In recent years, with the rapid development of the domestic rail transit industry, the requirements for lightweight rail vehicles have become higher and higher, and carbon fiber composite materials have become the next key research and development direction of the rail transit industry. This article introduces the advantages of carbon fiber composite materials in the field of rail transit, and analyzes in detail the technical progress of carbon fiber composite materials for rail transit in terms of carbon fiber, resin, molding process, etc. and their typical applications in the field of rail transit. The problems and challenges faced by the application in the transportation field, and put forward effective countermeasures.
1. Technical progress of carbon fiber composite materials for rail transit
1.1 Carbon fiber
Summarizing the experience of international advanced carbon fiber companies, it can be found that the current development direction of the carbon fiber industry mainly involves three aspects: the development of high-strength carbon fiber, the development of high modulus carbon fiber, and the low cost of carbon fiber, which can be summarized as "two highs and one low".
A typical example is Toray (Japan), which has developed from T300 carbon fiber (tensile strength 3 530 MPa) to current T1100 carbon fiber (tensile strength 6 600 MPa) in high-strength carbon fiber;
For high modulus carbon fiber, from M35J (tensile modulus 343 GPa) to M70J (tensile modulus 680 GPa);
In terms of low cost, it has developed high spinning speed dry jet wet spinning and acquired ZOLTEK (Zoltek) to produce large tow carbon fibers above 48K.
The development of domestic carbon fiber is mainly concentrated in the past 10 years. At present, the production scale of my country's carbon fiber industry is still small and the product specifications are single, which cannot meet the needs of the domestic market. On the other hand, the overall technology of the carbon fiber industry is not yet mature, and the product quality is stable and cost-effective. Lower. However, after continuous research and development in recent years, the progress of domestic carbon fiber technology is obvious to all, which has narrowed the gap with the international advanced level to a large extent.
The thermosetting resins commonly used in composite materials for rail transit mainly include unsaturated polyester resins, phenolic resins and epoxy resins. Epoxy resins are most suitable because of their better environmental protection, mechanical properties and better compatibility with carbon fibers. As a matrix material, it is combined with carbon fiber to manufacture load-bearing parts for rail transit.
Due to the poor flame-retardant performance of ordinary epoxy resins, the limiting oxygen index (LOI) is about 19.8%, which limits the application of epoxy resins in many important fields to some extent. Research has always received widespread attention.
In the past few years, halogenated epoxy resins have been widely used due to their excellent flame retardant properties and physical properties. At the same time, the extensive use of halogen-based flame retardants has also caused a series of problems, the most important of which is that halogen-based flame-retardant materials will continue to produce highly corrosive and toxic gases and smoke when heated or burned in a fire. , While bringing disasters to people, it also indirectly caused environmental pollution.
Therefore, the development of halogen-free, environmentally friendly, thermally stable epoxy resins with high flame retardant efficiency has become a research focus.
Prepreg resin has a higher viscosity at room temperature, which can be adjusted according to the requirements of rail locomotives for material fire performance (such as EN45545-2 "Railway Application-Fire Protection of Railway Vehicles-Part 2: Fire Protection Requirements of Materials and Components") The resin formula meets various indicators such as combustibility, heat release rate, smoke density, and toxic gas.
1.3 Molding process
Composite material forming process usually includes autoclave process, liquid forming process, molding process, vacuum bag pressing process, pultrusion process and winding process.
With the deepening and development of the application of carbon fiber composite materials, composite material molding methods are constantly appearing in new forms, but various molding processes have their own advantages and disadvantages. In actual applications, they are not developed in the form of new and alternative. Often multiple processes coexist and merge with each other to achieve a better synergistic effect.
In general, the development direction of composite material molding technology can be summarized as "four highs and one low", that is, using high-speed and efficient methods to improve material utilization, produce high-quality products, and reduce manufacturing costs. The traditional molding process in the aviation field is based on the autoclave process. From the perspective of Boeing and Airbus aircraft fuselage manufacturing, there are two processes of automatic laying and winding and automatic tape laying, both of which use autoclave curing. .
In recent years, in the process of cost reduction, the liquid molding process is beginning to replace the autoclave process. In the wind power field, a large number of vacuum infusion molding processes and prepreg vacuum bag pressing processes have been adopted. In the carbon fiber main beam production process in recent years, wind power companies headed by VESTAS have innovated structural design, which has changed the complexity Large-scale integrally formed blades are decomposed into several standard parts, which are integrally formed after assembly. The standard parts can be efficiently produced by traditional processes such as pultrusion, which greatly promotes the mass application of carbon fiber in the field of wind power.
2 Typical applications of carbon fiber composite materials in rail transit
The car body structure is an important load-bearing component of a rail locomotive, and its weight accounts for a large proportion of the whole car, generally 15% to 30%. Therefore, to achieve the weight reduction and speed increase of the vehicle, the lightness of the car body structure must be considered. Quantify. At present, aluminum alloy is still the main material for lightweight vehicle body. With the increasing requirements for vehicle lightweight, composite materials, especially carbon fiber composite materials, have become the next key research and development direction.
Fiber-reinforced composite materials used in rail transit equipment abroad are mostly carbon fiber or glass fiber reinforced composite materials, which have also experienced a development process from non-load-bearing structure to main load-bearing structure. Typical applications are: the roof, skin, pantograph edges and window frames of the Japanese Shinkansen N700 series high-speed trains are made of carbon fiber reinforced composite materials; the "efWING" bogie developed by Japan’s Kawasaki Heavy Industries is the world’s first master In the case of using carbon fiber reinforced resin-based composite materials for the load-bearing structure, the original rigid welded bogie frame was changed to a flexible structure, reducing weight by 40%.
This is also applicable to composite applications in the domestic rail transit field, including the low-cost issue that is more concerned in the rail transit field. In fact, it is not simply a carbon fiber price issue. The primary issue is still design.
The car body shell adopts a carbon fiber skinned aluminum honeycomb sandwich structure. A stainless steel rectangular section is embedded in the sandwich structure to improve the structural rigidity of the car body. A stainless steel underframe is used to facilitate the installation of auxiliary equipment. Compared with the old model, the weight of the TTX train body is reduced by about 39%, and the center of gravity is reduced by about 15%.
Based on the current application of carbon fiber in rail locomotives, although considerable progress has been made in research and development at home and abroad, there is still a certain distance from large-scale industrial applications.
3 Problems and challenges faced by the application of carbon fiber composites in the field of rail transit
In the aerospace field, there is a consensus on the research and development and application of composite materials, that is, design is the leader, material is the foundation, manufacturing is the key, application is the purpose, and maintenance is the guarantee. The most critical of these is design.
This is also applicable to composite applications in the domestic rail transit field, including low-cost issues that are more concerned in the rail transit field. In fact, it is not just a matter of carbon fiber prices. The primary issue is still design, because for carbon fiber composite materials, low cost Not only the low cost of materials, but also the low cost of design and manufacturing.
Recalling that the key to the industrialization of carbon fiber wind turbine blades is Vestas' breakthrough in structural design ideas. The breakthrough in the industrialization of carbon fiber applications in the rail transit industry must first innovate in design concepts, and it must inherit the traditional industrial field of carbon fiber composite Material technology must break away from the existing fixed thinking concept.