Tsu-Wei Chou (right), recently named among the top 100 materials scientists of the past decade, and mechanical engineer Erik Thostenson are using nanotubes to detect micro-cracks in composites.

Imagine what you could do with a material that is 30 times stronger than high-strength steel, as stiff as diamonds and a thousand times more conductive than copper, yet weighs only half as much as aluminum. While this might sound like the stuff of science fiction, the carbon nanotube actually has all of these properties and more.

Two researchers at the University of Delaware have done more than just imagine what they would do with these tiny cylinders that are about 1/50,000th as wide as a human hair — they have discovered a way to use them in detecting defects and damage in advanced composite structures. The technology is similar to the way the human body signals injury through the nervous system.

The research is the work of Tsu-Wei Chou, Pierre S. du Pont Chair of Engineering, and Erik Thostenson, assistant professor of mechanical engineering. In August 2010, the pair was awarded a patent on the method and system for this application.

The composite materials Chou and Thostenson are working with comprise a polymer matrix reinforced with glass fibers. The difference in strength between the matrix and the fibers can result in areas of weakness at the interface between the two, where tiny microcracks can develop. Over time, the microcracks can grow and threaten the integrity of the composite.

"Nanotubes are so small they can penetrate the areas in between the bundles of fiber and also between the layers of the composite, in the matrix-rich areas," Thostenson said. "Because the carbon nanotubes conduct electricity, they create a nanoscale network of sensors that work much like the nerves in the human body."

When an electrical current is passed through the network, any microcracks present will break the pathway of the sensors, and the response can be measured.

The work provides a new tool for laboratory research now and has many potential applications in the future. By identifying and tracking defects in a laboratory setting, the researchers can develop strategies for more accurate prediction of material lifespan.

"Being able to detect defects and understand the life cycle of a given composite is critical to the widespread use of these materials," Thostenson said. "It comes down to knowing how long the composite will last and at what point the structure will no longer be viable."

Chou, considered a pioneer in the science and technology of fiber-reinforced composites, credits his colleague with developing the technique for uniformly dispersing the carbon nanotubes in the matrix material. Thostenson earned his doctorate in materials science at UD in 2004 with Chou as his adviser. Chou joined the UD faculty in 1969 and was instrumental in founding the Center for Composite Materials. Earlier this year, he was named among the top 100 materials scientists of the past decade by Times Higher Education.

The two have received funding for their work from the Air Force Office of Scientific Research, the Office of Naval Research, the Army Research Office and the National Science Foundation. In addition, they are collaborating with researchers at the Korea Institute of Materials Science on a program funded by the South Korean government, and they currently have two related Phase II Small Business Technology Transfer grants with small companies aimed at addressing scale-up issues and new applications of the technology.