[Editors] MIT: ‘Nanostitching’ could strengthen airplane skins, more

[Elizabeth Thomson]

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MIT: ‘Nanostitching’ could strengthen airplane skins, more
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For Immediate Release
WEDNESDAY, MAR. 4, 2009

Contact: Elizabeth A. Thomson, MIT News Office
E: thomson at mit.edu, T: 617-258-5402

Photo and Graphic Available

CAMBRIDGE, Mass.--MIT engineers are using carbon nanotubes only  
billionths of a meter thick to stitch together aerospace materials in  
work that could make airplane skins and other products some 10 times  
stronger at a nominal increase in cost.

Moreover, advanced composites reinforced with nanotubes are also more  
than one million times more electrically conductive than their  
counterparts without nanotubes, meaning aircraft built with such  
materials would have greater protection against damage from lightning,  
said Brian L. Wardle, the Charles Stark Draper Assistant Professor in  
the Department of Aeronautics and Astronautics.

Wardle is lead author of a theoretical paper on the new nanotube- 
reinforced composites that will appear in the Journal of Composite  
Materials (http://jcm.sagepub.com/). He also described the work as  
keynote speaker at a Society of Plastics Engineers conference this week.

The advanced materials currently used for many aerospace applications  
are composed of layers, or plies, of carbon fibers that in turn are  
held together with a polymer glue. But that glue can crack and  
otherwise result in the carbon-fiber plies coming apart. As a result,  
engineers have explored a variety of ways to reinforce the interface  
between the layers by stitching, braiding, weaving or pinning them  
together.

All of these processes, however, are problematic because the  
relatively large stitches or pins penetrate and damage the carbon- 
fiber plies themselves. “And those fiber plies are what make  
composites so strong,” Wardle said.

So Wardle wondered whether it would make sense to reinforce the plies  
in advanced composites with nanotubes aligned perpendicular to the  
carbon-fiber plies. Using computer models of how such a material would  
fracture, “we convinced ourselves that reinforcing with nanotubes  
should work far better than all other approaches,” Wardle said. His  
team went on to develop processing techniques for creating the  
nanotubes and for incorporating them into existing aerospace  
composites, work that was published last year in two separate journals.

How does nanostitching work? The polymer glue between two carbon-fiber  
layers is heated, becoming more liquid-like. Billions of nanotubes  
positioned perpendicular to each carbon-fiber layer are then sucked up  
into the glue on both sides of each layer. Because the nanotubes are  
1000 times smaller than the carbon fibers, they don’t detrimentally  
affect the much larger carbon fibers, but instead fill the spaces  
around them, stitching the layers together.

“So we’re putting the strongest fibers known to humankind [the  
nanotubes] in the place where the composite is weakest, and where  
they’re needed most,” Wardle said. He noted that these dramatic  
improvements can be achieved with nanotubes comprising less than one  
percent of the mass of the overall composite. In addition, he said,  
the nanotubes should add only a few percent to the cost of the  
composite, “while providing substantial improvements in bulk  
multifunctional properties.”

Wardle’s co-authors on the Journal of Composite Materials paper are  
Joaquin Blanco, a visiting graduate student in the Department of  
Aeronautics and Astronautics, Enrique J. Garcia SM ’06, and Roberto  
Guzman deVilloria, a postdoctoral associate in the department.

This research was sponsored by MIT’s Nano-Engineered Composite  
aerospace STructures (NECST) Consortium (necst.mit.edu).

--END--

Written by Elizabeth A. Thomson, MIT News Office
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