Deformation and Fracture of Resin Matrix Composites in Combined Stress States*

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Abstract
The analytical prediction of elastic constants and strengths in highly anisotropic composites is complex and always requires experimental verifi cation. This paper describes a study of the room-temperature mechanical characterization of high performance reinforced-resin composite materials. The composites were fabricated from three high strength filaments: Union Carbide's graphite fibers, Thornel 75S and Thornel 400 and duPont's organic fiber, Kevlar 49. The matrix was a filament-winding epoxy resin, Dow Chemical DER-332 room-temperature cured with Jeffamine T-403. Test specimens were thin-walled, cylindrical tubes fabricated with unidirec tional (90° or hoop wound) or quasi-isotropic [±30/90] S filament orienta tions. Specimens were tested in uniaxial and biaxial tension; axial loads were applied with an electrohydraulic testing machine and circumferential loads by internal pressurization. Deformations were monitored with strain gages. Data from uniaxial tests and from the literature provided the elastic properties and strengths of the unidirectional composite. The stiffness data were used to calculate, from lamination theory, the macroscopic elastic stiffnesses of the quasi-isotropic tubes which were in good agreement with experimental values. Strength data are compared to four empirical strength criteria.

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