Stowage and Deployment of a Viscoelastic Orthotropic Carbon-Fiber Composite Tape Spring

Strain energy deployable composite structures offer spacecraft designs reduced payload and compact volume. One of the greatest advantages presented by deployable composite structures arises from their ability to maintain high-strain configurations for extended periods of stowage. Because of the viscoelastic nature of the polymer matrix, the stowed composite structure undergoes stress relaxation that results in a decrease of the energy available for deployment. This paper focuses on a three-layered (+/- 45 deg plain weave/0 deg unidirectional/ +/- 45 deg plain weave) carbon-fiber-reinforced polymer composite deployable structure, known as a tape spring. Stress relaxation testing was used to define the viscoelastic behavior of the epoxy matrix. Experimental long-term stowage and deployment testing was performed on the (+/- 45/0/ +/- 45 deg) tape spring specimens. Finite element simulations considering viscoelastic, orthotropic stress relaxation were developed to predict the effects of stress relaxation on the deployment of a (+/- 45/0/ +/- 45 deg) tape spring.