A combination of light weight AND strength makes advanced composite materials very useful when building something that's designed to go fast while being subjected to physical stress ... like an aircraft. On the downside, bulky equipment is required when it comes to inspecting these aircraft for damage – a problem that is MIT researchers hope to solve with the development of a new type of composite material that incorporates carbon nanotubes.
Aircraft composites consist of high-strength fibers, such as carbon or glass, embedded in a plastic or metal matrix. Unlike aluminum, they are not a uniform surface which means they can look fine on the outside despite being damaged internally – there's no noticeable crack or dent, so it's difficult to tell if there is damage?
"With aluminum, if you hit it, there's a dent there," said Associate Professor of Aeronautics and Astronautics at the Massachusetts Institute of Technology Brian L. Wardle. "With a composite, oftentimes if you hit it, there's no surface damage, even though there may be internal damage." Internal damage of course means that the part won't be as strong as it looks,
Currently advanced composites can be inspected using infrared thermography – the material is heated and any area that has been cracked or delaminated (i.e. the layers have separated) will show differing redirection of heat that is visible using a thermographic camera. The problem – heating an aircraft's surface requires bulky equipment which makes this method difficult.
To solve this, Wardle and his research team have developed an advanced composite material which can be subjected to infrared thermography without the need for an outside heat source. Carbon nanotubes are incorporated into the composite material and when a small electric current is applied to the surface, the nanotubes heat up. This means that abnormal flow of heat is then clearly visible to an inspector equipped with a thermographic camera or goggles and a simple handheld device to supply the electric current.
Not only are flaws now easier to detect, Wardle's materials have so far shown superior mechanical properties compared to existing composites.