Non-Newtonian substance uses 75% less fabric than previous body army, weighs less, and is half as thick

 By Brian Santo, contributing writer

stock_Goo

Nobody
has ever looked at ketchup, Silly Putty, or castor oil and thought, Hey, I wonder if that stuff is bulletproof?
Which is one reason why it has taken so long to stumble on an impact-resistant
material that could prove extremely effective for body armor, military vehicle
cladding, mortar-defying tents, emergency blankets, and any number of other
possible uses.

Researchers at the
U.S. Air Force Academy (AFA) have devised a material that can stop a bullet
from a .44 Magnum, uses 75% less fabric than previous body army, weighs less,
and is half as thick, according to the AFA.

During a 2015 chemistry class at the Air
Force Academy, cadets were handed three impact-resistant materials — Kevlar,
carbon fiber, and epoxy — and were asked to combine the materials to make a
more effective bulletproof material.

As
Cadet First Class Hayley Weir and her advisor, Ryan Burke, a military and
strategic studies professor at the academy, began working with the materials,
they became unsatisfied with the performance of the epoxy in the trio of
materials.

Epoxy happens to be a non-Newtonian fluid.
The vast majority of fluids in the world conform to Newton’s Law of Viscosity,
which predicts the behavior of fluids in response to the application of force.
Non-Newtonian fluids simply don’t conform to the law of viscosity. A factor in
the equation for viscosity is shear stress, and the shear stress
characteristics of different non-Newtonian fluids can vary wildly. Many of
them, such as epoxy, stiffen in response to force.

Weir and Burke began searching for another
material in the same class, with shear stress characteristics similar but
superior to those of epoxy.

Considering the total number of fluids,
there aren’t that many non-Newtonian fluids, but the substances that do fall into
that category are not rare. They include Silly Putty, ketchup, castor oil,
custard, whipped cream, some clays, latex paints, blood, and printer ink, among
others.

Weir has told several sources that she
remembered playing with Oobleck, a simple combination of corn starch and water, when
she was a child. Oobleck happens to be another non-Newtonian fluid.

It turned out that looking for another
non-Newtonian fluid to use in place of the epoxy was, in fact, a brainstorm. It
seems an obvious idea, but Weir and Burke couldn’t find reference to anyone
else ever having tried it, Burke told The Air Force
Times
.

Weir and Burke found what they were looking
for. They have not identified the substance, which they’re referring to as
“goo,” but it’s black, and Weir mixes it up with a kitchen blender.

The material they’re using actually failed
at first. The researchers eventually discovered that how the layers of Kevlar
and goo are ordered make a difference, however. After changing the layering,
they’re having a hard time making it fail, they say.

Interestingly, the layered material gets
harder with increasing force. In practical terms, that means the bigger the
bullet, the more bulletproof the material is. The material was tested against
rounds from a 9 mm, a .40 Smith & Wesson, and a .44 Magnum. In the 9 mm
testing, the rounds went through most of the layers but were caught by the
fiber backing, Burke told the Air Force Times. The larger .40-caliber round was
contained in the third layer of Kevlar. The .44 Magnum was caught in the first
layer.

Weir and Burke recently spoke with reporter Kyle
Clark of Channel 9 in Denver, Colorado. The interview includes slow-motion
video of one of their ballistic tests. See it below: