Engineered material for body armour inspired by conch shells

A conch shell is quite a resilient object. The ocean environment can be rather harsh and the shell itself stands up to tough conditions with cracking or breaking.

A new study by MIT graduate student Grace Gu (right), postdoc Mahdi Takaffoli (left), and McAfee Professor of Engineering Markus Buehler look at the strength of the conch shell. Photo credit: Melanie Gonick/MIT.

According to MIT graduate student Grace Gu, Conch shells have a really unique, three-tiered structure, making it extremely durable and resistant to fracture. The internal structure has three different levels of hierarchy, making it difficult for tiny cracks to spread. The material has a “zigzag matrix, so the crack has to go through a kind of a maze” in order to spread, she says.

The team was challenged when it came to replicating the material. They used 3D printing technology to replicate the structure while still being able to test it effectively, explains Markus Buehler, head of the Department of Civil and Environmental Engineering.

“In the past, a lot of testing [of protective materials] was static testing,” Gu explains. “But 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.

The team was able to 3D print composite materials with precisely controlled structures to use in the testing phase. By printing the samples, “we can use exactly the same geometry” as used in the computer simulations, “and we get very good agreement.” Now, in continuing the work, they can focus on making slight variations “as a basis for future optimization,” Buehler says.

The team tried making variations of the material with different levels of hierarchy. Higher levels of hierarchy are introduced by incorporating smaller length-scale features into the composite, as in an actual conch shell. Sure enough, lower-level structures proved to be significantly weaker than the higher level, which consisted of the cross-lamellar features inherent in natural conch shells.

The geometry with conch-like, criss-crossed features was 85 percent better at preventing crack propagation than the strongest base material, and 70 percent better than a traditional fiber composite arrangement, Gu says.

This makes the material preferable for impact-resistant gear or protective helmets and using 3D printing to develop these items allows for them to be personalized to fit the user.

Each helmet, for example, could be “tailored and personalized; the computer would optimize it for you, based on a scan of your skull, and the helmet would be printed just for you,” Gu says.

The findings are reported in the journal Advanced Materials, in a paper by MIT graduate student Grace Gu, postdoc Mahdi Takaffoli, and McAfee Professor of Engineering Markus Buehler.

www.mit.edu