Analysis of Cumulative Damage Failure for Driving Coil in Coilgun

Abstract

In the launching experiment of a coilgun, the driving coil, including winding and shielding, is always destroyed after several launching times. To improve the service life of a coilgun, the cumulative damage mechanism of the shielding and the fatigue life assessment of the winding are investigated in this paper. First, the electromagnetic field of a coilgun, considering the kinematic influence, is simulated using the field-circuit time-stepping finite-element method. Afterward, the result of the electromagnetic force (EMF) is applied to the structural field as the load to calculate the stress and displacement distributions. In addition, using the static strength assessment, it is determined whether there is a defect in the materials. For the shielding made of a nonmetallic material, if the stress is greater than the ultimate tensile strength (UTS), cracks must emerge. For the winding made of a metallic material, even though the stress is less than UTS, the fatigue failures still occur with the application of repetitive loads. The analysis results of the cumulative failure show that the shielding is destroyed after several launching times. According to the stress-life characteristics (expressed as S-N curves) of the winding material and the analysis results of fatigue, the service life of the winding is much longer than that of the shielding. Finally, a type of insulating material with higher UTS is proposed to improve the service life of the coilgun.