Recently, engineers at Massachusetts Institute of Technology (MIT), US, embedded such a sensing network made of carbon nanotubes (CNTs) into a traditional fibre-reinforced laminate architecture, by placing aligned CNTs throughout the architecture to create a hierarchical nanoengineered material.

When electrical current flows through the CNT network, the temperature of the material increases from Joule heating. If damage that disrupts this conductive network exists somewhere in the material, a localized change in electrical current results, which, in turn, manifests as a localized change in temperature.

A simple low-cost thermal camera or even night-vision goggles enable real-time visualization of damage in the composite. Reporting their results in the journal Nanotechnology, the researchers show that several kinds of damage can be detected in nanoengineered composites using this non-destructive in situ inspection technique including barely visible damage, internal damage produced by impact and other forms of otherwise hidden damage.

The structure is the sensor

This method has numerous advantages over existing non-destructive evaluation techniques. First, the structure itself is the sensor – no wiring, sensor grids or external heaters are necessary. In addition, this sensing technique is truly multifunctional – the nanoengineered composites are stronger and tougher mechanically, with the sensing benefit coming as a secondary effect. Finally, high-resolution inspection is easily obtained and, in the case of nanoengineered composites, with only a tiny amount of power.

The team believes that the strategy employed in the study can therefore serve as the basis for new, improved inspection techniques for monitoring future generations of safer vehicles and infrastructure.