New manufacturing technology will build better body armor.

As Ugandan dictator Idi Amin Dada pointed out, “You cannot run faster than a bullet.”  Current flack-jacket technology can protect the lucky from munition’s fatal consequences.  Working with his students, Dr. Robert Speyer, a professor of materials and engineering from the Georgia Institute of Technology, aims to make the protective material in bullet-proof vests harder, and to produce it in versatile shapes—essentially, making it better at saving lives.

“The process has two advantages: better properties and…if you put a certain shape into our process, it comes out the same shape,” said Speyer.

Today’s ballistic-protection wear has plates of boron carbide sewn into a pocket in the vest, which is typically made of the synthetic, lightweight polymer Kevlar. Boron carbide is the third hardest material in the world, behind diamond and cubic boron nitride. It is an ideal material for combat clothing because it is relatively lightweight—it has a low density (2.52 g/cm3 compared with 7.87 g/cm3 for iron)— and still provides good stopping-power for projectiles, due to its high elastic modulus (a measure of material stiffness).

The goal of protective armor is to spread the load of the projectile over a larger area. When a bullet hits a boron-carbide plate, either the hardness of the plate causes the bullet to break, or the bullet shatters the plate and the cracks dissipate the projectile’s energy. The problem with current bullet-proof vests: The protected area is only as large as the flat boron-carbide plate (approximately 30.5 by 25.5 cm). 

Because of the way boron carbide is currently manufactured, only flat shapes are possible. Speyer and his team have developed a new method of boron-carbide formation that allows for curvature. Their process—called post-sintering hot isostatic pressing (HIP)—is faster and cheaper than traditional methods. It also yields boron-carbide armor that is harder than the body armor currently worn by soldiers in Iraq.

If you wanted to make a helmet out of, let’s say, gold, you could simply melt the metal and pour it into a mold. But because boron carbide has a very high melting point—around 2,450° C—no mold will hold the melted material. Anything you construct from boron carbide must be made by sintering, the process of pressing very fine powders of your material into a desired shape, then heating the material until the particles fuse. A sintered material has very low porosity, which makes it ideal for halting ballistics. The fewer pores in the material, the less easily it cracks when hit with a projectile. Historically, boron carbide has never sintered well.

Dr. Speyer and his team used a specialized differential dilatometer to measure the expansion and contraction of boron carbide during the stages of sintering, noting when boron carbide particles coarsened. 

“We basically discovered why boron carbide did not sinter well,” Speyer said, “and developed a manufacturing process to work around that.”

Unlike previous sintering technologies, Speyer’s HIP process squeezes the material apart, uniformly, in all directions, rather than along one axis at a time. This system enables the production of complex shapes, such as a shin guard or a helmet with a lip that dips under the chin.  The military is very interested in Speyer’s work and has ordered several prototype parts.

As a result, Speyer has taken his research out of the lab and into the commercial arena.  He has formed a company called Verco Materials that will manufacture parts using his HIP technique.  Most products are in the prototype phase. 

“Lab scale and real scale are two different scales,” Speyer said. “The temperatures we need to go to are quite extreme. We’re working on a furnace that can go to these extreme temperatures, that can fire the size parts that we need.  We’ve also developed technologies to make greenbody, that is, unfired shapes, like helmets and thigh plates.”

Speyer’s manufacturing technology could have civilian as well as military applications. Bearings, blast nozzles, cutting and mining tools, and pump and turbine shafts are all products that could be improved with the use of low porosity, very hard boron carbide produced with his technique.

Originally published December 14, 2005


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