Search Results (18)

The muzzle velocity of electromagnetic rail launchers approaches 1550 m/s, exhibiting typical hypervelocity electrical contact characteristics. During the electromagnetic launching process, extreme conditions, such as high current density, high temperature rise, and strong strain can cause wear on the surfaces of the armature and rail. Electromagnetic launch tests are conducted to study the wear conditions of the rail surface and the relationship between the wear state and contact resistance. After the rail is abraded by hundreds of launching armatures, its surface 2D profile and morphological characteristics are measured and analyzed. Based on fractal theory, the static contact resistance model is developed. Concurrently, the contact resistance at various positions is measured to reveal the evolution of the static contact resistance between the armature and the rail under wear. The research results show that along the direction of the armature launch, the rail surface wear transitions from mechanical wear to electrical wear, the fluctuation range of the 2D profile becomes smoother, and the roughness of the rail surface shows a decreasing trend. When the roughness is greater, the contact resistance is more sensitive to changes in external load. Full article

During the electromagnetic launching process, the actual current input into the launcher is obtained by controlling the discharge of the pulsed power supply. Generally, the waveform of the pulse current is determined by the discharge characteristics and discharge time of the pulse power supply. Due to the limitation of control accuracy, the driving current is not an ideal trapezoidal wave, but there is a certain fluctuation (current ripple) in the flat top portion of the trapezoidal wave. The fluctuation of the current will affect the thickness of the liquefied layer at the armature–rail interface as well as the magnitude of the contact pressure, thereby inducing instability at the armature–rail interface and generating micro-arcs, which result in a reduction in the service life of the rails within the launcher. Consequently, it is imperative to conduct an in-depth analysis of the influence of current ripple on the liquefied layer during electromagnetic launching. In this paper, a thermoelastic magnetohydrodynamic model is constructed by coupling temperature, stress, and electromagnetic fields, which are predicated on the Reynolds equation of the metal liquefied layer at the armature–rail contact interface. The effects of current fluctuations on the melting rate of the surface of the armature, the thickness of the liquefied layer, and the hydraulic pressure of the liquefied layer under four different current ripple coefficients (RCs) were analyzed. The results show the following: (1) The thickness and the pressure of the liquefied layer at the armature–rail interface fluctuate with the fluctuation of the current, and, the larger the ripple coefficient, the greater the fluctuations in the thickness and pressure of the liquefied layer. (2) The falling edge of the current fluctuation leads to a decrease in the hydraulic pressure of the liquefied layer, which results in the instability of the liquefied layer between the armature and rails. (3) As the ripple coefficient increases, the time taken for the liquefied layer to reach a stable state increases. In addition, a launching experiment was also conducted in this paper, and the results showed that, at the falling edge of the current fluctuation, the liquefied layer is unstable, and a phenomenon such as the ejection of molten armature and transition may occur. The results of the experiment and simulations mutually confirm that the impact of current fluctuations on the armature–rail interface increases with increases in the ripple coefficient. Full article

An electromagnetic launcher is a kind of rail symmetrical distribution launcher. When a symmetrical current is passed between the rails, the strong magnetic field is symmetrically distributed between the two rails. The bore parameters affect the efficiency and accuracy of the launcher. Launching accuracy is an important evaluation content for assessing the technical index of the electromagnetic launcher. In this paper, experiments were carried out to investigate the influence factors of the launching accuracy of a small-caliber electromagnetic launcher. The experimental results show that: (1) The consistency of the muzzle velocity increases with the increase of the rail separation. When the rail separation is 16 mm, the mean deviation of the muzzle velocity is the smallest, at 16.71, 15.72, and 10.77, respectively. When the rail separation is constant, the mean deviation of the muzzle velocity is 10.77, while the convex arc height is 1 mm. Increasing the rail separation and the convex arc height is beneficial to improving the consistency of the initial velocity. (2) When the rail separation is certain, increasing the convex arc height significantly improves the firing accuracy and firing intensity, and when the convex arc height increases from 0 mm to 1 mm, the firing intensity is reduced from 9.6 to 4.41, and the firing intensity decreases from 10.34 to 5.79, which significantly reduces the firing deviation and increases the muzzle consistency of the armature under repeated firing conditions. (3) The muzzle attitude is mainly affected by the effective mass ratio. Within a certain range, adding load can make the muzzle attitude of the integrated projectile more stable. However, when the load mass is too large, it will have a negative impact on the muzzle attitude. The results show that under the two cases of the effective mass ratio of 0.43 and 0.49, the integrated projectile has a better muzzle attitude. Full article

Understanding the melting of the deposited layer is crucial for the armature’s melting process and sliding electrical contact performance. This study first establishes contact models for both the boundary lubrication state (BLS) and squeezed-film lubrication state (SFLS). A three-dimensional magnetic diffusion model is then constructed to simulate interface current distribution in these contact states. It is discovered that the maximum current density on the surface of the armature shows a decreasing trend as the thickness of the deposited layer grows. Then, a calculation model for the deposited layer’s melting thickness under BLS is developed. For SFLS, Reynolds and energy equations are used to construct models for liquid film thickness and the deposited layer’s melting thickness. The results indicate that the deposited layer’s melting thickness under BLS is significantly greater than that under SFLS. Specifically, the melting thickness decreases with launching displacement in BLS and increases under SFLS. In SFLS, the deposited layer’s melting can suppress armature melting, though it remains nearly equivalent to that observed with polished rail. These findings provide a foundation for deposited layer control technology, which is essential for enhancing sliding electric contact performance and launching efficiency. Full article

The work aims to enhance and modify the armature surface in electromagnetic rail launch systems and improve its anti-ablation performance to better resist the impact ablation effects of high-temperature and high-speed arcs during the electromagnetic rail launch process and improve launch reliability. TiC particles are widely selected as metal material reinforcements, with advantages such as high melting points and high hardness. In this paper, the arc impact model of pure aluminum alloy and the arc impact model of TiC particle-reinforced aluminum-matrix composite coating–pure aluminum alloy were constructed based on molecular dynamics simulation. The ablation resistance of the material was evaluated by analyzing the depth of arc impact, the mass loss of the model, the number of gasification atoms, and the surface temperature of the material. The protection mechanism of the modified layer on the substrate was revealed by analyzing the damage degree of the surface and subsurface of the material after arc impact. The results showed that the strengthening mechanism of TiC particle-reinforced aluminum-matrix composites included fine grain strengthening, dispersion strengthening, dislocation strengthening, and so on. Covering TiC particle-reinforced aluminum-matrix composite coating on the surface of aluminum alloy armature is helpful in improving its ablation resistance. The research results can provide a theoretical basis and technical support for the modification design and performance control of electromagnetic rail armature. Full article

Electromagnetic rail launch technology has attracted increasing attention owing to its advantages in terms of range, firepower, and speed. However, due to electricity-magnetism-heat-force coupling, the surface of the armature–rail friction pair becomes severely damaged, which restricts the development of this technology. A series of studies have been conducted to reduce the damage of the armature–rail friction pair, including an analysis of the damage mechanism and protection strategies. In this study, various types of surface damage were classified into mechanical, electrical, and coupling damages according to their causes. This damage is caused by factors such as mechanical friction, mechanical impact, and electric erosion, either individually or in combination. Then, a detailed investigation of protection strategies for reducing damage is introduced, including material improvement through the use of novel combined deformation and heat treatment processes to achieve high strength and high conductivity, as well as surface treatment technologies such as structural coatings for wear resistance and functional coatings for ablation and melting resistance. Finally, future development prospects of armature–rail friction pair materials are discussed. This study provides a theoretical basis and directions for the development of high-performance materials for the armature–rail friction pair. Full article

The augmented electromagnetic railgun has demonstrated more potent electromagnetic force, a low excitation current, and less rail thermal damage, showing good potential in heavy load launch. However, the augmented railgun’s load characteristics differ from the conventional double-rail railgun. In the augmented railgun launching experiment, it was found that the fly-wheel diode was damaged, and the capacitive power supply could not discharge fully, which led to residual energy and lower energy utilization. This paper began with the characteristics of the sequential trigger circuit, followed by the causes of the above faults, as well as the corresponding solutions. Based on the conventional excitation circuit, fault detection experiments were carried out first, and the fault mechanism was clarified. Furthermore, according to the solutions proposed, the conventional excitation circuit was improved so that it can work normally when a heavy inductance was loaded. Finally, the sequential trigger experiment was carried out again with the same circuit parameters. The research results showed that the fly-wheel diode could work normally after the circuit was improved, and the problem of residual energy could also be solved effectively. Moreover, the output performance was almost unaffected. Full article

The unique magnetic field environment during electromagnetic launch imposes higher requirements on the design and protection of the internal electronic system within the launch load. This low-frequency, Tesla-level extreme magnetic field environment is fundamentally distinct from the Earth’s geomagnetic field. The excessive change rate of magnetic flux can readily induce voltage within the circuit, thus disrupting the normal operation of intelligent microchips. Existing simulation methods primarily focus on the physical environments of rails and armatures, making it challenging to precisely compute the magnetic field environment at the load’s location. In this paper, we propose a computational rail model based on the magneto–mechanical coupling model of a railgun. This model accounts for the dynamic current distribution during the launch process and simulates the magnetic flux density distribution at the load location. To validate the model’s accuracy, three-axis magnetic sensors were placed in front of the armature, and the dynamic magnetic field distribution during the launch process was obtained using the projectile-borne-storage testing method. The results indicate that compared to the previous literature methods, the approach proposed in this paper achieves higher accuracy and is closer to experimental results, providing valuable support for the design and optimization of the launch load. Full article

Rail expansion significantly impacts the launch precision of a railgun system. Higher precision can be achieved when the extent of expansion is low. This paper investigates three main factors that influence the extent of rail expansion using the finite element method, including pre-stress, electromagnetic load, and stiffness of the insulators. The mean squared error between experiment results and simulating results is less than 0.06, validating the finite element model. The simulated results reveal that the extent of rail expansion increases with a decrease in pre-stress and an increase in electromagnetic pressure and the stiffness of the insulator is the most significant influencing factor, as the use of a stiff insulator not only results in a small extent of rail expansion but also delays the separation between the rails and insulators. The mechanism of how pre-stress influences the railgun system has been proposed. It has been expressed that the pre-stress maintains the integrity of the railgun system by hindering the process of a decrease in the contact surface area between rails and insulators during launch. The study provides a platform to improve the design of the railgun system. Full article

The rail inductance gradient is an important parameter of the electromagnetic launcher. The calculation of its value is important for the design of the launcher structure and for predicting the motion behavior of the armature. The current research on the inductance gradient analysis method of the electromagnetic rail launcher mostly does not take into account the effects of launcher size and current diffusion. This method cannot describe its dynamic characteristics, and it results in a large error compared with the actual launch. Therefore, the paper first establishes an electromagnetic rail launcher armature motion model to obtain the rail velocity skin depth under a U-shaped armature. Second, an analytical method for calculating the inductance gradient based on the dynamic skin depth of the rail is obtained, which takes into account the launcher size and velocity skin effect. Finally, the experimental results verify the correctness and accuracy of the method to achieve an accurate prediction of armature speed. Full article

The purpose of this article is to analyze the front door coupling effect that may occur in the projectile receiver due to the discharge pulse radiation in electromagnetic railguns, and to simulate the discharge pulse interference. This phenomenon will have an impact on the launch of the projectile, causing its fuse to be disturbed, ultimately affecting the weapon performance of the electromagnetic railgun. Discharge refers to when the armature carrying the projectile is fired out of the chamber, and the armature connected between the two rails detaches, causing a circuit break in the electrical circuit during the operation of the electromagnetic railgun. The current flowing through the armature is disturbed, causing an instantaneous high voltage to penetrate the air gap between the two rails, generating nanosecond pulse width discharge voltage pulse radiation, with a spectrum of up to tens of megahertz. In this paper, we establish a receiving antenna model on the projectile, which is essentially a horn antenna, receiving electromagnetic pulses from the discharge process, and coupling the pulse interference through its front door. During the analysis and calculation, we established an antenna receiver model located in the C-band with a frequency of 6 GHz for simulation, analyzed and calculated the actual interference loaded on the projectile after front door coupling, and verified the correctness of the simulation settings and results by comparing with the literature. Finally, we found that because the main energy spectrum of the pulse is at MHz level, when the front door of the C-band horn antenna is coupled, the standing wave ratio of the antenna is very large and the gain is very small, so the pulse interference is filtered, which can make the interference finally loaded on the projectile insufficient to affect the normal operation of the projectile. At the same time, it is recommended to add an RF filter to the receiving channel to further enhance anti-interference ability, so as to ultimately enable the electromagnetic railgun to function properly. Full article

The railgun is a promising weapon, but suffers from poor contact and harsh magnetic field environment. We used the moment of inertia to measure the deformation resistance of the rail, studied the contact characteristics of the railgun by contact force, and compared the performances of different structures of the rail. The magnetic field environment in the bore and the thrust on the armature of different structure railguns were studied by FEM-BEM simulation, and the final structure of the hyperbolic augmented quadrupole railgun was determined. The new structure of the railgun possesses better deformation resistance and contact characteristics, and can provide an electromagnetic shielding area and greater thrust. The test results show that the proposed railgun exhibits less rail damage and less armature ablation after launch. Full article

Electromagnetic rail launch technology has made impressive progress; however, the analytical method of calculating the inductance gradient for a complex electromagnetic launcher is still insufficient. By fully considering the characteristics of electromagnetics and current distribution in a device, this paper describes a model of the current skin effect by simplifying the line current distribution in the device. Based on Biot–Savart Law, an analytical method of calculating inductance gradient for an electromagnetic rail launcher with complex structure is proposed. This method has the advantages of fast calculation speed and accurate calculation results. Because of error analysis, the calculated value relatively corresponds to the simulation result of the eddy current field. To reflect the transient electromagnetic emission process, the effects of different configurations, current frequency, and armature position on the inductance gradient are further summarized. The results show that the error rate of this method in calculating the inductance gradient is about 4%, which meets the requirement for calculation accuracy. The inductance gradient of the enhanced four-rail electromagnetic launcher is about 2.22 times that of the nonenhanced one due to the equal conditions; the inductance gradient decreases with the increase in current frequency and decreases as the armature approaches the muzzle. Full article

The ablation and wear of the four-rail electromagnetic launcher during the working process will aggravate the damage of the armature and rail, and greatly affect the service life of the launcher. To effectively alleviate rail damage, this paper applies the copper-steel composite rail to the four-rail electromagnetic launcher and proposes a new four-rail electromagnetic launcher. Based on the quadrupole magnetic field theory, the physical model of the new four-rail electromagnetic launcher is established, and the electromagnetic characteristics of the ordinary and new launchers are compared and analyzed using the finite element method. On this basis, the influence of composite layer parameters on the electromagnetic characteristics of copper-steel composite quadrupole rail is explored. The study found that the new four-rail electromagnetic launcher can provide a better launch magnetic field environment for smart loads, and the current distribution of the armature and the rail contact surface is more uniform, which can effectively improve the contact condition between the armature and the rail. The composite layer parameters of copper-based composite rail will have a certain impact on electromagnetic characteristics, and copper-steel composite rail of appropriate proportions can be selected according to different needs. The model proposed in this paper has a certain degree of scientificity and rationality. Full article

Multiphysics problems represent an open issue in numerical modeling. Electromagnetic launchers represent typical examples that require a strongly coupled magnetoquasistatic and mechanical approach. This is mainly due to the high velocities which make comparable the electrical and the mechanical response times. The analysis of interacting devices (e.g., a rail launcher and its feeding generator) adds further complexity, since in this context the substitution of one device with an electric circuit does not guarantee the accuracy of the analysis. A simultaneous full 3D electromechanical analysis of the interacting devices is often required. In this paper a numerical 3D analysis of a full launch system, composed by an air-core compulsator which feeds an electromagnetic rail launcher, is presented. The analysis has been performed by using a dedicated, in-house developed research code, named “EN4EM” (Equivalent Network for Electromagnetic Modeling). This code is able to take into account all the relevant electromechanical quantities and phenomena (i.e., eddy currents, velocity skin effect, sliding contacts) in both the devices. A weakly coupled analysis, based on the use of a zero-dimensional model of the launcher (i.e., a single loop electrical equivalent circuit), has been also performed. Its results, compared with those by the simultaneous 3D analysis of interacting devices, show an over-estimate of about 10–15% of the muzzle speed of the armature. Full article