Performance and Applications of Carbon Fiber Composites
2021-05-18
Performance and Advantages of Carbon Fiber Composites
Mechanical Properties
Carbon fiber composites have high tensile strength, large modulus, and low density, exhibiting high specific strength and very high specific modulus. Compared to traditional metal materials, carbon fiber composites are lightweight, strong, and tough, offering significant advantages. When compared to silicon-based fiber composites, the tensile strength of carbon-based fibers is about 3-7 times greater. The elastic modulus of carbon-based fibers is higher than that of silicon-based fibers, so carbon fiber composites exhibit smaller strain under the same external load, resulting in higher stiffness than silicon-based fiber composite components. The elongation at break for high modulus carbon fibers is about 0.5%, for high strength carbon fibers about 1%, for silicon-based fibers about 2.6%, and for epoxy resin about 1.7%, allowing the strength of the fibers in carbon fiber composites to be fully utilized.
Due to the high brittleness and poor impact resistance of carbon fibers, the tensile failure mode of carbon fiber composites is brittle failure, meaning there is no significant plastic deformation before fracture, and the stress-strain curve is linear. This is similar to glass fibers, except that the modulus is higher and the elongation at break is lower than that of glass fibers. Carbon fiber composites have good high and low-temperature resistance. In an oxygen-free environment (under inert gas protection), they retain strength at 2000°C and do not become brittle under liquid nitrogen.
Carbon fiber composites have good thermal conductivity. The thermal conductivity coefficient is relatively high but tends to decrease with increasing temperature. The thermal conductivity coefficient along the fiber axis is 0.04 cal/(s*cm*°C); the thermal conductivity coefficient perpendicular to the fiber direction is 0.002 cal/(s*cm*°C). The linear expansion coefficient of carbon fiber composites along the fiber axis exhibits a negative temperature effect, meaning that with increasing temperature, carbon fiber composites tend to contract, demonstrating good dimensional stability and fatigue resistance.
Corrosion Resistance
Carbon fiber composites are generally resistant to acids and bases, except for strong oxidizers such as concentrated nitric acid, hypochlorous acid, and chromic acid. They have better corrosion resistance than silicon-based fiber composites. Unlike silicon-based fiber composites, carbon fiber composites do not undergo hydrolysis in humid air, exhibiting good water resistance and resistance to moisture aging. Additionally, they possess oil resistance, radiation resistance, and characteristics that reduce motion in the middle.
Advantages
In summary, carbon fiber composites have a series of advantages including lightweight, high modulus, large specific strength, low thermal expansion coefficient, high temperature resistance, thermal shock resistance, corrosion resistance, and good shock absorption. These properties are characteristics that traditional metal materials do not possess, and they also exhibit strong performance compared to other types of new composite materials. This enables carbon fiber composites to be widely applied in many fields and promotes further research into carbon fiber composites to continue improving their performance.
Applications of Carbon Fiber Composites
Due to their excellent performance, carbon fiber composites have been widely applied in various fields, including automotive, structural reinforcement engineering, new energy development, and leisure products.
Automotive
Currently, the world produces 50 million passenger cars annually, and if trucks and buses are included, the total reaches 70 million. With the rapid development of the automotive industry in countries like China and India, the annual global production of cars may soon exceed 100 million. Additionally, the current annual production of PAN-CF worldwide is only several tens of thousands of tons. Due to the high cost, difficulty in processing, slow molding speed, and limitations related to recycling of CFRP, it is currently only used in sports goods and industrial sectors. To use it in automobiles, it is crucial to quickly develop surface-active CF suitable for thermoplastic resins (such as polypropylene) and their CFRTP ultra-high-speed molding technology and secondary processing technology. Furthermore, when the demand for CF exceeds one million tons, it will require the development of CF made from biomass materials, although there are still certain difficulties. Lastly, when reaching such a large scale, it will be necessary to develop recycling technologies for CFRP and high reuse technologies for CF, as well as to address evaluation and standardization issues related to these materials and their processing.
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