Composites Aboard High-Speed Trains
When it comes to composite applications, two characteristics of high-speed trains distinguish their designs from those of conventional trains. First, notes François Lacôte, senior vice president, technical department of Alstom, "the higher the speed, the heavier the impact on infrastructure." Studies conducted by Alstom, a Saint Ouen, France-based manufacturer in the power and rail infrastructure markets, and French National Railways (SNCF) have led to a weight norm of 17 metric tonnes/18.7 tons per axle for high-speed train systems -- those operating at 300 kph (186 mph) or more -- compared to 22 metric tonnes/24.3 tons per axle for conventional trains traveling up to 200 kph (124 mph). While conventional trains increasingly use composites to lighten loads, especially as fuel costs rise, Lacôte points out, "there is an even stronger move towards finding ways to lighten loads in high-speed systems than is seen in conventional vehicles."
Second, aerodynamics become much more critical as speeds increase. Since air resistance rises geometrically with speed, "you can reduce the loads by going to good aerodynamic shape," says Frank Duschinsky, director of systems engineering and contracts for Bombardier (Berlin, Germany). "At 60 mph, you can push a square box through the air with no problem. But the faster you go, the more attention you have to pay to aerodynamics."
Moreover, he continues, while running noise (produced by the wheels on the track) is a conventional train's primary noise component, aerodynamic noise predominates in high-speed trains. Composite front ends, or "noses," abound in high-speed train sets because aerodynamically contoured composite structures are relatively simple to fabricate. By comparison, "metallic materials can require rather difficult metal beating to achieve a rounded form, for example," Lacôte says. "All front ends of very high-speed trains integrate composites -- not only those dedicated to very high-speed trains, but also conventional trains which run at relatively high speed."
Aerodynamic detailing also is a must for the ventilation system, which draws in outside air. Composites are the principal material for air inlets on high-speed trains because of the complex shapes and curvatures needed to alleviate noise. "The treatment of the outside becomes very important because of resonance, whistling noises, and the like," Duschinsky says.
Alstom and Bombardier are two of the world's leading manufacturers of rail vehicles. Alstom's name is associated especially with the SNCF-trademarked TGV high-speed trains of France. Bombardier teamed with Alstom to build train sets for the Amtrak Acela Express, the first high-speed transit in North America.
TGV LAUNCHES HIGH-SPEED ERA
A trademark of SNCF, the TGV train set has been operating for more than 20 years and has carried more than 400 million passengers. Nearly 500 TGV train sets operate worldwide, with 60 percent of these trains traveling at 270 kph (168 mph) or faster. Maximum TGV speed is 320 kph (199 mph). One of the most recent additions to the TGV fleet is TGV Korea, which carries passengers from Seoul to Busan and from Seoul to Mokpo in South Korea. Some 46 train sets entered service in April 2004, and South Korea's national railway, Korail, announced after its first 100 days of operation that more than 7 million passengers had already taken advantage of the high-speed service.
The 388m/1,273-ft-long TGV Korea trains consist of two power cars that pull 18 coaches at up to 300 kph (186 mph). The train's exterior nose consists of glass/polyester, incorporating woven glass fabrics along with chopped strand mat for added strength. A solid-laminate structure, the nose is hand layed up in epoxy and polyester tooling. Three-dimensional contouring and weight savings prompted the use of composites. Thickness of the nose laminate varies from 5 mm/0.2 inch to 10 mm/0.4 inch. Areas demanding high strength are reinforced with additional glass plies and/or with stainless steel inserts.
Key composite components include interior sidewalls, interiors of toilet modules, the driver's desk and covers around the doors. Most of these solid-laminate components are layed up by hand, using polyester resin and chopped glass strand mats, reports Christophe Pailler, Alstom Transport interiors specialist. He adds that Alstom also uses compression molding of sheet molding compound (SMC) and resin transfer molding (RTM) when the size and number of components justify tooling and equipment costs. The polyester resin includes fire-protection additives that make the resin compliant with the French fire standard NF F 16-101.
With a top speed of 240 kph (150 mph), Amtrak's Acela Express in the U.S. travels from Boston, Mass. to New York City in three hours, 23 minutes, and from New York City to Washington, D.C. in two hours, 44 minutes. Each Acela train consists of front and rear locomotives with six passenger coaches in between. Acela Express generates 12,500 hp using Alstom's electric propulsion designed for the TGV. Advanced tilt technology, developed by Bombardier, improves the ride quality as the train travels through curves at high speeds. The 20 train sets were part of an $800 million (USD) contract with Bombardier-Alstom that also included new maintenance facilities in Boston, New York City and Washington, D.C., and 15 high-hp locomotives to power existing trains (not part of Acela Express).
The nose of the Acela Express -- measuring approximately 3.6m/12-ft high by 3.2m/10.5-ft wide by 4.6m/15-ft long -- was hand layed up with fiberglass/polyester resin, says Duschinsky, who headed up the engineering effort for the consortium. Even with the sleek contouring of the nose, he points out, it still provides sufficient strength. North American regulations require trains to withstand intrusion into occupied areas in a collision at two times the maximum speed of the train. "Composites allowed us to easily build in high strength through the number of composite layers," he explains, adding that some carbon fiber was used in areas of high stress. "You could get sufficient strength with metals as well, but not with the nice shape that composites give the Acela nose." To meet flammability standards, the polyester resin for this and other composite components is filled with up to 60 percent aluminum trihydrate for fire resistance and smoke control.
The 40-plus noses (two for each train set, plus a few spares) were built by the now defunct fabricator GSM (Montreal, Quebec, Canada). Balsa wood core, up to 6.4-mm/0.25-inch thick, was used throughout the unsupported body of the nose where extra stiffness was needed. Solid, 15.9-mm/0.625-inch thick laminate was used in more complexly shaped areas, "where the geometry is very tight, such as around the light receptacles," explains Daniel Palardy, Bombardier's structural manager for the project. The ability to vary the design architecture within the part clinched the group's decision to use composite materials, he adds. The biggest challenge the designers encountered was fitting the nose to the tight tolerances of the rest of the train, which required a smooth, perfect fit. Attention to detail during fabrication achieved this end.
Another major composite set on the Acela are the shrouds that surround the two air conditioning units per coach car, which are positioned on car roofs. On low-speed trains, no shielding for roof-mounted units is required, but at high speeds, the Acela's shrouds control both noise and air-inlet volume. With four sides and a roof, the shrouds measure approximately 3.7m/12-ft wide by 2.4m/8-ft deep by 0.45m/1.5-ft high. Hand layup and vacuum bagging produced these solid-laminate fiberglass/polyester units. On the sides of each shroud, two composite air-intake "ears" are mounted in a secondary joining process. The complex-contoured intakes also were hand layed up and vacuum bagged from the same materials as the shrouds.
Composite undercarriage covers, developed for the high-speed Acela, shield the equipment mounted on the underside of the train. In conventional trains, this equipment can be left exposed. But increased aerodynamic demands as well as greater impact from rocks kicked up by the train warrant the Acela's undercarriage covers. Under each car, three covers are mounted adjacent to each other to shelter the entire underbody. The three covers differ from each other to fit around the particular equipment under that portion of the train car, and each sandwich structure includes a hinged bay for access to the equipment. Each cover was hand layed up and vacuum bagged using fiberglass/polyester around a balsa core.
Like most trains built today, the Acela carries many composite interior components. The train's large windows incorporate hand layed up composite masks, similar to the pull-down shades found on airplane windows, with fiberglass reinforcement to support these large polyester panels. Also similar to those in airplanes, luggage racks are hand layed up from fiberglass/phenolic with honeycomb core and include integrated metal hardware for opening and closing the racks and for suspension. Hand layed fiberglass composites also make up the toilet modules and the control panel in the engineer's cabin. Seat shells were compression molded from fiberglass/polyester SMC. Light weight and durability were factors in the selection of composites for these interior components, but for the Acela, use of composites provided a bonus. "As a premium service," Duschinsky explains, "the Acela received more attention from interior designers. Interior components possess more compound forms for aesthetics."
FASTER YET -- THE SIEMENS VELARO
Earlier this year, the Spanish National Railways (Red Nacional de los Ferrocarriles Espanoles, RENFE) ordered ten new high-speed train sets from Siemens AG (Erlangen, Germany), a 240 million Euro contract, or about $311 million (USD). RENFE plans a nationwide high-speed rail network, with an impressive goal of 7,200 km/4,474 miles of high-speed routes by 2010. Various lines in the network are currently in all phases of planning, design and implementation. Siemens had previously built 16 eight-car train sets back in 2002.
The Spanish trains are built on Siemen's Velaro platform, which evolved out of German Rail's (Deutsche Bahn AG) trademark Inter City Express, or ICE. A Siemens-led consortium created the ICE 3, a train design now widely used in Germany and The Netherlands (although the ICE moniker is used only in Germany). The Velaro E alters the ICE 3 air conditioning and ventilation design to accommodate the broader climate changes in Spain, where trains travel from the hot, dry summers and mild winters of Madrid through near-alpine terrain, then descend 1,200m/3,937 ft into the sea-level humidity of Barcelona. Siemens also upgraded the power system to achieve the 350 kph (218 mph) needed to complete the 630-km/391-mile Madrid-to-Barcelona trip in only 2.5 hours. These changes notwithstanding, the Spanish operating conditions left the use of composites on the train sets essentially the same as the ICE 3.
Siemens engineers note many advantages of composites, including aesthetic flexibility, the ability to increase pre-assembly of the train, and integration of multiple functions in one component. This last characteristic, according to Siemens, has changed the job specifications of components suppliers, enabling the company to assign responsibility for a whole system and its modular features to a single supplier. An interior panel, for example, might include three-dimensional geometries for aesthetics, yet also be designed to bear loads, incorporate warmth and noise insulation, and provide impact protection. Designers still prefer natural materials such as wood for many applications both for aesthetics and for costs. The need for more insulating layers within composite components as compared to wood can exacerbate the cost differential between the materials.
Design requirements for interior composite components of Velaro E and ICE trains do not differ significantly from Siemens' conventional train interiors. The company sees the most important influence coming from national requirements, which are different for each country. Both train types use composite panels for interior ceilings, walls, cabinet coverings and other components. Wall and roof panels in the high-speed trains, measuring 2,225 mm by 1,400 mm (87.6 inches by 55 inches), are formed in heated compression molds from fiberglass/polyester SMC. Thickness of these panels varies from 3 mm to 7 mm (0.12 inch to 0.28 inch), depending on localized strength requirements.
Tables, seat bowls and a luggage rack component also are made from fiberglass/polyester composites.
Like the Acela Express trains, Siemens' Velaro E and ICE trains also use composites for outer protection of the undercarriage, aerodynamic roof hoods, air ducts, and the train's head and bow noses. Pantographs (the extensions that connect the train to overhead electrical power) also are protected by composite covers.
Siemens reports that wet hand layup and heated compression molding are the predominant fabricating methods for these composite components, each used for about 40 percent of the parts. A few parts also are made from prepreg (5 percent), injection molding (5 percent) and extrusion (10 percent).
THE USUAL OBSTACLES
As in most emerging markets for composites, lack of familiarity with the materials and their performance characteristics is the biggest barrier to broader application. "For example," says Alstom's Lacôte, "we do not yet know enough about their fatigue resistance, nor exactly how they will age. Our customers expect vehicles with a lifespan of 30 to 40 years. We do not have enough experience with composites to guarantee this when using them in the vehicle's primary structure." He also points to lack of data on the impact behavior of composites when struck with ballast at very high speed. "We know how well steel and aluminum resist ballast spray, but not how well composites do."
Flame/smoke/toxicity (FST) standards, which generally do not differ between high-speed and conventional trains, still demand ongoing characterization of composites and development of new materials. "What we used 10 or 15 years ago, we can't use anymore," Duschinsky reports. "It narrows down the window of composite types."
All three train manufacturers nevertheless anticipate growing use of composites in the rail sector, especially as high-speed trains compete effectively with air transportation. Composites currently are used strictly on superstructure in trains, but experimentation with primary structures may not be far off. Weight savings are the primary motivation for such investigations. For an ever-expanding set of applications, Lacôte concludes, "We are very open to the arrival of composite materials."
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