In the 2005 movie Batman Begins, Batman's cape is flexible but can be made into a rigid glider. Now, engineers at Caltech and JPL have developed a material that can transform from flexible to rigid on command.
"We wanted to make materials that can change stiffness on command," said Chiara Daraio of Caltech, "We'd like to create a fabric that goes from soft and foldable to rigid and load-bearing in a controllable way."
A material that can transform from flexible to rigid isn't as unusual as one would think. In fact, Daraio added, many people have something that works like that in their pantries: a bag of vacuum-sealed coffee. When coffee grounds are packed, they are solid as the individual particles are jammed against each other. But when the package is opened, then the coffee grounds are no longer jammed and can pour out as if they were liquid.
To create a new material that has both flexible and rigid properties, Daraio and colleagues designed various configurations of linked particles, including linking rings, linking cubes and finally linking octahedrons (which look like two pyramids connected at the base).
The linked octahedron material is then 3D printed out of plastic polymers and even metal, resulting in a chainmail-like fabric.
"Granular materials are a beautiful example of complex systems, where simple interactions at a grain scale can lead to complex behavior structurally. In this chain mail application, the ability to carry tensile loads at the grain scale is game changer. It's like having a string that can carry compressive loads. The ability to simulate such complex behavior opens the door to extraordinary structural design and performance," said José E. Andrade of Caltech.
When it is compressed, the chainmail material is able to support more than 50 times the fabric's weight.
"These fabrics have potential applications in smart wearable equipment: when unjammed, they are lightweight, compliant, and comfortable to wear; after the jamming transition, they become a supportive and protective layer on the wearer's body," said the study's co-lead author Yifan Wang now at Nanyang University.
Images: Caltech and Nanyang University
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Linked octahedron material 3D-printed in aluminum.
When stiffened (in a vacuum-sealed bag), the material can act as a sturdy bridge supporting a load more than 50 times the material's own weight.
The material acts with more flexibility when it is unjammed.
The material acts with rigidity when the individual linked octahedrons are jammed.