Solid rocket motor cases for advanced tactical missile systems use lightweight, high strength carbon fiber reinforced composite materials to achieve high propellant mass fractions and increase overall propulsion system efficiency. In order to meet the challenging performance goals for next-generation missile systems, significant improvements in the performance of the motor case materials are desired. Recent advances in the development of carbon nanotube (CNT) reinforced composite materials provide an opportunity for achieving improved composite strength and multifunctional performance capability for advanced lightweight composite missile cases. While processes for producing relatively short lengths of CNT reinforced carbon fibers have been previously demonstrated on a laboratory scale, further research and development is needed to scale-up such processes to achieve production of significant lengths of CNT reinforced fibers that are suitable for incorporation into continuous fiber reinforced composite structures such as filament wound composite motor cases.Under a U.S. Army Small Business Innovation Research (SBIR) program, Materials Sciences Corporation (MSC) and Drexel University Fibrous Materials Research Laboratory (DU/FMRL) are collaborating on the development and characterization of CNT reinforced fibers produced via a modified electrospinning process. The ultimate goal of this research is to develop and demonstrate a robust, scaleable process for continuous production of CNT reinforced carbon fibers having significantly greater strength than commercially available carbon fibers (e.g., IM7, T1000) currently used in high performance filament wound composite structures. An integrated manufacturing, analysis and experimentation approach is being carried out to evaluate the influence of different CNT concentrations and process conditions on delivered fiber strength.As part of the Phase I research, single wall nanotube (SWNT) and multiwall nanotube (MWNT) reinforced PAN fibers were synthesized via a drum electrospinning process and tensile testing was performed to compare the mechanical properties and processing characteristics for electrospun yarns having different concentrations of SWNT and MWNT reinforcement. Characterization via Raman spectroscopy, Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM) was performed to assess SWNT and MWNT alignment and dispersion. A simplified analytical model based on proven micromechanics was also developed as part of this research for predicting the elastic properties of CNT reinforced fibers with different SWNT and MWNT concentrations. This model is intended to serve as a first level approximation tool for supporting the design and evaluation of CNT reinforced carbon fibers with different types and concentrations of CNT loading.
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