Viscoelastic Behavior of Thin-Ply Composites for Deployable Structures

摘要

Thin-ply carbon fiber reinforced composite laminates have shown potential for improving performance of deployable structures for space applications due to their high mass efficiency, bending curvature, and deployed stiffness. Deployable structures made of thin-ply composites can be folded into a compact configuration for stowage and self-deploy to recover their initial, operational geometry in orbit. Since these structures rely on the stored strain energy for deployment, viscoelastic response of the composite is critical to the deployment reliability and accuracy. Previous experimental investigations have shown that stress relaxation of the polymer matrix during stowage could stall the deployment and reduce accuracy of the deployed shape. However, viscoelastic behavior of thin-ply composites has not been investigated sufficiently for analysis of designs for space applications. Furthermore, computational models that consider anisotropic relaxation behavior and experimental characterization methods of relaxation under high-curvature bending are not directly available. This paper investigates the viscoelastic response of thin-ply composites both computationally and experimentally. Although viscoelastic properties of a composite are inherited from its polymer matrix, the reinforcement fiber architectures also significantly influence relaxation behavior. To avoid the computational cost of directly modeling the micro-scale fiber geometry in large deployable structure simulations, this paper directly measures the moment relaxation and curvature variation over time using a special fixture for thin materials. The relaxation bending stiffness of the composite is represented by a Prony series. The measured relaxation bending stiffness is utilized in simulating the deployment of a composite plate after stowage. A recursive integration algorithm is adopted to reduce the computational cost of time-dependent analysis. It is shown that the moment on the composite plate relaxes over