SillyPutty Armor – Promises to Save Soldiers

How do you get ketchup out of a bottle? Most people turn the bottle upside down and slap the bottom. Smarter people quickly move the inverted bottle towards their plate, and stop it suddenly against the thumb and forefinger of their other hand. In effect, when the bottle stops, the ketchup keeps moving.

This happens because ketchup is a shear thinning fluid: When subjected to a shock it becomes suddenly much less viscous – it gets thinner.

Remember SillyPutty? You can mould it and shape it all day long just like any modeling clay. But hit it with a hammer, and it shatters into a thousand pieces like a rock or a chunk of glass, and yet each “broken” SillyPutty chunk remains soft and pliable, and all the chunks can be molded back together again.

SillyPutty is a shear thickening fluid: When subjected to a shock it becomes suddenly much more viscous – it gets stiffer.

This simple scientific principle may soon dramatically improve the survivability of our soldiers in hot spots such as Iraq and Afghanistan, thanks to some Maryland and Delaware scientists working for the U.S. Army.

The mind of an applied scientist is a wonderful thing, but you and I are unlikely to understand the mental paths these guys (and gals) follow. Take, for instance, the folks at the Army Research Laboratory (ARL), Weapons and Materials Research Directorate at the Aberdeen Proving Ground. Working with The University of Delaware’s Dept. of Chemical Engineering and the Center for Composite Materials, and starting with somebody’s memory of childhood SillyPutty, these people ended up with a lightweight, flexible body armor that transforms into a harder-than-steel rigid shell the moment a bullet or shrapnel fragment commences penetration.

This stuff is lighter, thinner, and more flexible than traditional Kevlar armor. In fact, it’s so flexible that it can be used to protect a soldier’s neck, arms and legs, in addition to his or her torso.

It took some three years to get there, but once there, it turns out the technology is pretty simple. The “fluid” part of the shear thickening fluid (STF) is polyethylene glycol (PEG), which is a water-soluble, waxy “solid” used extensively in the cosmetic and toiletry industries. The “solid” part of the STF is nano-sized particles of silica, that’s right, beach sand, but very, very small particles, on the order of a millionth of a millimeter (normal sand is a couple tenths of a millimeter).

They soaked regular Kevlar material in this fluid, so that it permeated the entire fabric. That’s it – hit this stuff hard with anything, and it goes rigid, almost instantaneously. Then, like magic, a moment or two later it reverts to being soft and flexible. It works with the Kevlar, and allows the number of layers to be reduced dramatically. The resulting armor is light, flexible, and significantly more comfortable than earlier materials.

According to Dr. Eric Wetzel, who heads up the ARL research team, “During normal handling, the STF is very deformable and flows like a liquid. However, once a bullet or frag hits the vest, it transitions to a rigid material, which prevents the projectile from penetrating the soldier’s body.”

Wetzel’s team was assisted by Professor Norman Wagner, post-doctoral fellow Dr. Young Sil Lee, post-graduate student Ron Egres, and undergraduate Keith Kirkwood, all from the University of Delaware. For their efforts, they received the 2002 Paul A. Siple Memorial Award, the Army’s highest award for scientific achievement. This may be only the first of many awards and other kinds of recognition as the world comes to realize what these guys accomplished.

The applications for this stuff go far beyond just protecting a soldier, although this in itself is more than sufficient to justify the award. Obviously, STF armor offers police officers similar protection. Build it into the structure of paratrooper’s jump boots, and you have an ankle protection system that can save many sprained and broken ankles. Racecar drivers, mountain climbers, miners – in fact anyone subject to crushing injuries – can be protected by STF armor.

Space-suited astronauts currently deal with incredibly bulky suits to protect them from the vacuum of space, and from radiation and micrometeorites. Adding an STF layer to the suit may enable them to be lighter and more flexible, just as it works for battlefield soldiers. Even spacecraft can benefit from this technology so that more of the weight carried into orbit (or to the Moon or Mars or wherever) can be payload instead of protection.

Tanks, aircraft, baby carriages – the more you think about it, the longer the list gets. Imagine a stylish bonnet worn by a pretty bike rider that transforms into a rigid harder-than-steel shell should she tumble and strike her head, or a boxer’s shorts that go rigid in the event of an accidental low blow, or work gloves that protect fingers from hammer blows.

A new era of protecting the foot soldier from injury is upon us, and the SillyPutty principle is in the vanguard. Let’s hope the Army can move from research and testing into mass production as fast as possible.

Robert G. Williscroft is DefenseWatch Navy Editor

Submariner, diver, scientist, author & adventurer. 22 mos underwater, a yr in the equatorial Pacific, 3 yrs in the Arctic, and a yr at the South Pole. BS Marine Physics & Meteorology, PhD in Engineering. Authors non-fiction, Cold War thrillers, and hard science fiction. Lives in Centennial, CO.

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