Nanotube network detects cracks

Researchers have discovered a means to detect and identify damage within advanced composite materials using a network of carbon nanotubes which act like human nerves.

The discovery at the University of Delaware could help scientists better predict the life span of various composite materials. It could also become an important tool in monitoring the health of composite materials used in the construction of a variety of products, including commercial airliners.

Tsu-Wei Chou, Pierre S. du Pont Chair of Engineering, and Erik Thostenson, assistant professor of mechanical engineering, have been studying the reinforcement of fibre composites with carbon nanotubes.

Composite materials are generally laminates, sheets of high-performance fibres, such as carbon, glass or Kevlar, embedded in a polymer resin matrix. Traditional composite materials have inherent weaknesses because the matrix materials-plastics-surrounding the fibres are less strong than the fibres.

This results in weak spots in composites in the interface areas in the matrix materials, particularly where there are pockets of resin. As a result, defects, including tiny microcracks, can occur. Over time, those microcracks can threaten the integrity of the composite.

Thostenson said the carbon nanotubes could be used to detect defects at onset by embedding them uniformly throughout the composite material as a network capable of monitoring the health of the composite structures.

Because the carbon nanotubes conduct electricity, they create a nanoscale network of sensors that work much like the nerves in a human body. The researchers can pass an electrical current through the network and if there is a microcrack, it breaks the pathway of the sensors and gives a measurable response.

Thostenson said that the carbon nanotubes are minimally invasive and just 0.15 per cent of the total composite volume.

The work provides a new tool for research in the laboratory at present and has many potential applications in the future. By identifying and tracking defects in a laboratory setting, the researchers can now begin to develop strategies for more accurate predictions of the lifespan of composite materials.