Abalone in the armoury
24 Feb 2005
Abalone, a seaweed-eating marine snail, is prized for two reasons: seafood aficionados consider it a delicacy, and jewellery makers use its shell for mother-of-pearl.
The latter material, more properly called nacre, is also attracting attention from materials scientists, who believe its structure might be the key to making lightweight but extremely tough bullet-stopping armour.
The researchers at the Jacobs School of Engineering specialise in biomimetic projects, which aim to copy the properties of naturally-occurring materials in synthetic products.
The abalone project team, led by Marc Mayers, is looking at the toughness imparted by the structure of the shell, which is made up from stacks of 'tiles' of calcium carbonate, hexagonal in shape, around 10µm across and 0.5µm thick, held together with a protein adhesive.
The tiles comprise some 95% of the structure, yet the shell is much stronger than would be expected of something which is almost entirely chalk. There are two factors contributing to the strength, Mayers says — the way the tiles are arranged, in regular terrace-like patterns, and the protein glue, which is strong enough to hold the tiles together, but weak enough to allow the layers to slip past each other when the material experiences an impact.
The team has also discovered that the tiles are glued together on their top and bottom surfaces, but not on the sides. This allows the tiles to separate from each other easily.
'The adhesive properties of the protein glue, together with the size and shape of the calcium carbonate, explain how the shell interior gives a little without breaking,' Mayers says. 'On the contrary, when a conventional laminate material breaks, the whole structure is weakened.'
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