Stronger, Lighter Soldier Armor From Nanoscale Experiments
by Army Research Laboratory Public Affairs
U.S. Army Combat Capabilities Development Command
June 1, 2020

Soldier armor, such as bulletproof vests and helmets, depends upon high-performance ballistic fibers for its strength and effectiveness.

Army researchers are experimenting with how they can improve armor by making it lighter and stronger. At the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory, researchers examine high-performance fibers in an innovative soft armor research program.

By understanding how fibers behave under stress, researchers can predict their performance during a ballistic event. With this information, researchers can leverage a materials-by-design approach to create stronger, more effective body armor.

The Army researchers partner with U.S. industrial fiber manufacturers to study about the structure inside single fibers and how it influences the strength and stiffness of the fibers.Atomic force microscopy examines material surfaces at the extremely small scale ... on the order of fractions of a nanometer. Strawhecker uses the analogy of a tiny version of a blind man tapping his cane along the inside of the fiber. This is how atomic force microscopy maps the fibrils for length and width, he said.

The researchers discovered that these fibrils tend to form bundles of fibrils.

These findings leave the researchers optimistic that as they look at smaller and smaller structures within a fiber, they will understand what holds them together.

“Long polymer molecules form crystals which group into nano-fibrils, which group into fibril bundles, which group into single fibers,” Strawhecker said. “At each size we have found that there is a similar resistance to separation between these parts for a fiber with given chemical makeup and processing history.”

Understanding this structure means knowing how molecules are arranged together to form structures that ultimately will stop a bullet for the Soldier.

“Determining the best way to arrange them can be based upon these models and it depends on finding the strongest, stiffest overall fiber structure due to the arrangements within,” he said.

The American Chemical Society published this research as a cover in its Applied Materials & Interfaces, May 13, 2020, Vol. 12, Issue 19. The lead author for the paper, Dr. Taylor Stockdale, performed many of the experiments as a doctoral student at the University of Nebraska-Lincoln using techniques learned as an intern with Strawhecker at the lab’s Rodman Materials Research Laboratory during the summer of 2015.

Stockdale learned how to use the lab’s focused-ion beam instrument to shoot a beam of gallium ions at a fiber to mill out notches in the fiber. With those notches in place, he carefully used an ultra-fine platinum wire (typically used by a scanning transmission microscope to image atomic features) to dig-out and unzip the top half of the fibers, uncovering their interior ... like opening a convertible automobile, Strawhecker said.

Strawhecker said the initial work earned now-Dr. Stockdale the 2015 Army Research Laboratory Graduate Student Summer Internship award for Best Paper and resulted in the seminal publication of the mounting technique.

Besides U.S. fiber manufacturers, collaborative partners include the University of Nebraska-Lincoln, Northeastern University, CCDC Soldier Center, University of Delaware and Drexel University.

The Army goal is to make armor lighter and reduce bulk and burden on the warfighter.

This research fundamentally approaches the building block of armor packages, which comprises a large percentage of the overall Soldier burden.

As new experimental fibers are being produced, he said, the laboratory will continue to partner with manufacturers using these special techniques to understand how new chemistry and processing steps may change the structure and performance of the next generation of fiber materials.

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