Piecing Together the Construction of Soft Body Armor
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By Jeannine Heinecke Piecing together the construction of soft body armor hen I started in law today’s soft body armor is becoming “W enforcement in the mid- a more sleek, comfortable, flexible, 1970s, the first vest I got looked life-protecting second skin for law and felt like a Manhattan Yellow enforcement officers. With this evo- Pages wrapped in a plastic bag,” lution comes improved wear rates describes Georg Olsen, a long-time and more lives saved. “Officers aren’t veteran of law enforcement and obstinate or stupid,” comments general manager of U.S. Armor, Olsen. “They want the protection, located in Cerritos, California. but they have to have the flexibility Through the evolution of ballistic and mobility to do their jobs.” fibers and construction methods, Part of finding the right protec- U.S. Armor’s Tactical Assault Vest (T.A.V.) and Terminal Velocity series vest. tion is making an educated deci- Wagner, manager of technology construction allows for faster ener- sion when purchasing soft body for Honeywell’s Advanced Fibers gy dissipation and reduced back- armor. Officers need to know and Composites Group. “It has face deformation — the energy that the types of fibers used, how a an orientation and regularity. The was not dissipated by the vest and vest should properly fit and the order of the molecular chains is will impact the body. advancements in construction aligned along the length of the Honeywell discovered this pro- methods leading to more fiber, which helps with the trans- cess not only works for HPPE comfortable, wearable vests. mission of energy and gives it the fibers but for aramids as well. “The high-strength quality.” concept of aligning and position- Energy’s catcher’s mitt Once aligned on the molecular ing fibers to their ultimate perfor- Soft body armor is designed to level, it is important to maintain this mance level extends into any high- absorb energy — whether from the orientation in the spinning process. impact of a bullet, a vehicle or any “During the spinning process, being other life-threatening source — and able to orient those chains along the “In a soft armor disperse it over a wide area. Fibers length of the fiber is what imparts the product, you can affect are the filaments across which this ballistic performance,” says Wagner. performance by the impact energy is transmitted, and Weaving interlocks the fibers so how those fibers are created and the strength orientation is directed stitching, layering of aligned determines their ability to both vertically and horizontally. materials and use of disperse energy. But at these intersections of fiber, There are two basic types of bal- energy “roadblocks” are created, different materials.” listic fibers used in soft body armor reducing the rate at which energy — Dr. Lori Wagner, Honeywell construction: aramid and high- can be dissipated. performance polyethylene (HPPE) Honeywell, located in Colonial performance fiber that can be used fibers. Honeywell’s Spectra and Heights, Virginia, has developed in ballistics,” she says. DSM’s Dyneema are HPPE fibers, a rolled fabric material, called She also notes the market has while Dupont’s Kevlar and Teijin Spectra Shield, that instead of expanded significantly from the Twaron’s Twaron are aramid fibers. being woven is a laminate. In this early 1990s where monolithic — Whether aramid or HPPE, these process, the fibers are aligned in single fiber type — vests were the fibers have a few common traits. one direction, spread into a web norm. “In the ballistics arena, many They have high strength or tenac- and adhered with a resin. Then two times the two materials (aramid ity (tenacity being a strength per fiber resin sheets are layered — one and HPPE) are combined because weight ratio). They also tend to in a 0-degree direction and the the performance of each adds to have a high modulus or stiffness other in a 90-degree direction — the other synergistically,” explains and low elongation, which provides and fused. “This gives you strength Wagner. “The hybrids come out as for better energy dissipation. in all directions,” says Wagner. “At a benefit because each material adds “The structure of the fiber also the same time, it doesn’t disrupt all its own special component to the imparts some of the high-strength of the orientation we have worked vest. They create a great catcher’s characteristics,” explains Dr. Lori so hard to put in the fiber.” This mitt for energy absorption.” Original vest patterns, at left, are still the basis for the now computerized system. Above, a worker stitches the cover of the ballistic panel. Building the perfect sandwich manipulate the order and number of which the sandwich is mounted, are With the fibers now woven or lami- layers to achieve the desired effect. the chronograph’s three — start, nated into a rolled fabric product, the In the end, the 21 layers may break stop and proof screens — that manufacturing of a ballistic vest begins down into three Spectra Shield, measure the bullet’s velocity. “The with research, development and the two Gold Flex, seven Kevlar, four difference between Levels IIA, building of a sandwich. Manufacturers Spectra Shield and five Gold Flex. II and IIIA is in bullet speed,” weigh the benefits of aramid — releas- “The layers are put in the order that explains Olsen. “The faster the es body heat and moisture to create accomplishes those functions of bullet, the higher the threat level.” a more comfortable vest — and the stopping and dissipating in micro- At the front of U.S. Armor’s benefits of HPPE — higher tenacity seconds at impact,” says Olsen. range is the mounting tower which and chemical resistance. Based upon But not all sandwiches are creat- holds a Thompson Contender. U.S. these qualities and the goals for the ed equal. Each threat level requires Armor uses this single-shot hand- product, it is determined if the vest will a different composition and layer- gun because it has interchangeable be produced from a single fiber or a ing. Olson also notes that to reverse barrels and can test for a variety of combination of materials. the sandwich front to back would bullets and calibers. According to Wagner, manufac- create entirely different results, and Once the sample achieves the turers have found that combining may cause the vest to fail. appropriate response — less than materials allows for lighter weights, 44mm of backface deformation a greater range of threat protection, Putting the vest to the test and resistance to rounds with and improved comfort, flexibility and As the composition of the sand- an appropriate speed for the backface deformation performance. wich is being developed, 15-inch threat level in question — a vest- In the research and development by 15-inch sample sandwiches patterned sandwich is cut. “The process, a sandwich is created — a are shot. The shooting range is panel will perform better than the precise layering of ballistic materi- designed such that the bullet trap 15-by-15 sample because there is als to meet the desired threat level. is at the back preceded by a clay more area to disperse the energy, As an example, a sandwich may box. The clay in this box is kept but we want to put it in its worst- have 21 layers — seven Gold Flex, at a specific temperature and used case situation first,” Olsen explains. seven Spectra Shield and seven to measure backface deformation. Because the smaller sample Kevlar. “But not only are the ingre- Guidelines allow for up to 44mm already meets National Institute dients of the sandwich important, of backface deformation, although of Justice (NIJ) requirements, it is equally important at what medical professionals say the body when making the full-size vest, it is order they go in,” explains Olsen. can withstand 70mm to 80mm. inherently overbuilt with a greater In the research process, testers In front of the clay box, on margin of safety. “If you’re build- The Gerber cutting machine operates ing a product that peoples’ lives like a drill slicing through the layers are depending on, would you build of ballistic fiber and client-coded pattern. The CNC machining allows it just to the very edge of perfor- for replicable precision. mance? No,” says Olsen. “By mak- a V50 and get 1,600 fps,” describes ing it more difficult on ourselves Armellino. “I can then cut another when we create the product, we panel from the same roll, test it, end up with a product that has the and get 1,550 fps. There is a devia- overbuild already in it.” tion in brand new material from Once the sandwich achieves the same rolls of fabric.” NIJ-level testing, manufacturers Olsen adds that if 10 vests were then perform a V50 test. In this cut from the same roll, “you would test, the same piece of armor is not get any two to have the same shot by increasingly faster bullets results, but your expectation is that until a round penetrates the vest. they would all be the same,” he Throwing out the fastest and slow- says. “Look at the V50 as an over- est speeds, the remaining speeds view guide, not an absolute.” are averaged to determine the V50 rating. “The V50 will show if a Cutting, sewing, trimming vest is degrading and at what rate,” With the sandwich layering deter- explains Olsen. “You never want it mined and the measurements in hand to go below the speed of the NIJ (see “Weights and measurements on requirement bullet.” Page 86), it’s time to build the vests. Knowing the V50 rating on a Vests of the same polymer com- new vest allows departments to position are grouped together and take vests that have been used in constructed at the same time.