Researchers from Harvard University's John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute of Biologically Inspired Engineering have developed a general framework for designing reconfigurable metamaterials — materials whose function is determined by structure, not composition.
Metamaterials have been designed to bend light and sound, transform from soft to stiff, and even dampen seismic waves from earthquakes. But each of these functions requires a unique mechanical structure, making these materials great for specific tasks, but difficult to implement broadly.
The design strategy is scale-independent; it can be applied to everything from meter-scale architectures to reconfigurable nano-scale systems such as photonic crystals, waveguides, and metamaterials to guide heat.
“In terms of reconfigurable metamaterials, the design space is incredibly large, and so the challenge is to come up with smart strategies to explore it,” said Katia Bertoldi, John L. Loeb Associate Professor of the Natural Sciences at SEAS. “Through a collaboration with designers and mathematicians, we found a way to generalize these rules and quickly generate a lot of interesting designs. We realized that these simple geometries could be used as building blocks to form a new class of reconfigurable metamaterials, but it took us a long time to identify a robust design strategy to achieve this.”
The team found that assemblies of polyhedra can be used as a template to design extruded reconfigurable thin-walled structures, dramatically simplifying the design process. By combining design and computational modeling, the team identified different rearrangements and created a blueprint for building the materials.
The same computational models can also be used to quantify all the different ways in which the material could bend, and how that affected effective material properties like stiffness. The team could quickly scan close to a million different designs, and select those with the preferred response. Once a design was selected, working prototypes were constructed of each 3D metamaterial using laser-cut cardboard and double-sided tape, as well as multimaterial 3D printing.
The design framework could be used by structural and aerospace engineers, material scientists, physicists, robotic engineers, biomedical engineers, designers, and architects.
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