rails on the electromagnetic (EM) railgun is one of the key factors affecting the launching performance. In order to study the melting erosion law on the contact interface of a multiturn series-parallel (MSP) railgun, an EM structure thermal multiphysical field coupling model is built, and the armature velocity, contact force, and temperature of contact interface under different current peak values and shrink ranges are analyzed. Besides, the related verification experiments are carried out, and the melting erosion law of the contact interface is obtained. The results of simulations and experiments show the following conclusions: First, during the launching, the contact force between armature and rails varies with current fluctuation. Second, the friction heat power varies directly with the contact force, but Joule thermal power caused by contact resistance varies inversely with the contact force. Third, the ambient temperature of the sliding contact interface can be further improved by reasonable design of armature shrink range. Fourth, due to the inevitable wear during sliding, the melting area of the armature contact surface gradually transfers from the initial contact area to the tail. The above-mentioned conclusions can provide a technical reference for the high-speed experimental study of MSP railgun.

Analysis and discussion on launching mechanism and tactical electromagnetic railgun technology

Abstract This paper begins with a discussion on the significance of multi-physical fields in the research of railgun launching mechanism, followed by an introduction of research work about dynamic measurements and numerical simulations. The application of some measurement methods including the atomic emission spectrum, fiber-optic strain, optical level, pulsed X-ray, and high-speed video in observing the launching process was introduced. The models about the electromechanical dynamic processes and multi-physical fields in a railgun were developed. The mechanisms of the grooving, arc transition, and gouging were analyzed. These work provided a deeper understanding of launching mechanism of electromagnetic railgun. Some issues about the tactical railgun, such as the fiber composite overwrapped barrel, recoil, loading modes and eddy current loss were also discussed. Taking a medium-caliber launcher as an example, the basic process of design and analysis was introduced.

Analysis of in-bore magnetic field in C-shaped armature railguns

In order to analysis the distribution characteristics of in-bore magnetic field for C-shaped armature electromagnetic railgun, a computational model considering dynamic contact pressure is established. By solving the dynamic equation, the in-bore motion characteristics of the armature are obtained. The distribution of current in the rail and armature is analyzed based on the magnetic diffusion equation and Ampere's law. On this basis, three simulation models are proposed, which correspond to static state, motion state and motion state considering the velocity skin effect. The magnetic field of the investigated points along the central axes of the armature front end are obtained. The results show that, in static state, the peak magnetic flux density of each investigated point is greater than the other two states. Velocity skin effect leads to a decrease in peak magnetic flux density. The change of motion state has little influence on the peak magnetic flux density of the investigated point that far away from the armature. The calculated results can be used in the electromagnetic shielding design of intelligent ammunition.

Research Progress on Interface Lubricating of Sliding Electrical Contact with low velocity in Electromagnetic Railgun

As a kind of new concept kinetic weapons with hypervelocity, the electromagnetic railgun has a control technology on the sliding electrical contact between armature/rails. The initial sliding electrical contact belongs to the solid-solid dry friction state, which has a serious impact on the system launch efficiency and the rail life. This paper analyzes the research progress of liquid lubricated and solid lubricated technologies commonly used in the sliding contact of electromagnetic railgun in the initial launch stage. The application of hydrodynamic lubrication technique to electromagnetic railgun was discussed from the aspects of theory basis, preparation process, electro-thermal characteristics, mechanical properties and chemical properties. Finally, the application of low melting point alloy coating to improve the initial sliding contact of electromagnetic railgun was put forward. This article has important significance to the research of electromagnetic railgun technology.