Assessment of Transition by FBG Strain Measurement of Rails in EM Launchers

Electromagnetic launch is a new type of technology characterized by high current, high magnetic field, and strong interaction inside the system. The extreme condition may lead to transition which causes damage to the bore. In this paper, experiments at the current ranging from 210 kA to 288 kA are carried out and 3 couples of Fiber Bragg Grating (FBG) are used to measure the strain on both rails. Muzzle voltages are recorded as well to analyze the transition in the launch process. To investigate the influence of the material hardness on the interaction of the armature/rail surface, one couple of the rails applied in experiments are H62 brass with a hardened coating whereas the others are bare H62 brass. The results show that the strain increases with the driving current before the transition and drops significantly when the transition occurs. The strain measurement provides an assessment of transition, combined with the muzzle voltage, it can not only determine when but also estimate where the transition occurs. Moreover, the hardened rail is more easily to cause transition than the conventional one, which means the threshold driving current is lower and the duration is longer.