High Shear Strain Characterization of Plain Weave Fiber Reinforced Lamina

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 due to traditional mechanical systems typically required to deploy. One challenge to using such a structure is the high deployment accelerations that could potentially cause damage to the onboard payload if not managed properly. A solution to damp these deployments, while not sacrificing the performance benefits gained, is highly sought after within the aerospace community. The research presented herein suggests a method of passively damping deployments through means of tailoring the matrix constituent of composite materials typically used in fabrication of these strain energy deployed structural members. An optimal composite laminate for such members is described to include discrete elastic and viscoelastic plies. It has been identified that a pure shear stress state 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 structural damping while still preserving the deployment torque required for successful deployment. These factors lead to the design of a custom combined loading Picture Frame Shear (PFS) fixture 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 current plain weave materials of interest. Various load cases including variable displacement rates, variations in matrix constituents and early viscoelastic stress relaxation behavior were observed. Another interest to the aerospace community is fine tuning computationalnumerical techniques for simulating the viscoelastic behavior of orthotropic composite materials. It is desirable to employ methods that are easy and readily available to any interested party; not proprietary to a certain group. Techniques detailed include the method of coincident shell modeling; a method that shows promise in utilizing the natural capabilities of Abaqus CAE to model orthotropic-viscoelasticity. One may potentially leverage these modeling techniques, coupled with viscoelastic data collected from testing, to accurately simulate the response of a strain energy deployed structure, from stowage to deployment