Foreign research in the field of composite materials for rail transit has been nearly half a century. Although domestic rail transit and high-speed rail are developing rapidly, and the application of domestic composite materials in this field is in full swing, it is different from the large-scale use of carbon fiber composite materials in China. Among the composite materials widely used in foreign rail transit, most of the reinforcing fibers are glass fibers. For example, as mentioned in this article, TPI composite materials company developed carbon fibers for vehicle body composite materials, accounting for less than 10%, and the rest are glass fibers. Therefore, the cost can be balanced while ensuring light weight. Extensive use of carbon fiber inevitably makes it difficult to control the cost, so it can be used in some key structural parts such as bogies.
For more than 50 years, Norplex-Micarta, a producer of thermoset composites, has been in the steady business of manufacturing materials for rail applications, including trains, light rail braking systems, and electrical insulation for overhead rails. But today, the company's market is expanding from a relatively narrow segment to more other applications, such as walls, roofs and floors.
Dustin Davis, business development director at Norplex-Micarta, believes that the rail and other mass transportation markets will provide more and more 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 protection standard EN 45545-2, which imposes stricter fire, smoke and poison (FST) requirements for mass transport, through the use of phenolic resin systems , composite manufacturers can incorporate the necessary fire and smoke properties into their products.
In addition, operators of buses, subways and trains are beginning to realize the advantages of composite materials in reducing noise vibration and harshness. "If you've ever heard a metal panel rattle on the subway," Davis said. "If the panel is made of composite material, it dampens the sound, making the train quieter."
The lighter weight of composites also makes them attractive to bus operators interested in reducing fuel use and expanding its reach. In a September 2018 report by market research firm Lucintel, it forecasts that the global market for composite materials for mass transit and off-road vehicles will grow at an annual rate of 4.6% between 2018 and 2023, and is expected to grow by 2023. reach a value of $1 billion. Opportunities will come from a wide variety of applications, including exterior, interior, hood and powertrain parts, and electrical components.
The new parts now produced by Norplex-Micarta 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, combining it with faster-curing resin systems. "You can reduce cost, increase yield, and bring the full functionality of FST phenolic resins to market," explains Davis. While composites can be more expensive than comparable metal parts, Davis says cost isn't a decision for the application they're looking at. factor.
Lightweight and flame retardant
European rail operator Duetsche Bahn's fleet of 66 ICE-3 express trains has been refurbished, one of the capabilities of composites to meet customer-specific needs. The installation of the air conditioning system, passenger entertainment system and new seats added unnecessary weight to the ICE-3 railcar. Also, the original plywood floors did not meet the new European fire protection standards. The company needed a flooring solution that would help reduce weight and meet fire safety standards. Lightweight composite floors are the answer.
Germany-based composite fabric manufacturer Saertex supplies the LEO® material system for its floors. According to Daniel Stumpp, global head of marketing at Saertex Group, LEO is a layered, non-crimped fabric with higher mechanical properties and greater lightweighting potential than woven fabrics. The four-component composite system includes a special fire-retardant coating, fiberglass reinforcement, SAERfoam® (core material with integrated 3D-fiberglass bridges) and LEO vinylester resin.
Composites manufacturer SMT (also based in Germany) created the floors through a vacuum infusion process using reusable silicon vacuum bags made by British company Alan Harper. "We saved about 50 percent of the weight from the previous plywood," Stumpp said. “The LEO system is based on a continuous fiber laminate with a non-filled resin system, which has excellent mechanical properties…. In addition, the composite does not rot, which is a great advantage, especially in areas where it snows in winter and the floor is very wet .” The floor, the carpet on the top and the rubber material all meet the new flame retardant standard.
SMT produced more than 32,000 square feet of panels, which to date have been installed in about a third of the eight ICE-3 trains. During the refurbishment process, the size of each panel is being optimized to fit the specific car. The ICE-3 sedan's OEM was so impressed with the new composite floor that it ordered a composite roof to partially replace the old metal roof structure in the rail car.
go further
California-based Proterra, a designer and manufacturer of zero-emission electric buses, has been using composite materials in all of its bodies since 2009. In 2017, the company's battery-charged Catalyst® E2 bus set a record of 1,100 miles on a single trip. That bus features a lightweight body made by composites manufacturer TPI Composites.
Most recently, TPI partnered with Proterra to produce an integrated one-piece composite electric bus. Todd Altman, TPI's Director of Strategic Marketing, explained: "In a typical bus or truck, there is a chassis and the body is on top of that chassis. With the monocoque design of the bus, we have integrated the chassis and the body, similar to one piece. car design.” A single structure is more effective than two separate structures in meeting performance requirements.
The Proterra monocoque is purpose-built, designed from the ground up to be an electric vehicle. That's an important distinction, Altman said, because the experience of many automakers and electric bus makers has made limited attempts to adapt their traditional designs for internal combustion engines to electric vehicles. “They took an existing platform and tried to fit as many batteries as possible. From every point of view, it wasn’t the best solution,” Altman said.
For example, many electric buses have batteries mounted on the rear or top of the vehicle. But with Proterra, TPI is able to fit the battery under the bus. "If you're adding a lot of weight to the vehicle structure, you want that weight to be as light as possible, both from a performance and safety standpoint," Altman said. He noted that many electric bus and automakers are now back on the drawing board, developing more efficient and targeted designs for their vehicles.
TPI has signed a five-year agreement with Proterra to produce up to 3,350 composite bus bodies at TPI's facilities in Iowa and Rhode Island.
needs customization
Designing the Catalyst bus body required TPI and Proterra to constantly balance the strengths and weaknesses of all the different materials so that they could meet cost targets while achieving optimal performance. Altman noted that TPI's experience in producing large wind blades that are about 200 feet long and weigh up to 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 achieve the required structural strength through the selective use of carbon fiber, and retain it to reinforce areas subject to the greatest loads. "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 reinforcement, with fiberglass making up the rest.
TPI chose vinyl ester resins for similar reasons. "When we look at epoxy resins, they're great, but when you cure them, you have to raise the temperature, so you have to heat the mold. It's an extra expense," he continued.
The company uses vacuum-assisted resin transfer molding (VARTM) to produce the composite sandwich structure, which provides the necessary stiffness for the monocoque. During the manufacturing process, some metal fittings, such as threaded fittings and tapping plates, are incorporated into the body. The bus bar is divided into upper and lower parts and then glued together. Workers have to add some small composite trim pieces like fairings later, but the number of parts is a fraction of what would be on a metal bus.
Once the finished body is sent to the Proterra bus production facility, the flow of the production line will be faster because there is less work to do. "They don't have to do all the welding, grinding and fabrication, 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 monocoque.
Altman believes that 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, CNG or diesel hybrid buses. That's probably one of the reasons Proterra says battery-powered electric buses now account for 10% of sales in the overall transportation market.
There are still certain obstacles to the widespread use of composite materials in electric bus bodies. One is the specialization of different bus customer needs. “Each transit authority likes to get the bus in a different way - the seat configuration, the way the hatches open. It’s a huge challenge for the bus manufacturer, and many of those configuration items are likely to flow to us.” Altman Say. "Comprehensive body builders want to have a standard build, but if each customer wants a high degree of customization, that's going to be difficult." TPI continues to work with Proterra to enhance the bus design to better manage the final The flexibility customers demand.
explore possibilities
Composites companies are continuing to test their materials for new mass transit applications. In the UK, ELG Carbon Fibre, which specialises in technologies to recycle and reuse carbon fibre, is leading a consortium of companies to develop lightweight composites for bogies in passenger cars. The bogie supports the body of the car, guides the wheelset and keeps it stable. They help improve ride comfort by absorbing the vibrations of the rails and minimizing the effects of centrifugal forces when the train turns.
One goal of the project is to produce a bogie that is 50 percent lighter than comparable metal bogies. "If the bogie was lighter, it would cause less damage to the track, and because the load on the track would be lower, it would reduce maintenance time and maintenance costs," said Camille Seurat, Product Development Engineer at ELG. The additional goal is to turn the wheels sideways. Wheel-rail forces are reduced by 40% and lifetime condition monitoring is provided. The UK non-profit Railway Safety and Standards Board (RSSB) is funding the project with the aim of producing a commercially viable product.
Extensive manufacturing trials have been conducted, with a number of test panels made using compression molding, conventional wet layup, infusion and autoclave prepregs. Since bogie production would be limited, the company opted for autoclave-cured epoxy prepregs as the most cost-effective method of construction.
The full-scale 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 (a non-woven mat provided by ELG) and virgin carbon fiber fabric. Unidirectional fibers will be used for the main strength elements and will be placed in the mold using robotics. An epoxy resin with good mechanical properties was chosen, which will be a newly formulated flame retardant epoxy resin certified to EN45545-2 for railway use.
Unlike a steel bogie, which has a steering beam welded to two side members, a composite bogie will be fabricated with a different top and bottom and then joined together. To replace the existing metal bogie, the composite version will have to incorporate suspension and brake link brackets and other accessories in the same place. “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-style fittings so we can reduce the final weight even further,” Seurat said.
A consortium member of the University of Birmingham's Sensors and Composites Group is responsible for the development of the monitoring sensor, which will be integrated into the composite bogie during the manufacturing stage. "Most sensors will focus on monitoring strain at discrete points on the bogie, while others will be used for temperature sensing," Seurat said. The sensors will allow for real-time monitoring of composite structures, allowing the collection of service life load data. This will provide valuable information on peak loads and long-term fatigue.
Preliminary studies suggest that composite bogies should be able to achieve the required weight savings of 50 percent. The project team hopes to prepare a large bogie for testing by mid-2019. If the prototypes perform as expected, they will produce more bogies to test trams produced by Alstom Rail Transport.
According to Seurat, while much work remains to be done, initial indications are that it may be possible to create a commercially viable composite bogie that can compete with metal bogies in cost and strength. She added: "Afterwards, I thought that composite materials could be used in the railway industry with many options and potential applications."