Liangliang Tang

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.

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.

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.

The influence of mechanical preload on muzzle speed in solid armature railgun

Electromagnetic railgun is one of the most important new concept weapons. It is very important and necessary to maintain adequate contact pressure between rail and armature for avoiding transition in solid armature railgun. Based on Marshalls “one gram per amp” rule, the mechanical preload is analyzed. The lower limit of mechanical preload is about 0.1kN in both small and large caliber railgun. Based on Newtons second law, the upper limit of mechanical preload is also analyzed in different caliber railgun. The result shows that the mechanical preload permits very wide range of values. The influence of mechanical preload on rate of muzzle speed change is analyzed. The influence is remarkable in small and medium caliber railgun, which is larger than that in large caliber railgun. When rate of muzzle speed change is lower than 1%, the upper limit of mechanical preload is 38.6kN in 30mm×30mm caliber railgun and 1150kN in 90mm×90mm caliber railgun. When rate error of muzzle speed is lower than 0.1%, the upper limit of mechanical preload is 8.36kN in 30mm×30mm caliber and 251.02kN in 90mm×90mm caliber, which are still larger than 0.1kN in various calibers.

Investigations of the Armature–Rail Contact Pressure Distribution in a Railgun

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.

Optimizing Study on the Concave Arc Surfaced C-Shaped Armature With Medium and Small Calibers

Previous studies on solid armatures show that concave-arc-surfaced C-shaped armature (ASCA) can improve the contact pressure and current distribution at the armature/rail interface in a railgun system. However, concrete design or parameter study of the concave ASCA is rarely mentioned. In fact, besides the basic structural parameters for conventional C-shaped armatures, there are two more key structural parameters for the concave ASCA, namely, the radius (r) and the central angle (8) of their surface arc. In this paper, three matching models of the concave armatures contacting with the corresponding rail structures are discussed and compared, and consequently, the best structure pattern of the contact is presented. Meanwhile, the radius and the central angle of the arc in the ASCA are proposed and analyzed. With a fixed railgun caliber and minimum thickness of armature trailing edge, the optimal 8 and r are determined according to the current distribution obtained in simulation. The concave ASCAs for square-caliber railgun of 20, 30, 40, and 50 mm calibers are discussed, and their optimal structural parameters are presented, respectively.

Current Concentration of Large-Caliber C-Shaped Armature in Square Railgun

Compared with small- and medium-caliber railguns, large-caliber railguns (LCRs) could be applied in more occasions. Armatures for LCRs could be designed according to studies on small- and medium-caliber railguns, yet there are some unique features of the design. Current concentration is a special phenomenon in LCR systems, where it is more severe due to high energy density and large current. For a large-caliber armature (LCA) that has the same muzzle speed as small-caliber armatures (SCAs), which guarantees the identical velocity skin effect, the skin effect and the induced current are studied and have to be considered as the main influence factors. In this paper, the current distribution and concentration between LCA (90 mm × 90 mm) and SCA (20 mm × 20 mm) are studied and compared. The current distribution coefficients of these two armatures are obtained, and it is shown that current density in large armature is more concentrated than the small one. The proportions of induced current to the total current for 90 mm × 90 mm and 20 mm × 20 mm armatures are obtained, which indicate that the induced current is the main reason for current concentration in LCA. At last, measures to improve current distribution in LCAs are discussed.

Experimental study of armature melt wear in solid armature railgun

Transition is an important issue in rail electromagnetic launches; it limits the performance of electromagnetic launch systems. In launch progresses, wear on the contact surface of armature significantly affects the contact surface morphology and armature structure. Studying wear, contact resistance, and sliding friction coefficient of the contact surface between the armature and the rail is important to understand and suppress transitions. In this paper, specially designed armatures, which make the wear on armature contact surface all melt wear, are used in rail launch experiments, to measure the wear rate of melt wear and observe how it is affect by loading. In the experimental results, average wear rate is represented by the average thickness of aluminum debris left on the rails: the average wear rate is within 0.6-2 mm/m and the average debris thickness is in a range of 3-10 μm . Based on the idea that melt wearing is the main mechanism, the heat balance of contact surface is analyzed. It is concluded that melt wear absorbs much of the heat generated in the surface, and the remainder goes into the rails. Equations based on this heat balance based are then derived to establish relationship among melt wear, launch parameters, and material parameters. According to the equations and the experimental results, the contact resistance of armatures with 80 mm2 contact areas is 2.56 μΩ, the contact resistance of armatures with 50 mm2 contact areas is 4.09 μΩ and the sliding friction coefficient is 0.11.

Optimizing study on the concave arc surfaced C-shaped armature with medium and small caliber

Previous studies on solid armatures show that in a railgun system, concave arc surfaced C-shaped armature (ASCA) can improve the contact pressure and current distribution at the armature/rail (A/R) interface. However, concrete design or parameter study of the concave ASCA is rarely mentioned. In fact, besides the basic structural parameters for conventional C-shaped armatures, there are two more key structural parameters for concave ASCA, namely the radius (r) and the central angle (θ) of their surface arc. In this paper, three matching models of concave armature contacting with corresponding rail structure are discussed and compared, and consequently the best structure pattern of the contact is presented. Meanwhile, the radius and the central angle of the arc in the ASCA are proposed and analyzed. With a fixed railgun caliber and minimum thickness of armature trailing edge, the optimal θ and r are determined according to the current distribution obtained in simulation. The concave ASCAs for square-caliber railgun of 20 mm, 30 mm, 40 mm and 50mm calibers are discussed, and their optimal structural parameters are presented respectively.