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Mechanical Properties and Fatigue Behavior of Unitized Composite Airframe Structures at Elevated Temperature

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Technical Report

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AFIT WPAFB United States

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The tension-tension fatigue behavior of a newly developed unitized composite material system was investigated. The unitized composite consisted of a polymer matrix composite PMC co-cured with a ceramic matrix composite CMC. The PMC portion consisted of an NRPE high-temperature polyimide matrix reinforced with carbon fibers woven in an eight harness satin weave 8HSW. The CMC layer is a single-ply non-crimp 3D orthogonal weave composite consisting of ceramic matrix reinforced with glass fibers. In order to assess the performance and suitability of this composite for use in aerospace components designed to contain high-temperature environments, mechanical tests were performed under temperature conditions simulating the actual operating conditions. In all elevated temperature tests the CMC side of the test specimen was at 329 deg C while the PMC side was exposed to ambient laboratory air. The tensile properties were measured at elevated temperature for both on-axis 090 and off-axis -45 fiber orientations. Tension-tension fatigue tests were conducted at elevated temperature at a frequency of 1.0 Hz with a ratio of minimum stress to maximum stress of R 0.05.

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