University of Wisconsin–Madison engineers have created a nanofibre material that outperforms its widely used counterparts – including steel plates and Kevlar fabric – in protecting against high-speed projectile impacts.

“Our nanofibre mats exhibit protective properties that far surpass other material systems at much lighter weight,” says Ramathasan Thevamaran, a UW-Madison assistant professor of engineering physics who led the research.

He and his collaborators detailed the advance in a paper published recently in the journal ACS Nano.

To create the material, Thevamaran and postdoctoral researcher Jizhe Cai mixed multi-walled carbon nanotubes with Kevlar nanofibres. The resulting nanofibre mats are superior at dissipating energy from the impact of tiny projectiles moving faster than the speed of sound.

The advance lays the groundwork for carbon nanotube use in lightweight, high-performance armour materials such as bulletproof vests, to better protect the wearer, or in shields around spacecraft to mitigate damage from flying high-speed micro-debris.

“Nanofibrous materials are very attractive for protective applications because nanoscale fibres have outstanding strength, toughness, and stiffness compared to macroscale fibres,” Thevamaran said. “Carbon nanotube mats have shown the best energy absorption so far, and we wanted to see if we could further improve their performance.”

Dynamic bonds

The team synthesized Kevlar nanofibres and incorporated a tiny amount of them into the carbon nanotube mats, which created hydrogen bonds between the fibres. The hydrogen bonds modify the interactions between the nanofibres and cause a dramatic leap in the overall material combination’s performance.

“The hydrogen bond is a dynamic bond, which means it can continuously break and re-form again, allowing it to dissipate a high amount of energy through this dynamic process,” Thevamaran said. “In addition, hydrogen bonds provide more stiffness to that interaction, which strengthens and stiffens the nanofibre mat. We were able to achieve a nearly 100% improvement in energy dissipation performance at certain supersonic impact velocities.”

The researchers tested their new material using a laser-induced microprojectile impact testing system in Thevamaran’s lab which uses lasers to shoot micro-bullets into the material samples.

“Our system is designed so that we can actually pick a single bullet under a microscope and shoot it against the target in a very controlled way, with a very controlled velocity that can be varied from 100 metres per second all the way to over 1 kilometre per second,” Thevamaran said. “This allowed us to conduct experiments at a time scale where we could observe the material’s response — as the hydrogen bond interactions happen.”

In addition to its impact resistance, another advantage of the new nanofibre material is that, like Kevlar, it is stable at both very high and very low temperatures, making it useful for applications in a wide range of extreme environments.

The researchers are patenting their innovation through the Wisconsin Alumni Research Foundation.

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