A newly developed carbon-based material could provide a lightweight replacement for Kevlar and steel in a wide range of impact-resistant applications.
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The development of micro and nanoarchitected materials has opened up an entire range of materials with extraordinary physical properties that were unattainable in ‘traditional’ materials. One of the most impressive and revolutionary applications of this technique so far has been the creation of substances that have a staggeringly high strength to mass ratio with extreme powers of resilience.
New research conducted by scientists and engineers from the Massachusetts Institute of Technology (MIT), the California Institute of Technology (Caltech), and ETH Zürich has demonstrated that some materials with precision nanoscale structures are resistant to supersonic impacts. The fact that this material comprising of nanoscale carbon struts is also incredibly lightweight means it could find specific uses in protective coatings, body armor, blast shields, and a slew of other impact-resistant materials.
The multi-institutional team tested the lightweight carbon substance, which is thinner than a human hair, for toughness by blasting it with mini-projectiles traveling at supersonic speeds. They found that the projectiles were unable to breach the material which proved to be more efficient at absorbing impacts than aluminum, Kevlar, and even steel at a similar weight.
This means a given mass of the team’s material would be better equipped to halt a projectile than a similar mass of any of those substances, meaning that if its production can be scaled up, it could serve as an impact-absorbing alternative to Kevlar and steel that is lighter and possesses more stopping power.
The team’s research is reported in the latest edition of the journal Nature Materials¹.
Putting a Nanoarchitected Material to the Test
Nanoarchitected materials comprise nanometre-scale structures that are patterned in particular ways. These arrangements are responsible for granting these substances their extraordinary properties. Until now, these materials have not been widely tested with only their response to slow deformation well-explored.
This limits the real-world applications that nanoarchitected materials have enjoyed, simply because there are not many situations in which slow-deformation occurs outside the lab. The team set out to investigate some more rapid deformations, and that includes high-velocity impacts from supersonic projectiles.
To do this the Caltech contingent first fabricated the material by using a high-energy laser to solidify microstructures in a photosensitive resin. The shape carved into this resin took the form of a repeated lattice pattern with integrated nano-struts.
This arrangement resembles the microscopic geometry of foams that are capable of absorbing energy and had the net result of transforming the carbon from which the material was made from brittle to elastic. This delivered to the ordinarily stiff material a flexible, impact-absorbing quality.
Once the remaining waste resin was washed away and the material was exposed to high temperatures to leave behind only carbon. The Caltech team created materials of two different densities, with the less dense material being comprised of thinner carbon struts.
Once created, the materials were transferred to MIT to receive some high-impact punishment. All in the name of science, of course.
Nanoarchitected Materials in the Firing Line
The MIT researchers turned to an ultrafast laser to expose the material to microparticle impacts. These microparticles are fired as the laser generates plasma in a thin film of gold pushing out silicon oxide particles at high velocities.
The speed of these particles could be adjusted by lowering or raising the power of the laser with the team exploring a range of velocities from 40 to 1000 meters per second — well into the supersonic range of 340 meters per second.
The resulting impacts on the nanoarchitected material were recorded by high-speed cameras. The team discovered that the denser material was more resilient to impacts, with the microparticles embedding in it rather than ripping through.
Studying these embedded particles showed the team that even though the collisions had crumpled the carbon struts they hit, the surrounding regions escaped unscathed. This means that the material can absorb a lot of kinetic energy thanks to the shock-compacting structure.
Further to this, by employing a mathematical framework, the team could predict the kind of damage the material would sustain from a range of different impacts.
An Impact Resistant Nanomaterial That is Out of This World
The framework adopted by the team to assess damage to this nanoarchitected impact-resistant material is similar to the analysis used by astronomers and planetary scientists to assess the effect of asteroid and meteorite collisions on planets and moons.
This framework considers the physical characteristics of a system such as meteorite velocity and planet surface strength to develop a ‘cratering efficiency’ and thus calculate the depth of craters that an impact will carve out on a planetary body. The team found this methodology is also a good way of modeling the damage a supersonic projectile impact will have on a nanoarchitected material.
This is not the only way that the team’s research could extend beyond the surface of Earth. Aside from theoretical modeling, the material could have practical applications in orbit and beyond.
The material pioneered by the team could have impressive applications resisting impacts here on Earth, but its use could extend beyond the limits of our atmosphere.
Impacts from meteoroids and space debris upon spacecraft and satellites can cause consequences ranging from superficial damage, to equipment failure, or even complete disintegration of a target.
That means a material that can effectively resist impacts is vitally needed as we expand our technological reach into orbit. This impact resistance needs to be delivered by a lightweight material as the heavier a substance, the more fuel required to launch it into space.
That means space agencies are constantly on the lookout for material just like the one developed by the MIT, Caltech, ETH Zürich team. For now, however, the researchers are keeping their feet on the ground.
The next step for the team is to use the framework they have developed to test the resilience of other nanoarchitectured materials, experimenting with alternative configurations and materials other than carbon.
In addition to this, materials scientists will attempt to see if the production of such materials can be scaled up, something that is key to wider adoption of any technology.
Nanoarchitectured materials are still something of an unknown quantity and the quest to understand such substances has only just begun. Yet, even in these early stages of discovery, the potential impact of these materials is strikingly clear.
References and Further Reading
¹Portela. C. M., Edwards. B. W., Veysset. D., et al, , ‘Supersonic impact resilience of nanoarchitected carbon,’ Nature Materials, https://doi.org/10.1038/s41563-021-01033-z