| Institution: | 1. National Institute of Aerospace, Hampton, VA 23666, USA;2. Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, VA 23681, USA;3. Durability, Damage Tolerance and Reliability Branch, NASA Langley Research Center, Hampton, VA 23681, USA;4. Structural Dynamics Branch, NASA Langley Research Center, Hampton, VA 23681, USA;5. NASA Langley Student Intern, University of Puerto Rico, Mayagüez 00682, Puerto Rico;6. NASA Langley Student Intern, North Carolina A&T State University, Greensboro, NC 27405, USA;7. NASA Langley Student Intern, Iowa State University, Ames, IA 50011, USA;8. NASA Langley Student Intern, Germanna Community College, Fredericksburg, VA 22408, USA;9. NASA Langley Student Intern, Princeton University, Princeton, NJ 08544, USA |
| Abstract: | Deployable space structures are being built from thin-walled fiber-reinforced polymer composite materials due to their high specific strength, high specific stiffness, and designed bistability. However, the inherent viscoelastic behavior of the resin matrix can cause dimensional instability when the composite is stored under strain. The extended time of stowage between assembly and deployment in space can result in performance degradation and in the worst case, mission failure. In this study, the viscoelastic properties of candidate commercial polymers consisting of difunctional and tetrafunctional epoxies and thermoplastic and thermosetting polyimides were evaluated for deployable boom structures of solar sails. Stress relaxation master curves of the candidate polymers were used to predict the relaxation that would occur in 1 year at room temperature under relatively low strains of about 0.1%. A bismaleimide (BMI) showed less stress relaxation (about 20%) than the baseline novolac epoxy (about 50%). Carbon fiber composites fabricated with the BMI resin showed a 44% improvement in resistance to relaxation compared to the baseline epoxy composite. |
