1) Carbon fiber reinforced plastics (CFRP). Carbon fiber is made of fiber and polypropylene fiber after high temperature heating treatment. It has high heat resistance, smaller specific gravity than aluminum and glass fiber, and its strength can match that of steel and aluminum when compounded with plastic. However, the cost of CFRP is much higher than that of GFRP (glass fiber reinforced plastic), which is mostly used in aerospace and sports goods.
In 1979, Ford Motor Company of the United States published a new idea of using GFRP to make light experimental vehicles (see Figure 1), in which CFRP is about 300kg, and the fuel cost can be reduced by about 35%. The experimental vehicle mainly applies CFRP material to the body panel, other functional parts such as transmission shaft and plate spring, and also tries to apply it to engine body, connecting rod, piston and other parts. CFRP material is light in weight, high in rigidity and strength. Due to the anisotropy of the material, its strength and rigidity can be maintained in the required direction during design. The elastic modulus of CFRP is 4~9 times that of GFRP and 3~4 times that of metal materials. If it is produced in batches, the cost will fall further, so it will be a composite material with high expectations.
2) Fiber reinforced metal (FRM). CFRP and GFRP have various superior mechanical properties, but their base is plastic, which has poor heat resistance compared with metal. Therefore, the research of FRM used as high-temperature strength material is very popular, and the possibility of its use in automobiles has been revealed. Reinforcing fibers include: carbon element, silicon carbide, boron, aluminum oxide, etc. The substrate begins with aluminum, copper and nickel, and then comes with titanium, magnesium, zinc and tin suitable for various purposes. The combination of reinforcing fiber and various metals will produce FRM with various characteristics. FRM is now being applied to piston, connecting rod and other sliding parts. Due to the high price of this kind of fiber and the fact that it has not reached the scale of mass production, its use value as a material with good high-temperature strength is quite high.
3) Metal-plastic laminated materials. The material that closely combines high-strength steel plate with aluminum and plastic is an ideal lightweight material, and also a laminated material of sandwich structure. Because it is bonded with thin steel plate or aluminum plate on both sides of the plastic core, it has excellent heat insulation and sound insulation performance. Laminated material, which is called to play the advantages of good rigidity compared with steel plate, is subjected to bending stress by the metal plate on both sides of the plastic core and shear stress by the plastic core. Under the same rigidity, the quality of the laminated steel plate is 30%~- 70% of that of the ordinary steel plate. If there are certain restrictions on the quality of the laminated plate, it can be solved by changing the thickness of the metal plate and the core plate on both sides of the core. The cost of laminated material is generally 1~3 times that of steel plate, but it still has some problems to be solved, such as: how to bond with each panel when it is used in the car body panel; When the metal plate on its surface is corroded, the rigidity will be reduced. However, with the progress of research and development of laminated materials, there is a great possibility to make it practical.
4) Glass fiber reinforced composites for vehicles. Due to the wide variety of reinforcement materials and filler materials, the material using glass fiber as reinforcement material is called GFRR. Because the addition of glass fiber has greatly improved the physical and mechanical properties of plastics, the reinforced plastics can also be used as engineering materials. At present, glass fiber reinforced plastics used in automobiles mainly include glass fiber reinforced PP, glass fiber reinforced PA66 or PA6, and a small amount of PBT and PPO materials. Glass fiber reinforced composites used in automobiles include glass fiber reinforced thermoplastics, glass fiber felt reinforced thermoplastics (GMT), sheet molding materials (SMC), resin transfer molding materials (RTM) and hand lay-up FRP products.
Reinforced PP is mainly used to make products such as engine cooling fan blades and upper and lower cover of timing belt, but some products have defects such as poor appearance quality and warpage, so non-functional parts are gradually replaced by talcum powder filled PP. Reinforced PA materials have been used in cars, vans and trucks, and are generally used to make small functional parts, such as lock body protective cover, safety wedge, embedded nut, accelerator pedal, gear shift upper and lower protective frame-protection cover and opening handle. GMT is a very active composite material development variety in the world at present. It is a novel, energy-saving and lightweight composite material with thermoplastic resin as the matrix and glass fiber felt as the reinforcement skeleton. Generally, it can produce semi-finished sheet materials, and then directly process them into products of the required shape. The fiber can be short glass fiber or continuous glass fiber felt.
SMC is an important and widely used semi-finished product of molded composite products. Compared with steel auto parts, SC has a short production cycle, is convenient for auto modification, and has good investment efficiency; Light weight, fuel saving; Design freedom; The integrity of the parts is good, and the number of parts is small; Good durability and heat insulation. However, SMC cannot be recycled and pollutes the environment; Although the performance and price are relatively good, the one-time investment is often higher than the corresponding steel parts, such as the lower radiator bracket in the front panel of the Ford Taurus and Mercury Sable cars. The original steel parts have 22 parts, while the SMC has only 2 parts, which greatly reduces the quality and costs by 14%.
Although many automobile factories have replaced relatively heavy metals with glass fiber reinforced materials when producing automobile bodies, glass fiber is a fiber drawn from molten glass, which is very easy to re-solidify after melting at high temperature, which brings great difficulties to the recovery and treatment of waste cars. To this end, the French National Center for Scientific Research is studying a synthetic material based on hemp and polyurethane. This material is characterized by cheaper price, lighter weight, stronger toughness, and biodegradation in addition to the advantages of metal and glass fiber. At present, the center is testing the strength and other properties of this material. The first phase is to produce car doors with this material.