Neutrally stable behavior in fiber-reinforced composite tape springs

Thin cylindrical shells such as metallic storable tubular extendable members (STEM’s) and carpenter-tape springs have been used as deployable structural members since the early stages of space exploration. Typically these metallic STEM’s and tape springs have been elastically strained and held with some restraint in the packaged configuration. For deployment, either the restraint is released and the structure springs into its deployed configuration, or the structure is fed out using a motor. More recently, fiber-reinforced composites have been considered for these applications because of the mass efficiency of composites and the ability to tailor composites to exhibit behavior not seen with isotropic materials. Considered in this paper is a new type of neutrally stable tape spring that does not show an inclination to spring out to the fully extended configuration when partially rolled. Neutrally stable tape springs do not need to be constrained in the packaged state and deployment can be easily controlled with low-force, unobtrusive actuators. An analytical study is used to explore this form of neutral stability and to determine the necessary conditions for neutral stability. Those necessary conditions are confirmed by fabricating a series of composite tape springs. Finally, a simple experiment is performed to demonstrate that the deployment of the neutrally stable tape spring can be started and stopped at any point of deployment.