An Overview on Bulletproof Jacket

An Overview on Bulletproof Jacket
Md. Ferdus Alam
Department of Textile Engineering
Southeast University
Email: ferdus.j@gmail.com
Mobile: 01723300700
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Introduction:
A bulletproof jacket, bulletproof vest, ballistic vest or bullet-resistant vest is an item of personal armor that helps absorb the impact from firearm-fired projectiles and shrapnel from explosions, and is worn on the torso. Soft vests are made from many layers of woven or laminated fibers and can be capable of protecting the wearer from small-caliber handgun and shotgun projectiles, and small fragments from explosives such as hand grenades. This textiles are commonly worn by police forces, private citizens who are at risk of being shot (e.g., national leaders), security guards, and bodyguards, whereas hard-plate reinforced vests are mainly worn by combat soldiers, police tactical units, and hostage rescue teams.It is also called safety textile.
Fig: Bulletproof jacket.
History of Bulletproof Jacket:
Fig: A test in 1901.
Humans throughout recorded history have used various types of materials as body armor to protect themselves from injury in combat and other dangerous situations. The first protective clothing and shields were made from animal skins. As civilization became more advanced, wooden shields and then metal shields came into use. Eventually, metal was also used as body armor, what we now refer to as the suit of armor associated with the knights of the Middle Ages. However, with the invention of firearms around 1500, metal body armor became ineffective. Then only real protection available against firearms was stone walls or natural barriers such as rocks, trees, and ditches. It was not until the late 19th century that the first use of soft body armor in the United States was recorded. At that time, the military explored the possibility of using soft body armor manufactured from silk. The project even attracted congressional attention after the assassination of President William McKinley in 1901. While the garments were shown to be effective against low-velocity bullets, those traveling at 400 feet per second or less, they did not offer protection against the new generation of handgun ammunition being introduced at that time. Ammunition that traveled at velocities of more than 600 feet per second. This, along with the prohibitive cost of silk made the concept unacceptable. The U.S. Patent and Trademark Office lists records dating back to 1919 for various designs of bullet proof vests and body armor type garments. One of the first documented instances where such a garment was demonstrated for use by law enforcement officers was detailed in the April 2, 1931 edition of the Washington, D.C., Evening Star, where a bullet proof vest was demonstrated to members of the Metropolitan Police Department. It was not until the late 1960s that new fibers were discovered that made today's modern generation of cancelable body armor possible. The National Institute of Justice or NIJ initiated a research program to investigate development of a lightweight body armor that on-duty policemen could wear full time. The investigation readily identified new materials that could be woven into a lightweight fabric with excellent ballistic resistant properties. Performance standards were set that defined ballistic resistant requirements for police body armor.

How does it work?
When a handgun bullet strikes body armor, it is caught in a “web” of very strong fibers. These fibers absorb and disperse the impact energy that is transmitted to the bullet proof vest from the bullet, causing the bullet to deform or “mushroom.” Additional energy is absorbed by each successive layer of material in bullet proof vests, until such time as the bullet has been stopped.
Fig: Additional energy is absorbed by each successive layer of material in the ballistic panel.
Because the fibers work together both in the individual layer and with other layers of material in the vest, a large area of the bullet proof vest becomes involved in preventing the bullet from penetrating. This also helps in dissipating the forces which can cause non penetrating injuries to internal organs. Unfortunately, at this time no material exists that would allow body armor to be constructed from a single ply of material.

Raw Materials:
A bulletproof vest consists of a panel, a vest-shaped sheet of advanced plastics polymers that are composed of many layers of either Kevlar, Spectra Shield, or, in other countries, Twaron (similar to Kevlar) or Bynema (similar to Spectra). The layers of woven Kevlar are sewn together using Kevlar thread, while the nonwoven Spectra Shield is coated and bonded with resins such as Kraton and then sealed between two sheets of polyethylene film. The panel provides protection but not much comfort. It is placed inside of a fabric shell that is usually made from a polyester/cotton blend or nylon. The side of the shell facing the body is usually made more comfortable by sewing a sheet of some absorbent material such as Kumax onto it. A bulletproof vest may also have nylon padding for extra protection. For bulletproof vests intended to be worn in especially dangerous situations, built-in pouches are provided to hold plates made from either metal or ceramic bonded to fiberglass. Such vests can also provide protection in car accidents or from stabbing. Various devices are used to strap the vests on. Sometimes the sides are connected with elastic webbing. Usually, though, they are secured with straps of either cloth or elastic, with metallic buckles or Velcro closures.

The Manufacturing Process:
Manufacturing process of Bulletproof Jacket
Manufacturing process of Bulletproof Jacket
Some bulletproof vests are custom-made to meet the customer's protection needs or size. Most, however, meet standard protection regulations, have standard clothing industry sizes and are sold in quantity.

Making the panel cloth
To make Kevlar, the polymer poly-para-phenylene terephthalamide must first be produced in the laboratory. This is done through a process known as polymerization, which involves combining molecules into long chains. The resultant crystalline liquid with polymers in the shape of rods is then extruded through a spinneret (a small metal plate full of tiny holes that looks like a shower head) to form Kevlar yarn. The Kevlar fiber then passes through a cooling bath to help it harden. After being sprayed with water, the synthetic fiber is wound onto rolls. The Kevlar manufacturer then typically sends the fiber to throwsters, who twist the yarn to make it suitable for weaving. To make Kevlar cloth, the yarns are woven in the simplest pattern, plain or tabby weave, which is merely the over and under pattern of threads that interlace alternatively.

Unlike Kevlar, the Spectra used in bulletproof vests are usually not woven. Instead, the strong polyethylene polymer filaments are spun into fibers that are then laid parallel to each other. Resin is used to coat the fibers, sealing them together to form a sheet of Spectra cloth. Two sheets of this cloth are then placed at right angles to one another and again bonded, forming a nonwoven fabric that is next sandwiched between two sheets of polyethylene film. The vest shape can then be cut from the material.

Cutting the panels:
Fig: Cutting the panels.
Kevlar cloth is sent in large rolls to the bulletproof vest manufacturer. The fabric is first unrolled onto a cutting table that must be long enough to allow several panels to be cut out at a time; sometimes it can be as Kevlar has long been the most widely used material in bulletproof vests. To make Kevlar, the polymer solution is first produced. The resulting liquid is then extruded from a spinneret, cooled with water, stretched on rollers, and wound into cloth. A recent competitor to Kevlar is Spectra Shield. Unlike Kevlar, Spectra Shield is not woven but rather spun into fibers that are then laid parallel to each other. The fibers are coated with resin and layered to form the cloth long as 32.79 yards (30 meters). As many layers of the material as needed (as few as eight layers, or as many as 25, depending on the level of protection desired) are laid out on the cutting table. A cut sheet, similar to pattern pieces used for home sewing, is then placed on the layers of cloth. For maximum use of the material, some manufacturers use computer graphics systems to determine the optimal placement of the cut sheets. Using a hand-held machine that performs like a jigsaw except that instead of a cutting wire it has a 5.91-inch (15-centimeter) cutting wheel similar to that on the end of a pizza cutter, a worker cuts around the cut sheets to form panels, which are then placed in precise stacks.

Sewing the panels:
While Spectra Shield generally does not require sewing, as its panels are usually just cut and stacked in layers that go into tight fitting pouches in the vest, a bulletproof vest made from Kevlar can be either quilt-stitched or box-stitched. Quilt-stitching forms small diamond of cloth separated by stitching, whereas box stitching forms a large single box in the middle of the vest. Quilt-stitching is more labor intensive and difficult, and it provides a stiff panel that is hard to shift away from vulnerable areas. Box-stitching, on the other hand, is fast and easy and allows the free movement of the vest. To sew the layers together, workers place a stencil on top of the layers and rub chalk on the exposed areas of the panel, after the cloth is made, it must be cut into the proper pattern pieces. These pieces are then sewn together with accessories to form the finished vest making a dotted line on the cloth. A sewer then stitches the layers together, following the pattern made by the chalk. Next, a size label is sewn onto the panel.

Finishing the Vest
The shells for the panels are sewn together in the same factory using standard industrial sewing machines and standard sewing practices. The panels are then slipped inside the shells, and the accessories—such as the straps—are sewn on. The finished bulletproof vest is boxed and shipped to the customer.

Quality Control:
Fig: It is checked for defects by National Institute for Justice (N.I.J.)
Bulletproof vests undergo many of the same tests a regular piece of clothing does. The fiber manufacturer tests the fiber and yarn tensile strength, and the fabric weavers test the tensile strength of the resultant cloth. Nonwoven Spectra is also tested for tensile strength by the manufacturer. Vest manufacturers test the panel material for strength, and production quality control requires that trained observers inspect the vests after the panels are sewn and the vests completed. Bulletproof vests, unlike regular clothing, must undergo stringent protection testing as required by the National Institute of Justice (NIJ). Not all bulletproof vests are alike. Some protect against lead bullets at low velocity, and some protect against full metal jacketed bullets at high velocity. Vests are classified numerically from lowest to highest protection: I, II-A, II, and III-A, III, IV, and special case (those for which the customer specifies the protection needed). Each classification specifies which type of bullet at what velocity will not penetrate the vest. While it seems logical to choose the highest-rated vests (such as III or IV), such vests are heavy, and the needs of a person wearing one might deem a lighter vest more appropriate. For police use, a general rule suggested by experts is to purchase a vest that protects against the type of firearm the officer normally carries. The size label on a vest is very important. Not only does it include size, model, style, manufacturer's logo, and care instructions as regular clothing does, it must also include the protection rating, lot number, date of issue, an indication of which side should face out, a serial number, a note indicating it meets NIJ approval standards, and—for type I through type III-A vests—a large warning that the vest will not protect the wearer from sharp instruments or rifle fire. Bulletproof vests are tested both wet and dry. This is done because the fibers used to make a vest perform differently when wet. Testing (wet or dry) a vest entails wrapping it around a modeling clay dummy. A firearm of the correct type with a bullet of the correct type is then shot at a velocity suitable for the classification of the vest. Each shot should be three inches (7.6 centimeters) away from the edge of the vest and almost two inches from (five centimeters) away from previous shots. Six shots are fired, two at a 30-degree angle of incidence, and four at a 0-degree angle of incidence. One shot should fall on a seam. This method of shooting forms a wide triangle of bullet holes. The vest is then turned upside down and shot the same way, this time making a narrow triangle of bullet holes. To pass the test, the vest should show no sign of penetration. That is, the clay dummy should have no holes or pieces of vest or bullet in it. Though the bullet will leave a dent, it should be no deeper than 1.7 inches (4.4 centimeters). When a vest passes inspections, the model number is certified and the manufacturer can then make exact duplicates of the vest. After the vest has been tested, it is placed in an archive so that in the future vests with the same model number can be easily checked against the prototype. Rigged field testing is not feasible for bullet-proof vests, but in a sense, wearers (such as police officers) test them every day. Studies of wounded police officers have shown that bulletproof vests save hundreds of lives each year.

Future Developments:
Fig: Future development (High comfort, protection and low garment weight).
  • The Defence Department of Canada posted a contract tender Monday asking companies for proposals for high- tech body suits that could help Canadian soldiers carry bigger loads into battle. 
  • The Pentagon agency eventually awarded a contract to Sarcos, a Salt Lake City, Utah, and company now owned by Raytheon that produced a test version this year. Known as the XOS Exoskeleton, it uses a single engine and hydraulics to assist movement. Included in the Pentagon's Future Warrior Concept are a powerful exoskeleton, a self-camouflaging outer layer that adapts to changing environments and a helmet which translates a soldier's voice into any foreign language. The future soldier will also benefit from 'intelligent' armour, which remains light and flexible until it senses an approaching bullet, then tenses to become bullet proof. 
  • Bullet-proof brassieres designed to be comfortable and injury-proof have been issued to 3,000 policewomen in Germany for their protection. The brassieres are made of cotton or polyester and are padded. Unlike bullet-proof vests, they have no metal or plastic under-wire or fasteners that can pierce skin and injure the wearer when a bullet hit the body armor.
Bullet-proof brassiere
  • Super carbon nanotube vest which bounces back the incoming projectiles have been developed in the University of Sydney.
Fig: Carbon nanotube
  • Dragon Skin is a type of ballistic vest made by Pinnacle Armor. It is currently produced in Fresno, California. It’s characteristic two-inch-wide circular discs overlap like scale armor, creating a flexible vest that allows a good range of motion and can allegedly absorb a high number of hits compared with other military body armor. The discs are composed of silicon carbide ceramic matrices and laminates, much like the larger ceramic plates in other types of bullet resistant vests.
Fig: Dragon skin
  • The armor is available in three basic protection levels: SOV-2000, which has previously had certification to Level III protection; SOV-3000, which is rated as Level IV by the manufacturer, but has not officially certified as such; and a rating-unspecified "Level V" variant not available to the general public. 
  • SOV-2000 armor is made of an imbricated overlapping configuration of high tensile steel discs encased in an aramid textile cover. Different layout configurations with variations in coverage are available. 
 

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