Biomimetics and Biomimicry in Engineering

Learning from natural ‘sandwich’ structures

In Info on 2013/07/16 at 10:28 am
porcupine quill

porcupine quill

The porcupine quill is a quite interesting material. A pretty large shear modulus, flexible in 3-pt bending tests, but very stiff in the longitudinal direction, which serves well as a defensive weapon.

It is surprisingly lightweight, so the first thought is for a sandwich structure of different materials, but what type of structure?

The photos below show images of a longitudinal slice of a quill under the optical microscope. As expected, a soft core (cellular-foam like) and a denser ‘skin’.

Optical micrsocope images: transversal section and several magnifications

Optical microscope images: transverse section and longitudinal at several magnifications

As it commonly happens, the interesting story starts when you get to see beyond what the human eye can. At higher magnifications, the ‘skin’ shows a complex structure, with layers of material oriented so they form another ‘skin’ structure within the ‘skin’ itself, with a core oriented vertically (in these photos) and the skin running horizontally. (The big black vertical scars could be scratches at the time of polishing, though)

Transverse sections at different magnifications

Transverse sections at different magnifications

This multiscale ‘skin’ is a good solution for providing stiff properties but not at the expense of heavy, dense materials.

Special thanks to Andy Sandaver, who recently retired from the Wolfson School and we already miss his exceptional technical skills. And my gratitude to Edinburgh Zoo, where the samples were collected.

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