Nanotechnology involves designing and producing nanomaterials by controlling their shape and size on the nanoscale. As an indication of the nanoscale’s dimensions, a human hair is about 70,000 to 80,000 nanometers thick. Nanotechnology has already brought us improved suntan lotions, better tires and stain-resistant clothes. Soon “liquid armor” using a shear thickening fluid (STF), an application of nanotechnology, could be protecting police officers and soldiers.
Armor Holdings has plans to market a new type of bullet-resistant vest that features liquid armor. This will be offered first to prison guards because these vests provide good protection against knives and other handmade sharp weapons, as well as bullets and shrapnel. By the end of 2007, Armor Holdings hopes to offer the technology to law enforcement officers, as well.
The liquid armor was co-developed over the past five years by a research team headed by professor Norman Wagner at the University of Delaware’s Center for Composite Materials and Dr. Eric Wetzel of the Weapons and Materials Research Directorate at the U.S. Army Research Laboratory. Armor Holdings bought the rights to market the technology and has selected Barrday Inc. to further develop and produce the new ballistic fabrics. Barrday has extensive experience in weaving fabrics from high-strength fibers, as well as applying films, resins, finishes and coatings for both soft and hard armor applications.
The heart of the liquid armor is a shear thickening fluid composed of hard particles suspended in a liquid. The liquid, polyethylene glycol, is non-toxic and can withstand a wide range of temperatures. Hard, nano-particles of silica are the other components of STF. This combination of fluidic and hard components results in a material with unusual properties. Together, they produce an STF that stiffens instantly into a shield when hit hard by an object. It reverts to its liquid state just as fast when the energy from the projectile dissipates.
According to Dr. Wetzel, “The STF treatment changes the way in which yarns and fibers interact with each other and with the stabbing or ballistic threat during impact. In puncture applications, for example, the STF treatment prevents pointed weapons from penetrating between yarns in the fabric. The novelty of the STF treatment is that it provides these additional protective benefits without compromising the inherent thinness or flexibility of a woven fabric.”
A simple experiment shows how STFs work. Put a stick in a wet paste of cornstarch. Stir slowly, and the viscous liquid flows around the stick, and the path left in the paste slowly fills in. Move the stick quickly through the paste and it suddenly becomes solid, the wet gloss of its surface disappears, and the paste cracks and breaks like a hard material. The force applied by the stick to the paste transforms it from liquid to solid state. Upon release of stress, it becomes liquid again.
Testing showed that the STF materials worked best when intercalated or integrated into the DuPont™ Kevlar®. By holding the fibers tight like a flexible glue, the compound spreads out the impact of a blow better than fibers alone, allowing the energy to be dissipated over a larger area. The STF can be applied to conventional ballistic fabrics or other materials used in armor applications. The material remains flexible under normal wear, but instantaneously become resistant to penetration when impacted by a spike, knife or high-velocity projectile or fragment.
Extensive testing has shown that conventional ballistic fabrics treated with STF can resist penetration by an ice pick that would otherwise easily penetrate the fabric. Also fabrics treated with STF have shown reduced “back face deformation,” an indication of blunt trauma, from high-energy ballistic impacts. This increased protection comes without compromising the weight, comfort, feel, look, texture or flexibility of the garment.
To make liquid armor, the STF is soaked into all layers of a Kevlar vest. The Kevlar fabric holds the STF in place while helping stop penetration. The saturated fabric can be soaked, draped, and sewn just like any other fabric. Kevlar fiber vests soaked with STF remain pliable under normal conditions.
Dr. Wetzel said, “We would first like to put this material in a soldier’s sleeves and pants, areas that aren’t protected by ballistic vests but need to remain flexible.” STF could be applied to jump boots, so they would stiffen to support ankles if impacted. It could also be used for vehicle armor, helmets and gloves. Bomb blankets made with liquid armor could be use to cover suspicious packages or unexploded bombs.
Liquid armor has another important advantage. Because it enhances the functioning of materials such as Kevlar when integrated as a composite, it may be possible to reduce the number of fabric layers required to defeat ballistic and stab threats. New STF armor-based vests could be lighter than current vests that weigh 4 pounds or more. They should be cheaper to produce, as well. Armor Holdings hopes to keep its basic products priced at about $500 to $600 each.
Bill Siuru is a retired USAF colonel. Since retiring, he has done consulting and writing. He currently is the technical editor for several publications—Diesel Progress, Green Car Journal, and Police and Security News. He has a Ph.D. in mechanical engineering. Highlights of his military career include a professor at West Point, commander of the research laboratory at the Air Force Academy and director of Engineering at Wright-Patterson AFB. He can be reached at firstname.lastname@example.org.