1972-02-01

Fabrication and Analysis of Tetra-Core: A Layered Anisotropic Fiber Composite 720343

Tetra-Core is the name given to a fiber composite-material developed by the U.S. Army Aviation Materiel Laboratory, Fort Eustis, Va. This report discloses the initial studies conducted at the University of Kansas on Tetra-Core, including fabrication methods, analytical strength analyses, and experimental test results.
The Tetra-Core composite is formed by stacking oriented, spaced-fiber lamina in a repeating -60, 0, +60 deg pattern. Layers are offset slightly as the stacking occurs to produce a tetrahedrally shaped element.
An improved fabrication loom was conceived and tested. The loom concept is predicated on the fact that the intersection of two planes is a straight line. In the case of Tetra-Core, planes are formed by the buildup of lamina, intersecting to produce tetrahedrally shaped elements. The straight lines formed at these intersections are at an angle of 35 deg 15 min from the vertical. This sloped-wall loom concept provides for more positive fiber placement, higher fiber density, and greater flexibility than afforded by the first methods of Tetra-Core fabrication. This loom concept can be automated to produce either individual panels or a continuous sheet of Tetra-Core. Patent applications have been filed.
Tetra-Core is an orthotropic material that falls into the special category of quasi-isotropic fiber composites. Three strength analyses, based on the macroscopic properties have been conducted: netting analysis, layered anisotropic stringer analysis, and layered anisotropic lamina analysis. Results of all three analyses compare favorably.
An experimental test program was conducted to determine the coefficients of the compliance and stiffness matrices. Four elastic properties were measured: Young's modulus in the 1 and 2 directions, in-plane shear modulus in the 1-2 direction, and Poisson's ratio in the 1-2 direction.

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