Carbon fiber — by far the most widely used fiber in high-performance applications — is produced from a variety of precursors, including polyacrylonitrile (PAN), rayon and pitch. The precursor fibers are heated and stretched to create the high-strength fibers. The first high-performance carbon fibers on the market were made from rayon precursor. PAN- and pitch-based fiber have replaced rayon-based fiber in most applications, but the latter’s “dogbone” cross-section often makes it the fiber of choice for carbon/carbon (C/C) composites. PAN-based carbon fibers are the most versatile and widely used. They offer an amazing range of properties, including excellent strength — to 1,000 ksi — and high stiffness. Pitch fibers, made from petroleum or coal tar pitches, have high to extremely high stiffness and low to negative axial CTE. Their CTE properties are especially useful in spacecraft applications that require thermal management, such as electronic instrumentation housings. Although they are stronger than glass or aramid fibers, carbon fibers are not only less impact-resistant but also can experience galvanic corrosion in contact with metal. Fabricators overcome the latter problem by using a barrier material or veil ply — often fiberglass/epoxy — during laminate layup.
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