Body armor for your average infantry troop has come a long way. Today's soldiers, sailors, airmen, and Marines are issued amazing technology designed to stop the most common threat they will likely face in combat: the rifle round. But the tech that will stop a lethal bullet isn't just one miracle material that they can wear all over their bodies. There is a combination of forces at work, working to stop another combination of forces.
Soldiers don the Interceptor Armor before going on patrol in Iraq.
Kevlar itself is a plastic material five times stronger than steel. Everything about the material, from how it's woven, right down to its molecular structure just screams strength. Its tensile strength is eight times that of steel. It doesn't melt, it doesn't get brittle with cold, and is unaffected by moisture. Kevlar is an awesome antiballistic material because it takes incredible amounts of kinetic energy to pass through it. Its molecular structure is like that of rebar through solid concrete, and forces a bullet to fight its way through at every level.
When layered, the material can sort of "soak up" a lot of the kinetic energy from a projectile. For most low-velocity handguns and even some of the more powerful handguns, a few layers of Kevlar is enough protection. But for high-velocity rifles, it needs some help. That's where ceramic plates come in.
The standard AK-47 fires with a muzzle velocity of 716 meters per second. For Kevlar alone to protect a soldier from that kind of kinetic energy, the Kevlar would have to have more layers than a troop could carry while retaining the mobility necessary to perform his or her job functions. Kevlar is lightweight, but it's not weightless, after all. The standard-issue Interceptor body armor was not tested to stop rounds at that velocity, which is classified as Level III protection. The Interceptor Armor does have pockets on the outside of the vests, so ceramic plates can be inserted to upgrade the armor to Level-IIIA.
Just like the Kevlar, the ceramic plates redistribute the kinetic energy of an incoming rifle round, slowing it down enough that it would not be able to penetrate the Kevlar, if it passed through the ceramic at all. It also prevents blunt force trauma from other rounds that may not penetrate the Kevlar, but still cause indentations in the material. The impact from bullets that don't penetrate the Kevlar can still cause internal injuries. Ceramic inserts are rated to stop whatever projectiles are listed on the plate, and can take up to three hits before failing.
The ESAPI plate saved Sgt. Joseph Morrissey when he was hit in the chest with a 7.62mm round from about 30 meters while deployed to Afghanistan.
While ceramic may seem like an odd choice for stopping bullets, this isn't the ceramic material used to make vases or coffee mugs. A lot of materials are actually ceramic, including titanium diboride, aluminum oxide, and silicon carbide, one of the world's top ten strongest materials – the material used in the U.S. military's Enhanced Small Arms Protective Inserts, or ESAPI plates. These enhanced plates, combined with the Kevlar are capable of stopping a Springfield 30.06 round with a tungsten penetrator.
That's why the U.S. military uses ceramic plates and Kevlar body armor. It not only protects troops but allows them enough mobility to do their jobs in a hostile environment. And body armor tech is only getting better. Materials like spider silk and nanotubes are being tested that are even lighter and don't take on as much heat as Kevlar. Maybe one day, we all won't be drenched in our own sweat when we take off our armor.