Dynamic Response of Interior Ballistic Process and Rail Stress in Electromagnetic Rail Launcher

The dynamic response of interior ballistic process in an electromagnetic (EM) rail launcher (EMRL) directly affect the stress concentration of the rails and the launch performance of the projectile. By simplifying the rail as a Bernoulli-Euler beam fixed on the elastic support under the action of moving loads and acquiring the equivalent stiffness of the elastic support through a static EM-structural coupled model, the critical velocity of the EMRL is captured. Also, the hybrid finite-element/boundary-element method is used to establish a coupled EM-structural-motion model to derive the dynamic contact force between the armature and the rail as well as the stress distribution of the rails. Finally, the measuring data of fiber Bragg grating strain sensors fixed on the back of the rails are used to verify the stress concentration of the rails and analyze the stability of the projectile in the bore. For the typical 30 mm × 30 mm rectangular caliber launcher whose critical velocity is less than muzzle velocity, analysis and test results show that the EM extrusion force of the C-type armature exerted on the rail reaches the peak value at the beginning of the flat-top stage and gradually decreases as time goes on; the stress waves aroused by armature passing are easily resonant with the reflected stress waves in the rail in the high-speed stage of the armature, in which the stresses of rails are the severest, and the stress concentration level is about 2.44 times that in the initial low-speed stage; when the armature operates in the high-speed stage, there will be a vibration phenomenon which will lead to the asymmetry of loads on the upper and lower rails. These results have guiding significance to design the EMRL.