Researchers at Rensselaer Polytechnic Institute have developed a new technique for identifying and repairing small, potentially dangerous cracks in aircraft wings and other structures made from polymer composites. By infusing a polymer with electrically conductive carbon nanotubes, and then monitoring the structure's electrical resistance, they were able to pinpoint the location and length of a stress-induced crack in a composite structure.

When the crack is located, engineers can send a short electrical charge to the area to heat up the nanotubes and melt an embedded healing agent that will flow into and seal the crack with a 70 percent recovery in strength. The team made a structure from common epoxy, but added enough multi-walled carbon nanotubes to comprise 1 percent of the structure's total weight.

Since the nanotubes are ubiquitous through the structure, the technique can be used to monitor any portion of the structure by performing resistance measurements without the need to mount external sensors or electronics. The crack detection method is an effective way to combat microcracks and less-common structural damage called delamination.

The new system method could be integrated into the built-in computer system of a fighter jet or large piece of equipment, allowing the operator to monitor a structure's integrity in real time. The team is now working to optimize the system, scale it up to larger structures, and develop new information technology to better collect and analyze the electrical resistance data created from the embedded grid and embedded carbon nanotubes.

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