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An accelerated study has been performed to determine the feasibility of applying Hughes Aircraft Company's patented In Situ Fiberization (ISF) process to the fabrication of: (1) improved Strain Isolation Pads (SIPs) for the Space Shuttle, and (2) improved graphite/epoxy (GR/EP) composites. The ISF process involves the formation of interconnected polymer fiber networks by agitation of dilute polymer solutions under controlled conditions. Most previous work was performed using aliphatic hydrocarbon polymers which have limited high temperature capabilities. In Task 1 of the program, attempts were made to advance ISF technology by fiberization of high temperature polymers which would be suitable for SIP use. Progress was made toward that objective with the successful fiberization of polychlorotrifluoroethylene, a relatively high melting polymer. Attempts to In Situ Fiberize polymers with even greater thermal stability were not successful. The latter difficulty is presumed to derive from poor solubility, low molecular weight, and/or high chain stiffness, all caused by the presence of aromaticity in the backbone of such materials. During Task 2, two dimensional arrays of graphite fiber were interconnected with polypropylene In Situ Fibers. Following epoxy resin impregnation and lamination of the arrays into panels, mechanical property tests were performed to gauge the effectiveness of the In Situ Fibers for improvement in intralaminar shear strength, and hence fracture toughness. Test results were generally, though not universally, unpromising. Poor performance is believed to reflect incomplete In Situ fiber/resin wetting, poor graphite fiber packing, and perhaps low In Situ Fiber moduli. (MM)

The feasibility of applying the in situ fiberization process to the fabrication of strain isolation pads (SIP) for the Space Shuttle and to the fabrication of graphite-epoxy composites was evaluated. The ISF process involves the formation of interconnected polymer fiber networks by agitation of dilute polymer solutions under controlled conditions. High temperature polymers suitable for SIP use were fiberized and a successful fiberization of polychloro trifluoroethylene, a relatively high melting polymer, was achieved. Attempts to fiberize polymers with greater thermal stability were unsuccessful, apparently due to characteristics caused by the presence of aromaticity in the backbone of such materials. Graphite-epoxy composites were fabricated by interconnecting two dimensional arrays of graphite fiber with polypropylene IS fibers with subsequent epoxy resin impregnation. Mechanical property tests were performed on laminated panels of this material to evaluate intralaminar and interlaminar shear strength, and thus fracture toughness. Test results were generally unpromising.