Advantages of composite materials in rail transit

In recent years, China's rail trains have developed vigorously, with the continuous improvement of train running speed, the lightweight requirements of rail trains continue to improve, and the application of composite materials in the field of rail transit is more and more. By comparing composite materials with traditional metal materials, this paper analyzes the application advantages of composite materials such as light weight, high strength, good flame retardant, fatigue resistance, corrosion resistance, high damping and good designability in the field of rail transit, and introduces the specific application of composite materials in the field of rail transit vehicle body, bogie, brake structure, luggage rack and so on.

Composite material is a material composed of two or more materials with different chemical and physical properties. The composite material consists of a matrix material and a reinforcing material, and the matrix material includes various resins or metallic and non-metallic materials. Reinforcement materials include various fibrous materials or other materials. The reinforcement material provides the stiffness and strength of the material in the composite material, and the matrix material is used to support and fix the fiber material, transfer the load between the fibers, protect the fiber, etc. Common composite materials are glass fiber composite materials (GFRP), carbon fiber composite materials (CFRP) and so on(CFRTP). The rapid development of composite materials in recent years, because of its excellent performance is widely used in aerospace, wind power blades, sports and leisure and automotive fields, especially in the field of rail transit composite materials more and more applications.

By 2020, China's high-speed railway has a total operating mileage of 38,000 kilometers, accounting for two-thirds of the world's operating mileage. According to the national "Medium and long-term railway network planning", by 2030, China's high-speed railway will reach 45,000 kilometers of total operating mileage. In terms of urban rail transit, the total operating mileage of 7,900 kilometers is expected to reach 14,000 kilometers by 2025. With the rapid development of China's rail transit industry, composite materials with obvious advantages over traditional materials have been widely used in the design of rail vehicles. The structural parts made of composite materials have the advantages of light weight, high stiffness and high strength, and can also effectively improve the comfort and safety of the vehicle, reduce vibration and noise, and reduce the weight of the body. Composite materials have become an indispensable key material in the field of rail transit.

This paper introduces the advantages of composite materials compared with traditional materials, analyzes the application advantages of composite materials in rail transit, and reviews the application status of composite materials in various fields of rail transit.

Advantages of composite materials

The fiber composite materials used most in rail transit are carbon fiber composite materials, glass fiber composite materials and aramid composite materials. Compared with traditional materials, composite materials have many application advantages in rail vehicles.

2.1 Light weight and high strength

With the increase of the operation speed of rail transit vehicles, the requirement of lightweight rail vehicles is getting higher and higher. Composite materials have the characteristics of light weight and high strength. The mechanical properties of several common composite materials and metal materials are compared, as shown in Table 1. Taking carbon fiber and aluminum as an example, the density of carbon fiber is 1.6g/cm3, which is only 57% of the density of aluminum, but the strength is 3.6 times that of aluminum. Under the premise of ensuring the structural strength, the structural parts made of carbon fiber composite materials can greatly reduce the weight.

2.2 Good flame retardant

One of the core of rail transit vehicle safety is fire prevention, because the carriage is a closed space, if a fire passenger can not escape in time, the flame retardant performance of the material is an important indicator. The flame retardant elements such as silicon and boron can be added to the molecular structure of the composite material, and flame retardants can be added to the matrix to improve the flame retardancy of the material and improve the fire safety of the train.

2.3 Good fatigue resistance

In general, the fatigue strength of metal materials is much smaller than its static strength, while the difference between fatigue strength and static strength of composite materials is small. The gap generated by the metal material under the action of dynamic load is easy to expand and crack is formed quickly. However, due to the layered characteristics of composite materials, cracks are not easy to spread in the material, and there will be no long-term deformation, which improves the fatigue resistance of the structure.

2.4 High damping

Compared with metal materials, composite materials also have the characteristics of high damping, which can reduce vibration, protect the safety of vehicle operation, reduce vehicle noise, improve vehicle comfort and reduce equipment damage.

2.5 Good corrosion resistance

When rail transit vehicles operate, they need to face the complex outdoor environment, and the corrosion of metal materials has always been a technical difficulty. The composite material has good corrosion resistance, can cope with corrosion problems well, extend the service life of rail vehicles, reduce maintenance costs.

2.6 Good designability

The composite material has the characteristics of high specific modulus and high specific strength, and the mechanical properties can be varied in a wide range, through the selection of composite material matrix, fiber and changing the molding process of the material can meet different design needs.

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