Engineers at Caltech and JPL have developed a material inspired by chain mail that can transform from a foldable, fluid-like state into specific solid shapes under pressure.
The material has potential applications as a smart fabric for exoskeletons, or as an adaptive cast that adjusts its stiffness as an injury heals, or even as a deployable bridge that could be unrolled and stiffened, according to Chiara Daraio, Caltech’s G. Bradford Jones Professor of Mechanical Engineering and Applied Physics and corresponding author of a study describing the material that was published in Nature on August 11.
“We wanted to make materials that can change stiffness on command,” Daraio says. “We’d like to create a fabric that goes from soft and foldable to rigid and load-bearing in a controllable way.” An example from popular culture would be Batman’s cape from the 2005 movie Batman Begins, which is generally flexible but can be made rigid at will when the Caped Crusader needs it as a gliding surface.
Materials that change properties in similar ways already exist all around us, Daraio notes. “Think about coffee in a vacuum-sealed bag. When still packed, it is solid, via a process we call ‘jamming.’ But as soon as you open the package, the coffee grounds are no longer jammed against each other and you can pour them as though they were a fluid,” she says.
Individual coffee grounds and sand particles have complex but disconnected shapes, and can only jam when compressed. Sheets of linked rings, however, can jam together under both compression and tension (when pushed together or pulled apart). “That’s the key,” Daraio says. “We tested a number of particles to see which ones offered both flexibility and tunable stiffness, and the ones that only jam under one type of stress tended to perform poorly.”