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Self-Healing Technology for Gas Retention Structures ... - Team-Logic

Self-Healing Technology for Gas Retention Structures ... - Team-Logic

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microencapsulated healing agent. Expansion of thefoam from a compressed state would augment flow ofthe gel and would deliver the foaming reactant to thepenetration site. Use of a healing agent in combinationwith the foam would create a more permanent seal thanfoam alone.A final hybrid concept is the use of shape memorypolymers in a carrier solution or gel. Fibers impregnatedwith a shape memory polymer (SMP) are cured in the flatthen tightly coiled and dispersed in a carrier solutionencapsulated between bladder barrier layers. Breach ofthe bladder would expose the SMP to oxygen or waterthat would trigger the return to the flat state. In the flatstate, the fibers would mechanically “clog” the void. Themixture could be tailored by altering fiber length, degreeof coiling, and percent SMP loading to optimizeapplications <strong>for</strong> different areas. In addition, secondarybenefits could be realized by use of materials thatimprove thermal or radiation protection.CONCEPT TRADESTrade studies were conducted to downselect concepts<strong>for</strong> further research. The requirements discussed abovewere weighted according to their perceived importance<strong>for</strong> the self-healing layer of a flexible inflatable structure.In general, aerial density, ability to function with all threattypes (slow, fast, hole, slit, etc.), material safety to crew,and permanence of the seal were among thoserequirements weighted the highest. Fourteen specificconcepts were then ranked as to their estimated ability tomeet these requirements. Trades were considered <strong>for</strong>specific inflatable applications. Requirements areweighted differently and concepts are ranked differently<strong>for</strong> a space suit than <strong>for</strong> a habitat. In addition to thetrade studies, feasibility of the top ranking concepts wasdetermined through technology review and evaluations ofpreliminary configurations. The trade study andfeasibility review suggested that chemical reactants, bothmicroencapsulated and macroencapsulated, close cellfoam mechanical and hybrid solutions, and viscoelasticgels should be pursued.macroencapsulated two part chemical reactant wasproduced and tested. Microcapsules were investigatedin conjunction with the University of Illinois at Urbana-Champaign because of their experience with self healingof rigid composites using embedded microcapsules.Blank microcapsules were studied to evaluate size,loading, and survivability. Macroencapsulatedviscoelastic materials were fabricated both in 2000 underthe NRA and in 2005 during the In-Flex program.Several configurations have been fabricated andoptimized <strong>for</strong> viscosity and thickness.CLOSED CELL FOAMThree types of closed cell foam were laminated withbladder barrier films. Various thicknesses andcompression percentages were achieved. Initialscreening tests at 34.5 kPa (5 psi) with a 2mm punctureprobe demonstrated that complete healing is unlikelywithout an adjacent functional layer.A five layer compressed foam sample was constructedwith two layers of viscoelastic gel, 1.65 mm thick each,sandwiched between three layers of 3.18 mm thickpolyethylene closed cell foam. Puncture tests with both2 mm and 3 mm probes show rapid healing with onlybackground level pressure loss. Figure 11 shows results<strong>for</strong> the five layer self healing sample.SELF HEALING TEST METHODOLOGYFor the initial studies, ILC Dover had developed a testmethod that measures the time required to seal apressurized test fixture after a puncture probe penetratesthe specimen ply-up causing leakage. All specimenswere tested with a fabric restraint layer necessary toaccurately reflect the behavior of the bladder laminatewhen punctured. The puncture probe diameter andpressure could be varied. Tests were conducted atambient conditions. See Figure 10.RESEARCH RESULTSFigure 10. Pressurized <strong>Self</strong>-<strong>Healing</strong> Test FixtureFour self-healing concepts were pursued to differentextents. Several configurations of closed cell foam werefabricated and tested. One configuration of a

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