Benchtop Test Identifies Extremely Impact-Resistant Materials

Published: Wednesday, February 21, 2024 – 12:03

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

An intricate, honeycomb-like structure of struts and beams could withstand a supersonic impact better than a solid slab of the same material. What’s more, the specific structure matters, with some being more resilient to impacts than others.

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

In their new study, the researchers developed a way to test free-standing metamaterials to observe how the materials withstand impacts purely on their own without a backing or supporting substrate.

The researchers then tested each metamaterial’s impact resilience 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 caught each impact on camera and studied the resulting images, frame by frame, to see how the projectiles penetrated each material. Next, they examined the materials under a microscope and compared each impact’s physical aftermath.

In their experiments, the team suspended tiny printed metamaterial lattices between microscopic support structures, then fired even tinier particles at the materials at supersonic speeds. With high-speed cameras, the team then captured images of each impact and its aftermath with nanosecond precision.

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

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

“What we’re learning is that the microstructure of your material matters, even with 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 made into coatings or panels for spacecraft, vehicles, helmets, and anything that needs to be lightweight and protected.”

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

“What I’m most excited about is showing we can do a lot of these extreme experiments on a benchtop,” Portela says. “This will significantly accelerate the rate at which we can validate new, high-performing, resilient materials.”


Benchtop Test Identifies Extremely Impact-Resistant Materials

High-speed experiments help identify lightweight, protective ‘metamaterials’

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

In a study appearing in Proceedings of the National Academy of Sciences, the engineers report on a new way to quickly test an array of metamaterial architectures and their resilience to supersonic impacts.

The researchers print intricate, honeycomb materials suspended between supporting pillars of the same material (pictured). The microscopic structure is as tall as the width of three human hairs. Image courtesy of the researchers.

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

Pure impact

In their current setup, the researchers suspend a metamaterial of interest between two microscopic pillars made from the same base material. Depending on the dimensions of the metamaterial being tested, the researchers calculate how far apart the pillars must be to support the material at either end while allowing the material to respond to any impacts without any influence from the pillars themselves.

Going forward, the team plans to use the new rapid testing and analysis method to identify new metamaterial designs in hopes of tagging architectures that can be scaled up to stronger and lighter protective gear, garments, coatings, and paneling.

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

Punctures and cracks

Overall, the team observed that the fired particles created small punctures in the latticed metamaterials, and the materials nevertheless stayed intact. In contrast, when the same particles were fired at the same speeds into solid, nonlatticed materials of equal mass, they created large cracks that quickly spread, causing the material to crumble. The microstructured materials, therefore, were more efficient in resisting supersonic impacts as well as protecting against multiple impact events. And in particular, materials that were printed with the repeating octets appeared to be the most hardy.

Published Jan. 29, 2024, in MIT News.


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

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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 stills of a microparticle hitting a structure made of metamaterials. Image courtesy of the researchers.