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Opposites attract: Stable and unstable materials couple for high performance

Walter J. Drugan

Walter J. Drugan (large image)

Roderic S. Lakes

Roderic S. Lakes (large image)

Robert W. Carpick

Robert W. Carpick (large image)

Reid F. Cooper

Reid F. Cooper (large image)

An ear-splitting, bone-jarring ride in a small, propeller-driven airplane illustrates the need for better materials that deaden vibration, says Professor Walt Drugan. "You'd very much like it to be full of high-damping materials," he says.

But materials with such extreme properties, including high stiffness and high damping, don't yet exist.

With a four-year, $800,000 grant from the National Science Foundation's Engineering Directorate-Division of Civil and Mechanical Systems, Drugan, Professor Rod Lakes, Assistant Professor Rob Carpick, and Materials Science and Engineering Professor Reid Cooper, are studying how to couple stable and unstable materials to yield new high-performance materials.

In the structural stiffness sense, says Drugan, if you push on a stable material, it will push back, like a spring. An unstable material will push away or revert to a form in which positive, or stable, stiffness governs.

And while the idea of composite materials has been around literally forever — for example, early bricks of mud and straw — combining two opposite-reacting materials in just the right quantities and geometries to get super-high performance is very new, he says.

Generally, when people do the mathematics of materials, they assume everything is stable, says Lakes. "What we've found is you don't necessarily have to assume that, because you can have an unstable part that's stabilized by other parts that are in fact stable," he says.

In a 2002 paper in the Journal of the Mechanics and Physics of Solids, he and Drugan showed theoretically that combining stable and unstable materials in a certain way would produce materials with "super" properties such as high damping or stiffness.

In addition to an aircraft or spacecraft, there are many situations in which such materials are desirable, says Lakes, including quieter cars, more stable bridges and tall buildings, or more efficient electronics.

The group, which also includes graduate students Amelia Berta, Yun-Che Wang, Pat Frascone, Tim Jaglinski and Sara Blair, began the project last fall and is focusing not only on the general theory, but also on developing specific material systems. Carpick is applying the work to carbon nanotubes, while Cooper is investigating materials that easily undergo crystal transformations.