How Body Armor Works


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How Body Armor Works

  1. 1. CLASSIFICATION OF BULLET RESISTANT JACKETS & TECHNICAL DETAILS How Body Armor WorksIntroduction to How Body Armor WorksHumans have been wearing armor for thousands of years. Ancient tribesfastened animal hide and plant material around their bodies when they went outon the hunt, and the warriors of ancient Rome and medieval Europe coveredtheir torsos in metal plates before going into battle. By the 1400s, armor in theWestern world had become highly sophisticated.All that changed with the development of cannons and guns in the 1500s. Theseweapons hurl projectiles at a high rate of speed, giving them enough energy topenetrate thin layers of metal. You can increase the thickness of traditional armormaterials, but they soon become too cumbersome and heavy for a person towear. It wasnt until the 1960s that engineers developed a reliable bullet-resistantarmor that a person could wear comfortably. Unlike traditional armor, this softbody armor is not made out of pieces of metal; it is formed from advancedwoven fibers that can be sewn into vests and other soft clothing. A Progressive Technologies bullet-resistant vest, designed for easy concealment under normal clothing.Modern body armor is divided into two main categories: hard body armor and softbody armor.Hard body armor, made out of thick ceramic or metal plates, functions basicallythe same way as the iron suits worn by medieval knights: It is hard enough that abullet or other weapon is deflected. That is, the armor material pushes out on theA White paper by Sardar Sanjay Matkar 2009Email:, CC:
  2. 2. CLASSIFICATION OF BULLET RESISTANT JACKETS & TECHNICAL DETAILSbullet with the same force (or nearly the same force) with which the bullet pushesin, so the armor is not penetrated.Typically, hard body armor offers more protection than soft body armor, but it ismuch more cumbersome. Police officers and military personnel may wear thissort of protection when there is high risk of attack, but for everyday use theygenerally wear soft body armor, flexible protection that you wear like an ordinaryshirt or jacket. Ceramics? Why would body armor be made with ceramic plates? The ceramic used in body armor is called alumina, with the chemical formula Al2O3. Sapphires are made of alumina, and sapphire is a very strong material You can also find rigid plates made out of the plastic polyethylene. It is thicker than ceramic and not quite as strong, but lighter.Soft Body ArmorSoft body armor is a fairly mystifying concept: How can a soft piece of clothingstop bullets? The principle at work is actually quite simple. At its heart, a piece ofbullet-proof material is just a very strong net.To see how this works, think of a soccer goal. The back of the goal consists of anet formed by many long lengths of tether, interlaced with each other andfastened to the goal frame. When you kick the soccer ball into the goal, the ballhas a certain amount of energy, in the form of forward inertia. When the ball hitsthe net, it pushes back on the tether lines at that particular point. Each tetherextends from one side of the frame to the other, dispersing the energy from thepoint of impact over a wide area.The energy is further dispersed because the tethers are interlaced. When theball pushes on a horizontal length of tether, that tether pulls on every interlacedvertical tether. These tethers in turn pull on all the connected horizontal tethers.In this way, the whole net works to absorb the balls inertial energy, no matterwhere the ball hits.A White paper by Sardar Sanjay Matkar 2009Email:, CC:
  3. 3. CLASSIFICATION OF BULLET RESISTANT JACKETS & TECHNICAL DETAILS In a bullet resistant vest, several layers of bullet-resistant webbing (such as KEVLAR) are sandwiched between layers of plastic film. These layers are then woven to the carrier, an outer layer of traditional clothing material.If you were to put a piece of bulletproof material under a powerful microscope,you would see a similar structure. Long strands of fiber are interlaced to form adense net. A bullet is traveling much faster than a soccer ball, of course, so thenet needs to be made from stronger material. The most famous material used inbody armor is DuPonts KEVLAR fiber. KEVLAR is lightweight, like a traditionalclothing fiber, but it is five times stronger than a piece of steel of the sameweight. When interwoven into a dense net, this material can absorb a greatamount of energy.In addition to stopping the bullet from reaching your body, a piece of body armoralso has to protect against blunt trauma caused by the force of the bullet. In thenext section, well see how soft body armor deals with this energy so that thewearer doesnt suffer severe injuries. Beyond Kevlar To Spectra Kevlar is by far the most common fiber used to make body armor, but other materials are being developed. The most readily available alternative fiber is called Spectra, which is approximately twice as strong as Kevlar. Spectra is 5 to 10 times stronger than steel.A White paper by Sardar Sanjay Matkar 2009Email:, CC:
  4. 4. CLASSIFICATION OF BULLET RESISTANT JACKETS & TECHNICAL DETAILS Another rapidly emerging fiber is spider silk. Yes, spider silk. Goats have been genetically engineered to produce the chemical constituents of spider silk, and the resulting material is called Bio-steel. A strand of Bio-steel can be up to 20 times stronger than an equivalent strand of steel. Another candidate is carbon nanotubes, which promise to be even stronger than spider silk. Carbon nanotube thread is still rare, and fabric is even rarer. CNet reports the current price of nanotubes at $500/gram. In time, prices should fall and make carbon nanotubes a viable fiber for body armor.Blunt Trauma and Ranking ResistenceIn the last section, we saw that a piece of soft bulletproof material works in thesame basic way as the net in a soccer goal. Like a soccer goal, it has to "give" acertain amount to absorb the energy of a projectile.When you kick a ball into a soccer goal, the net is pushed back pretty far, slowingthe ball down gradually. This is a very efficient design for a goal because it keepsthe ball from bouncing out into the field. But bulletproof material cant give thismuch because the vest would push too far into the wearers body at the point ofimpact. Focusing the blunt trauma of the impact in a small area can causesevere internal injuries.Bulletproof vests have to spread the blunt trauma out over the whole vest so thatthe force isnt felt too intensely in any one spot. To do this, the bulletproofmaterial must have a very tight weave. Typically, the individual fibers aretwisted, increasing their density and their thickness at each point. To make iteven more rigid, the material is coated with a resin substance and sandwichedbetween two layers of plastic film.A person wearing body armor will still feel the energy of a bullets impact, ofcourse, but over the whole torso rather than in a specific area. If everythingworks correctly, the victim wont be seriously hurt.Since no one layer can move a good distance, the vest has to slow the bulletdown using many different layers. Each "net" slows the bullet a little bit more,until the bullet finally stops. The material also causes the bullet to deform at thepoint of the impact. Essentially, the bullet spreads out at the tip, in the same waya piece of clay spreads out if you throw it against a wall. This process, whichfurther reduces the energy of the bullet, is called "mushrooming."No bulletproof vest is completely impenetrable, and there is no piece of bodyarmor that will make you invulnerable to attack. Theres actually a wide range ofbody armor available today, and the types vary considerably in effectiveness. IA White paper by Sardar Sanjay Matkar 2009Email:, CC:
  5. 5. CLASSIFICATION OF BULLET RESISTANT JACKETS & TECHNICAL DETAILSModern soft body armor consists of several layers of super-strong webbing. Thismaterial disperses the energy of a bullet over a wide area, preventing penetrationand dissipating blunt trauma. This sort of armor, as well as hard armor, rangesconsiderably in effectiveness, depending on the materials used as well as thearmor design.In the United States, body armor levels are certified by the National Institute ofJustice (NIJ), which is an agency of the U.S. Department of Justice. The levelsare I, II-A, II, III-A, III, and IV. Based on extensive laboratory tests, researchersclassify any new body-armor design into one of seven categories: Category Ibody armor offers the lowest level of protection, and category IV offers thehighest. The body-armor classes are often described by what sort of weaponrythey guard against. The lowest-level body armor can only be relied on to protectagainst bullets with a relatively small caliber (diameter), which tend to have lessforce on impact. Some higher-grade body armor can protect against powerfulshotgun fire. Categories I through III-A are soft and concealable. Type III is thefirst one to utilize hard or semi-rigid plates. The front (left) and back (right) of a hard-armor steel plate. The plate has been shot with several different rifle rounds, all of which were deflected. The highest caliber round created a slight dent in the back of the plate, but none of the shots would have caused significant blunt trauma.Generally speaking, armor with more layers of bulletproof material offers greaterprotection. With some bulletproof vests, you can add layers. One common designis to fashion pockets on the inside or outside of the vest. When you need extraprotection, you insert metal or ceramic plates into the pockets. When you dontneed as much protection, you can wear the vest as ordinary soft armor.A White paper by Sardar Sanjay Matkar 2009Email:, CC:
  6. 6. CLASSIFICATION OF BULLET RESISTANT JACKETS & TECHNICAL DETAILSTo determine how effective a particular armor design is, researchers shoot it withall sorts of bullets, at all sorts of angles and distances. For a piece of armor to beconsidered effective against a particular weapon at a particular range, it has tostop the bullet without causing dangerous blunt trauma. The researchersdetermine blunt trauma by molding a layer of clay onto the inside of the armor. Ifthe clay is deformed more than a certain amount at the point of impact, the armoris considered ineffective against that weaponry.Choice of ArmorIt may seem odd that a police officer would wear category I body armor, whichwill only stop relatively small-caliber bullets, when they could have superiorprotection from higher-ranked armor. But there is a very good reason for thisdecision. Typically, higher-ranked armor is a lot bulkier and heavier than lower-ranked armor, which results in several problems:An officer has reduced flexibility and comfort in bulkier armor, which impedespolice work. You cant chase a criminal very well when youre carrying amassive weight on your torso. Heavier armor may actually increase thechances of an officer being severely wounded. An attacker would be moreaware of a heavy armored jacket than a thin concealed vest, and thereforemight aim at an unarmored part of the body, such as the head. The discomfortof heavier armor makes it more likely that an officer wont wear any protectionat all. Police departments are very careful to select bulletproof vests that arerelatively comfortable in order to encourage officers to actually put them on.Armor effectiveness and comfort are sure to improve in the future as technologycompanies develop lighter, stronger materials. We are certainly a long way fromimpenetrable armor; but in 50 years, advanced armor will give police officers amuch greater level of protection when theyre walking the beat. Most likely, wewill also see an increase in civilian body armor in the years ahead. There is anever-growing market for comfortable soft body armor that can fit under clothes, oreven be worn as an outer jacket. With gun violence on the rise, many citizensfeel as if theyre walking onto a battlefield every day, and they want to dressaccordingly! *****A White paper by Sardar Sanjay Matkar 2009Email:, CC: