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Textile Preforms for Carbon-Carbon
Frank K. Ko
Structural Geometry of 2-D Fabrics 78
Woven Fabrics 78
Knitted Fabrics 78
Braided Fabrics 80
Woven 3-D Fabrics 82
Orthogonal Nonwoven Fabrics 84
Knitted 3-D Fabrics 85
3-D Braided Fabrics 89
Textile preforms for carbon-carbon composites (CCC) are reviewed in this paper. From the structural geometry point of view, the various levels of fiber architecture are classified into linear, planar (2-D), and 3-D fibrous assemblies. The role of fiber architecture in the processing and strengthening of CCC is discussed. To provide a basis for the mechanistic analysis of CCC reinforced by textile structures, unit cell-based modeling methods are reviewed.
Textile preforming is the method of placing reinforcing fibers in a desired arrangement prior to formation of a composite structure. Starting with linear assemblies of fibers in continuous and/or discrete form, these micro-fibers can be organized into two-dimensional (2-D) and three-dimensional (3-D) structures by means of textile processes such as interlacing, intertwining, or interlooping. Properly selecting the geometry and the method of placement or geometric arrangement of the fibers can tailor the resulting structural performance of the composite. These fiber placement methods create textile preforms that possess a wide spectrum of pore geometries and pore distribution; a broad range of structural integrity and fiber volume fraction; and fiber orientation distribution as well as a wide selection of formed-shape and net-shape capabilities. In linear form, the carbon threads can serve as stitch yams for stitched structures. These linear structures also can be used as fasteners. Planar systems are suitable for skin structures, although 3-D structures find varying uses ranging from rocket nozzles to large-scale structural components for hypersonic vehicles.
Combining with high-performance fibers, matrices, and properly tailored fiber/matrix interfaces, fiber architecture promises to expand the design options for tough and reliable structural CCC. With an integrated network of structural cells in two- and three-dimensional arrangements, textile structures not only provide a mechanism for structural toughening of composites but also facilitate composite processes into net or near net-shape structural parts.
Classification of Preforms
On the basis of structural integrity and fiber linearity and continuity, fiber architecture can be classified into four categories: discrete, continuous, planar interlaced (2-D), and fully integrated (3-D) structures. In table I, the nature of the various levels of fiber architecture is summarized (ref. 1).
The first category of fiber architecture is a discrete fiber system, such as a whisker or fiber mat, which has no material continuity. The orientation of the fibers is difficult to control precisely, although some aligned discrete fiber systems