Superiority of aramid fiber compared with carbon fiber

Both aramid fibers and carbon fibers are widely used raw materials in the field of new composite materials. Although they both have very high tensile strength and modulus, there are many differences in performance and usage, so what are the differences?

Carbon fiber is a high-strength, high-modulus fiber containing more than 90% carbon, with high temperature resistance, anti-friction, electrical and thermal conductivity, and corrosion resistance, etc. It is fibrous, soft, and can be processed into various fabrics. Use mainly made of reinforced composite materials for aircraft structural materials, electromagnetic shielding in addition to electrical materials, artificial ligaments and other body substitute materials and for the manufacture of rocket shells, motor boats, industrial robots, automotive panels and other high-tech product materials.

    Aramid is a new high-tech synthetic fiber, also has super high strength, high modulus and high temperature resistance, acid resistance and alkali resistance, light weight and other excellent performance. At a temperature of 560℃ temperature, does not decompose, does not melt, has good insulation and anti-aging properties, also has a long life cycle. Aramid fiber is a very important military material for national defense, and very adaptable to the needs of modern warfare, other also widely used in aerospace and aviation, mechanical and electrical, construction, automotive, sporting goods and other aspects of the national economy. At present, aramid products for bulletproof vests, helmets, etc. accounted for about 7 ~ 8%, aerospace materials, sports materials accounted for about 40%; tire skeleton materials, conveyor belt materials, etc. accounted for about 20%, and high-strength rope and other aspects accounted for about 13%.

    Although the two are currently the most popular reinforcing materials, but its performance is still some gap, mainly in:

1. In mechanical properties, aramid tensile strength up to 2815Mpa, modulus of elasticity 126Gpa, elongation at break 2.5%, density 1.44g/cm^3, slightly inferior to carbon fiber strength, but aramid significant features in the impact resistance, has a higher ductility, and lighter weight.

2. Stability, aramid has very good thermal stability, in the role of high temperature can be until the decomposition does not deformation, can be used for a long time at 180 ℃, the role of a week at 150 ℃ strength and modulus are not changed, the coefficient of thermal expansion of -2x10^-6, compared to aramid, carbon fiber thermal stability is also superior.

3. thermochemical properties, aramid has good resistance to media, the resistance to neutral chemicals is very strong, but vulnerable to strong alkali strong acid erosion, this compared to the thermochemical properties of carbon fiber, or slightly inferior.

But compared to carbon fiber, aramid fiber also has other advantages:

1. Aramid fiber does not conduct electricity, in similar to the concrete structure reinforcement, completely without considering similar to must be isolated from the steel reinforcement and other restrictions.

2. Carbon fiber shear degree is low and easy to break, construction chamfer radius must not be less than 20mm, aramid only need half (10mm) can be.

3. Aramid's elasticity advantage is more able to withstand dynamic load and local impact, in terms of operability of construction aramid is undoubtedly the most suitable material.

4. The mode of damage after carbon fiber reinforcement is brittle, without obvious signs, so as a structural design, a large safety factor must be used. In contrast, the aramid fiber cloth has low elastic modulus and large elongation, and it is proved through experiments that the damage process is still plastic after the already damaged plain concrete members are reinforced with aramid cloth overwrap and loaded again.

In summary, compared to carbon fiber, aramid is slightly less strong and chemical, but its other properties expand the field of application. For example, aramid fiber does not conduct electricity, so in the subway, industrial plants and other structures with more electrical equipment, the use of carbon fiber cloth is obviously not very suitable, in addition, carbon fiber for concrete reinforcement, it is necessary to ensure that it is isolated from the reinforcement to prevent electrochemical corrosion, while the use of aramid fiber is not subject to this condition. In addition, carbon fiber can be used in the field of house reinforcement where the load is more stable. For ductile reinforcement with dynamic load and local impact, and for frequent vibrations in the field of roads and bridges, aramid fiber material is undoubtedly the best choice.