Network-inspired metamaterials withstand impacts better
· BehindLines newsroom
Engineers at MIT and Northeastern University have designed materials whose internal structure is a disordered network of beams of widely varying sizes, rather than a pattern repeated identically. According to MIT's release, these "scale-rich metamaterials" absorb impacts better than conventional ordered versions. The study appeared on 11 November in the journal Nature.
Breaking with repetition
In a metamaterial, it is the internal structure that gives the material its exceptional properties. Until now, one elementary cell was generally repeated, such as a square or honeycomb lattice. Carlos Portela, an MIT associate professor in mechanical engineering, explains that such uniform patterns have limits: if one zone is punctured or cracked, the identical neighboring cells deform the same way and the whole quickly gives way.
The team turned to network science, which describes everything from neural circuits to the internet, with physicist Albert-László Barabási of Northeastern. An algorithm draws lines at random angles and positions, progressively shorter and thinner. Just two parameters, the starting thickness and the speed at which it decreases, are enough to produce a wide variety of networks and to tune stiffness.
The tests
The researchers 3D-printed polymer samples the size of a credit card, with beams ranging from microns to centimeters. They subjected them to a dropped weight and to compression, and compared them with conventional lattice and honeycomb samples. The networks proved more resistant to compression and impacts. Portela attributes this to the abundance of scales: if one part fails, the web around it prevents sudden rupture. The paper's abstract also mentions highly tunable elastic anisotropy and strong energy absorption.
In another demonstration, a material whose density varies like the thick rind of a pomelo, with denser edges, protected a fragile object placed at its center.
Why it matters
According to MIT, the method could be used to design helmets, armor or acoustic lenses. Tim Chen of Imperial College London, who was not involved in the study, sees a design framework for any structure that must carry a load, absorb energy or control vibration. The tests described involve 3D-printed polymer samples. The work was supported by the U.S. National Science Foundation's DMREF program.