Carbon fiber components versus alternative composite fibers.
Due to their low cost, high tensile strength, high impact resistance and good chemical resistance, glass fibers are used extensively in commercial composite applications. However, their properties can not match those of carbon fiber components for high-performance composite applications. They posses a relatively low modulus and have inferior fatigue properties compared to carbon fiber components. The three most common glass fibers used in composites are E-glass, S-2 glass and quartz.
Aramid fibers have a combination of good tensile strength and modulus, light weight, excellent toughness with an outstanding ballistic and impact resistance. However, due to the lack of adhesion to the matrix, they exhibit relatively poor transverse tension, longitudinal compression and interlaminar shear strengths.
Carbon fiber components and graphite fiber components are the most prevalent fiber forms in high performance composite structures. Carbon and graphite fibers can be produced with a wide range of properties; however, they generally exhibit superior tensile and compressive strength, possess high moduli, have excellent fatigue characteristics and do not corrode. Carbon and graphite fibers can be made from rayon, pitch or PAN precursors, although rayon is rarely used because of its low yield and high cost. PAN-based carbon fibers having strengths ranging from 500 to 1,000 ksi and moduli ranging from 30 to 45 msi with elongations of up to 2% are commercially available.
Fibers and Reinforcement: The String That Provides the Strength.
Pitch-based high-modulus graphite fibers having a modulus between 50 and 145 msi are often used in space structures requiring high rigidity. Two-dimensional woven products are usually offered as 0 °, 90 ° constructions. Weaves are made on a loom by interlacing two orthogonal (mutually perpendicular) sets of yarns (warp and fill). The warp direction is parallel to the length of the roll, while the fill, weft, or woof direction is perpendicular to the length of the roll. Weaves may be reclassified by the pattern of interlacing including plain weaves, basket weaves, satin weaves, twill weaves, leno and mock leno weaves. Reinforced mats (chopped fibers or swirled fibers) and chopped fibers are also available for parts requiring lower mechanical properties.
Carbon fiber prepregs.
Prepregging is a process in which a predetermined amount of an advanced resin is put on the fibers by the supplier. It can be accomplished by (1) hot-melt impregnation, (2) resin filming or (3) solvent impregnation. Hot-melt impregnation has been replaced to a large extent with the resin filming process because of the better quality and tighter controls obtainable with resin filming. Solvent impregnation is used for materials that are not amenable to hot melt or resin filming; however, the presence of residual solvent can cause processing problems in the form of voids and porosity during cure.
Reinforcing fibers can be supplied in dry unimpregnated forms or as prepregs ready for lay-up.