Structures are tougher than bulletproof vests

Researchers at UT Dallas have created structures that are stronger than Kevlar, which is commonly used in bulletproof vests.
Researchers at UT Dallas have created structures that stretch to up to seven times their length, while remaining tougher than Kevlar, the material often used to make bulletproof vests.

The structures exploit the electromechanical properties of specific nanofibres to absorb up to 98joule/g. Kevlar can absorb up to 80joule/g. Researchers hope the structures will one day form material that can reinforce itself at points of high stress, potentially for use in military airplanes or other defence applications.

Researchers twisted nanofiber into yarns and coils and then stretched the twisted nanofiber. They found that the electricity generated by stretching the twisted nanofibre formed an attraction 10 times stronger than a hydrogen bond, which is considered one of the strongest forces formed between molecules.

Dr. Majid Minary (pictured), an assistant professor of mechanical engineering in the University's Erik Jonsson School of Engineering and Computer Science and senior author of the study said: "We reproduced this process in nanofibres by manipulating the creation of electric charges to result in a lightweight, flexible, yet strong material".

First, researchers spun nanofibres from polyvinylidene fluoride (PVDF) and its co-polymer, polyvinvylidene fluoride trifluoroethylene (PVDF-TrFE). These fibres were twisted into yarns, and the material was twisted into coils, using, says Minary, the same basic process used in making conventional cable.

Mechanical properties of the yarn and coils were measured to see how far it can stretch and how much energy it can absorb before failure.

"Our experiment is proof of the concept that our structures can absorb more energy before failure than the materials conventionally used in bulletproof armours," reports Minary. "We believe. . . that this flexibility and strength comes from the electricity that occurs when these nanofibers are twisted."

The next step in the research is to make larger structures out of the yarns and coils.

Other UT Dallas authors on the paper are Mahmoud Baniasadi, Zhe Xu, Yang Xi and Salvador Moreno, all research assistants in the Jonsson School; alumnus Jiacheng Huang; Jason Chang, a biomedical engineering senior; and Dr Manuel Quevedo-Lopez, professor of materials science and engineering. Dr. Mohammad Naraghi, an assistant professor of aerospace engineering at Texas A&M University, also participated in the work.

The study was published by ACS Applied Materials and Interfaces, a journal of the American Chemical Society,

The work was funded by the Air Force Office of Scientific Research Young Investigator Research Program and the National Science Foundation.

Caroline Hayes

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