http://worldcat.org/entity/work/id/28392381

Five Year Ground Exposure of Composite Materials Used on the Bell Model 206L Flight Service Evaluation

During the past ten years, NASA has sponsored programs to build a data base and establish confidence in the long-term durability of advanced composite materials. Flight service experience is being obtained on primary and secondary structural components installed on commercial aircraft and from material specimens exposed at different locations. Although commercial aircraft and helicopters may fly in the same environment the behavior of composite materials on each vehicle may differ substantially. Most of the projected usage for composites in helicopter fuselage is Kevlar-49/epoxy with selective reinforcement of graphite/epoxy using 250 F curing epoxies. Most commercial aircraft are using 350 F cure graphite/epoxy systems with very little use of Kevlar/epoxy. Considering only the effects of moisture, materials in the minimum gage structure in most helicopter fuselage would reach equilibrium moisture content in a short time whereas the heavier gage structure on a commercial aircraft could take months to reach an equilibrium condition.

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