Analysis of Factors Affecting the Mechanical Properties of Carbon Fiber

As a high-performance composite material, carbon fiber has been widely used in aerospace, automotive manufacturing, and other fields. This article analyzes the main factors affecting the mechanical properties of carbon fiber, including raw materials, preparation processes, post-treatment processes, and environmental factors. Through systematic study of these factors, it aims to provide theoretical basis and practical guidance for the research and application of carbon fiber materials. The study found that the selection of raw materials, optimization of preparation processes, improvement of post-treatment processes, and control of environmental factors have significant impacts on the mechanical properties of carbon fiber.

With the development of technology, carbon fiber, as a high-performance composite material, has been widely used in aerospace, automotive manufacturing, sports equipment, and other fields due to its excellent properties such as light weight, high strength, and corrosion resistance. However, the mechanical properties of carbon fiber are affected by various factors, such as raw materials, preparation processes, post-treatment processes, and environmental factors. Therefore, in-depth research on the factors affecting the mechanical properties of carbon fiber is of great significance for improving the performance and application of carbon fiber materials. This article reviews the factors influencing the mechanical properties of carbon fiber, aiming to provide theoretical basis and practical guidance for the research and application of carbon fiber materials.

1. Basic Properties and Classification of Carbon Fiber

1. Basic Properties of Carbon Fiber

(1) Carbon fiber is a new type of high-performance fiber material obtained by high-temperature carbonization of organic fibers, with carbon atoms as its main component. This material has many unique properties, making it widely used in various fields. Firstly, carbon fiber has an extremely low density, about one-quarter that of steel, which significantly reduces product weight and improves structural strength in aerospace, automotive manufacturing, and other fields. Secondly, carbon fiber has very high strength and modulus, with tensile strength reaching 3.5-7.0 GPa and elastic modulus up to 300-700 GPa. These excellent mechanical properties allow carbon fiber to maintain good shape stability under heavy loads. Additionally, carbon fiber has excellent corrosion resistance and high-temperature resistance, maintaining stable performance in extreme environments.

(2) At the microscopic level, carbon fiber consists of numerous carbon atoms forming a hexagonal honeycomb planar structure through sp2 hybrid orbitals. These planes are connected by carbon-carbon bonds, forming a three-dimensional network structure. This structure gives carbon fiber good electrical conductivity and thermal conductivity, as well as excellent chemical stability. The electrical conductivity of carbon fiber makes it widely applicable in electromagnetic shielding and sensors; its thermal conductivity provides unique advantages in heat dissipation materials and high-temperature furnace linings. Moreover, the chemical stability of carbon fiber ensures good durability in corrosive environments, suitable for demanding applications such as marine engineering and chemical equipment.

(3) The surface properties of carbon fiber are also an important factor in its applications. Carbon fiber surfaces usually have low surface energy, resulting in low bonding strength with resin matrices. To improve the bonding performance between carbon fiber and resin matrices, surface treatments such as surface oxidation and coatings are often required. Additionally, the surface morphology of carbon fiber affects its mechanical properties. For example, fiber surface roughness and fiber diameter distribution influence tensile strength, modulus, and other mechanical properties of carbon fiber. Therefore, research and control of surface properties are of great significance in the preparation and application of carbon fiber.

2. Classification of Carbon Fiber

(1) Carbon fiber can be mainly divided into two categories based on preparation methods and raw materials: polyacrylonitrile (PAN)-based carbon fiber and pitch-based carbon fiber. PAN-based carbon fiber is currently the most widely used type, derived from polyacrylonitrile fibers and obtained through high-temperature carbonization. This type of carbon fiber has excellent mechanical properties and chemical stability, widely used in aerospace, sports equipment, automotive manufacturing, and other fields. Pitch-based carbon fiber is obtained by high-temperature carbonization of petroleum pitch, with relatively lower cost but slightly inferior mechanical properties and chemical stability compared to PAN-based carbon fiber. Pitch-based carbon fiber has good application prospects in composites and construction reinforcement.

(2) Among PAN-based carbon fibers, based on production processes, they can be further divided into pre-oxidized carbon fiber and directly oxidized carbon fiber. Pre-oxidized carbon fiber is produced by pre-oxidizing the surface of polyacrylonitrile fibers to partially oxidize them into carbon fiber, followed by carbonization. This carbon fiber has lower shrinkage and higher strength, suitable for high-performance fields such as aerospace. Directly oxidized carbon fiber is produced by directly oxidizing polyacrylonitrile fibers and then carbonizing them. This production process is relatively simple and cost-effective but has slightly lower performance than pre-oxidized carbon fiber.

(3) Besides the two main types mentioned above, there are other special types of carbon fiber, such as viscose-based carbon fiber and polyethylene-based carbon fiber. Viscose-based carbon fiber is obtained by high-temperature carbonization of viscose fibers, with a production process similar to PAN-based carbon fiber but relatively lower cost. Polyethylene-based carbon fiber is produced from polyethylene raw materials through high-temperature carbonization, featuring good corrosion resistance and high-temperature resistance, suitable for chemical and petroleum fields. Additionally, new types of carbon fibers such as carbon nanotubes and graphene have higher strength and conductivity, promising wider applications in the future.

3. Structural Characteristics of Carbon Fiber

(1) The structural characteristics of carbon fiber are mainly reflected in its microscopic structure. Carbon fiber is formed by countless tiny carbon atoms connected by covalent bonds, arranged in sp2 hybrid orbitals to form a hexagonal honeycomb planar structure. This structure gives carbon fiber extremely high strength and modulus while maintaining its lightweight nature. The planar structure forms a continuous carbon atom chain along the fiber axis, while laterally connected by carbon-carbon bonds to form a three-dimensional network. This unique structure endows carbon fiber with excellent mechanical properties and chemical stability.

(2) The surface structure of carbon fiber is also one of its characteristics. The surface of carbon fiber is usually relatively smooth, but through specific surface treatment techniques such as oxidation and coating, its surface properties can be altered to improve the bonding strength with matrices like resin. The surface energy of carbon fiber is relatively low, which is beneficial for its application in composite materials, but surface treatment is also needed to enhance its interaction with resin. Additionally, the surface roughness and fiber diameter distribution of carbon fiber also affect its mechanical properties to some extent.

(3) The internal structural characteristics of carbon fiber also include its pore structure. During the manufacturing process, carbon fiber forms a certain amount of pores, which help improve the material's thermal conductivity and electrical conductivity, and also facilitate the penetration and distribution of resin in composite materials. Parameters such as porosity, pore size, and distribution have significant impacts on the mechanical properties of carbon fiber and the performance of composite materials. By optimizing the pore structure, the mechanical properties of carbon fiber and the overall performance of composites can be further enhanced.

4. Application Fields of Carbon Fiber

(1) The application of carbon fiber in the aerospace field is particularly prominent. Due to its lightweight and high strength characteristics, carbon fiber composites are widely used in structural components of aircraft, such as wings, fuselage, and tail. Using carbon fiber composites can significantly reduce aircraft weight, improve fuel efficiency, and enhance structural strength and fatigue resistance. In addition, carbon fiber applications in aerospace also include manufacturing key components of satellites, missiles, and other spacecraft, as well as producing high-performance bulletproof vests and helmets for personal protection equipment.

(2) In the automotive manufacturing field, the application of carbon fiber composites is increasing. Carbon fiber composites are used to manufacture car bodies, chassis, suspension systems, and other parts to reduce vehicle weight, improve fuel efficiency, and acceleration performance. The use of carbon fiber in the automotive field helps enhance overall vehicle performance while reducing environmental impact. Additionally, carbon fiber is used to produce high-performance sports cars, racing cars, and luxury car high-end components to enhance vehicle aesthetics and functionality.

(3) The application of carbon fiber in the sports equipment field is also very extensive. Carbon fiber composites, due to their high strength, light weight, and impact resistance, are used to manufacture sports goods such as golf clubs, tennis rackets, and badminton rackets. These carbon fiber products not only improve athletes' performance but also increase the lifespan of the equipment. Furthermore, carbon fiber is applied in manufacturing outdoor sports equipment like skis and bicycles, providing athletes with a better sports experience. With the continuous development of carbon fiber technology, its application in the sports equipment field will become even more widespread.