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Body armorTesting polymer fibers for body armor

Published 24 October 2017

High-performance polymer fibers have been used in ballistics applications for more than forty years. Although effective at stopping or slowing down bullets, users have sometimes found these vests, which are worn either under or over clothing, to be heavy and bulky—akin to wearing 15 to 20 shirts at once on a hot summer day. Many would like a more comfortable alternative. NIST scientists have developed a new way to investigate the high-performance fibers used in modern body armor.

Scientists at the National Institute of Standards and Technology (NIST) have developed a new way to investigate the high-performance fibers used in modern body armor. The research, described in the Journal of Polymer Science, may help increase confidence in the apparel that protects military units, police departments and public figures from gunfire. It may also lead to the development of new, lighter weight materials for body armor in the future.

High-performance polymer fibers have been used in ballistics applications for more than forty years. Traditionally, these fibers are woven together into a fabric and then layered 15-20 times over to make a vest with a thickness of anywhere from about 6 to 13 millimeters (a quarter to half an inch). Although effective at stopping or slowing down bullets, users have sometimes found these vests, which are worn either under or over clothing, to be heavy and bulky—akin to wearing 15 to 20 shirts at once on a hot summer day. Many would like a more comfortable alternative.

NIST says that the testing of soft body armor has been a big concern because the deployment of a new kind of fiber—believed to be superior to the previous material—unexpectedly failed in 2003, resulting in the death of a police officer. That and other incidents prompted a 2005 recall of some of the vests made with the new material.

Although the performance of these vests was superior when they were fresh out of the box and in pristine condition, tests later showed that the mechanical properties of the fibers inside the vests began to deteriorate after a few months of normal wear. The new vests were eventually removed from market entirely and the manufacturer was sued by the Department of Justice (DOJ).

The DOJ enlisted NIST to help evaluate the problem and determine why these vests were failing. As the nation’s measurement lab, NIST researchers are especially qualified to develop ways to characterize both the fibers and their eventual deterioration.

“The fibers in these ballistic applications cannot fail [in the field], period,” said Gale Holmes, a materials research engineer at NIST. “But previously, we had no way to know if they were changing over time as people were wearing and using them.”