Failure Mechanics of Composites Subjected to Compressive Loading.
Technical rept. 15 Mar 71-1 May 72,
MCDONNELL DOUGLAS ASTRONAUTICS CO-WEST HUNTINGTON BEACH CALIF
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Theoretical and experimental studies are presented on compressive strength and filure modes of laminae-reinforced and fiber- reinforced composite models as well as on actual composites made of Thornel 5OS GRAPHITE FIBERS AND 828CL epoxy resin. The laminae reinforcement consisted of 6061-T6 aluminum strips. Three epoxy resins that were used in the models had Youngs moduli of approximately 2.5 ksi, 22 ksi, and 62 ksi. Existing two-dimensional theory, corrected for the influence of laminae end restraint, was found to show good correlation with test data. Similar experimental studies were also performed on compressive strength and failure modes of circular fiberrod reinforced composites. A NEW THEORY FOR THE COMPRESSIVE MICROBUCKLING STRENGTH OF CIRCULAR FIBER-REINFORCED COMPOSITES WAS DERIVED AND VERIFIED EXPERIMENTALLY. In both laminae and fiber- reinforced composites the compression failure was found to be caused by microbuckling in the case of composites made with low modulus resins. As the resin modulus increased, the failure mode changed to compression strength failure of the reinforcement. Actual graphite-epoxy composites, tested in compression, also were found to fail by compression strength failure rather than by microbuckling. Transverse tensile stresses induced in these composites by compression load applied in the fiber-direction were found to have a significant influence on the compressive strength. An approximate interaction equation coupling the axial compressive strength with transverse tensile strength was derived. The results predicted by the interaction equation show agreement with test data and provide an explanation for the low compressive strength of graphite-epoxy composites. Author, modified-PL
- Laminates and Composite Materials