Composite materials are increasingly a feature of our engineering–they’re super-strong and light, outperforming metals like steel with ease, which is why they’re often used in aeronautical engineering. Now a group at MIT has figured out a way to stitch carbon nanotubes around carbon fiber composite materials to make them up to ten times stronger and with only a fractional increase in cost.
An order of magnitude improvement like that is amazing, and is doubly so when you learn how simple it is to do, and that it only causes a nominal price hike.
A composite typically consists of a matrix of strong fibers arranged in layers which are held together and fuzed into a solid body by a glue or resin. When a composite fails its usually because the glue binding the fibers together has separated–that 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. To get around this you can stitch the fibres together, braid them or even weave and pin the layers of the matrix together–all improve the failure mode of the material but aren’t necessarily ideal.
Enter the Department of Aeronautics and Astronautics at MIT with an idea involving carbon nanotubes. These miraculous objects, vanishingly small and closely related to the other “wonder” material Buckminster Fullerene, have been identified as the strongest fiber materials yet identified. 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.
As Professor Brian L. Wardle puts it “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.” And he notes that with a nanotube “dose” of just one percent of the mass of the composite, dramatic strength improvements can be achieved.
Moreover the nanotubes boost the electrical conductivity of the material by a factor of a million–particularly helpful if you’re going to use the material 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.