Material Science

Nano-architected material with high impact resistance

The material made from tiny carbon struts that is, pound for pound, more effective at stopping a projectile

August 26, 2021
The Scitech

Engineers at Caltech, MIT, and ETH Zürich have developed a nano-architected material made from tiny carbon struts that is, pound for pound, more effective at stopping a projectile than Kevlar, a material commonly used in personal protective gear. Pioneered by Caltech materials scientist Julia R. Greer, nano-architected materials have a structure that is designed at a nanometer scale and exhibit unusual, often surprising properties—for example, exceptionally lightweight ceramics that spring back to their original shape, like a sponge, after being compressed. "The knowledge from this work could provide design principles for ultra-lightweight impact resistant materials for use in efficient armor materials, protective coatings, and blast-resistant shields desirable in defense and space applications," says Greer, the Ruben F. and Donna Mettler Professor of Materials Science, Mechanics and Medical Engineering, whose lab led the material's fabrication. Greer is co-corresponding author of a paper on the new material that was published in Nature Materials on June 24.

The material, which is thinner than a human hair, consists of interconnected tetrakaidecahedrons made out of carbon struts that have been formed under extreme heat (known as pyrolytic carbon). Tetrakaidecahedrons are structures with 14 faces: six with four sides and eight with eight sides. They are also called "Kelvin cells" because, in 1887, Lord Kelvin (physicist William Thomson, 1st Baron Kelvin, in whose honor we state absolute temperatures in units of "Kelvin") suggested that they would be the best shape to fill an empty three-dimensional space with equal-sized objects using minimal surface area. While the strength of nano-architected materials has been studied using slow deformation (compression and tension, for example), Portela wanted to know how such a material might survive a high-speed impact. The researchers found that the denser version of the material was more resilient, with the microparticles tending to embed in the material rather than tearing straight through, as would be the case with either fully dense polymers or carbon sheets of the same thickness. Under closer examination, they discovered that individual struts directly surrounding the particle would crumple, but the overall structure remained intact until the projectile stopped. Pound for pound, the new material outperformed steel by more than 100 percent and Kevlar composites by more than 70 percent. "We show the material can absorb a lot of energy because of this shock compaction mechanism of struts at the nanoscale versus something that's fully dense and monolithic, not nano-architected," Portela says.

Source: Caltech news release