Piecing together the construction of soft body armor

Transcription

1 By Jeannine Heinecke Piecing together the construction of soft body armor W hen I started in law enforcement in the mid- 1970s, the first vest I got looked and felt like a Manhattan Yellow Pages wrapped in a plastic bag, describes Georg Olsen, a long-time veteran of law enforcement and general manager of U.S. Armor, located in Cerritos, California. Through the evolution of ballistic fibers and construction methods, today s soft body armor is becoming a more sleek, comfortable, flexible, life-protecting second skin for law enforcement officers. With this evolution comes improved wear rates and more lives saved. Officers aren t obstinate or stupid, comments Olsen. They want the protection, but they have to have the flexibility and mobility to do their jobs. Part of finding the right protec- U.S. Armor s Tactical Assault Vest (T.A.V.) and Terminal Velocity series vest.

2 tion is making an educated decision when purchasing soft body armor. Officers need to know the types of fibers used, how a vest should properly fit and the advancements in construction methods leading to more comfortable, wearable vests. Energy s catcher s mitt Soft body armor is designed to absorb energy whether from the impact of a bullet, a vehicle or any other life-threatening source and disperse it over a wide area. Fibers are the filaments across which this impact energy is transmitted, and how those fibers are created and aligned determines their ability to disperse energy. There are two basic types of ballistic fibers used in soft body armor construction: aramid and highperformance polyethylene (HPPE) fibers. Honeywell s Spectra and DSM s Dyneema are HPPE fibers, while Dupont s Kevlar and Teijin Twaron s Twaron are aramid fibers. Whether aramid or HPPE, these fibers have a few common traits. They have high strength or tenacity (tenacity being a strength per weight ratio). They also tend to have a high modulus or stiffness and low elongation, which provides for better energy dissipation. The structure of the fiber also imparts some of the high-strength characteristics, explains Dr. Lori Wagner, manager of technology for Honeywell s Advanced Fibers and Composites Group. It has an orientation and regularity. The order of the molecular chains is aligned along the length of the fiber, which helps with the transmission of energy and gives it the high-strength quality. Once aligned on the molecular level, it is important to maintain this orientation in the spinning process. During the spinning process, being able to orient those chains along the length of the fiber is what imparts the ballistic performance, says Wagner. Weaving interlocks the fibers so the strength orientation is directed both vertically and horizontally. But at these intersections of fiber, energy roadblocks are created, reducing the rate at which energy can be dissipated. Honeywell, located in Colonial Heights, Virginia, has developed a rolled fabric material, called Spectra Shield, that instead of being woven is a laminate. In this process, the fibers are aligned in one direction, spread into a web and adhered with a resin. Then two fiber resin sheets are layered one in a 0-degree direction and the other in a 90-degree direction and fused. This gives you strength in all directions, says Wagner. At the same time, it doesn t disrupt all of the orientation we have worked so hard to put in the fiber. This In a soft armor product, you can affect performance by the stitching, layering of materials and use of different materials. Dr. Lori Wagner, Honeywell construction allows for faster energy dissipation and reduced backface deformation the energy that was not dissipated by the vest and will impact the body. Honeywell discovered this process not only works for HPPE fibers but for aramids as well. The concept of aligning and positioning fibers to their ultimate performance level extends into any highperformance fiber that can be used in ballistics, she says. She also notes the market has expanded significantly from the early 1990s where monolithic single fiber type vests were the norm. In the ballistics arena, many times the two materials (aramid and HPPE) are combined because the performance of each adds to the other synergistically, explains Wagner. The hybrids come out as a benefit because each material adds its own special component to the vest. They create a great catcher s mitt for energy absorption.

3 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 With the fibers now woven or laminated into a rolled fabric product, the manufacturing of a ballistic vest begins with research, development and the building of a sandwich. Manufacturers weigh the benefits of aramid releases body heat and moisture to create a more comfortable vest and the benefits of HPPE higher tenacity and chemical resistance. Based upon these qualities and the goals for the product, it is determined if the vest will be produced from a single fiber or a combination of materials. According to Wagner, manufacturers have found that combining materials allows for lighter weights, a greater range of threat protection, and improved comfort, flexibility and backface deformation performance. In the research and development process, a sandwich is created a precise layering of ballistic materials to meet the desired threat level. As an example, a sandwich may have 21 layers seven Gold Flex, seven Spectra Shield and seven Kevlar. But not only are the ingredients of the sandwich important, it is equally important at what order they go in, explains Olsen. In the research process, testers manipulate the order and number of layers to achieve the desired effect. In the end, the 21 layers may break down into three Spectra Shield, two Gold Flex, seven Kevlar, four Spectra Shield and five Gold Flex. The layers are put in the order that accomplishes those functions of stopping and dissipating in microseconds at impact, says Olsen. But not all sandwiches are created equal. Each threat level requires a different composition and layering. Olson also notes that to reverse the sandwich front to back would create entirely different results, and may cause the vest to fail. Putting the vest to the test As the composition of the sandwich is being developed, 15-inch by 15-inch sample sandwiches are shot. The shooting range is designed such that the bullet trap is at the back preceded by a clay box. The clay in this box is kept at a specific temperature and used to measure backface deformation. Guidelines allow for up to 44mm of backface deformation, although medical professionals say the body can withstand 70mm to 80mm. In front of the clay box, on which the sandwich is mounted, are the chronograph s three start, stop and proof screens that measure the bullet s velocity. The difference between Levels IIA, II and IIIA is in bullet speed, explains Olsen. The faster the bullet, the higher the threat level. At the front of U.S. Armor s range is the mounting tower which holds a Thompson Contender. U.S. Armor uses this single-shot handgun because it has interchangeable barrels and can test for a variety of bullets and calibers. Once the sample achieves the appropriate response less than 44mm of backface deformation and resistance to rounds with an appropriate speed for the threat level in question a vestpatterned sandwich is cut. The panel will perform better than the 15-by-15 sample because there is more area to disperse the energy, but we want to put it in its worstcase situation first, Olsen explains. Because the smaller sample already meets National Institute of Justice (NIJ) requirements, when making the full-size vest, it is inherently overbuilt with a greater margin of safety. If you re build-

4 ing a product that peoples lives are depending on, would you build it just to the very edge of performance? No, says Olsen. By making it more difficult on ourselves when we create the product, we end up with a product that has the overbuild already in it. Once the sandwich achieves NIJ-level testing, manufacturers then perform a V50 test. In this test, the same piece of armor is shot by increasingly faster bullets until a round penetrates the vest. Throwing out the fastest and slowest speeds, the remaining speeds are averaged to determine the V50 rating. The V50 will show if a vest is degrading and at what rate, explains Olsen. You never want it to go below the speed of the NIJ requirement bullet. Knowing the V50 rating on a new vest allows departments to take vests that have been used in the field for two, three or more years and compare the V50 ratings. Olsen describes the V50 as an early warning system to how quickly vests are degrading, which may lead departments to update replacement timelines. Stephen Armellino, president of U.S. Armor, cautions that just because a product brochure lists a specific V50 rating not every vest will test to this exact same number. I can cut one panel of the material as it s configured and sewn, run The Gerber cutting machine operates like a drill slicing through the layers of ballistic fiber and client-coded pattern. The CNC machining allows for replicable precision. a V50 and get 1,600 fps, describes Armellino. I can then cut another panel from the same roll, test it, and get 1,550 fps. There is a deviation in brand new material from the same rolls of fabric. Olsen adds that if 10 vests were cut from the same roll, you would not get any two to have the same results, but your expectation is that they would all be the same, he says. Look at the V50 as an overview guide, not an absolute. Cutting, sewing, trimming With the sandwich layering determined and the measurements in hand (see Weights and measurements on Page 86), it s time to build the vests. Vests of the same polymer composition are grouped together and constructed at the same time. This may include orders from a department outfitting all its officers with the same vest or individual orders that have accumulated over time. Each officer s measurements are inputted into a computer, which then lays out the patterns for each vest component to maximize fabric efficiency. Because of the cost of materials, You don t want to be wasting a lot of material, notes Olsen. The inevitable scraps of ballistic material that do accumulate through the production process are recycled. They are ground into a course powder and converted into clutch plates and brake shoes. A technician then rolls the layers of ballistic fiber onto the cutting table in the order developed during the research process. Once this layering is complete, the pattern sheet is placed on top. The Gerber cutting machine is integrated with the software that writes the pattern, and therefore, doesn t actually read the pattern sheet rolled across

5 the ballistic sandwich. But the pattern sheet is still used because it lists the corresponding name and serial number so the custom-fit vest ends up in the hands of the appropriate person. When custom orders are being produced, only one layer of vests can be cut at a time. If stock sizes are being produced, thin sheets of plastic can be rolled between the ballistic sandwiches so that multiple layers of vests can be cut at the same time. At U.S. Armor, a fan system beneath the Gerber draws air down, holding the material in place so it doesn t slide or move. A dry run of the cutter is performed. The technician watches that the cutter follows the lines on the pattern, although at this point, just a laser guide indicates where the cut will take place the blade is not yet in motion. After a successful dry run, the pieces are cut. The blade actually operates more like a drill, notes Olsen. The CNC machining allows for replicable precision. As the pieces are excised from the fabric, the technician stacks them, making sure to keep the paper pattern with the ballistic sandwich, ballistic cover or outside carrier whichever of the three components is being produced. Weights and measurements How a vest fits and feels is just as important as the protection it provides. As Georg Olsen, general manager of U.S. Armor, points out, The best recommendation for body armor happens on the bench in the police locker room or in the front seat of a patrol car. An officer is more likely to ask a co-worker what vest he selected and why. Comfort is the key guiding factor in armor use. If a vest is not comfortable, it will not be worn. If it is not worn, it will not provide the life-saving protection. When purchasing soft body armor, officers have two options: standard sizing and custom measurement. Some officers will comfortably and accurately fit standard sizes, but most people do not fit the mold and will benefit from a custom, tailored fit. Standard measurement points when purchasing a vest include around the chest, around the waist, front of vest standing, front of vest sitting and length of back. U.S. Armor includes the third dimension measurement, measuring from the top of the belt in the front to the top of the belt in the back. As Olsen points out, The third dimension is the great equalizer. Human bodies are three dimensional, not two. If they were, this would be simple. We d just use a pair of scissors and a cardboard cutout. Although three officers may have the same height and weight, they may have different vest needs. One may have a long torso and short legs while another has a short torso and long legs. If one officer is more rotund, he will have different fit and measurement needs as well. Females particularly need the third dimension, notes Olsen. Aside from cut, weight is often a determining factor in armor purchases. Olsen warns that the weights printed on promotional brochures often can be deceiving. If a department chooses to consider the weight, they should consult the National Institute of Justice test results. With these reports, all vests from all manufacturers are being weighed at the same location and by the same people. Using U.S. Armor s own products as an example, Olsen brings to light the difference in weights between the Enforcer Terminal Velocity and the Enforcer XLT. Although the XLT weighs slightly more than the Terminal Velocity (a difference of 0.29 ounces ballistic weight per square foot at Level IIA protection), to feel the two vests in hand and on the body, an officer would assume the XLT were the lighter vest. Comfort and wearability have much less to do with weight than base materials used and methodology in the construction of those materials, says Olsen. Because of this, Olsen recommends all departments conduct a wear test before purchasing. Departments should select a couple officers including a female officer and the officer known to complain the most or the harshest critic to wear various vests for a couple weeks at a time. Manufacturers should be willing to supply vests for this test period. How the vest fits and wears, how the officer feels about it, and whether he feels comfortable wearing it and inclined to wear it, all come into play when purchasing vests, says Olsen.

6 Following cutting, the pieces are moved to the sewing line. Different pieces of armor are stitched in different ways, notes Olsen. Vests may just have a few lines of sewing to keep the layers of material together, while the ballistics in a breaching blanket are quilted. You can affect ballistic performance by the way you construct the vest, adds Wagner. In a soft armor product, you can affect performance by the stitching, layering of materials and use of different materials. Each vest is marked with its appropriate sewing lines. The ballistic sandwich is then sewn into its cover, and the carrier is also sewn. At the assembly stage, any loose threads are trimmed both inside and outside the carrier and vest. Once again, the serial numbers are checked to be sure that both the vest These hybrid ballistic sandwiches, composed of Spectra Shield, Gold Flex and Kevlar, are tacked in specific areas before being enclosed in their covers. and carrier match. They are checking when they are assembling, cutting, cleaning, packing, all throughout the process, reiterates Olsen. Now ready for boxing, the vests are placed in a plastic bag with an information sheet and a copy of the original order. But the story does not end with the vest in the box. It continues today with further research and development and an ongoing effort to increase wear rates. Innovation is still happening, promises Wagner. There is a constant drive to develop lighter weight, more comfortable solutions to protect officers against all threats. And there is a lot of technology still left out there to be able to achieve that. Long gone are the days of the phone book strapped to an officer s chest. Tomorrow s soft armor vest may truly be a second skin. Proper protection Determining the appropriate threat level of soft body armor to wear on patrol is not so much dictated by National Institute of Justice (NIJ) recommendations but by the daily threats on an officer s beat. The NIJ recommends Level IIA for day-to-day wear, but this may not be sufficient depending on what the criminals in the area are carrying or even what the standard duty handgun is. You want to key what you are wearing to what you are carrying, recommends Georg Olsen, a former law enforcement officer and general manager of U.S. Armor. More than 10 percent of police officers are shot with their own weapons or friendly fire, so you need to stop at least what your agency is carrying. What the criminals on the street are packing varies greatly depending on location. Olsen recommends an easy, quick test that helps determine this threat. Ask yourself, what were the guns I took off the last 10 guys I arrested? he says. Because the criminal s primary source of obtaining weaponry is robbery, he is getting bigger caliber and better weapons. Olsen notes the.380 automatic that once topped the list of criminal weapons, and is resistant to a Level IIA vest, has quickly been replaced by the 9mm. Therefore, as a manufacturer, U.S. Armor recommends officers wear Level IIIA. The protection range granted by the Level IIIA far surpasses the weight difference between the IIA and IIIA. You re talking about a weight difference between the Level IIA and Level IIIA of half a pound per square foot less than 2 pounds over the entire vest, says Olsen. The weight is more psychological than anything else. It s really all about the officer s perception of fit, comfort and flexibility. Reprinted with permission from Law Enforcement Technology magazine June 2007