Instant Armor

(Sciencentral News) When danger looms in the new Matrix movie, the heroes step into flexible armor. The U.S. Army wants something even more amazing for our soldiers?uniforms that turn into lightweight armor on command. As this ScienCentral News video reports, one nanotechnologist says that instant armor could be real in ten years.

Not-So-Heavy Metal

On the battlefield of the future, soldiers could be wearing uniforms that turn from soft, comfortable fabric to light, flexible, durable armor with a flip of a switch.

At Massachusetts Institute of Technology (MIT), the Institute for Soldier Nanotechnologies is dedicated to using nanoscale science?s potential to produce a protective uniform for the U.S. Army. One research team headed by professor of mechanical engineering Gareth McKinley starts with an oily fluid full of very tiny iron particles, and a magnet.

“What we’re working with is a class of fluids called magnetorheological fluids,” says McKinley. “These are liquids that change their properties when we apply a magnetic field to them. They are made up of very, very small iron particles, much smaller than individual red blood cells,” which the researchers then mix into a silicon oil, or even corn syrup, so they don’t rust. The oil or syrup also makes the solution mayonnaise-thick, with just enough stiffness to prevent it from running.

Oily fluid full of tiny iron particles before being near a magnet (above); and after.

McKinley is director of MIT?s Hatsopoulos Microfluids Lab, which studies the properties of complex fluids and how fluids move in very small channels. Just as matter behaves in unusual ways at the scale of atoms and molecules, fluids also move differently at very small scales. When McKinley and his researchers apply a magnetic field to their solution, the tiny iron particles align with the magnetic field, and stack up on top of each other. As they do so, the fluid turns into a peanut butter-like substance that feels very hard. When the researchers remove the magnet, the solid instantly reverts to liquid. McKinley says that the change happens incredibly quickly??in about 20 thousandths of a second. We can keep applying a magnetic field, turning off a magnetic field, and the material will keep going backwards and forwards, from liquid-like to solid-like and back again.”

McKinley and his team are investigating ways to put this switchable solution into the material currently used to make bulletproof vests, which is essentially a woven fabric full of air gaps. Once the researchers immerse that fabric in magnetorheological fluid, “what we have without a magnetic field is a very soft, very flexible fabric, and when we apply a magnetic field, then the stiffness of that fabric changes by a factor of about 50 at the moment,” says McKinley. “The stiffness change depends on the strength of the magnetic field. As the magnetic field gets stronger and stronger, then the stiffness change gets larger and larger.? The research team hopes that eventually, the fabric-fluid combination could resist a shockwave or shrapnel.

Since troops won’t be carrying magnets on the battlefield, McKinley says he would wire the fabric of military uniforms with electric current that soldiers could switch on to produce electromagnetic fields. “Ultimately, the way the magnetic field would be applied in a suit, would be that the electromagnets or micro magnets would be part of the actual fabric suit system,” says McKinley. “Working with Patrick Doyle, professor of chemical engineering at MIT, we’ve already explored the possibility of using very small magnets as valves to turn these fluids on and off.”

McKinley emphasizes that this “instant armor” is definitely not combat-ready yet. “We’ve got five to ten years of research before we can make this material truly bullet-resistant,” he says. Right now, he?s working with T. Alan Hatton, also of MIT?s chemical engineering department, on making his tiny iron particles in different shapes. ?The particles that we?re using now look like soccer balls. They?re spherical,” says McKinley. “If you were to stack a pile of those together, you don?t get very far. What would be better would be to have faceted particles, particles with flat faces, or particles that look more like donuts. You could stack a pile of donuts on top of each other.?

McKinley and his team also would like their fluid to change even faster, and to remain reversible for years.

McKinley?s research was presented at the Society of Rheology meeting in October 2003 and is funded by the U.S. Army Research Office.

Mystech: Special thanks to Speaks for this lead.