Biaxial Characterization of Carbon/Epoxy Unidirectional and Quasi-Isotropic Composites

An experimental test program is described in which biaxial failure envelopes were generated for unidirectional [0]₈ and quasi-isotropic [0/+45/90/−45]_s specimens made from Toray T800HY/3910 graphite/epoxy. Data was generated in all four quadrants of the biaxial stress plane. Fiber direction failure strengths were also found by uniaxial tension and compression tests. The quasi-isotropic compressive failure strengths are approximately 50 percent of the tensile strengths. Failure strengths in the tension-tension quadrant were essentially the same as previous tubular specimen tests made of a similar material (Swanson and Christoforou, 1986) indicating that free-edge and stress concentration effects may not preclude using flat cruciform specimens to generate biaxial failure data.