Mighty molluscs with transparent shells could help protect soldiers in battle. Analysis of oyster shells shows how they can take repeated beatings without shattering, perhaps inspiring tougher combat armour.
Current transparent shields and visors are made from laminated glass, which fractures if it takes a bullet. That makes it hard to see through and vulnerable to breaking with a second hit, says Christine Ortiz at the Massachusetts Institute of Technology. "Right now, once they're shot, that's it," she says. "So any sort of transparent armour that has multi-hit capability but can also stop penetrations would be of interest."
In nature, many creatures use transparent shells for camouflage, which can survive repeated attacks from predators. "If you just hit the shell and it fell apart, the whole animal would be dead," says Ortiz.
Damage limitation
So Ortiz and her team studied the nanoscale structure of shells of the windowpane oyster, which are made of 99 per cent calcite mineral. Pure calcite crystals shatter easily, but the oyster shell is organised in thin layers that shift orientation when stressed, confining damage to shallow craters and stopping fractures spreading (see picture, above right).
While natural shells would not stop a bullet, finding a way to create such nano-layers in military-grade ceramics could one day help build better transparent shields, says Ortiz.
"This work is fascinating, but the real punch line is if you could actually make a material," says Robert Ritchie at Lawrence Berkeley National Laboratory in California, whose team made a material based on mother-of-pearl in 2008.
Constructing such materials with ceramics is challenging, because right now the temperatures needed to harden the ceramics will destroy the polymers used to slide in between them and create layers. "It's feasible, but it will be very difficult."
Journal reference: Nature Materials, DOI: 10.1038/nmat3920
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