12 Aug, 2020 By Johny 2 Comments
Analysis of key technical issues in the application and development of automotive Composite Materials
As China’s new energy vehicle sales and ownership both increase, advanced Composite materials, as one of the most obvious lightweight and reliable lightweight materials, will play an important role in the lightweight process of new energy vehicles. With the advancement of automotive lightweight and the rapid development of new energy vehicles, Composite materials for automobiles have received extensive attention and applications. The development and application ratio of automotive composite materials has gradually increased. Therefore, this article will combine the research progress and development of automotive composite materials. According to the situation, the key to the application and development of automotive composite materials is discussed from the perspective of vehicle development and application.
1.Application of composite materials for vehicles:
1.1. Automobile lightweight: automobile lightweight refers to the premise that the original safety, comfort, reliability and other objectives of the automobile meet the design requirements, and the cost of the automobile itself meets the design expectations, so as to reduce the maintenance of the automobile as much as possible Quality, thereby improving performance indicators such as energy saving, emission reduction, and fuel consumption reduction.
Material lightweight technology refers to the use of new lightweight materials to achieve technical measures to reduce weight on the premise of ensuring that the original functions and performance goals are achieved.
Under the influence of the lightweight trend, various new materials, such as lightweight metal materials (aluminum alloys, magnesium alloys), lightweight non-metal materials (low density, thinner walls) and advanced composite materials will be more and more used In the lightweight design of automobiles, the proportion of the material composition of the entire vehicle will also increase accordingly.
1.2. Advanced composite materials for automobiles:
Polymer composite materials can be divided into general composite materials and high-performance (advanced) composite materials according to their performance. High-performance polymer composite materials are composite materials with excellent performance or special functions developed by using new technologies, new processes or new equipment. Internationally, it generally refers to a composite material composed of carbon fiber, aromatic polyamide synthetic fiber (aramid fiber), boron fiber and other fibers and high-performance reinforcement such as whiskers, and a matrix such as high-temperature resistant polymers. It has a high ratio Strength and specific modulus, anisotropy and designability, good fatigue resistance, easy to form as a whole, and can also have wave absorption, wave transmission, conductivity, semiconductivity, heat generation, heat resistance, memory, damping, friction, absorption Sound and other functions.
(1) Small proportion and light weight. The density is lower than that of steel, aluminum, magnesium and other metal materials. Taking carbon fiber composite materials for example, its density is about 1.7g/cm3, while the density of steel in metal materials is 7.85g/cm3 and the density of aluminum is 2.75g/cm3;
(2)High specific strength and specific modulus. The specific strength is up to 14 times that of steel and 10 times that of aluminum, and the specific modulus is more than 3 times that of steel and aluminum;
(3)Good reliability. The laminated composite material has an “anti-expansion” effect on fatigue crack expansion. This is because when the crack propagates from the surface to the inner layer, it will cause the crack to propagate when it reaches a plane with different fiber orientations. The fracture energy diverges in this layer, this characteristic makes the fatigue strength of FRP greatly improved. Studies have shown that the fatigue strength of steel and aluminum is 50% of the static strength, while composite materials can reach 90%;
(4)Good abrasion resistance. The abrasion resistance can be greatly improved by incorporating a small amount of chopped carbon fiber. For example, polypropylene is 2.5 times that of itself; polyamide is 1.2 times that of itself;
(5) Excellent chemical stability. Can be used in strong acid, strong alkali and other environments for a long time;
(6) High temperature resistance. In fiber-reinforced composite materials, the melting point (or softening point) of other fibers is generally above 2 000 ℃ except for the lower softening point of glass fiber (700～900℃); (7) High degree of design freedom. According to the design goals of the construction, free design can be achieved through the distribution of reinforcement materials, the number of layers, and the type of fiber and resin content. Automotive composite materials have the characteristics of light weight, high specific strength and specific modulus, good stiffness, good reliability, good wear resistance, excellent chemical stability, and high design freedom, which are more conducive to the promotion of automotive parts application.
1.3 Application of composite materials for vehicles Automobile composite materials have been widely used with the advancement of automobile lightweight and the rapid development of new energy vehicles.
The application of composite materials to the automotive industry first began in 1953. Automotive composite materials were initially used by a small number of car enthusiasts and commercial vehicles, and car enthusiasts used them for modification and decorative parts; in the commercial vehicle field, they were mainly used in heavy trucks. Used on. At present, the applications of automotive composite materials in automobiles are mainly carbon fiber composite materials (CFRP), glass fiber reinforced composite materials (GFRP), and metal matrix composite materials (MMC). The exploration of composite materials by Chinese brand OEMs is mainly applied to the body, interior and exterior trim, chassis transmission, powertrain and other systems. Typical system components are as follows: Interior and exterior decoration system: bumper mask, rearview mirror housing, spoiler, grille, door inner panel, instrument panel, etc.; Body system: upper body, roof and roof beams, rear floor, door outer panels, etc.; The intake manifold, engine cylinder head cover, engine gear lever, engine decorative cover, etc. in the engine system; Transmission shaft, brake pedal, clutch plate, etc. in the transmission system; suspension, swing arm, frame, leaf spring, etc. in the chassis system.
2.The key to the development of automotive composite materials:
2.1 Exploration of composite materials for automobiles
As the domestic sales and ownership of automobiles continue to increase, and fuel and energy consumption continue to rise, the state encourages and supports the development of new energy vehicles and provides special subsidies for new energy vehicles. To vigorously develop new energy vehicles, cruising range is one of the key factors for consumers to consider whether to buy a car. Under the premise of constant battery energy density, continuous weight reduction can increase cruising range, and automotive composite materials can replace traditional metal materials used in automobiles To reduce the weight of the vehicle’s curb weight. The major vehicle manufacturers have also begun to increase R&D investment, exploring the application of automotive composite materials in various automotive systems and beginning to find special composite materials suitable for automotive applications. After investigation and exploration, it is found that it is difficult to replace traditional sheet metal with composite materials according to the design goals of metal materials, and there are also many problems based on traditional manufacturing processes. Especially in mass production and manufacturing, composite materials are still used. The limitations include the research and development of composite materials for automobiles, the integration with the traditional manufacturing process of the entire vehicle, the maintenance of composite materials, the connection with metal materials and the recycling of composite materials.
The exploration of vehicle composite materials by vehicle companies has been continuously developed from the market research stage, in-depth learning stage, practical digestion stage to deepening practice stage and innovative application stage.
2.2. The key to the development of automotive composite materials:
At the beginning, most R&D personnel of vehicle companies used the principle of “equivalent replacement” to develop and design composite parts, that is, adopting the structural form and performance requirements of traditional steel parts as design goals and requirements. This is because most of the R&D personnel of vehicle companies do not have a comprehensive understanding of the performance and knowledge of composite materials. At the same time, the current design manuals and design cases are mainly made of metal materials. The composite material is mainly composed of a matrix material and a reinforcement material. The characteristics of the matrix material and the reinforcement material determine the characteristics of the composite material. Composite materials and metal materials have different properties. Composite materials are anisotropic; metal materials are isotropic. The failure modes of composite materials and metal materials are different. The failure modes of composite materials are complex and changeable, and belong to progressive ductile fracture failure, while the failure mode of metal materials is yield fracture failure caused by plastic deformation.
The development of composite materials for automobiles requires comprehensive design based on forward design, combining materials, structures, manufacturing processes, and costs. Only in accordance with the design of the structure and the design of ignoring the material can not make the composite material achieve the optimal design. At the same time, it is also facing problems such as insufficient composite material characteristic parameters, lack of automotive special composite materials, high composite material costs, and composite material parts repair and maintenance. The development of composite materials for vehicles should be comprehensively considered from the aspects of material selection, manufacturing, spraying, maintenance, connection with metal materials, and recycling on the premise of having a database of vehicle-specific composite characteristics. Related standards for automotive composite materials should also be gradually improved and formulated.
2.3.Suggestions for the development of composite materials for vehicles:
According to the relevant lightweight development goals, it is expected that from 2026 to 2030, the weight of the whole vehicle will be reduced by 35% compared with 2015. The focus will be on the development of magnesium alloy and carbon fiber composite material technology to realize the large-scale application of carbon fiber composite material hybrid body and carbon fiber parts. , Magnesium alloy for bicycles reaches 45kg, and carbon fiber usage accounts for 5% of vehicle weight. The R&D designers and material engineers of vehicle companies do not have a deep understanding of composite materials, and are currently entering the stage of exploration and practice. After recent years of market research and exploration, they initially have a design and development team for composite materials. However, composite material manufacturers are often unfamiliar with the development process, quality system, supplier management, supply chain logistics, material approval and experimental certification of automobile OEMs. As a result, OEMs cannot find the required composite material suppliers, and composite materials companies cannot fully meet the requirements of OEMs. In particular, the identity advancement and transformation from a composite material supplier to a composite material component supplier needs to be accelerated. OEMs often purchase composite material components instead of composite fiber.
Therefore, it is recommended that vehicle companies gradually conduct in-depth research on composite materials, and establish R&D project teams and talent echelons to meet the design requirements of composite materials. At the same time, composite materials companies should also go to the OEM to communicate and gradually improve relevant requirements. Meet the requirements of vehicle companies to realize joint development and simultaneous development.
As a terminal carrier, vehicle companies need to be responsible for the overall industry chain. In view of the current incomplete performance parameter data of composite materials, imperfect test methods for composite materials and parts, and inconsistent design rules for composite material structures, corresponding measures should be established. System and process.
Composite material companies should promote the cost optimization of composite materials, and realize the process from material to parts, establish and improve the quality system in accordance with the requirements of the OEMs to meet the requirements of the OEMs, and deepen the exchanges of composite materials to promote the OEMs Its application in automobiles.
3 .Concluding remarks:
The application range of automotive composite materials in the entire vehicle continues to expand. As composite materials manufacturers increase R&D investment in automotive composite materials, automotive composite materials have promoted the use of composite materials in automobiles and the amount of use both increase. The development of automotive composite parts requires team collaboration, and comprehensive design is carried out through the top-level forward design combining materials, structures, manufacturing processes, and costs. Composite material manufacturers should advance to the status change of composite parts manufacturers earlier, and intervene in the R&D team of the OEM to provide technical support and process trial production for the development of automotive composite parts during the development of composite parts. Through the joint promotion of OEMs and composite material manufacturers, the industrialization of composite materials for automobiles will be accelerated faster.