Overview of the application of carbon fiber composite materials in automobiles

Carbon fiber composite is a high performance composite material which is prepared by advanced composite molding method with resin, metal and ceramic as matrix and carbon fiber as reinforcement. Among them, CarbonFiber composite materials for automotive are usually resin-based carbon fiber Reinforced Polymers (CFRP). CFRP has a series of advantages such as low density, high modulus and high specific strength, and it is one of the lightweight materials with remarkable weight reduction effect after high-strength steel, magnesium aluminum alloy and engineering plastics. Therefore, it is widely used in aerospace, wind power generation, leisure sports, military and other fields. In recent years, with the increasingly serious environmental pollution of the earth, "energy saving and emission reduction, the development of low-carbon economy" has formed a high degree of consensus on a global scale. Lightweight vehicles can effectively reduce energy consumption and reduce exhaust emissions. Because the specific energy of the new energy vehicle battery is very large compared with the liquid fuel, its lightweight is more important and urgent. As an excellent lightweight material, CFRP also has high temperature resistance, corrosion resistance, shock absorption and other properties, and its products have a cool appearance. Therefore, it is increasingly favored by automotive engineers. In order to promote the application of CFRP in automobiles, many universities and enterprises have carried out the application research of CFRP in automobiles in recent years.

Application of CFRP on body frame

Due to its low density, high modulus and specific strength, CFRP is often suitable for lightweight applications of large structural parts. As the system that contributes the most to the quality of the vehicle, the body skeleton is the most important object of CFRP lightweight, and it is also the earliest place where CFRP is applied. As early as 1992, General Motors developed the concept car of CFRP ultra-light body skeleton structure, and BMW's i3 body launched in 2013 adopted CFRP occupant cabin, which triggered a wave of CFRP application research. Since then, the application of CFRP in the body skeleton has gradually expanded from super sports cars to luxury cars and new energy vehicles. The BMW i3 crew compartment consists of a total of 34 CFRP parts, 13 of which are monolithic (consisting of 48 preforms), achieving a high degree of integration, as shown in Figure 1. Taking the i3 side body as an example, the side body was divided into 9 preforms, and then the 9 preforms were formed by Resin Transfer Moulding (RTM) technology to form the inner and outer panels of the side body. BMW i8, BMW 7 Series, Lexus LFA, Lamborghini AventadorLP700-4 body frame structural parts use a large number of CFRP components, Audi A8 body backplane also uses CFRP. In addition, Mercedes-Benz, Ford, Toyota and other foreign mainstream car companies have CFRP application research and model releases on body skeleton structural parts.

Lightweight is one of the main goals of vehicle development, and the weight reduction of vehicle parts has been the focus of the industry. The application of CFRP in the body skeleton, weight reduction of about 100 kilograms (BMW i3CFRP passenger cabin is only 148kg, 57.6% lighter than the steel body, weight reduction of about 200 kg), for all model designs, has great appeal. However, due to the high cost of CFRP, ordinary vehicle development is often difficult to bear the high cost.

Due to the high cost of CFRP, complex process, low efficiency, and many key technologies such as connection, electrochemical corrosion, durable deformation have not been completely overcome, therefore, there is no mass production application case of integrated CFRP body skeleton in China. Changan Automobile has developed an integrated CFRP body skeleton, which is the only all-carbon body skeleton in China at present. This project is still in the development and verification stage, as shown in Figure 2. In addition, the CFRP floor developed by Chery was tested for the whole vehicle; The CFRP skylight strengthening plate, the front top beam of the top cover, the middle support plate of the B-pillar, the outer plate of the threshold, the outer plate of the longitudinal beam, the central channel strengthening plate, and the fender plate developed by Zotye have been integrated into the whole vehicle, but these are in the development and verification stage, and there is no mass production plan.

Application of CFRP in body coverings and interior and exterior finishes

CFRP is also a hot spot in the application research of body coverings and exterior trim parts in China. Basically all Oems in China have the application research of CFRP in body coverings and exteriors, and the application is on the rise. In recent years, the main models developed and applied CFRP body covering parts and exterior parts are promising K50, Geely Lynk & Co 03+/05+, Volvo Pole Star 1, Great Wall WEYVV7, SAIC MG6, etc., in addition, Lotus and other models have been in mass production development. Table 1 shows the main models that have developed and applied CFRP body coverings and exterior trim parts in recent years.

High configuration of the way to develop. In addition, affected by the after-sale modification of foreign models, there is also a large number of domestic demand for after-sale CFRP modification of exterior parts.

For the interior parts, in view of the bright appearance of carbon fiber, it can bring a gorgeous style to the vehicle, but most models are modified and promoted to the interior through the form of carbon fiber film. This is mainly because the automotive interior parts mainly use Polypro-pylene (PP) type of plastic, CFRP has no outstanding advantages in lightweight, on the contrary, it will bring about a surge in costs, so it is usually a lower cost of the film.

Application of CFRP in chassis system

Most of the chassis parts belong to the "unsprung quality", and its lightweight has a more obvious improvement on the vehicle performance. However, the chassis parts are in a harsh environment, and most of them are sports parts, which have higher requirements for reliable performance such as durability, fatigue and corrosion. CFRP is often more challenging in the chassis than in the body structure. Therefore, whether at home or abroad, the application of CFRP in chassis parts is extremely difficult. At present, the components of CFRP application research on chassis mainly include drive shaft, subframe, control arm, stabilizer bar, steering knuckle, wheel hub, spring, etc. The drive shaft is an important part of the transmission of power in the automobile transmission system, and its role is to transmit the power of the engine to the wheels together with the gearbox and the drive axle, so that the car can produce driving force. The traditional automobile drive shaft is mainly made of metal materials, such as high-quality carbon alloy steel 40Cr, 30CrMo, 42CrMo and so on. The use of CFRP instead of the original metal material for the transmission shaft can meet the requirements of high strength, stiffness and fatigue of the transmission shaft, achieve substantial weight reduction, and reduce the energy loss of the transmission system and the weight of the vehicle by improving the vibration resistance and reducing noise.

Carbon fiber composite automotive drive shafts have been used in General Motors' trucks since the 1880s, and have a mass reduction of 60% compared to steel. With the continuous improvement of technology and production equipment, the production and application of carbon fiber composite transmission shaft is also tending to scale.

CFRP has the advantages of low density, high modulus and high specific strength, so it has broad application prospect in automobile. However, due to the higher cost factor, CFRP is still mainly used in some high-end models.

The beautiful appearance of CFRP is deeply loved by young people, and many models are developed in the form of high matching or optional models with the "sports kit" as the publicity point. After the sale, the modification of the exterior "sports kit" occupies a large market in CFRP applications.

Although the application of CFRP in automobiles has a good prospect, it still faces a series of problems such as high cost, low process efficiency, difficult design technology, and difficult recovery and maintenance.

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