How new materials are solving old problems
Flying high with new polymer composites
R. Byron Pipes has his eye on the sky—or at least on the aviation industry that fills the sky with aircraft. And if things for the airline business are looking up, it’s because of work down at the molecular level. Polymer composite materials are driving the evolution of airplanes to become leaner, less fuel-thirsty machines. The strategy goes something like this: Develop good new materials, build better airplanes, best your competition in the marketplace. Pipes, the John Leighton Bray Distinguished Professor of Engineering, notes that commercial aircraft manufacturing remains one of the major U.S. exports, contributing significantly to the health of the economy. But in recent years, the U.S. market share has been shrinking, losing ground to European-based Airbus. “The future of aviation depends on this polymer composite technology. It’s not only advancing the industry in the U.S.,” says Pipes, “it’s saving it.”
Case in point: Boeing’s new 787 Dreamliner, the first polymer composite commercial aircraft to take flight, represents a major victory in the race to rule the skies. By replacing up to 50 percent of heavy aluminum and titanium components with polymer composites (including the fuselage and the wings), the Boeing 787 Dreamliner is lighter and therefore uses 20 percent less fuel. This brings longer flight range capability to mid-sized planes and enables travel speeds similar to today’s fastest wide bodies (Mach 0.85). Lighter planes reduce the cost of flying, not to mention the simple green goodness of decreasing fossil fuel consumption and reducing emissions at high altitudes. The 787 flight testing began in summer 2009, and the planes are slated for delivery in 2010. Boeing has orders for 878 of the new airplanes to 57 customers.
That’s just the beginning. The Boeing 787 Dreamliner is the progenitor of a new family of polymer composite aircraft. What the next generation will look like depends largely on the work of a team of engineers at Purdue who are further advancing composite polymer science. Pipes, who has joint appointments in chemical, aeronautical, and materials engineering, is part of this team involved in a program called “Atoms to Aircraft.” It is a collaborative effort with Boeing to “understand a polymer composite material’s behavior with much greater clarity,” Pipes explains. The plan is
to build models of new polymer composite materials across 12 orders of magnitude—from 10-10 m up to 102 m—connecting these models from small to large scales and studying how the materials behave. “The multiplicity of physics and chemistry we need to do this is enormous and it is growth in computing power that will enable this new approach,” says Pipes, undaunted.
Enter Jim Caruthers, professor of chemical engineering and director of Purdue’s Center for Integrated Materials and Product Design. With a bachelor’s degree in chemistry, a master’s and doctorate in chemical engineering, and a gift for high-end computer applications, he characterizes himself as “an integrator.” Caruthers says, “I take the chemistry
and the chemical engineering, then the mechanics, and then add the high-end computer science. I cross discipline boundaries.” He is also considered one of the world’s experts in the nonlinear behavior of polymers.
For the Atoms to Aircraft project, Caruthers is focused on the performance of potential aviation-grade polymeric materials under challenging use conditions. He and his group develop models to describe the complex “life history” of each new material as it is manipulated: What happens in the chemical reactions when heating it to shape it? As it cools, how much “cure shrinkage” occurs? Then, once it is a structural part of a plane, say a wing, Caruthers’ computer models test the effect of forces such as the complex deformation that occurs during flight. Finally Caruthers has also to consider that polymers are organic, and over a 20-year life span, the material can “evolve” unlike traditional materials like steel which are basically inert; for example, polymer composites may change because of factors such as ultraviolet degradation. Caruthers’ models have to account for all this variability.
Computer modeling of new polymer composites is the key to this process. “It saves prototype dollars,” says Pipes. To fully test a new material all the way through the Federal Aviation Administration certification process costs hundreds of millions of dollars. By starting with small-scale lab bench experimentation and applying major computer power to the problem, says Caruthers, “we are optimizing testing dollars and enabling innovation. Our process accelerates the introduction of new materials.”
Pipes, Caruthers and their students delivered their research to the worldwide scientific community in Edinburgh this July at the International Conference on Composite Materials. No matter how much of a race it might be to produce new fleets of aircraft, the science must advance like any other—with global agreement about the principles underpinning new technologies. The Atoms to Aircraft team intends to show the world the way.