Baird says military forces are expanding the use of ballistic composites. “Up until maybe the early 2000s only battlefield platforms – main battle tanks, armored fighting vehicles and attack helicopters – were armored,” he says. “Now as we face increased threats from terrorism and engage in asymmetric warfare, the battlefield is not so well defined. There is less willingness amongst the general public to accept casualties, which creates political pressure.” Baird adds that it’s now commonplace for logistic and patrol vehicles, transport helicopters and even naval ships to be fitted with protection against small arms fire and improvised explosive devices (IEDs).
In order to optimize and better integrate composite materials for these applications, armor manufacturers have been working with composites companies earlier in the design stage of a project, he adds.
Honeywell introduced the first generation of its UHMWPE spun ballistics fiber, Spectra Shield®, in 1989. Variations of the fiber have been used for vehicle protection, helmets, breast plates, personal shields and soft armor vests.
Spectra is generally based on a normal composite unidirectional fiber substrate. “What’s unique about our material in the unitape form is that unlike most composites, which are resin rich, ours is resin starved,” says Lori Wagner, Honeywell special projects leader. “That allows the fiber to work in its best condition, to be able to react to the high stream rates of the ballistic offense and respond without being constrained by resins. The fiber is actually the component that is stopping the bullet, so we want to pack as much fiber in as possible.” The resin’s role is to supply enough structure so that the fiber can respond.
Resin-starved structures are more delicate to handle during the manufacturing process. “There are a lot of extra steps that are taken because we need to have the fiber in a form that will respond best to the bullet contact,” says Wagner. The final product, however, is a very robust system that can be handled just like any other type of composite.
Honeywell uses a variety of resins, including elastomers, polyurethanes, polyolefins and vinyl esters, with the choice dependent on the application. Helmets need resins that provide stiffness so the helmet will retain its shape. A vest, which should be supple and comfortable, requires a resin that isn’t hard or rigid. Much of Honeywell’s research and development goes into finding the right combination of resin, matrix system and lay up.