Engineering topics
Publications and source records attributed to Ledbetter, Frank E., III.
The utilization of composite materials in the Space Shuttle and Advanced Space Transportation Programs is reviewed. Topics include goals and challenges, descriptions of multi-generational launch vehicles, and an overview of composite materials research and technologies that support program objectives. A brief discussion of planned composite materials research and technology concludes the presentation.
The Access to Space Study identified the requirement for lightweight structures to achieve orbit with a single stage vehicle. The use of composite components partially fulfills that requirement. The purpose of this presentation is to review the technical challenges in the use of composite materials and processes for lines and ducts on next generation launch vehicles. This presentation will identify current requirements for space and missile system components; review the state of the art for existing system components; identify show stoppers to advancing the state of the art; identify technical issues that might limit the application of advanced materials; identify key materials that might provide a high payoff; and identify opportunities for joint partnerships to overcome these multiple technical challenges.
A method for boring well defined holes in a composite material such as graphite/epoxy is discussed. A slurry of silicon carbide powder and water is projected onto a work area of the composite material in which a hole is to be bored with a conventional drill bit. The silicon carbide powder and water slurry allow the drill bit, while experiencing only normal wear, to bore smooth, cylindrical holes in the composite material.
Improvement upon recommended procedures saves time and expense. Autoclave molding in vacuum bag cleaner if adhesive-backed covering placed around caul plate as well as on mold plate. Covering easy to remove after curing and leaves caul plate free of resin deposits.
Efficient process aids production of silicon carbide/silicon nitride fibers. Fibers 10 to the sixth power times as electrically resistive as carbon fibers having similar mechanical properties; promising replacements for carbon fibers in composite materials in which high conductivity poses hazard.
Corroded fasteners taken apart more easily. Lubricating holes bored to thread from three of flats. Holes facilitate application of penetrating oil to help loosen nut when rusted onto bolt. Holes make it possible to apply lubricants and rust removers directly to more of thread than otherwise reachable.
Fixture for flexural tests of glass-fiber-reinforced epoxy rods 1/4 in. (6.4 mm) in diameter easy to fabricate. Little machining done by relatively unskilled. Flexural-test fixture allows bending stress applied to specimen rod while holding rod securely. Dowel pins, blocks, and plate that make up fixture joined by adhesive.
Slurry of silicon carbide powder in water fed onto bit while drilling. Slurry contains about 60 percent silicon carbide by weight. Slurry recirculated by low-power pump. With slurry, dull tools cut as fast as, or faster than, sharp ones. Holes drilled rapidly and efficiently regardless of ply orientation; whether unidirectional, quasi-isotropic symmetrical, or cross-ply.
Orientation of fibers in graphite-fiber-reinforced plastics easily determined with new method. Materials scientists thus ensure that fibers, usually not visible after graphite/plastic composite has been cured, properly oriented in test specimens and test results accurately represent the characteristics of composite. Method based on fact that continuous graphite fibers embeded in cured polymer matrix actually parallel conductors. Thus, resistance measured across laminate is at minimum when probes of ohmmeter connected to opposite ends of fibers.