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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Breaking the Stiffness Barrier
3 April 2001 7:00 pm
Engineers thought they knew how to make materials as stiff as possible. But now a trick has shattered the old bounds. The finding may lead to new materials that could be used in cars, planes, and spacecraft.
Stiffness is a material's capacity to push back when pushed, like a spring digging into your hand when you squash it. This behavior determines the material's strength and ability to dampen vibrations. Engineers can calculate the maximum stiffness of a given material in a given shape; for instance, they know how to give airplane wings their maximum strength using a given alloy. But these upper limits are calculated using equations that only take into account springlike, or positive, stiffness. Some materials, however, have "negative stiffness": Their structure has been buckled or contorted in such a way that if pressure is applied, their stored energy only causes more compression in the same direction. Imagine a spring that, as you begin to press it, collapses all the way down on its own.
Mixing tiny amounts of these bizarre materials with compounds that have positive stiffness can result in materials that are stiffer than anybody thought possible, says physicist Roderic Lakes and his team at the University of Wisconsin, Madison. In a series of papers last week in Nature, Physical Review Letters, and Philosophical Magazine Letters, the team outlined that theory--and proved that it could work.
For instance, they made rods of tin to which negatively stiff bits of a ceramic called vanadium dioxide had been added. At certain temperatures, they found that the combined material's stiffness was greater than the conventionally calculated maximum--greater even than if they had embedded the tin with diamond. Lakes says that the negative bits essentially kick back against the surrounding material to neutralize force applied to the rods.
The work is still in its early stages, but new superstiff, superdamping materials might be used to make the quietest cars and airplanes ever, experts say. The materials could improve spacecraft, says structural dynamicist Keats Wilkie of the NASA Langley Research Center in Hampton, Virginia, if they're light enough to lower launch costs, yet stiff enough to protect sensitive, pricey equipment. Says Wilkie: "It's very interesting stuff."