Engineering: Honeycomb for sandwiches

An innovative new material could revolutionise construction and manufacturing.

A Bristol University-led project has developed CHISMACOMB (CHIral SMArt honeyCOMB) material that can be embedded with sensors and electromagnetic actuators to provide information about the structural integrity of sandwich structures used in civil, naval, aerospace, construction and electromagnetic shield applications.
 
This auxetic (amplifying) material uses an optimised chiral cellular core configuration - honeycomb- structured material that also becomes thicker when stretched. It provides more flexibility without compromising its strength.

Negative Poisson’s ratio 

The material’s unusual behaviour can be explained by the scientific principle Negative Poisson’s ratio – auxetic material stiffens when stretched in one direction. The auxetic behaviour also leads to the material’s bowl-shaped curve, which the researchers say is useful when manufacturing curved sandwich shells.
 
Project leader Fabrizio Scarpa, of the aerospace engineering department at Bristol, says that scientists have talked about using a material with Negative Poisson’s ratio since the 1920s. He told The Engineer: “This was known from the theoretical point of view for years, but the problem was no-one could come up with a working material with these sorts of properties.”
 
Scarpa begun co-ordinating the honeycomb material when it matured in 2005 so it could work outside the lab. The result is a chiral structure that is suitable for manufacturing techniques such as rapid prototyping or possibly injection moulding.
 
The aim now is to dedicate the structures for production in niche markets, such as orthopaedic processes or aerospace design.

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