Engineers from the University of Wisconsin–Madison (UW–Madison) have developed a nanofiber material that surpasses its extensively used equivalents — including Kevlar fabric and steel plates — in guarding against impacts from high-speed projectiles.
Ramathasan Thevamaran. Image Credit: University of Wisconsin–Madison.
Fundamentally, it is better than bulletproof.
“Our nanofiber 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 headed the study.
Thevamaran and his colleagues illustrated the advance in an article published recently in the journal ACS Nano.
To develop the material, Thevamaran and postdoctoral researcher Jizhe Cai blended multi-walled carbon nanotubes — carbon cylinders just one atom thick in each layer — with Kevlar nanofibers. The ensuing nanofiber mats are better at dispelling energy from the impact of miniature projectiles traveling faster than the speed of sound.
The advance paves the way for use of carbon nanotubes in lightweight, high-performance armor materials, for example, in bulletproof vests to better guard the wearer or in shields covering spacecraft to lessen damage from flying high-speed microdebris.
“Nano-fibrous materials are very attractive for protective applications because nanoscale fibers have outstanding strength, toughness, and stiffness compared to macroscale fibers,” Thevamaran says. “Carbon nanotube mats have shown the best energy absorption so far, and we wanted to see if we could further improve their performance.”
They discovered the precise chemistry. The researchers created Kevlar nanofibers and added a minute amount of them into their carbon nanotube mats, which formed hydrogen bonds between the fibers. Those hydrogen bonds altered the interactions between the nanofibers and, along with just the precise blend of Kevlar nanofibers and carbon nanotubes, caused a significant leap in the overall performance of the material.
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.
Ramathasan Thevamaran, Study Lead and Assistant Professor of Engineering Physics, UW–Madison
“In addition, hydrogen bonds provide more stiffness to that interaction, which strengthens and stiffens the nanofiber mat. When we modified the interfacial interactions in our mats by adding Kevlar nanofibers, we were able to achieve nearly 100% improvement in energy dissipation performance at certain supersonic impact velocities,” Thevamaran added.
The team verified their new material using a laser-induced microprojectile impact testing system in Thevamaran’s lab. The system is one of only a handful like it in the United States, and it uses lasers to fire micro-bullets into the material samples.
Our system is designed such 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 meters per second all the way to over 1 kilometer per second.
Ramathasan Thevamaran, Study Lead and Assistant Professor of Engineering Physics, UW–Madison
“This allowed us to conduct experiments at a time scale where we could observe the material’s response — as the hydrogen bond interactions happen,” Thevamaran added.
Besides its impact resistance, another benefit of the new nanofiber material is that, like Kevlar, it is steady at very high as well as very low temperatures, making it suitable for applications in a wide variety of extreme environments.
The scientists are patenting their advance through the Wisconsin Alumni Research Foundation.
Claire Griesbach, a doctoral student in Engineering Physics, is the study’s co-author.
This study received funding support from the U.S. Army Research Office and the UW–Madison Office of the Vice-Chancellor for Research and Graduate Education.
Journal Reference:
Cai, J., et al. (2022) Extreme Dynamic Performance of Nanofiber Mats under Supersonic Impacts Mediated by Interfacial Hydrogen Bonds. ACS Nano. doi.org/10.1021/acsnano.1c07465.
Source: https://wisc.edu