Since man discovered that the other guy can hit you without warning, armor or shielding has been in high demand. Usually this involves a trade-off of strength and flexibility vs. weight. The knights of old found this out up close and personal. Not only was their armor inflexible, but it was so heavy that war horses were specially bred to handle the great weight of a fully-equipped knight.
Up until the Vietnam War, the flak jacket with removable steel plates was the de-facto standard of personal armor. Then, the wonder material of Kevlar was developed. Kevlar is flexible, light, and stronger than steel. It works by surrounding the projectile like a catcher’s mitt.
That’s all well and good if you are protecting a vehicle, tank, or ship, but personal armor still allows for a great deal of blunt-force trauma. This is because the round still concentrates its energy in one focused spot. Ceramic plates are available that distribute the energy across a wide area, but the total weight of the vest exceeds 25 pounds and tends to restrict movement.
Enter shear thickening fluid (STF). This is a class of liquids that hardens when struck (shear). A science class experiment using equal parts of water and corn starch can demonstrate the principle. The fluid can be poured and stirred with a spoon, but strike the liquid with the spoon, and it suddenly solidifies until the energy of the strike has been expended.
Researchers have made vast improvements on STFs recently through the use of nanotechnology. Defense contractor BAE’s Advanced Technology Center is developing a new substance that uses spheres of silica (sand) that average 446 nanometers. The STF is 57% silica by weight suspended in ethylene glycol (a non-toxic chemical used as antifreeze in solar water heaters). The mixture is mixed with an equal amount of ethyl alcohol to help the liquid permeate layers of Kevlar material. The material is then baked to remove the alcohol (much like Aunt Juanita’s ballistic rum cake… also known to stop small-arms fire).
The result is a much thinner, lighter, and more flexible Kevlar vest that can stop even larger calibers of bullets. When struck by gunfire, the liquid in the vest becomes rigid within milliseconds, distributing the force across a wide area. The result is reduced bruising to the wearer while maintaining agility and freedom of movement. You can see the result in this YouTube video: http://www.youtube.com/watch?feature=player_embedded&v=EhdgkziFhrY#!.
In the meantime, vest up with what you’ve got. It may be hot, sticky, and bulky, but some of us out here want to see you get home “vertical”. Hang in there; better stuff is coming your way.
Bruce Bremer, MBA is LET’s technology contributor. Bruce retired from the Submarine Service after 21 years of in-depth experience with complex electronic technology. Since then, he has been involved in fleet modernization and military research analysis. He teaches electronics and alternative energy at a Virginia college. Besides his MBA, Bruce earned a Bachelor of Science degree in computer networking. He has been volunteering in public safety for many years.
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