Influence of the critical velocity on deformation of launcher components

This paper is related to the dynamics of hypervelocity electromagnetic launchers. A projectile accelerating along launcher rails may cross a range of critical velocities and induce structural resonance. As a result, the rails and other components exhibit increased displacements and stress that may affect launcher performance and lead to premature launcher failure. This work is a continuation of our previous studies of the critical velocity and resulting transient resonance that was performed for a notional hypervelocity launcher [Nechitailo NV, Lewis KB. Critical velocity for rails in hypervelocity launchers. In: Proceedings of the 2005 hypervelocity impact symposium. International Journal of Impact Engineering Dec. 2006; 33: 485–495; Lewis KB, Nechitailo NV. Transient resonance in hypervelocity launchers at critical velocities [Selected papers from the 13th Electromagnetic Launch Technology (EML) Symposium, Potsdam, Germany, May 22–25, 2006]. IEEE Transactions on Magnetics Jan. 2007; 43 (No. 1, Part II): 157–162 [1,2]]. Analytical models including Bernoulli–Euler model of a beam resting on an elastic foundation and the Timoshenko and Flügge tube models as well as finite element tools helped to better understand the transient resonant regimes in launcher components and offered insight on how to alter the launching device materials and geometry to reduce the critical-velocity effects. Analysis showed that the various components of a launcher can have different critical velocities and there is a possibility of enhanced group resonance in the assemblies. The resonance in the launcher assembly can be reduced by controlling the bending stiffness of the individual components. Finite element models were used to illustrate the influence of variations in materials of launcher components on the resulting critical velocities, intensity of the group resonance, and resulting maximum displacements and stress.