MIT scientists have unveiled the secrets behind the extraordinary toughness of conch shells that help create the best-ever protective headgear and body armour. The shells of marine organisms take a beating from impacts due to storms and tides, rocky shores, and sharp- toothed predators. Recent research has demonstrated that the conch shell stands out above all the others in its toughness. Conch shells “have this really unique architecture,” said Grace Gu, graduate student at Massachusetts Institute of Technology (MIT) in the US. The structure makes the material 10 times tougher than nacre, commonly known as mother of pearl. This toughness, or resistance to fractures, comes from a unique configuration based on three different levels of hierarchy in the material’s internal structure.
The three-tiered structure makes it very hard for any tiny cracks to spread and enlarge, Gu said. The material has a “zigzag matrix, so the crack has to go through a kind of a maze” in order to spread, she said. Until recently, even after the structure of the conch shell was understood it could not be replicated. “But now, our lab has developed 3D printing technology that allows us to duplicate that structure and be able to test it,” said Markus Buehler from MIT.
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Part of the innovation involved in this project was the team’s ability to both simulate the material’s behaviour and analyse its actual performance under realistic conditions. “In the past, a lot of testing of protective materials was static testing,” Gu said. A lot of applications for military uses or sports involve highly dynamic loading, which requires a detailed examination of how an impact’s effects spread out over time.
Researchers did tests in a drop tower that enabled them to observe exactly how cracks appeared and spread – or did not spread – in the first instants after an impact. “There was amazing agreement between the model and the experiments,” Buehler said. That is partly because the team was able to 3D print composite materials with precisely controlled structures, rather than using samples of real shells, which can have unpredictable variations that can complicate the analysis.
Using the 3D printing technology, it may possible to produce individualised helmets or other body armour. “Each helmet could be “tailored and personalised; the computer would optimise it for you, based on a scan of your skull, and the helmet would be printed just for you,” Gu said. The research was published in the journal Advanced Materials.