April 24, 2024

MIT’s microscopic metamaterials defy supersonic impacts

Impact Testing of Metamaterials

Metamaterials with specific microstructures outperform solid materials in resisting supersonic impacts, offering potential for advanced protection solutions. (Artist’s concept.) Credit: SciTechDaily.com

High-speed experiments can help identify “Resilience Testing of Microparticle Firing Metamaterials at Supersonic Speeds

By firing microparticles at supersonic speeds, MIT engineers can test the resilience of various metamaterials made from structures as small as a red blood cell. Pictured are four video images of a microparticle hitting a structure made of metamaterials. Credit: Courtesy of researchers

In their experiments, the team suspended tiny networks of printed metamaterials between microscopic support structures and then fired even smaller particles at the materials at supersonic speeds. Using high-speed cameras, the team captured images of each impact and its consequences, with nanosecond precision.

Their work has identified some metamaterial architectures that are more resilient to supersonic impacts compared to their fully solid, unarchitected counterparts. The researchers say the results they observed at the microscopic level can be extended to comparable impacts at the macroscale, to predict how new material structures on length scales will withstand impacts in the real world.

Microscopic Structure of Honeycomb Material

Researchers print intricate honeycomb-shaped materials, suspended between support pillars of the same material (photo). The microscopic structure is the height of three human hairs. Credit: Courtesy of researchers

“What we’re learning is that the microstructure of your material matters, even at high-rate deformation,” says study author Carlos Portela, the Brit and Alex d’Arbeloff Career Development Professor in Mechanical Engineering at MIT. “We want to identify impact-resistant structures that can be turned into skins or panels for spacecraft, vehicles, helmets and anything that needs to be lightweight and protected.”

Other authors of the study include first author and MIT graduate student Thomas Butruille and Joshua Crone of the DEVCOM Army Research Laboratory.

Pure Impact

The team’s new high-speed experiments build on their previous work, in which engineers tested the resilience of an ultralight carbon-based material. This material, thinner than the width of a human hair, was made from tiny carbon struts and beams, which the team printed and placed on a glass slide. They then fired microparticles toward the material at speeds greater than the speed of sound.

These supersonic experiments revealed that the microstructured material resisted high-speed impacts, sometimes deflecting the microparticles and sometimes capturing them.

“But there were many questions we couldn’t answer because we were testing the materials on a substrate, which may have affected their behavior,” says Portela.

Microparticles fired through precisely engineered metamaterial

MIT engineers captured video of a microparticle being fired through a precisely engineered metamaterial measuring thinner than the width of a human hair. Credit: Courtesy of researchers

In their new study, the researchers developed a way to test stand-alone metamaterials, to observe how the materials resist impacts on their own, without a support or supporting substrate.

In the current setup, researchers suspend a metamaterial of interest between two microscopic pillars made from the same base material. Depending on the dimensions of the metamaterial under test, the researchers calculate how far apart the pillars must be to support the material at each end and, at the same time, allow the material to respond to any impacts, without any influence from the pillars themselves.

“This way, we ensure that we are measuring the material property and not the structural property,” says Portela.

Once the team decided on the pillar support design, they moved on to testing a variety of metamaterial architectures. For each architecture, the researchers first printed the support pillars on a small silicon chip and then continued to print the metamaterial as a layer suspended between the pillars.

“We can print and test hundreds of these structures on a single chip,” says Portela.

Punctures and Cracks

The team printed suspended metamaterials that resembled intricate honeycomb-shaped cross sections. Each material was printed with a specific three-dimensional microscopic architecture, such as a precise structure of repeating octets or more faceted polygons. Each repeating unit was as small as a red blood cell. The resulting metamaterials were thinner than the width of a human hair.

The researchers then tested the impact resilience of each metamaterial by firing glass microparticles toward the structures at speeds of up to 900 meters per second (more than 2,000 miles per hour) – well within the supersonic range. They captured each impact on camera and studied the resulting images, frame by frame, to see how the projectiles penetrated each material. They then examined the materials under a microscope and compared the physical consequences of each impact.

“In engineered materials we saw this morphology of small cylindrical craters after the impact,” says Portela. “But in solid materials, we saw a lot of radial cracks and larger pieces of material that were ripped off.”

Overall, the team observed that the fired particles created small holes in the cross-linked metamaterials, and yet the materials remained intact. In contrast, when the same particles were fired at the same speeds into solid, uncrosslinked materials of equal mass, they created large cracks that spread quickly, causing the material to disintegrate. Microstructured materials, therefore, were more efficient in resisting supersonic impacts, as well as protecting against multiple impact events. And in particular, materials printed with repeating octets seemed to be the most resilient.

Observations and future directions

“At the same speed, we see that the octet architecture is more difficult to fracture, which means that the metamaterial, per unit mass, can withstand impacts up to twice as much as the bulk material,” says Portela. “This tells us that there are some architectures that can make a material stronger and offer better impact protection.”

In the future, the team plans to use the new rapid testing and analysis method to identify new metamaterial designs, hoping to score architectures that can be scaled up for stronger and lighter protective equipment, clothing, coatings and panels.

“What excites me most is showing that we can do many of these extreme experiments on a bench,” says Portela. “This will significantly accelerate the rate at which we can validate new, resilient, high-performance materials.”

Reference: “Decoupling Particle Impact Dissipation Mechanisms in 3D Architected Materials” by Thomas Butruille, Joshua C. Crone, and Carlos M. Portela, February 2, 2024, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2313962121

This work was funded, in part, by the DEVCOM ARL Army Research Office through the MIT Institute for Soldier Nanotechnologies (ISN), and performed, in part, using ISN and MIT.nano facilities.

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