Fiber Reinforce Composites Material (1)

Depending on different applications, glass fibers used to reinforce composites are supplied directly by fiber manufacturers and indirectly by converters in a number of different forms.

Roving is the simplest and most common form of glass fiber. It can be chopped, woven or otherwise processed to create secondary fiber forms for composite manufacturing, such as chopped strand mats, woven fabrics, braids, knitted fabrics and hybrid fabrics. Rovings are supplied by weight, with a specified filament diameter. The term yield is commonly used to indicate the number of yards in each pound of glass fiber rovings. Similarly, tow is the basic form of carbon fiber. Typical aerospace-grade tow size ranges from 1K to 24K (K = 1,000, so 12K indicates that the tow contains 12,000 carbon filaments). PAN- and pitch-based 12K carbon fibers are available with a moderate (33-35 Msi), intermediate (40-50 Msi), high (50-70 Msi) and ultrahigh (70-140 Msi) modulus. (Modulus is the mathematical value that describes the stiffness of a material by measuring its deflection or change in length under loading.) Newer heavy-tow carbon fibers, sometimes referred to as commercial-grade fibers, with 48K-320K filament counts, are available at a lower cost than aerospace-grade fibers. They typically have a 33-35 Msi modulus and 550-ksi tensile strength and are used when fast part build-up is required, most commonly in recreational, industrial, construction and automotive markets. Heavy-tow fibers exhibit properties that can approach those of aerospace-grade fibers but can be manufactured at a lower cost because of precursor and processing differences. 

A potentially significant recent variation is carbon fiber tow that features aligned discontinuous fibers. These tows are created in special processes that either apply tension to carbon tow at differential speeds, which causes random breakage of individual filaments, or otherwise cut or separate individual carbon filaments such that the filament beginnings and ends are staggered and their relative lengths are roughly uniform so that they remain aligned and the tow maintains its integrity. The breaks permit the filaments to shift position in relation to adjacent filaments with greater independence, making the tow more formable and giving it the ability to stretch under load, with greater strength properties than chopped, random fibers. Fiber forms made from aligned discontinuous tows are more drapable; that is, they are more pliable and, therefore, conform more easily to curved tool surfaces than fiber forms made from standard tow.