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Materials
At ACI we have used numerous types of fiber-reinforcing and resin matrices for countless specifications and custom product designs. The most common fibers used in polymeric composites are various types of glass, carbon and aramid. Less common fibers used include silicon carbide, basalt, stainless steel and pitch-based high modulus carbon fiber. Filaments of these materials are produced in various manners. Individual filaments are then grouped into large bundles of filaments called either a roving in the case of glass and aramid, or a tow in the case of carbon.
A coating is applied to the filaments before they are bundled together. This coating is called sizing and protects the filaments surface from corrosion, oxidation, and mechanical damage occurring from abrasion. This coating also helps the filament to adhere to the matrix material. For instance, different sizing material would be applied for epoxy matrices than for polyester matrices. The roving and tows can be packaged as spools or woven fabric. In general, ACI uses epoxy resins due to overall strength, operating temperature, ease of use and cure and for environmental considerations.
Types of Materials
Fiberglass is the most common material used for commercial fiber reinforced polymer composites. Called glass or fiberglass, this material is processed in several different ways to form products with varying features:
- E-Glass is the most inexpensive and commonly used fiber. The "E" designation stands for "electrical" because of its superior insulative properties. E-Glass has good fiber strength (~500 Ksi) and relatively low fiber modulus (~10.5 Msi).
- S-Glass is a standard aerospace formulation of glass that is stronger (~600 Ksi) and higher modulus (~12.5 Msi) than E-glass. The "S" designation is for "strength," and is a trade name of Owens-Corning Inc. Other fiberglass manufacturers with comparable products use designation such as "T-glass" and "R-glass."
- C-Glass is a corrosion resistant type of glass, and is usually used as a surfacing veil cloth on outer surfaces of laminates, or against tool surfaces to protect the laminate from corrosion.
Carbon fiber (sometimes called graphite fiber) possesses both high fiber modulus (>33 to 120+ Msi), and high fiber strength (>200 to 1000+ Ksi). Carbon fiber can be made from a variety of organic or petroleum polymer fibers. Most commonly, it is made from either of two precursor materials: pitch or polyacrylonitrile (PAN). Most standard intermediate modulus fiber is made from PAN, while pitch is used for the production of high modulus fibers. The precursor material is spun into fibers and processed in three steps: oxidation, carbonization, and graphitization. This processing forms a turbostratic graphitic structure in which graphitic crystallites are aligned with the fiber axis and intermingled with each other. The processing of carbon fibers produces three types of fiber:
- High Modulus fibers have marginal strength and marginal elongation to failure.
- Intermediate Modulus/Intermediate Strength fibers have higher elongation to failure.
- High Strength fibers have standard modulus and elongation to failure.
Aramid fiber is an organic fiber produced by axially aligned aromatic polyamide polymer molecules that are hydrogen bonded together into radial plates. Aramid is often combined with a polyester or epoxy matrix, offers exceptional tensile strength and toughness, but poor compressive and moisture resistant properties. The most widely used aramid fibers are Kevlar® and Twaron®.
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