Into the Wild Green Yonder: Materials Innovation in Transportation
by Andrew H. Dent, PhD.
This year, two major milestones in the evolution of passenger transport highlight materials development. These events not only focus on the limits of current performance, but also demonstrate how transport has become a hot political issue in the concerns over sustainability.
The first and most heralded is the first flight of Boeing’s 787 Dreamliner. A new plane would not normally be such important news in terms of materials, save for the amount non-metals used in the structure. For the first time in modern aviation history, half of the plane will be constructed from composite materials (I say modern, because the original planes built by the Wright brothers were constructed from wood, itself a composite material). As a point of comparison, Boeing’s previous model, the 777, is comprised of 12 percent composites (and 50 percent aluminum), and composites also make up only 25 percent of the total airframe on the Airbus A380 – that company’s recent offering.
Despite concerns over flying in a “plastic plane,” this change in materials offers a number of advantages over conventional aluminum and titanium: the most significant of which is weight. Weighing in at some 30 to 40,000 pounds less than the comparably sized Airbus A330-200, the Dreamliner achieves 20% better fuel efficiency with 20% less emissions. Admittedly, the weight reductions are not all due to the change from metal to composite; for example, 60 miles of copper wiring (a dense metal) has been eliminated simply by reductions in systems complexity.
While some might argue that aluminum – an easily recycled material – might be more “sustainable” than the non-recyclable composites. Boeing’s thinking, however, is that the fuel efficiency resulting from the weight reduction, coupled with significantly lower maintenance requirements, trumps any other material considerations. While the composites cannot be recycled, they are far more resistant to the fatigue and corrosion that requires aluminum panels to be replaced.
The composites used in the 787 are predominantly a mid-range stiffness carbon fiber (T-800) with a toughened epoxy that cures at 350C. Boeing uses both unidirectional fibers and woven mats, which are easily cut (without heating) using water jets, with some titanium and aluminum still used in more complex geometries. We are some way yet to the wholesale use of composites seen in the B2 stealth bomber, but it shows the material direction airlines are taking to improve fuel efficiencies.
The second event was a much lower profile launch, but significant none the less. Taiwan debuted its first commercial Maglev train line, using updated Japanese 700 series Shinkansen technology on a 12-car train. “Maglev” is a contraction of “magnetic levitation,” which uses a high-powered magnetic array to both suspend and propel the train along specially-designed tracks.
Though Maglev trains have been around since the 80’s (the first commercial version was used to transport passengers from airport to train hub in Birmingham, England), the launch in Taiwan heralds a new era in this form of transport, suggesting an acceptance of the technology as a viable alternative to existing electric and diesel powered rolling stock.
The materials science behind the invention is both simple and complex. The simple part is that magnetic surfaces of similar polarity repel (this is how the train levitates); the complex is that in order to start, stop and maintain a safe distance from the ground and other obstacles, the superconducting magnets (cooled by liquid nitrogen) and linear induction motors need to be precisely controlled.
The high speed of some Maglev trains translates to more sound due to air displacement, which gets louder as the trains go faster, however, at low speeds, maglev trains are nearly silent. Despite this air disturbance, two trains passing at a combined 1,000 km/h (621 mph) has been successfully demonstrated without major problems in Japan.
This noiseless, frictionless, pollution free transport system has much to promote it when one considers its sustainability. In addition to these points, the lower vibration increases the life of the materials used in the construction of the train. Indeed, the Railway Technical Research Institute of Japan has conducted a Life Cycle Assessment (LCA) on the trains to demonstrate their sustainability compared to other forms of transport.
Lighter planes and more efficient trains are dependent upon advances in materials that are not necessarily sustainable themselves, but offer significant improvements such that the type of material used (such as the very unsustainable carbon fiber composite) become unimportant. It shows that advancements in sustainability are more complex that we often care to think and that these advances often need not come from a recycled or natural source.
For more information on the materials mentioned in this article, and other materials for architectural applications, contact our Strategic Materials Solution team.