Airplane manufacturers have been changing over from aluminum to advanced composite materials. These lighter, stronger composites are made of fibers of carbon or glass ____1____ a second material, often plastic.

One advantage is that composite-based planes use significantly less fuel. But there’s an important disadvantage. When aluminum is hit, you can see a dent. Composites, though, ____2____ to the original shape, which could hide internal damage.

One technique to test composite material ____3____heat transfer. Inspectors place large heaters next to a section of the plane. Any cracks will alter the flow of heat, and these changes can be picked up with a heat-sensitive camera. But this involves ____4____and expensive equipment.

Now M.I.T. researchers have designed a new system. All you need is carbon nanotubes included in the composite, because nanotubes will heat up in response to a small electric current. This can be produced with a handheld device. Any internal deformations will still change the heat flow, which can be picked up by the ____5____ camera. The research was published in the journal Nanotechnology.

This technique offers the ability to detect very small cracks—which could help keep passengers safer in the skies.
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