Quickly identify highly impact-resistant materials with benchtop testing

Complex honeycomb-like post-and-beam structures can withstand supersonic shocks better than solid slabs of the same material. Additionally, specific construction is important, with some being more resistant to impact than others.

That’s what MIT engineers are discovering when experimenting with microscopic metamaterials — materials intentionally printed, assembled, or otherwise engineered with tiny structures that give the material superior properties overall. is.

in research Appearing today inside Proceedings of the National Academy of Sciencesengineers report on a new method to rapidly test a range of metamaterial architectures and their resistance to supersonic shock.

In the experiment, the team suspended tiny printed metamaterial lattices between microscopic support structures and fired even smaller particles into the material at supersonic speeds. The team then used high-speed cameras to take images of each impact and its aftermath with nanosecond precision.

Their research identified several metamaterial architectures that are more resistant to supersonic shocks compared to metamaterial architectures that are not designed to be completely solid. The researchers say they can extend their microscopic observations to equivalent macroscale impacts and predict how new material structures across length scales will withstand real-world impacts.

“What we’re learning is that the microstructure of a material is important, even at high deformation rates,” said study author Alex Dalbelov, a British career development professor of mechanical engineering at the Massachusetts Institute of Technology. Carlos Portela says. “We want to identify impact-resistant structures that can be used in coatings and panels for spacecraft, vehicles, helmets, and anything else that needs to be lightweight and protected.”

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

pure impact

The team’s new high-speed experiment previous workIn , engineers tested the resiliency of ultra-light carbon-based materials. The material, which is thinner than the width of a human hair, is made from tiny struts and carbon beams, which the researchers printed and placed on glass slides. They then fired microparticles at the material at speeds that exceeded the speed of sound.

These supersonic experiments revealed that microstructured materials can withstand high-velocity impacts, sometimes deflecting microparticles, and sometimes trapping them.

“But because we were testing the material on a substrate, there were a lot of questions we couldn’t answer, which could have affected the material’s behavior,” says Portella.

In a new study, researchers developed a method to test free-standing metamaterials, observing how the materials withstand impacts purely on their own, without any lining or supporting substrate.

In the current setup, the researchers suspend their metamaterial of interest between two microscopic pillars made from the same base material. Depending on the dimensions of the metamaterial being tested, the researchers determined how far apart the columns should be to support the material at each end while still allowing the material to react to impacts without being affected by the columns themselves. Calculate how much you need to separate.

“This allows us to reliably measure material properties rather than structural properties,” says Portella.

Once the team decided on the pillar support design, they proceeded to test different metamaterial architectures. For each architecture, the researchers first printed support pillars on small silicon chips, then continued printing the metamaterial as a floating layer between the pillars.

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

holes and cracks

The research team printed a floating metamaterial that resembles a complex honeycomb-like cross section. Each material is printed with her specific three-dimensional microscopic architecture, including precise scaffolding of repeating octets and more faceted polygons. Each repeating unit was measured to be as small as a red blood cell. The resulting metamaterial was thinner than the width of a human hair.

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

“In the engineered material, we observed the morphology of small cylindrical craters after impact,” says Portela. “However, in the solid material, we saw numerous radial cracks and large chunks of material that had been gouged out.”

Overall, the team observed that the ignited particles created small holes in the lattice-like metamaterial, yet the material remained intact. In contrast, firing the same particles at the same velocity into a solid, non-lattice material of the same mass creates a large crack that quickly propagates and causes the material to collapse. Therefore, the microstructured material could not only protect against multiple impact events but also withstand supersonic impacts more effectively. And in particular, materials printed using repeating octets appeared to be the most durable.

“We find that at the same speed, the octet structure is less susceptible to failure, meaning that the metamaterial can withstand up to twice as much impact per unit mass as the bulk material,” Portella said. Masu. “This shows that there are some architectures that can make materials tougher that can provide better impact protection.”

Going forward, the team will use new rapid testing and analysis methods to identify new metamaterial designs, tagging architectures that can be scaled up into stronger and lighter protective gear, clothing, coatings, and panels. I hope so.

“What I’m most excited about is showing that many of these extreme experiments can be done on the benchtop,” Portela says. “This will greatly accelerate the speed at which new high-performance, resilient materials can be validated.”

reference: Butreuil T, Krone JC, Portela CM. Isolation of particle impact dissipation mechanisms in 3D building materials. PNAS. 2024;121(6):e2313962121. Doi: 10.1073/pnas.2313962121

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