Carbon nanotubes are vanishingly small and have been identified as the strongest fiber materials yet identified. Massachusetts Institute of Technology (MIT) engineers are using carbon nanotubes that are billionths of a meter thick to stitch together aerospace materials that could make airplane skins and other products about 10 times stronger at a nominal increase in cost. Since advanced composites reinforced with nanotubes are also more than one million times more electrically conductive than their counterparts without nanotubes, aircraft built with such materials would have greater protection against damage from lightning. A composite typically consists of a matrix of strong fibers arranged in layers which are held together and fused into a solid body by a glue or resin. A composite usually fails because the glue binding the fibers has separated and lets the fiber matrix fall apart, potentially failing as excessive forces are applied to particular groups and layers of fibers, rather than being distributed throughout the material. As a solution to this, fibres can be stitched together, braided or woven to pin the layers of the matrix together--all improve the failure mode of the material but aren't necessarily ideal. They are problematic because the relatively large stitches or pins penetrate and damage the carbon-fiber plies themselves.
The MIT team is proposing a technique called "nanostitching" that would incorporate nanotubes directly into a carbon fiber composite material. The polymer glue between carbon fibers is heated to a more liquid state, meanwhile nanotubes are introduced between the layers, and are sucked into the glue at each end of the layer. Since the tubes are much smaller than the fibers, they don't detrimentally affect the fiber's integrity, instead they fill up the space between the fibers with a glue/nanotube composite that's even stronger than the glue alone would be.
In this method, the team has put the strongest fibers known to humankind in the place where the composite is weakest, and where they are most needed. With a nanotube dose of just 1% of the mass of the composite, dramatic strength improvements can be achieved.
Since the nanotubes boost the electrical conductivity of the material by a factor of a million, it is particularly helpful if used to fabricate aircraft or giant blades for wind-turbines that are at risk of lightning strikes. The material may also find its way into advanced racing cars, due to the potential weight savings that could be achieved by using a stronger material, and, of course, the space industry. |
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