Nanotube Heals Itself
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3/30/2007
8:58 AM
Page 300
RESEARCH/RESEARCHERS
Nanotube Heals Itself Pound for pound, carbon nanotubes are stronger and lighter than steel, but unlike other materials, the miniscule cylinders of carbon remain remarkably robust even when chunks of their bodies are destroyed with heat or radiation. Scientists at Rice University offer an explanation: tiny blemishes crawl over the skin of the damaged tubes, sewing up larger holes as they go. “The shape and direction of this imper-
fection does not change, and it never gets any larger,” said lead researcher Boris Yakobson, professor of mechanical engineering and materials science and of chemistry. “We were amazed by it, but upon further study we found a good explanation. The atomic irregularity acts as a kind of safety valve, allowing the nanotube to release excess energy, in much the way that a valve allows steam to escape from a kettle.”
The research appears in the February 16 issue of Physical Review Letters (075503; DOI: 10.1103/PhysRevLett.98.075503). The carbon atoms in nanotubes are joined together in six-sided hexagons. Yakobson’s “smart repair machine” is a deformity, a blemish in this pattern. The blemish consists of a five-sided pentagon joined to a seven-sided heptagon and contains a total of 10 atoms. Yakobson, who specializes in using computers to
Model Simulates Atomic Processes in Nanomaterials to Explain Ductility and Strength Researchers from the Massachusetts Institute of Technology, Georgia Institute of Technology, and the Ohio State University have developed a computer modeling approach to study how materials behave under stress at the atomic level, offering insights that could help engineers design materials with an ideal balance between strength and resistance to failure. When designing materials, there is often a trade-off between strength and ductility—properties that are critically important to the performance of materials. Recent advances in nanotechnology have allowed researchers to manipulate a material’s nanostructure to make it both strong and ductile. Now, a research team led by Subra Suresh, the Ford Professor of Engineering in the Department of Materials Science and Engineering at MIT, has determined why some nanodesigned metals behave with that desirable compromise between strength and ductility. The researchers developed a simulation method derived from experimental data that allows them to visualize the deformation of materials on a timescale of minutes. Previous methods allowed for only a nanosecond-scale glimpse at the atomic-level processes. “It’s a method to look at mechanical properties at the atomic scale of real experiments without being bogged down by limitations of nanosecond timescales of the simulation methods such as molecular dynamics,” said Suresh, the senior author of an article on the work that appears as the cover story in the February 27 issue of the Proceedings of the National Academy of Sciences (p. 3031; DOI: 10.1073/pnas. 0611097104). Using the new method, the researchers found that the ductility and str
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