GLASS FIBERSЖ Most versatile industrial materials known today.Ж Produced from raw materials, which are available in unlimited supplyЖ They exhibit useful bulk properties such as Hardness Resistance to chemical attack Stability and Inertness, as well as desirable fiber properties such as strength, flexibility, and stiffness
GLASS FIBER TYPESЖ Glass fibers fall into two categories, low-cost general-purpose fibers and premium special-purpose fibers. Over 90% of all glass fibers are general-purpose products.Ж These fibers are known by the designation E-glass and are subject to ASTM specificationsЖ The remaining glass fibers are premium special-purpose products. Many, like E-glass, have letter designations implying special propertiesЖ Some have tradenames, but not all are subject to ASTM specifications. Specifically:
ARAMID FIBERSЖ ARAMID FIBERS having the highest strength-to-weight ratio of any commercially available reinforcement fiber at the time of their first commercial introduction in the early 1970s.Ж Characteristics light weight, high strength, and high toughnessЖ Used in tires, ropes, cables, asbestos replacement, and protective apparelЖ The disadvantage of aramid fibers is that they are difficult to cut and machine.Ж Aramid fibers are produced by extruding an acidic solution (a proprietary polycondensation product of terephthaloyol chloride and p-phenylenediamine) through a spinneret. The filaments are drawn through several orifices.Ж During the drawing operation, aramid molecules beome highly oriented in the longitudinal direction.
CARBON FIBER MANUFACTURINGЖ Major raw materials PAN and pitchЖ 90% of the carbon fibers are made from polyacrylonitrile (PAN).Ж 10% of carbon fibers are made from pitchЖ PAN is pre-manufactured synthetic fiber.Ж Pitch is coal-tar petroleum product that is melted, twisted, and stretched into fibers.
CARBON FIBER MANUFACTURINGЖ Typical sequence of operations used to form carbon fibers from polyacrylonitrile (PAN): Thermoset treatment Carbonizing Graphitizing Surface Treating Epoxy Sizing
CARBON FIBER MANUFACTURINGЖ THERMOSET TREATMENT Fibers are stretched and heated to no more than 400 C. Cross-links carbon chains so that the fibers will not melt in subsequent treatments.Ж CARBONIZING fibers are heated to about 800 C in an oxygen free environment. removes non-carbon impurities.Ж GRAPHITIZING heats them to temperatures ranging from 1100 C to 3000 C. stretches the fibers between 50 to 100% elongation. The stretching ensures a preferred crystalline orientation
SURFACE TREATINGЖ After carbonizing, the fibers have a surface that does not bond well with the epoxies and other materials used in composite materials.Ж To give the fibers better bonding properties, their surface is slightly oxidized.Ж provides better chemical bonding properties better mechanical bonding properties.Ж The surface treatment process must be carefully controlled to avoid forming tiny surface defects, such as pits, which could cause fiber failure.
EPOXY SIZINGЖ Fibers are coated to protect them from damage during winding or weaving. This process is called sizing.Ж Typical coating materials include epoxy, polyester, nylon, and others.Ж The coated fibers are wound onto cylinders called spools.Ж The spools are loaded into a spinning machine and the fibers are twisted into yarns of various sizes.
CERAMIC FIBERSЖ CERAMIC FIBERS are commercially available in two general classes for the reinforcement of ceramic-matrix composites. oxide fibers, based on the alumina-silica (Al2O3-SiO2) system non-oxide fibers, silicon carbide (SiC).Ж Fibers are typically produced with small diameter (<20 μm)Ж A key characteristic of ceramic fibers is their ultrafine microstructure, sometimes in the nanometer range. Fine grains are required for good tensile strength >2000 MPa
CERAMIC FIBERS PRODUCTIONЖ For oxide fibers, sol-gel processing is used. sol- gel process uses chemical solutions or colloidal suspensions, which are shaped into fibers, then gelled (usually by drying) and heat treated to convert the gelled precursor to ceramic.Ж In the case of fibers based on SiC and silicon nitride, fibers are twisted from organometallic “pre-ceramic” polymer precursors, followed by cross- linking (curing) and heat treatment steps to convert the fibers to ceramic materials.