Metamaterial that changes its mechanical properties while maintaining morphological features

A metamaterial is a microstructure made up of smaller elements, such as bars or plates, that on a larger scale functions like a standard material, but with properties controlled by the designer. These small-scale materials are made up of identical blocks that repeat, which is called a unit cell.

A material is auxetic when, when compressed in one direction, it contracts in the others, instead of expanding, which is what materials usually do due to the so-called Poisson effect. Similarly, stretching it will expand in the other directions, instead of contracting.

Researchers at the Polytechnic University of Madrid (UPM) in Spain have invented a metamaterial that changes its mechanical properties without changing morphologically at the cell level.

Specifically, it is a new type of metamaterial capable of changing its auxetic properties with a small internal geometric variation, without the need for morphological change at the cell level.

The researchers have registered it as a national patent in the Spanish Patent and Trademark Office with number ES2907514 A1. It is titled “Metamaterial unit cell and material formed from said unit cell”.

The metamaterial patented by the GAMOSINOS research group (Advanced Group for Nonlinear Solid Modeling and Simulation) of the Higher Technical School of Aeronautical and Space Engineering (ETSIAE) of the UPM can present both auxetic and non-auxetic properties depending on the different settings. “The main power of our invention is that it can change its mechanical properties without changing the shape of this cell, and therefore parts with variable properties can be reproduced very easily. This is achieved by changing the vertical and lateral connection between the cells, which is done by means of bars that can be connected to some nodes and others. This variation is what generates different configurations with different mechanical properties”, explain the researchers from the Polytechnic University of Madrid.

(Image: UPM)

Given this configuration, its potential is to present greater resistance to impact damage than other currently existing materials. “For this reason, it can be of great application in the aerospace sector to improve the performance of various elements and even reduce their weight. It can be used as a filling element for leading edge cells in aircraft and wind turbines, which have to be impact resistant and open cell to prevent water accumulation. Right now, some of these cells are filled with foam sandwich panels, which have the problem of accumulating water and not being able to be easily extracted. These elements can suffer, for example, the impact of a bird or projectile or be damaged by the freezing of the water that remains locked up”, they maintain from GAMOSINOS.

“More specifically, helicopter or wind turbine blades, which are generally also foam-filled sandwich panels, can be improved with this metamaterial. Similarly, nose radomes in aircraft have to be permeable to radiation because they usually house the frontal radar antennas, but at the same time they have to offer good resistance to a possible impact. These are aspects on which the research group is currently working”, they conclude.

The invention is part of the final degree project by Guillermo Gómez Carano, inventor of the metamaterial together with Luis Saucedo Mora, Miguel Ángel Sanz Gómez and Francisco Javier Montans Leal, all of them belonging to the GAMOSINOS group. Guillermo Gómez Carano is currently finishing the Master’s Degree in Industrial Mathematics (MUMI), an interuniversity postgraduate program offered by the ETSIAE, combining it with his work as a data engineer at the WhiteBox company.

The patent has taken more than a year to be granted due to the necessary external review to demonstrate its originality against existing patents according to different international databases.

Research on this metamaterial continues within the GAMOSINOS group. José María Benítez Baena, Laura Moreno Corrales, Ismael Ben-Yelun Insenser and Ricardo Callado Sanz are collaborating in its current development and implementation, including both experimental validation and numerical study to introduce it into optimized structures. (Source: UPM)