Learn about aramid fiber composites, including impact resistance, lightweight properties, stiffness, abrasion resistance, and key military and industrial applications.
Aramid fiber, also known as "poly(p-phenylene terephthalamide)," possesses excellent properties such as ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, and light weight. Aramid fiber was successfully developed and commercialized in the 1960s by DuPont (under the trade name Kevlar), and therefore, before the advent of carbon fiber, aramid fiber dominated the high-performance fiber market.
1. A Brief History of Aramid Fiber Development
In the 1960s, DuPont was the first company in the world to introduce and produce aramid fiber under the registered trademark Kevlar. Aramid fiber has been sold on the market since 1973. Aramid was discovered by a Polish-born female chemist, Stephanie Kwolek, who was conducting research hoping to find a lightweight, exceptionally strong material to replace nylon in tire manufacturing.
The inventor of Kevlar fiber – Polish-born female chemist Stephanie Kwolek
Today, the most famous aramid composite material is DuPont's Kevlar fiber. Over time, other suppliers have also supplied aramid under different trade names, including: Nomex from DuPont, Twaron and Technora from Teijin of Japan, Arawin from Toray of South Korea, Kolon from Heracron of South Korea, and some products from Chinese companies.
Therefore, any material called Kevlar, Twaron, or Nomex actually refers to aramid, which has special properties, including excellent impact and abrasion resistance, high temperature resistance, and low weight. Due to these characteristics, this material is frequently used in the army, air force, water sports, and motorsports, as well as in the manufacture of tires, clothing, protective gloves, and many other applications.
Protective gloves made of aramid fiber material
2.1 High Impact and Crack Resistance
Aramid fiber has excellent impact resistance and does not crack under pressure due to its toughness and ability to absorb a large amount of energy. It is widely used in the manufacture of bulletproof vests, boats, kayaks, and armor for military vehicle components. The impact resistance of aramid fiber composites is five times that of carbon fiber composites (tested using the drop-weight impact method). This extraordinary impact resistance or bulletproof capability is due to the long atomic chains that form the aramid structure.
Given its excellent impact resistance properties, aramid fibers are widely used in military applications for manufacturing bulletproof vests and tank armor materials. Bulletproof vests are typically made of a material composed of dozens of layers of aramid (such as Kevlar), with a ceramic plate included between two layers. The protective shields used in some armored vehicles are made of steel-aramid-steel material, which can withstand anti-tank missiles up to 700mm in diameter.
Aramid fibers are widely used in bulletproof vests.
Furthermore, in addition to protecting the tank itself, the steel-aramid-steel shield also protects the crew by absorbing the kinetic energy generated by penetrating missiles. Another application of Kevlar is in the Boeing AH-64, a US military attack helicopter equipped with Kevlar rotor blades. Here, Kevlar provides protection against bullets up to 23 mm in diameter.
Aramid fibers provide bulletproof protection for helicopters.
Due to its high impact resistance, Kevlar is widely used in the construction of boats and kayaks, such as the hulls of yachts designed for the Volvo Ocean Race, one of the most demanding sporting challenges. Most high-performance kayaks for water sports are made of aramid fibers or carbon fiber/aramid fiber composite materials.
Aramid fibers protect kayaks from damage.
2.2 Low Density/Low Weight
Aramid fibers have extremely low weight, which is an advantage in the manufacture of composite materials. While carbon fiber composites themselves are considered very lightweight, aramid fiber composites are approximately 20% lighter than carbon fiber composites. The use of aramid fabric in composite materials increases impact resistance and wear resistance, and reduces the weight of the composite components.
The density of aramid fiber is approximately 1.45 g/cm³, while the density of aramid-epoxy resin composite material is approximately 1.3 g/cm³. This calculation is based on the mixed density of epoxy resin and hardener (~1.1 g/cm³) and the advanced technology used in composite material production, namely autoclave prepreg. While carbon fiber composites, generally considered very lightweight, have a density of approximately 1.55 g/cm³, aramid fiber composites are 20% lighter.
How does the weight of aramid fiber composites compare to metals? Aluminum is 2.7 g/cm³, titanium is 4.5 g/cm³, and steel is 7.9 g/cm³. Therefore, aramid fiber composites are twice as light as aluminum, three or four times lighter than titanium, and six times lighter than steel.
2.3 Moderate Stiffness, Between Glass Fiber and Carbon Fiber
Aramid fiber composites have higher stiffness than glass fiber composites, but are significantly lower than carbon fiber composites. Similar to carbon fibers, aramid fibers come in many types, including standard, medium, and high modulus fibers, which offer different stiffness and strength.
The stiffness of different types of fibers is shown below:
Glass fiber fabric – from 72 GPa (standard E-glass) to 87 GPa (S-reinforced strength glass fabric);
Carbon fiber fabric – from 230 GPa (Toray T300) to 588 GPa (Toray HM grade M60J);
Aramid fiber fabric – from 96 GPa (standard aramid, i.e., Kevlar 129) to 186 GPa (aramid used in the aircraft/aerospace industry, i.e., Kevlar 149).
In summary, aramid composites made from standard fabrics have 30-40% higher stiffness than glass fiber composites, but are 50% lower compared to carbon fiber composites.
2.4 Abrasion Resistance
Aramid fiber composites have been widely used in wear-prone components, such as skid plates protecting racing car engines. Aramid is commonly used in the extractive industries (such as mining) to reinforce rubber conveyor belts, ensuring higher strength and abrasion resistance. According to the manufacturer of Kevlar, this reinforcement can increase abrasion resistance by 50-70%. Due to these properties, the material can be used in composites as well as workwear, such as cut-resistant safety gloves using aramid fabrics like Twaron or Kevlar. 2.5 Low Dielectric Constant
Aramid fiber composites have a low dielectric constant of approximately 3.85 (at 10 GHz), ensuring good signal penetration and strength through the aramid protective cover/radome. This type of antenna is widely used for military purposes, such as on military aircraft.
Aramid fibers used in military radomes
Aramid fiber composite casings/radomes protect antennas from damage and ensure good signal performance. In contrast, E-glass fiber composites offer a dielectric constant of 6.1 (at 10 GHz), resulting in a 60% reduction in antenna signal power and performance. Besides aramid, quartz fiber is also used, with a dielectric constant of 3.78 (at 10 GHz).
2.6 Other Characteristics
Aramid fibers have low thermal expansion characteristics, are very stable at high temperatures, with almost zero thermal expansion, and a slightly negative coefficient of thermal expansion, equivalent to (-2.4 x 10⁻⁶ /°C). Aramid fibers are excellent insulators and do not conduct electricity.
A special property of aramid fiber composites is related to vibration absorption, making them suitable for manufacturing components that withstand vibration, such as aircraft structural components.
2.7 Mixed Composites with Other Fabrics
Aramid fiber fabrics can be parametrically adjusted as needed for use in carbon fiber composites and glass fiber composites, providing suppliers of composite products with a wide range of possibilities.
For carbon fiber composites, impact resistance can be improved by adding several layers of aramid fiber fabric. Hybrid composites composed of 50% carbon fiber and 50% aramid fiber show up to a 25% improvement in impact resistance compared to composites made solely of carbon fiber.
Aramid fiber-carbon fiber hybrid fabric
