CARBON-FIBER ARCHITECTURE

This section covers PAN, pitch and cellulose based carbon fibers, but does not include vapor grown carbon fibers, although such fibers can be spun into staple yarns and converted to chopped fiber. A classification designating the various levels of carbon fiber architecture is outlined in Figure 21.1. 

An ample selection of carbon-fiber architecture is now available as a result of recent advances in sizing and weaving technology. However, a carbon fiber is inherently brittle and cannot be bent over a small radius without breaking. Consequently, the use of complicated weaving procedures such as knitting and braiding is limited. 

Carbon-fiber architecture can be divided into four categories discrete, linear (continuous), laminar (two-dimensioneil weave), and integrated (three-dimensional weave). The characteristics of each category are shown in Table 9.1.W... 

Carbon-Fiber Network. Rayon-based carbon fibers were used in the early development of carbon-carbon and are still used as carbon felt. PAN-based fibers are now used extensively and pitch-based fibers are under investigation. jhe selection of the carbon-fiber architecture is determined by the application and include felt, short (chopped) fibers, continuous filament such as small-tow T-300 fiber, filament winding or tape-layup, and 3D structures (see Sec. 2.0 above). The effect of carbon-fiber type and architecture is reviewed in Refs. 22 and 23. The effect of carbon-fiber... 

Carbon-carbon composites made with the functionally graded fiber arrangement technique present the opportunity to tailor thermo-physical properties into carbon materials. In this paper, the changing of the fiber architecture is the method for FGM. Fibers or matrices are other options for FGM. This functionally graded fiber arrangement technique can be applied to a wide range of materials processing. 

Carbon fibers reviewed in this chapter are continuous multifilament yams, fabricated from organic polymer precursors whose molecular architectures prefigure, in a more or less pronounced manner, the hexagonal structure of the graphene layers [3j. The typical process consists of three stages (1) fabrication of the solid precursor fiber, (2) orientation and stabilization of the precursor fiber, and (3) carbonization of the precursor fiber. 

The precursor fiber type for reinforcing the carbon matrix can be an oxidized PAN fiber (opf), or either a PAN or pitch based carbon fiber. In some instances, for special applications, such as the Shuttle, a cellulose based carbon fiber is used. The reinforcements can be unidirectional have a random chopped fiber presentation as in a felt format a woven product from continuous fiber presented in a 2D, 3D, or in a Multi-D format (Section 21.1), or a non-woven carbon fiber. The chosen fiber architecture is most important for a given application and Lei et al [4] describe how, for example, 3-D braiding can be applied to carbon-carbon composites. One of the early forms of near net shape reinforcement used for carbon-carbon aircraft brakes was based on a weft knitted 3-D fabric made by the Pressure Foot process (Figure 14.1). 

Fiber-reinforced plastics are the most successful composite materials. In spite of the poor load-bearing ability of polymeric materials, excellent mechanical properties are achieved by using fiber architectures of glass and carbon hbers in a manner similar to the reinforcement of concrete with steel rods and frames. For example, toughened polymeric materials with dispersed rubber particles in a polymer matrix exhibit high fracture energy. In composite materials, introduction of secondary materials into the matrix can improve the mechanical properties considerably. 

Since the oxidation resistance of SiC is much better than that of carbon, SiC/SiC composites have been developed for aerospace application such as propulsion and high velocity systems. Similar to carbon/carbon composites, the SiC/SiC continuous fiber composites consist of a fiber architecture made of silicon car-hide fibers in a matrix of silicon carbide. The matrix is usually produced by CVl or preceramic polymer impregnation and pyrolysis. 

Figure 9.25 shows a 3D woven, 50-mm-thick panel made from AS4-12K carbon fibers. An orthogonal weave architecture, as shown in Figure 9.48, has been used for this panel. 3D orthogonally woven structures consist of noninterlaced reinforcing fibers that generally orient perpendicular or nearly perpendicular to each other in the... 

OgawaH (2000), Architectural application of carbon fibers. Development of new carbon fiber reinforced glulam . Carbon, 38, 211-226. 

Many of the advancements for improving current densities in bioelec-trocatalytic systems have come about as a result of the utilization of high surface area electrode architectures. Categories of high surface area electrodes range from porous carbon electrodes such as carbon fiber paper, carbon felt, carbon cloth, and graphene to metallic nanoparticles, nanorods, and carbon nanotubes. All such materials provide an increased electrical contact interface between the electrode and bulk... 

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