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AEROSPACE EQUIPMENT AND INSTRUMENT STRUCTURE 47 Gay C. Krumweide and Eddy A. Derby 47.1 INTRODUCTION It is necessary to discuss GFRP (graphite fiber reinforced plastics) thoroughly in order to understand the importance of composites in the manufacture of aerospace equipment and instrument structures. Before composite mate- rials such as GFRP became viable candidate materials for aerospace primary structures, or even for sporting equipment, they were first used for aerospace equipment and instrument structures. Because composites exhibited both unique and superior properties, designers were willing to pay the prevailing high prices to achieve their design goals. For space hard- ware, where a pound of weight saved was worth thousands of dollars, designers were motivated to characterize composite materials suitable to their applications. Understandably, composites for primary and secondary struc- ture (e.g. launch vehicles, aircraft frames, wing spars and skins, etc.) were a 'hard sell', and temperature extremes were too severe for 'thermosetting' GFRP to be used on missiles. The quantity of GFRP required for a particular piece of aerospace equipment or instrument structure was usually minimal, so relative costs were low, and composite materials' supe- rior properties compared to heavy Invar, or high coefficient of thermal expansion (CTE) Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 aluminum, or very expensive beryllium fur- ther justified the material selection. Consequently, numerous mirror bezels, telescopes, optical benches and reflectors were designed and built from GFRP in the early 1970s. As a result of these efforts, today more and more structures are being fabricated from GFRP materials, principally because specific materials matching specific property require- ments are now available. Although GFRP has dominated composite materials applications, DuPont's Kevlar-49 has been found to be ideal for antenna reflec- tors because of its extremely light weight and RF transparency. Many communication satel- lites utilize this type of Kevlar reflector, such as the SatCom-F, Telstar, ANIK-E, SpaceNET, and Superbird SCS (Fig. 47.1). Fig. 47.1 SuDerbird SCS Kevlar dual-shell reflector.
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Historical perspective and progress 1005 For aerospace equipment and instrument structures, generally, thermoplastic versions of GFRP have not seen as much application as the thermosets due to high investment costs in tooling and facilities. Considering the rela- tively small quantities that are usually bought, thermoplastic applications are not often cost effective. Also, the required high temperature cures subject the laminate to microcracking instabilities. Metal matrix composite applications have
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