Microbuckling of Unidirectional Composites
Technical rept. Sep 1969-May 1971
MCDONNELL DOUGLAS ASTRONAUTICS CO-HB HUNTINGTON BEACH CA
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A review is presented of the theories for microbuckling of unidirectional composites subjected to compressive loading parallel to the fiber direction. The results predicted by the various theories are compared. Large differences in predicted results are shown to exist for microbuckling in the extension mode. In the case of microbuckling in the shear mode, the various theories predict the same results. Nearly perfect as compared to actual composites model composites consisting of circular rods in an epoxy matrix are employed to obtain experimental data on failure of unidirectional composites subjected to compressive loading. The constituent materials used in preparation of model composites are characterized for their mechanical properties. Two types of reinforcement materials, steel and graphite, and four different resins, urethane and epoxy, are used in the experimental phase of the program. Most of the tests are performed on composite specimens consisting of nine rods imbedded in a resin. The nominal volume fraction of the reinforcement is 50 percent. The test variables are specimen geometry, fiber diameter, and properties of constituents. In the case of low-modulus resin composites, the failures are by microbuckling in the shear mode. For intermediate-modulus resin composites, the failures are by inelastic microbuckling in the case of ductile reinforcement and by transverse tension in the case of brittle reinforcement. In the case of high- modulus resin composites, the failure is by compressive failure of the reinforcement. The experimental results for specimens that failed by microbuckling are shown to be higher.
- Laminates and Composite Materials