Foreign research in the field of composite materials for rail transit has been going on for nearly half a century. Although the rapid development of rail transit and high-speed rail in China and the application of domestic composite materials in this field are in full swing, the reinforced fiber of composite materials widely used in foreign rail transit is more glass fiber, which is different from that of carbon fiber composites in China. As mentioned in this article, carbon fiber is less than 10% of the composite materials for body developed by TPI Composites Company, and the rest is glass fiber, so it can balance the cost while ensuring lightweight. The massive use of carbon fibre inevitably leads to cost difficulties, so it can be used in some key structural components such as bogies.
For more than 50 years, Norplex-Micarta, a maker of thermosetting composites, has had a steady business making materials for rail transit applications, including trains, light-rail braking systems, and electrical insulation for elevated electric rails. But today, the company's market is expanding beyond a relatively narrow niche into more applications such as walls, roofs and floors.
Dustin Davis, director of business development for Norplex-Micarta, believes that rail and other mass transportation markets will increasingly provide opportunities for his company, as well as other composite manufacturers and suppliers, in the coming years. There are several reasons for this expected growth, one of which is the European adoption of the Fire standard EN 45545-2, which introduces more stringent fire, smoke and gas protection (FST) requirements for mass transport. By using phenolic resin systems, composite manufacturers can incorporate the necessary fire and smoke protection properties into their products.
In addition, bus, subway and train operators are beginning to realize the advantages of composite materials in reducing noisy vibration and cacophony. "If you've ever been on the subway and heard a metal plate rattling," Davis said. If the panel is made of composite material, it will mute the sound and make the train quieter."
The lighter weight of the composite also makes it attractive to bus operators interested in reducing fuel use and expanding its range. In a September 2018 report, market research firm Lucintel predicted that the global market for composites used in mass transportation and off-road vehicles would grow at an annual rate of 4.6 percent between 2018 and 2023, with a potential value of $1 billion by 2023. Opportunities will come from a variety of applications, including exterior, interior, hood and powertrain parts, and electrical components.
Norplex-Micarta now produces new parts that are currently being tested on light rail lines in the United States. In addition, the company continues to focus on electrification systems with continuous fiber materials and combines them with faster curing resin systems. "You can reduce costs, increase production, and bring the full functionality of FST phenolic to market," Davis explained. While composite materials can be more expensive than similar metal parts, Davis says cost is not the application determining factor they are studying.
Light and flame-retardant
The refurbishment of European rail operator Duetsche Bahn's fleet of 66 ICE-3 Express cars is one of the capabilities of composite materials to meet the specific needs of customers. The air conditioning system, passenger entertainment system and new seats added unnecessary weight to the ICE-3 rail cars. In addition, the original plywood flooring did not meet the new European fire standards. The company needed a flooring solution to help reduce weight and meet fire protection standards. Lightweight composite flooring is the answer.
Saertex, a manufacturer of composite fabrics based in Germany, offers a LEO® material system for its flooring. Daniel Stumpp, global head of marketing at Saertex Group, said LEO is a layered, non-crimped fabric that offers higher mechanical properties and greater lightweight potential than woven fabrics. The four-component composite system includes special fire-resistant coatings, fiberglass reinforced materials, SAERfoam®(a core material with integrated 3D-fiberglass Bridges), and LEO vinyl ester resins.
SMT(also based in Germany), a composite material manufacturer, created the floor through a vacuum filling process using reusable silicon vacuum bags made by Alan Harper, a British company. "We saved about 50 percent of the weight from the previous plywood," Stumpp said. "The LEO system is based on continuous fiber laminates with a non-filled resin system with excellent mechanical properties... . In addition, the composite does not rot, which is a big advantage, especially in areas where it snows in winter and the floor is wet." The floor, top carpet and rubber material all meet the new flame retardant standards.
SMT has produced more than 32,000 square feet of panels, which have been installed in about a third of the eight ICE-3 trains to date. During the refurbishment process, the size of each panel is being optimized to fit a particular car. The OEM of the ICE-3 sedan was so impressed with the new composite flooring that it has ordered a composite roof to partially replace the old metal roof structure in the rail cars.
Go further
Proterra, a California-based designer and manufacturer of zero-emission electric buses, has been using composite materials in all of its bodies since 2009. In 2017, the company set a record by driving 1,100 one-way miles on its battery-charged Catalyst®E2 bus. That bus features a lightweight body made by composite manufacturer TPI Composite.
* Recently, TPI collaborated with Proterra to produce an integrated all-in-one composite electric bus. "In a typical bus or truck, there is a chassis, and the body sits on top of that chassis," explains Todd Altman, director of Strategic marketing at TPI. With the hard shell design of the bus, we integrated the chassis and body together, similar to the design of the all-in-one car." A single structure is more effective than two separate structures in meeting performance requirements.
The Proterra single-shell body is purpose-built, designed from scratch to be an electric vehicle. That's an important distinction, Altman said, because the experience of many automakers and electric bus makers has been to try limited attempts to adapt their traditional designs for internal combustion engines to electric vehicles. "They're taking existing platforms and trying to pack as many batteries as possible. It doesn't offer the best solution from any point of view." "Altman said.
Many electric buses, for example, have batteries in the back or on top of the vehicle. But for Proterra, TPI is able to mount the battery underneath the bus. "If you're adding a lot of weight to the structure of the vehicle, you want that weight to be as light as possible, both from a performance standpoint and from a safety standpoint," Altman said. He noted that many electric bus and car manufacturers are now going back to the drawing board to develop more efficient and targeted designs for their vehicles.
TPI has entered into a five-year agreement with Proterra to produce up to 3,350 composite bus bodies at TPI's facilities in Iowa and Rhode Island.
Need to customize
Designing the Catalyst bus body requires that TPI and Proterra constantly balance the strengths and weaknesses of all the different materials so that they can meet cost goals while achieving optimal performance. Altman noted that TPI's experience in producing large wind blades that are about 200 feet long and weigh 25,000 pounds makes it relatively easy for them to produce 40-foot bus bodies that weigh between 6,000 and 10,000 pounds.
TPI is able to obtain the required structural strength by selectively using carbon fiber and retaining it to reinforce the areas that bear the greatest load. "We use carbon fiber where you can basically buy a car," Altman said. Overall, carbon fiber makes up less than 10 percent of the body's composite reinforcing material, with the rest being fiberglass.
TPI chose vinyl ester resin for a similar reason. "When we look at epoxies, they're great, but when you cure them, you have to raise the temperature, so you have to heat the mold. It's an additional expense, "he continued.
The company uses vacuum-assisted resin transfer molding (VARTM) to produce composite sandwich structures that provide the necessary stiffness to a single shell. During the manufacturing process, some metal fittings (such as threaded fittings and tapping plates) are incorporated into the body. The bus is divided into upper and lower parts, which are then glued together. Workers must later add small composite embellishments such as fairings, but the number of parts is a fraction of the metal bus.
After sending the finished body to the Proterra bus production plant, the production line flows faster because there is less work to be done. "They don't have to do all the welding, grinding and manufacturing, and they have a very simple interface to connect the body to the drivetrain," Altman added. Proterra saves time and reduces overhead because less manufacturing space is required for the monocotic shell.
Altman believes demand for composite bus bodies will continue to grow as cities turn to electric buses to reduce pollution and cut costs. According to Proterra, battery electric vehicles have the lowest operating life cycle cost (12 years) compared to diesel, compressed natural gas or diesel hybrid buses. That may be one reason why Proterra says sales of battery-powered electric buses now account for 10% of the total transport market.
There are still some obstacles to the wide application of composite materials in electric bus body. One is the specialization of different bus customers' needs. "Every transit authority likes to get buses in a different way -- seat configuration, hatch opening. It's a big challenge for bus manufacturers, and many of those configuration items could go to us." "Altman said. "Integrated body manufacturers want to have a standard build, but if every customer wants a high degree of customization, it's going to be difficult to do that." TPI continues to work with Proterra to enhance the bus design to better manage the flexibility required by end-customers.
Explore the possibility
Composites is continuing to test whether its materials are suitable for new mass transportation applications. In the UK, ELG Carbon Fibre, which specialises in technology for recycling and reusing carbon fibre, leads a consortium of companies developing lightweight composite materials for bogies in passenger cars. The bogie supports the body of the car, guides the wheelset and maintains its stability. They help improve ride comfort by absorbing rail vibrations and minimizing centrifugal force as the train turns.
One goal of the project is to produce bogies that are 50 percent lighter than comparable metal bogies. "If the bogie is lighter, it will cause less damage to the track, and because the load on the track will be lower, maintenance time and maintenance costs can be reduced," says Camille Seurat, ELG product development engineer. Additional objectives are to reduce side-to-rail wheel forces by 40% and provide lifetime condition monitoring. The UK's non-profit Rail Safety and Standards Board (RSSB) is funding the project with the aim of producing a commercially viable product.
Extensive manufacturing trials have been conducted and a number of test panels have been made using prepregs from die pressing, conventional wet layup, perfusion and autoclave. Because production of the bogies would be limited, the company chose epoxy prepreg cured in autoclaves as the most cost-effective method of construction.
The full-size bogie prototype is 8.8 feet long, 6.7 feet wide and 2.8 feet high. It is made from a combination of recycled carbon fiber (nonwoven pads provided by ELG) and raw carbon fiber fabric. The one-way fibers will be used for the main strength element and will be placed in the mold using robotic technology. An epoxy with good mechanical properties will be selected, which will be a newly formulated flame retardant epoxy that has been certified EN45545-2 for use on railways.
Unlike steel bogies, which are welded from steering beams to two side beams, composite bogies will be built with different tops and bottoms that are then joined together. To replace the existing metal bogies, the composite version will have to combine the suspension and brake connection brackets and other accessories in the same position. "For now, we have chosen to keep the steel fittings, but for further projects, it might be interesting to replace the steel fittings with composite type fittings so that we can further reduce the final weight," Seurat said.
A consortium member of the Sensors and Composites Group at the University of Birmingham is overseeing the development of the sensor, which will be integrated into the composite bogie at the manufacturing stage. "Most sensors will focus on monitoring strain at discrete points on the bogie, while others are for temperature sensing," Seurat said. The sensors will allow real-time monitoring of the composite structure, allowing lifetime load data to be collected. This will provide valuable information about peak load and long-term fatigue.
Preliminary studies indicate that composite bogies should be able to achieve the desired weight reduction of 50%. The project team hopes to have a large bogie ready for testing by mid-2019. If the prototype performs as expected, they will produce more bogies to test trams made by Alstom, the rail transport company.
According to Seurat, although there is still much work to be done, early indications suggest that it is possible to build a commercially viable composite bogie that can compete with metal bogies in cost and strength. "Then I think there are a lot of options and potential applications for composites in the railway industry," she added. (Article reprinted from Carbon Fiber and Its Composite Technology by Dr. Qian Xin).
Post time: Mar-07-2023