Sai Tan

The electromagnetic rail launcher (EMRL) G10 insulator is prone to delamination failure during launch, which affects the life of EMRL. In order to explore the reasons for the delamination failure of the insulator, the EMRL eddy current field calculation model is constructed firstly, and then the transient electromagnetic (EM) force distributions of the armature and the rail are calculated and verified by the combination of finite element and experiment. Finally, the EM force is used as the input, and combined with bolt pretightening force, friction force, and impact force, the multitype mechanical coupling solution is carried out. The simulation indicates that stress concentration occurs at the inner chamfer of the insulator end. The interlaminar shear stress exceeding the ultimate strength of the material and the fatigue damage caused by stress cyclic loading are the main reasons for the delamination failure of the insulator. The delamination crack is parallel to the direction of the glass fiber layer, and the interlaminar shear force peels off the upper fiber from the resin, forming a through-type delamination damage of the test prototype insulator. Optimizing the structure or material to improve the shear resistance of the insulator can prolong the life of the insulator.

Armature is the key component of electromagnetic launcher (EML), but in the process of launching, its working environment is bad and the surface is seriously worn. Excessive wear will seriously weaken the mechanical properties of armature and affect the launching safety. Therefore, it is necessary to deal with the surface state of armature to reduce wear and improve the performance of armature. First, the properties of the candidate materials are analyzed. According to the principle of maximum current carrying capacity per unit mass, aluminum is the most suitable material for armature manufacturing. At the same time, the defects of material selection in single material system are pointed out. Second, based on the above problems, the surface coating design scheme is proposed. From the point of view of material melting point and hardness, it is proposed that tungsten can be used as the coating material for armature surface. According to the wear amount of armature tail under launch condition, the coating shape and thickness are designed. The best coating forming process is determined by calculating the shear force between coating and substrate; finally, the effect of the coating on the electric contact performance, system efficiency, and projectile gouging threshold velocity is analyzed. The results show that the maximum shear force between the coating and the substrate is above 171 MPa under the launching condition, and the laser cladding technology can meet the process requirements. After coating treatment, the contact resistance between the armature and rail (AR) increases by 6%, which has little effect on the system efficiency. Although it will affect the projectile gouging threshold velocity, it can be improved by modifying the tungsten coating or rail surface treatment. The analysis results are of great significance to reduce the armature wear, improve the contact performance between the AR, and improve the launch safety.

Using the dynamic panel threshold model and data of 41 countries along “the Belt and Road” from 2003 to 2017, this paper empirically tests the impact of China’s outward foreign direct investment (OFDI) on technological progress of these countries and its threshold effect. The results show that OFDI exerts different effects on technological progress of countries along the route within different thresholds range. Based on the classification of different country types, when FD is below than the threshold value, China’s OFDI in transitional and developing countries has no significant impact on their technological progress, while developed countries have a more significant positive correlation; other, when FD is higher than the threshold value, both types of countries are significantly positively correlated, and the coefficient is greater in developed countries than in transitional and developing countries. In further research, it is divided into two periods based on the time node of 2013. Request access from your librarian to read this article's full text.

Arc ignition technology is one of the most feasible strategies for releasing the residual energy of electromagnetic rail launch (EMRL). The muzzle arc characteristic must be considered in the design of arc ignition devices, because it is a main factor affecting the intermediate ballistic trajectory. Based on the theory of magnetohydrodynamics (MHDs), this work has made numerical simulation of muzzle arc and analyzed the temperature field, electromagnetic (EM) field, and flow field of the muzzle arc at different stages. The results show that the temperature is the highest, the EM field is the most intensive, and the flow is the strongest at the initial stage of the muzzle arc. The optimization of arc ignition device is pointed out to be reducing the current transfer time to improve the temperature, EM, and flow environments of the launcher, projectile, and guidance device.

According to the characteristics of an actual electromagnetic rail launcher (EMRL), this paper points out defects in the traditional dynamic response model of EMRL, proposes an improved dynamic response model, and analyzes its dynamic and stopping response characteristics. On this basis, it present a fast and accurate numerical calculation method for three-dimensional (3-D) transient electromagnetic “EM” force of the EMRL and an order-reduced model of EMRL dynamic response. Furthermore, a second development of commercial software leads to the establishment of an interior ballistic simulation model (IBSM) with EM- structural coupling. The model is used to analyze the interior ballistic characteristics of the EMRL under sequential discharge and continuous firing. The finding is that the dynamic response of the first launching rail will cause a deformation in the second launching rail, in which a greater fluctuation happens. When the time interval between successive launches reaches 1.0 s, the deformation of the second launching rail will no longer be affected by the dynamic response of the first launching rail.

Based on the characteristics of the actual electromagnetic rail launcher (EMRL), the defects of the traditional dynamic response model of EMRL are pointed out and an improved dynamic response model of the EMRL is proposed. The dynamic response characteristics and stop response characteristics of the EMRL improved model are studied. A fast and accurate numerical calculation method for three-dimensional transient electromagnetic （EM） force of EMRL and a step-down method for high-order partial differential control equation of the EMRL dynamic response are proposed. Furthermore, the interior ballistic simulation model (IBSM) of EM and structural coupling of EMRL is established through self-programming. This model is used to study the interior ballistic characteristics of the EMRL during the continuous launching process under the condition of sequential discharge. It is found that the first dynamic response of the EMRL will lead to a greater fluctuation in the second rail deformation. When the time interval between successive launches reaches 1.0 s, the deformation of the second launching rail will no longer be affected by the first launching dynamic response of EMRL

To solve the sliding electrical contact problems, it is necessary to take into account the interface conditions of magnetic field intensity H and magnetic flux density B and also those of electric field strength E and current density J when the armature is in contact with the rail. As the interface condition of E is not implicitly included in the simplified weak forms of governing equations, the discontinuous electric scalar potential φ is used in the nodal element, the continuous φ in the edge elements, and meanwhile v · A = 0 serves as a gauge condition by tree technique to deal with the interface condition of E. The penalty method is adopted to set up the coupling equations for the interface conditions and the boundary conditions of current inlet surface. The use of the above methods leads to the establishment of the finite-element equations for the motion in the conditions of the nodal and edge elements and to the construction of the corresponding numerical model. The comparison of the result obtained from the model with the result of calculating the eddy current of the 2-D or 3-D electromagnetic rail launchers proves the proposed methods to be feasible and effective.