A material made of overlapping layers of graphene (atom-thick sheets of carbon) changes colour according to the level of stress applied. This could be used in structures to provide early warning of damage.

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A team led by Shanglin Gao of the Leibniz Institute of Polymer Research in Dresden, Germany, designed the coating so that it changes colour more dramatically with increasing amounts of deformation. The material was placed on a glass-fibre surface and mimics fish scales (pictured) and butterfly wings, which reflect different colours depending on the viewing angle, because of interference between light waves bouncing off the surface.

The authors say that the coating could be placed on buildings or vehicles to provide a visual indication of potential structural failure, which usually starts as tiny, invisible cracks and deformations.

Mater. Horiz. http://dx.doi.org/10.1039/C6MH00559D (2017)