Monday, December 17th, 2012
Several interesting technologies aimed at improving body armor have been announced recently—plastics technologies. That should not be a surprise: Plastics of various types and in various forms have been a critical component of security systems and protective devices for some time. But it most likely surprises the average person.
Many people don’t think of things such as bulletproof glass and Kevlar as plastics, but both of them and many more are polymers. When someone mentions bulletproof glass they most likely are talking about polycarbonate, an ultra-tough plastic material also used to make helmets for football players, cyclists, and astronauts. Nearly every article about personal ballistic protection includes the word Kevlar, but rarely is it noted that Kevlar is an aramid fiber—and a DuPont registered trademark.
On the other side, the specialists who develop and design protective gear such as body armor know full well the advantages of plastics in their work, and are using polymers as they relentlessly advance the state of the art. An outstanding example is Auxetix, a small company in southwest England creatively ignoring the law of elasticity that says a material stretches in proportion to the force applied, and becomes thinner.
But if the material is auxetic the force makes it fatter. Picture an elastic bungee cord with a string wrapped around it in a spiral. Pulling the string distorts the bungee cord into a spiral that’s wider than the original bungee, but not shorter. Put several wrapped bungees side by side, pull the strings, and they all become wider, pushing each other to increase the area they cover and the total volume.
Auxetix wraps a thin cord of a high-strength material such as Kevlar around a core of special elastic polyester to make threads that can be woven into cloth. The shape change of auxetic materials also lets them absorb and stores energy very rapidly. When Auxetix’s woven cloth is hit in one place, the energy is diffused through the whole sheet and is dissipated from the entire surface.
The English firm has tested a translucent bomb-resistant curtain that is expanded from the force of a blast, creating pores that allow air to pass through while solid debris such as glass fragments and other shrapnel is stopped. The cloth itself absorbs the kinetic energy of the blast debris.
Patrick Hook, who leads Auxetix, intends to use the auxetic technology to make body armor that will be about 10% lighter than the Interceptor Body Armor currently worn by American soldiers. Interceptor weighs about 33 pounds. You can find more info on the Auxetix technology here.
Body armor design is a trade-off between mobility and protection. The goal has always been a system that’s light yet still offers high protection. One of the most basic advantages of virtually all plastic materials is their high strength-to-weight ratio, so plastics have a natural fit here. Other plastics-based approaches to body armor are emerging. We’ll post more soon.