SYMPOSIA PAPER Published: 01 January 1972

Evaluation of Unidirectional Glass-Graphite Fiber/Epoxy Resin Composites


As an all-fiberglass reinforcement is progressively replaced by graphite fiber, the longitudinal composite fracture stress and strain decrease rapidly for all loading modes except shear, accompanied by a substantial increase in the tensile and compressive stiffness. Conversely, upon introducing some fiberglass into a graphite composite, its strength declines in proportion to the decrease in graphite fiber content. The maximum torsional shear stress is approximately 8 ksi for all combinations of glass and graphite. Most of the transverse mechanical properties decrease linearly upon progressive replacement of the fiberglass by graphite. The transverse torsional shear properties are about 20 percent lower than the longitudinal ones.

The magnitude of the flexural modulus, which depends not only on the graphite content but even more so on the distance of the graphitic plies from the center plane of the laminate, may be calculated by means of the existing theory of bidirectional laminates. It is concluded that the large increase in composite stiffness upon addition of a small amount of oriented graphite fiber is the most salient characteristic of glass-graphite hybridization.

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Kalnin, IL
Celanese Research Co., Summit, N. J.
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Developed by Committee: D30
Pages: 551–563
DOI: 10.1520/STP27769S
ISBN-EB: 978-0-8031-4606-8
ISBN-13: 978-0-8031-0134-0