Aramid fibers are characterized by excellent environmental and thermal stability, static and dynamic fatigue resistance, and impact resistance. These fibers have the highest specific tensile strength (strength/density ratio) of any commercially available continuous-filament yarn. Aramid-reinforced thermoplastic composites have excellent wear resistance and near-isotropic properties — characteristics not available with glass or carbon-reinforced composites.
Aramid fiber, trade-named Kevlar, is available in several grades and property levels for specific applications. The grade designated simply as Kevlar is made specifically to reinforce tires, hoses, and belting, such as V-belts and conveyor belts.
Kevlar 29 is similar to the basic Kevlar in properties but is designated specifically for use in ropes and cables, protective apparel, and as the substrate for coated fabrics. In short fiber or pulp form, Kevlar 29 can substitute for asbestos in friction products or gaskets. Fabrics of Kevlar 29 can be made into bullet-resistant vests. Clothing made from Kevlar 29 can be as heat resistant as that made from asbestos and also be extremely cut resistant.
Kevlar 49 has half the elongation (2.5%) and twice the modulus (117,885 MPa) of Kevlar 29. Applications are principally in reinforcing plastic compounds used in lightweight aircraft boat hulls and sports equipment. Composites containing Kevlar are also used as interior panels and secondary structural parts, such as fairings and doors on commercial aircraft.
Kevlar 149 is a highly crystalline aramid that has a modulus of elasticity 40% greater than that of Kevlar 49 and a specific modulus nearly equal to that of high-tenacity graphite fibers. It is used to reinforce composites for aircraft components.
Nomex aramid fiber is characterized by excellent high-temperature durability with low shrinkage. It will self-extinguish and does not melt, retaining a high percentage of its initial strength at elevated temperatures. It is available as continuous-filament yarn, staple, and tow. Nomex is used in military and civilian protective apparel, dry gas filtration, rubber reinforcement, and industrial fabrics. Nomex aramid fibers are also available as a paper for use in high-temperature electrical insulation and in resilient, corrosion-proof honeycomb core for aerospace and other transportation applications.
