High Shear Strain Characterization of Plain Weave Fiber Reinforced Lamina

Abstract

Strain energy driven deployable structures have recently become of high interest to the deployable space structures community. Made out of thin composite sections, these structures possess increased stiffness and stabilization while reducing payload masses significantly. The added capability of self-deploying provides additional benefit in reducing structural complexity. One challenge to using such a structure is the high deployment kinetic energy resulting from conservation of strain energy during stowage. At the end of deployment, excessive kinetic energy can damage the onboard payload through high shock loads. The research presented herein suggests that viscoelastic laminates can effectively dissipate energy during deployment and greatly reduce shock loads. One method to achieve this is tailoring the matrix constituent of the composite materials. An optimal laminate for such members is described to include discrete elastic and viscoelastic plies. It has been identified that a pure shear stress state is induced in the viscoelastic plies of typical cylindrical members (tape springs, slit tubes, etc.) when subjected to high shear strains. The intention is to key on this respective viscoelastic lamina and tailor it in a way that provides a sufficient amount of energy dissipation while still preserving the deployment torque and energy required for successful deployment. A custom combined loading Picture Frame Shear (PFS) fixture was designed to test plain weave composite lamina in high shear strain load cases similar to operational conditions. Before viscoelastic characterization can occur, the PFS fixture was tested using plain weave materials of interest. Material selection consisted of an IM10/PMTF7 carbon/epoxy plain weave lamina. Shear strain rate dependency was investigated in the form of variable load head displacement rate testing. Varying content levels of rubberized toughener matrix additive were examined.