Engineers inspect advanced composites with nanotube-based thermography

Cambridge, MA--By including carbon nanotubes in advanced composites for aircraft, engineers at the Massachusetts Institute of Technology (MIT) have simplified conventional thermography techniques to find flaws in the composites. Their approach uses the nanotube additive as an emitter of electric-current-induced heat for IR thermography.¹

Many airplane manufacturers have started building their planes from advanced composite materials, which consist of high-strength fibers such as carbon or glass embedded in a plastic or metal matrix. Such materials are stronger and more lightweight than aluminum, but they are also more difficult to inspect for damage, because their surfaces usually don't reveal underlying problems.

Damage without dents

"With aluminum, if you hit it, there's a dent there," says Brian Wardle, associate professor of aeronautics and astronautics at MIT. "With a composite, oftentimes if you hit it, there's no surface damage, even though there may be internal damage."

One method that inspectors now use to reveal damage in advanced composite materials is IR thermography, which detects infrared radiation emitted when the surface is heated. In an advanced composite material, any cracks or delamination will redirect the flow of heat. That abnormal flow pattern can be seen with a thermographic camera.

This is effective but cumbersome because it requires large heaters to be placed next to the surface, Wardle says. With his new approach, carbon nanotubes are incorporated into the composite material. When a small electric current is applied to the surface, the nanotubes heat up, which eliminates the need for any external heat source. The inspector can see the damage with a thermographic camera or goggles.

The approach could allow airlines to inspect their planes much more quickly, Wardle says. This project is part of a multiyear, aerospace-industry-funded effort to improve the mechanical properties of existing advanced aerospace-grade composites. The U.S. Air Force and Navy are also interested in the technology, and Wardle is working with them to develop it for use in their aircraft and vessels.

Uncovering damage without causing it

Douglas Adams, associate professor of mechanical engineering at Purdue University, who was not involved in the research (and who did not write "The Hitchhiker's Guide to the Galaxy"), notes that two fundamental challenges remain: developing a practical way to manufacture large quantities of the new material, and ensuring that the addition of nanotubes does not detract from the material's primary function of withstanding heavy loads.

The new carbon nanotube hybrid materials that Wardle is developing have so far shown better mechanical properties, such as strength and toughness, than existing advanced composites.

REFERENCE:

1. Roberto Guzmán de Villoria et al., 2011 Nanotechnology 22 185502 doi: 10.1088/0957-4484/22/18/185502