Armature Material Research Articles

Research on the anti-ablation performance of TiC particle reinforced aluminum matrix composite coating

During the electromagnetic rail launching process, the severe ablation of the armature caused by the arc can easily lead to launch failure. Therefore, it is necessary to study methods of enhancing the anti-ablation property of the armature. One effective method is to prepare metal-ceramic composite coating on the surface of aluminium alloy armature. This paper conducts molecular dynamics simulation on the ablation protection effect of TiC particle reinforced aluminum matrix composite coatings on the aluminum armature substrate. By applying a surface Gaussian heat source to simulate the arc ablation effect, the micro-enhancement mechanism of TiC particles is analyzed through the depth of ablation craters, material mass loss, and the evolution of TiC particle morphology. The results show that the degree of material ablation intensifies with the increase of arc discharge power. The composite coating helps to improve the anti-ablation performance of the armature, and the anti-ablation performance first increases and then decreases with the increase of TiC mass fraction. The results can provide a theoretical foundation and technical support for optimizing design of anti-ablation performance of armature materials.

Influence of dry frictional heating on acceleration disruption in a railgun with a metal armature

The main problem associated with the realization of the concept of the electrodynamic accelerator with a metal armature (MA) is the complexity of providing metal contact MA/rail at the velocity over 1 km/s. Here, a complex of physical phenomena is analyzed, which leads to the destruction of the metal contact of the rail/armature due to its melting and the ignition of an electric arc. A mathematical model of the dry frictional heating of the contact zone is formulated and its analytical solutions are obtained using fractional calculus. The criterion of no melting of the contact zone is derived. The generalization of the experimental data showed that to ensure the metal contact, the choice of rail and armature materials is a dilemma. A possible way to resolve this dilemma has been proposed.

Multiparametric Investigation of Thermal Limitations in a Rapid-Fire Multirail Railgun Powered by a Pulsed MHD Generator

The operation of rapid burst firing multi-rail railguns was analyzed by numerical simulation using coupled 2-D and 3-D nonstationary formulations. In the calculations, a Sakhalin-type pulsed magnetohydrodynamic generator is assumed as a power source for the launcher. Launchers with three and five pairs of parallel rails connected into a series electrical circuit are considered. The simulation was performed for different numbers of projectiles in a burst and for different projectile masses. It is established that a major factor limiting the operation of launchers in such modes is the heating of the rails. It is shown that the rate of rail heating is determined by the inhomogeneity of the current density distribution along the rail section due to the nonstationary diffusion of the magnetic field into the rails and by the velocity skin effect. It has been shown previously that the maximum heating of the rails occurs in regions located outside the launcher channel provided that the width of the outer rail extends beyond the section of the launcher channel. We investigated the possibilities of reducing the heating of rails in these regions using rails of different widths in the rail launcher channel, using rails of different materials and rails with inhomogeneous electrophysical properties, and using armatures of different materials. The calculations show that with an optimal choice of the material and structure of the rails and the armature material corresponding to this structure, multirail launchers 5–6-m long can provide a projectile velocity of 2–2.5 km/s in a burst of 10–16 projectiles with masses of up to 800 g at a firing rate of 200–300 shots per second with no melting of the rails in the launcher channel.

Study of Current Pulse Form for Optimization of Railguns Forces

Electromagnetic force on rails of railgun is the effective factor which impacts on input current pulse, rails and armature geometry, dimensions, and materials. This paper investigates how the stimulated current form affects the electromagnetic force on rails. A transient analysis with a finite-element method is discussed to simulate a 3-D railgun in this paper. In the first section, we consider the effect of flat-top length of stimulated current pulse on electromagnetic force distribution on rail and armature velocities. In the second section, we consider the effect of stimulated currents that have the same areas but have various amplitudes and flat-top lengths and at the last section, the flat-top length and amplitude of current are exactly the same, but the flat-top part replaces during time. Consequences are shown in several figures.

Ultimate Kinematic Characteristics of Rail Electromagnetic Launchers With an External Magnetic Field

The thermal limitations due to the circuit current are the major factors preventing the attainment of high projectile velocities and acceptable service life of railguns. To reduce the thermal load on the rails and armatures, it is necessary to reduce the amount of current flowing through them, but this decreases the electromagnetic accelerating force and limits the maximum velocities of projectiles of a given mass at a predefined acceleration distance. One method of lowering the current without reducing the electromagnetic force on the projectile is to use a railgun with augmenting rails. This paper presents the results of 3-D numerical simulations of the Joule heating of armatures and rails in railguns with one and two pairs of augmenting rails. The objective of this paper is to reduce the rate of Joule heating of armatures during acceleration and to increase the ultimate (under heating conditions) kinematic characteristics of the railguns by choosing the optimal configuration of the outer turns and optimizing the current pulse in the augmenting rails. The ultimate projectile velocities are obtained when the Joule heating of the rails and armature by electric current during the shot does not tend to increase the temperature at any point of the railgun above the melting point of the rail and armature materials. It is shown that by controlling the position and total current in the augmenting rails, it is possible to significantly reduce the thermal limitations during high-velocity electromagnetic acceleration of solids and increase the ultimate kinematic characteristics of railguns in crisis-free acceleration regimes.

Significance of Armature Resistivity and Deformation in Modeling Coilgun Performance

We have performed 2-D axisymmetric magnetohydrodynamic simulations for a single stage induction coilgun system and validated the results against in-house experiments. The simulations, besides computing the currents and electromagnetic forces, also capture the associated hydrodynamic phenomena. This paper highlights the importance of appropriate material strength for handling hydrodynamic phenomena and temperature-dependent electrical resistivity model for self-consistent electromagnetic calculations. These are very essential for accurate prediction of armature dynamics and velocity. Inappropriate resistivity model, even in case of no deformations, produced velocity deviation of up to 50% as compared with experiments. Inclusion of appropriate models shows <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&lt;}{4\%}$</tex></formula> average deviation when compared with experiments for known armature material (Al6061-T6). For higher energies, predicted armature deformations appear to be in a good agreement with experiments. If material deformation is ignored, velocities get over-estimated. Finally, subsequent to our validation at low energies, an optimized armature profile and dimensions are reported that have allowed our armatures to achieve velocity <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&gt;}{\rm 200}~{\rm m}/{\rm s}$</tex></formula> with single stage operation and 300 m/s with two-stage operations of the coilgun. This paper shows that accurate modeling of Joule heating and armature deformation, along with self-consistent evolution of currents, is essential for coilgun modeling. Although the system is not presently optimized for efficient energy conversion <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\sim}{1.5\%})$</tex></formula> , the performance of induction accelerator at moderate velocity of armature (50–300 m/s) is not only useful for validating our code, but can act as an effective catapult for impact testing of materials.

电磁发射枢轨界面初始接触状态研究

Sliding interface status during whole electromagnetic rail launch process depends on contact status after initial assembly in which initial contact force between armature and rails(A-R) is provided by trailing arm elastic deformation in the C-armature rail launcher, which influences launcher system efficiency and rail lifespan. This paper focuses on the contact status of initial C-armature assembly of rail launcher with constructing the contact model for simulating computation and designing many groups of experiments for contrast testing. Considering safe deformable limits of armature material, variation laws of contact pressure, contact region(area) and contact force are analyzed under conditions of small-range feasible heads and tail sizes. Interferential proportion is proposed as a contact status dependent key parameter. Contact region transformed from tail to head of trailing arm as interferential proportion increasing, maximum of contact area is about half of whole outer surface of trailing arm. Optimal contact status for favorable electric contact and engineering implement technique are also discussed.

Ablation and geometry change study of solid armature in a railgun

Armature plays an important role in the electromagnetic launch process. Due to the skin effect, the current density distribution is neither uniform on the rail, nor on the armature. High current density centralization in one part could lead to a partial high temperature and make the armature material melt down and be ablated, especially at low velocity. In this paper we try to change the geometry of a Cshaped armature to improve the current density distribution and reduce the ablation. Four variants of C-shaped armatures are designed to study the specific features, including a conventional C-shaped armature (CCA), a rounded leading edge C-shaped armature (LCA), a rounded trailing edge C-shaped armature (TCA), and a rounded incorporate edge C-shaped armature (ICA). A novel low-speed experiment is constructed and tested. The armatures are ablated and recovered to compare the improved effects. Then finite element simulations according to the experimental results are performed to further analyze the experimental results. It is proved that the current density and hence the temperature distribution can be immensely improved by simply changing the armature geometry. LCA and ICA show that the erosion is more uniform on the contact surface due to the rounded leading edge. The curved trailing edge could improve the uniformity of the current on the interface. ICA which combines the effects of LCA and TCA is the best option in the four armatures. How much the leading edge and the trailing edge should be curved involves the geometry of CCA and the posture of the interface on the rail. A saddle shape is a good option to improve the current density and temperature distribution in the throat. Erosion mechanism is analyzed finally. The experiments and simulations support the erosion and transition mechanism. A detailed description of the experiments and simulations is also presented in this paper.

스톱모션 퍼핏을 위한 몰드 제작과 캐스팅

This paper covers the manufacturing process to improve the quality of the puppet for stop-motion films, especially focuses on the mold making and casting process those are the key steps of the puppet making. Unlike the general mold for a duplication, the mold for puppets has special functions to fix an armature and inject casting materials stably inside, and it is repeatedly baked at high temperature. The practical information about puppet makings is provided including various predictable problems, expertise from many professionals, vender list, and so on.

Comparison Simulation of Friction Heat and Joule Heat in Electromagnetic Railgun

A large amount of heat will be produced in the railgun launching process, the heat-induced temperature mutation is an important cause of material failure. To obtain temperature field variation law in railgun, mechanism of heat generation was analyzed according to the basic working principle of railgun. Temperature field was discussed through the method of combining theoretical calculations and Finite Element simulation. The results show that friction heat results in temperature rise on the materials only near the contact interface; temperature rise under the action of current heat around the corner of U-shaped armature is obvious, while maximum temperature is appeared at the side surface and exceeds the melting point of the armature material. The temperature of railgun mainly depends on the current value, while friction heat has smaller effect on it.

Electric-Current-Induced Liquid Al Deposition, Reaction, and Flow on Cu Rails at Rail&amp;#x2013;Armature Contacts in Railguns

When a railgun is fired, the aluminum armature typically undergoes melting at the rail-armature contacts and deposits liquid metal on the rails. Rail life is affected by these deposits. Localized aluminum armature melting has been attributed to current crowding and localized Joule heating. This paper reports on 1) the characterization of debris on fired rails and their role in rail damage and 2) experiments to elucidate the role of electric current in the transport of liquefied armature material along the rail surfaces. A miniature static railgun model was constructed by wrapping an Al foil around a quartz core and placing the Al foil in contact with two thin-film Cu stripes deposited on Si substrates. In this arrangement, the Cu thin films simulated the surface skins on the two rails, whereas the Al foil represented the skin of the armature. The circuit was subjected to a constant current under high vacuum and various ambient temperatures. The part of the Al foil in contact with Cu melts quickly due to Joule heating, and the liquefied Al starts flowing down the negative rail. In all instances, the direction of liquid flow was from the positive to the negative terminal. The kinetics of Al migration was measured, and it was found that the activation energy for Al migration is close to that for self-diffusion in liquid Al. The observed liquid transport is attributable to liquid electromigration under the influence of the applied current.

Experiments With Armature Contact Claddings

This paper summarizes experiments to investigate the possibility of delaying the onset of transition by using armatures with high melting temperatures. The rationale for the experiments was that armature materials with high melting points might outperform aluminum by reducing melting and erosion at the rail-armature interface. The tests used a novel technique that consists of placing thin claddings on the rail-contacting surfaces of the armatures. Two low-speed tests with copper armature claddings proved that claddings affixed to the trailing arms can survive a railgun launch. These tests were followed by four tests at about 2 km/s that used titanium armature claddings. These tests showed that titanium-clad armatures can perform well; however, this performance cannot be maintained beyond the first shot because the titanium armature claddings cause significant damage to the rails

Physics of solid armature launch transition into arc mode

The railgun launch of a solid armature is conventionally divided into two stages, namely, the initial stage, where a metallic contact is retained between the armature and the rails, and the second, starting at a velocity /spl sim/0.3-2 km/s, where the contact occurs through the arc plasma. While a variety of reasons for the transition were considered, no universally accepted physical picture supported by experiment has thus far been formulated. We showed experimentally that under usual launch parameters, 3D MHD instabilities form in the contact gap because of the absence of shear resistance, which result in the formation, collapse, and, eventually, explosion of pinch waists (see E.M. Drobyshevski et al. Tech. Phys. Letts., vol.25 no.3, p.245-7, 1999). The destruction of the pinch waists gives rise not only to termination of current flow from the armature to the rail through the metal and transformation of the metallic contact in the armature/rail interface into an arc gap, but to ejection of the liquid metal and dusty plasma from the gap forward and back into the railgun bore as well. Even in the absence of MHD instabilities, armature material can be shed due to very inhomogeneous distribution of fields of thermal, electric, and dynamic parameters in the armature body. Appearance of easily-ionized matter in the bore results in the formation of shunting arcs there, which naturally reduce the armature launching efficiency. The new physics revealed by the authors in the railgun solid-armature launch transition to the arc regime provides a basis for a search for ways of increasing the launch efficiency.

Thermal control of railgun armatures

The present approach for thermal management in metallic railgun armatures relies on using the thermal capacity of the armature material to limit the adiabatic temperature rise during launch. In this, the armature is designed so that, as the accelerating current passes through it, the armature heats up to a maximum temperature that is close to the melting point of the armature material. Careful attention to design has to be exercised in regard to local inhomogeneities where current concentrations and associated temperature excursions may occur. Alternatives to this approach are discussed in this paper. These include the possibilities of conductive gaseous cooling and utilization of the latent heat of evaporation of materials contained within the armature. Further work on these concepts is recommended.

Demonstration of a hypervelocity mass-efficient integrated launch package

Tests were conducted whereby a kinetic energy penetrator was launched from an electromagnetic launcher. The penetrator was fabricated from a tungsten alloy. An armature, which supported the penetrator during acceleration and conducted the rail current, was fabricated from 7075-T6 aluminum. The transition of the armature contacts from a low voltage to a high voltage was identified as the mechanism that caused the aft section of the subprojectile to fail. Transition occurred fairly consistently at an average velocity of 2050 m/s. Removal of armature material at the rod-armature interface increased the survivability of the subprojectile and was demonstrated with a launch package mass of 308.5 gm, yielding a useful mass fraction of 49%. Structural integrity of the subprojectile at a launch velocity of 2350 m/s was verified with an orthogonal flash X-ray image at the muzzle.

Erosion observations on recovered large caliber armatures

A unique feature of the Kirkcudbright EML facility is its ability to fire over an open range. The primary purpose of this is to enable projectile firings at target distances of up to 2 km. An additional benefit however, is the ability to recover fired items. It has now become normal practice to follow a day's bring with a thorough down-range search. Despite the rough terrain, around 70% of all 90 mm armatures are recovered. Most of these armatures are intact with little or no ground impact damage. Examination of recovered armatures has proved an invaluable aid to armature development and optimization. Over the last few years, our 90 mm armature design mass has dropped from around 1.2 kg to 800 g, despite ever increasing energy levels. Previous analysis efforts have concentrated mainly on surface phenomena and hot zones within the bulk of the armature material. This paper examines material loss, which frequently amounts to around 10% of the total armature mass. With a large quantity of recovered armatures available, data exists to enable correlation with various firing parameters. This process provides an insight into the nature of armature erosion and assessment of the relative significance of heating mechanisms. Muzzle kinetic energy and post-transition charge transfer both enable mass loss to be quantified with a typical accuracy of around 7%.

Thermal stress in EML rail-conductor overlays

In an electromagnetic (EM) railgun, a thin, unbonded overlay on the rail conductor develops residual strains as evident from its post-shot curvature. Heating due to the transient EM field and a large thermal gradient due to deposition of a molten layer of armature material contribute to the straining of the overlay. In this paper, the authors solved the one-dimensional coupled magnetic and thermal diffusion equations to estimate the thermal gradient in the overlay. Heat sources included both Joule heating and the enthalpy from a resolidified thin layer of molten aluminum deposited by the armature. The thermal gradient so calculated was used in a one-dimensional stress model to compute residual stresses from which residual curvature was calculated. The calculated curvature compares well with the experimental value. Finally, based on the estimated residual stress, they present an estimate for the remaining life of the overlay.

Calculating the liquid film effect on solid armature rail-gun launching

In existing EM launchers with solid electroconductive armatures the achievement of high velocities is limited by the velocity skin-effect (VSE) and wearing of contact surfaces due to inhomogeneities of the electric current, and frictional tearing and heating. Inevitably, a liquid phase appears that is considered usually to be undesirable. We believe the deliberate injection of electroconductive liquid in the gaps between the armature and rails is capable of significantly decreasing friction between these surfaces and the resulting wear, of improving electric contact and reducing armature overheating in zones of electric current concentration caused by imperfectness of surface manufacturing or by the VSE. We present the calculation of temperature fields in the armature/rail interface with due account of VSE, energy release, and heat transfer in a continuous liquid film that completely covers the contacting surfaces. The motion of viscous liquid in the gap is considered with due regard to Ampere forces and inertial forces caused by acceleration of the armature. We have found that the rate of the armature heating, which ultimately leads to melting in a region at the trailing edge, depends essentially on thickness and material of the film. By optimizing these parameters it is possible to delay the crisis phenomena associated with melting of the armature material and subsequent transition of the armature/rails contact into the plasma mode of operation.

The study of sliding contact in railgun with metal armature

An experimental technique for the study of the current distribution in the rails and a moving metal armature is developed. The work was carried out on a special experimental railgun with a capacitor power supply. The set of small dB/dt probes as well as wire contact probes were arranged in close vicinity of the rail and armature contact surface. For interpretation of dB/dt measurements, a computation technique and program of restoration of current density distribution along the armature were developed. The size and the location of the current concentration zone in the contact area were obtained for several combinations of rail and armature materials; bronze and copper rails, Al and Ti alloy armature. Teats on a stationary armature with resistive stainless steel and graphite layers were also made to estimate the influence of the layer material resistivity on the current distribution.

Investigation of techniques to increase armature transition velocity

The cause of armature contact transition in railguns arises from the velocity skin current effect. Connected with this event is the evaporation of thin layer of the armature contact surface in a high evaporation leading to an increased voltage drop interface between the armature and the rail and this is followed by arc ignition. Earlier, we showed that the transition velocity depends very weakly on the current and its period in the railgun. In this work we examine the influence on armature transition velocity from other railgun parameters: inductance gradient, mass and dimensions of the armature, and the choice of the armature and rail materials. It has been postulated that a method of increasing the armature transition velocity involves the use of a graphite layer on metallic rails. The experiment carried out by us on the acceleration of the aluminium armature with mass 2.6 g in the nonarc regime up to the velocity 4.6 km/s in a railgun with the copper-graphite rails confirms these expectations. In this work we have compared calculated results with experimental data to give a physical picture of the transition of a metallic contact to an arcing contact. This report discusses a new method of increasing the transition velocity with the use of the sectioned rails and presents results of the new experiments.