On the advantages of aramid fibers compared to carbon fibers

Currently, in the field of new composite materials, aramid fibers and carbon fibers are widely used raw materials. Although both have extremely high tensile strength and modulus, there are many differences in performance and usage. So what are the differences reflected in?
Carbon fiber is a high-strength and high modulus fiber with a carbon content of over 90%. It has characteristics such as high temperature resistance, friction resistance, conductivity, thermal conductivity, and corrosion resistance. Its appearance is fibrous, soft, and can be processed into various fabrics. In terms of usage, it is mainly made into reinforced composite materials for aircraft structural materials, electromagnetic shielding and de electrification materials, artificial ligaments and other body substitute materials, as well as high-tech product materials for manufacturing rocket casings, motor ships, industrial robots, automotive panels and so on.
Aramid is a new type of high-tech synthetic fiber, which also has excellent properties such as ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, and light weight. At 560 ℃, it does not decompose or melt, has good insulation and aging resistance, and has a long life cycle. Aramid fiber is a very important material for national defense and military industry, which is very suitable for the needs of modern warfare. It is also widely used in various aspects of the national economy, such as aerospace, electromechanical, construction, automobiles, sports goods, etc. At present, about 7-8% of aramid products are used for bulletproof vests, helmets, etc., while aerospace materials and sports materials account for about 40%; Materials such as tire frame and conveyor belt account for about 20%, and high-strength ropes account for about 13%.
Although the two are currently the most popular reinforcement materials, there are still some differences in their performance, mainly manifested in
1. In terms of mechanical properties, the tensile strength of aramid can reach 2815Mpa, the elastic modulus is 126Gpa, the elongation at break is 2.5%, and the density is 1.44g/cm ^ 3, which is slightly inferior to the strength of carbon fiber. However, the notable feature of aramid is its impact resistance, higher elongation, and lighter weight.
2. In terms of stability, aramid has very good thermal stability, which can decompose without deformation under high temperature. It can be used for a long time at 180 ℃, and its strength and modulus do not change after one week at 150 ℃. The coefficient of thermal expansion is -2x10 ^ -6. Compared with aramid, carbon fiber also has superior thermal stability.
3. In terms of thermochemical properties, aramid has good resistance to media and strong resistance to neutral chemicals. However, it is easily corroded by strong alkalis and acids, which is slightly inferior to the thermochemical properties of carbon fiber.
However, compared to carbon fiber, aramid fiber also has other advantages:
1. Aramid fibers are non-conductive, and when used for reinforcement similar to concrete structures, there is no need to consider restrictions such as the need to isolate from steel bars.
2. Carbon fiber has low shear resistance and is prone to breakage. The construction chamfer radius should not be less than 20mm, and only half (10mm) of aramid is needed.
3. The elastic advantage of aramid lies in its ability to withstand dynamic loads and local impact forces. In terms of operability during construction, aramid is undoubtedly the most suitable material.
The failure mode after carbon fiber reinforcement is brittle without obvious signs, therefore, as a structural design, a larger safety factor must be adopted. However, the elastic modulus of aramid fiber cloth is low and the elongation is high. Through experiments, it has been proven that the failure process of damaged plain concrete components reinforced with aramid fiber cloth is still plastic when loaded again.
In summary, compared to carbon fiber, aramid has slightly lower strength and chemical properties, but its other characteristics have expanded its application fields. For example, aramid fibers are non-conductive, so it is obviously not suitable to use carbon fiber cloth in structures with more electrical equipment such as subways and industrial plants. In addition, when carbon fiber is used for strengthening concrete structures, it is necessary to ensure that it is isolated from steel bars to prevent electrochemical corrosion, and the use of aramid fibers is not limited by this condition. In addition, carbon fiber can be used for the reinforcement of houses with relatively stable loads. For ductile reinforcement under dynamic loads and local impacts, aramid fiber materials are undoubtedly the best choice for frequent vibration in road and bridge fields.