Unexplored dimensions of porous metamaterials

It is all about how you slice it when it comes to porous metamaterials.

The Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Harvard Graduate School of Design (GSD) have collaborated on a new paper.

"Porous metamaterials have been studied in great depth and have been well understood for many, many years, but we have shown that there are still surprising new avenues to explore."

The research is published in a journal.

When porous metamaterials with a square array of holes or channels are compressed, the beam-like ligaments separating the pores buckle lead to a sudden transformation of the circular holes into ellipses. This change has been harnessed to build structures with unusual mechanical properties that can be used in a variety of ways.

The surface of the material remained flat during the entire process.

The Harvard researchers figured out how to enable out-of-plane, or three-dimensional, transformations by simply cutting the periodic geometry at an angle. The team covered both sides of the material with a thin elastic film and attached an air pump after cutting it. When the air is removed from the material, there are ridges on the surface of the material. The ridges disappear when air is pumped back in.

"These types of geometric transformations haven't been explored in this class of materials because no one has thought of cutting them in this way." said Matheus C. Fernandes, a former graduate student at the Harvard Graduate School of Arts and Sciences.

The change in surface structure can be used to alter the surface's behavior. The team attached small spheres to the surface of the porous block to demonstrate the effect. As the block slid down the ramp, the spheres remained in contact with the underlying surface, acting as wheels. As the air was evacuated, the spheres were pulled into the material as the higher ridges buckled, and the block stayed put. When the air was evacuated, the researchers attached skate-like fins that made the block skate down the surface when it was fully inflated.

The researchers built a worm-like robot that inched forward by changing the friction between its body and the ground.

In another experiment, the team covered the block with a reflective paint and showed that light scattering from the block could be altered when the surface changed.

Saurabh Mhatre, a senior research associate at GSD and co-first author of the paper, said that the change in the third dimensions opens up a lot of possibilities. It can be used on the soles of sneakers to change the levels of traction.

James Weaver said that the material is more applicable to real-world devices and applications since you don't need to add additional components to the system to achieve these different behaviors.

This project is yet another success story in the almost decades-long collaboration between researchers at SEAS and at the GSD, according to Martin Bechthold, Kumagai Professor of Architectural Technology at the GSD.

More information: Matheus C. Fernandes et al, Surface texture modulation via buckling in porous inclined mechanical metamaterials, Extreme Mechanics Letters (2021). DOI: 10.1016/j.eml.2021.101549 Citation: Unexplored dimensions of porous metamaterials (2022, March 18) retrieved 18 March 2022 from https://phys.org/news/2022-03-unexplored-dimensions-porous-metamaterials.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.