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Bulletproof vest
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A ballistic vest is an item of protective clothing that absorbs the impact from firearm-fired projectiles and shrapnel fragments from explosions. This protection is for the torso. Soft vests are made from many layers of woven or laminated fibers and protect wearers from projectiles fired from handguns, shotguns, and small fragments from explosives such as hand grenades. When metal or ceramic plates are used with a soft vest, it can also protect wearers from shots fired from rifles.
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A ballistic vest is an item of protective clothing that absorbs the impact from firearm-fired projectiles and shrapnel fragments from explosions. This protection is for the torso. Soft vests are made from many layers of woven or laminated fibers and protect wearers from projectiles fired from handguns, shotguns, and small fragments from explosives such as hand grenades. When metal or ceramic plates are used with a soft vest, it can also protect wearers from shots fired from rifles. In combination with metallic components or tightly-woven fiber layers, soft armor can offer some protection to the wearer from stab and slash from a knife. Soft vests are commonly worn by police forces, private citizens and private security guards, and hard-plate reinforced vests are mainly worn by combat soldiers in the armies of various nations as well as police armed-response units.
Modern body armor may combine a ballistic vest with other items of protective clothing, such as a helmet. Vests intended for police and military use may also include ballistic shoulder, and side protection armor components.
Overview
Ballistic vests use layers of very strong fiber to catch and deform a bullet and spread its force over a larger portion of the vest fiber. A deformable handgun bullet mushrooms into a dished plate on impact with a well designed textile vest. The vest absorbs the energy from the deforming bullet, bringing it to a stop before it can penetrate the overall matrix. Some layers may be penetrated but as the bullet deforms, the energy is absorbed by a larger and larger fiber area.
While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's energy. Even without penetration, modern pistol bullets contain enough energy to cause blunt force trauma under the impact point. Vests' specifications include both penetration resistance requirements and limits on the amount of impact energy that is delivered to the body. Vests designed for bullets offer little protection against blows from sharp implements, such as knives, arrows or ice picks, or from bullets manufactured of non-deformable materials i.e. steel core instead of lead. The force of the impact of these objects is concentrated in a relatively small area, allowing them to puncture the fiber layers of most bullet-resistant fabrics. Textile vests may be augmented with metal (steel or titanium), ceramic or polyethylene plates that provide extra protection to vital areas. These hard armor plates have proven effective against all handgun bullets and a range of rifles. These upgraded ballistic vests have become standard in military use, as soft body armor vests are ineffective against military rifle rounds. Corrections officers and other law enforcement officers often wear vests which are designed specifically against bladed weapons and sharp objects. These vests may incorporate coated and laminated para-aramid textiles or metallic components.
History
The Late Middle Ages
In 1538, Francesco Maria della Rovere commissioned Filippo Negroli to create a bullet proof vest. In 1561, Maximilian II, Holy Roman Emperor is recorded as testing his armor against gun-fire. Similarly, in 1590 Sir Henry Lee expected his Greenwich armor to be "pistol proof". Its actual effectiveness was controversial at the time. The etymology of "bullet" and the adjective form of "proof" in the late 1500s would suggest that the term "bulletproof" originated shortly thereafter to identify a dent on the armor which proved it would resist bullet penetration.
1800s-1930s
The first soft ballistic vest, Myunjebaegab, was invented in Joseon Korea in the 1860s shortly after the French campaign against Korea. Heungseon Daewongun ordered development of bullet-proof armor because of increasing threats from Western armies. Kim Gi-Doo and Gang Yoon found that cotton could protect against bullets if thick enough, and devised bullet-proof vests made of 30 layers of cotton. The vests were used in battle during the United States expedition to Korea, when the US Navy attacked Ganghwa Island in 1871. The US Army captured one of the vests and took it to the US, where it was stored at the Smithsonian Museum until 2007. The vest has since been sent back to Korea and is currently on display to the public.
One of the early instances of ballistic armor being used was in 1879 when a gang of Australian outlaws led by Ned Kelly made armor from scrap metal. The armor covered their torsos, upper arms, and upper legs, and was worn with a helmet. The home-made suits had a mass of 44 kg (96 lbs), making the gang clumsy and unwieldy during a police raid at Glenrowan in 1880. Its use proved futile as the suit lacked protection for the legs.
During the early 1880s, Dr. George Emery Goodfellow of Arizona began investigating silk vests resembling medieval gambesons, which used 18 to 30 layers of cloth to protect the wearers from arrow penetration. Dr. Goodfellow's interest in silk bulletproof vests arose after he learned about several cases where silk fabric slowed the impact of bullets in the bodies of people who were shot.
Casimir Zeglen of Chicago used Goodfellow's findings to develop a bulletproof vest made of silk fabric at the end of the 1800s, which could stop the relatively slow rounds from black powder handguns. The vests cost $800 USD each in 1914, a small fortune at the time. On 28 June 28 1914, Franz Ferdinand, Archduke of Austria, heir to the Austro-Hungarian throne, was wearing a silk bulletproof vest when he was attacked by a gun-wielding assassin. Because he was shot in the neck above the vest, the vest did not protect him. A similar vest, made by Jan Szczepanik in 1901, saved the life of Alfonso XIII of Spain when he was shot by an attacker.
During World War I, the United States developed several types of body armor, including the chrome nickel steel Brewster Body Shield, which consisted of a breastplate and a headpiece and could withstand Lewis Gun bullets at 2,700 ft/s (820 m/s), but was clumsy and heavy at 40 pounds (18 kg). A scaled waistcoat of overlapping steel scales fixed to a leather lining was also designed; this armor weighed 11 pounds (5 kg), fit close to the body, and was considered more comfortable.
During the late 1920s through the early 1930s, gunmen from criminal gangs in the United States began wearing less-expensive vests made from thick layers of cotton padding and cloth. These early vests could absorb the impact of handgun rounds such as .22 Long Rifle, .25 ACP, .32 S&W Long, .32 S&W, .380 ACP, and .45 ACP traveling at speeds of up 300 m/s (1000 ft/s). To overcome these vests, law enforcement agents such as the FBI began using the newer and more powerful .38 Super, and later the .357 Magnum cartridge.
World War II
In the early stages of World War II, the United States designed body armor for infantrymen, but most models were too heavy and mobility-restricting to be useful in the field and incompatible with existing required equipment. The military diverted its research efforts to developing flak jackets for aircraft crews. These jackets were made of nylon fabric and capable of stopping flak and shrapnel, but were not designed to stop bullets.
The British Army issued Medical Research Council body armor, as did the Canadian Army, in northwestern Europe, in the latter case primarily to medical personnel of the 2nd Canadian Infantry Division. The Japanese army produced a few types of infantry body armor during World War II, but these did not see much use. Near the middle of 1944, development of infantry body armor in the United States restarted. Several vests were produced for the US military, including but not limited to the T34, the T39, the T62E1, and the M12.
The Red Army used several types of body armor, including the SN-42 ( "Stalynoi Nagrudnik" is Russian for "steel breastplate", and the number denotes the design year). All were tested, but only the SN-42 was put in production. It consisted of two pressed steel plates that protected the front torso and groin. The plates were 2 mm thick and weighed 3.5 kg (7.7 Lbs.). This armor was supplied to SHISBr (assault engineers) and to Tankodesantniki (infantry that rode on tanks) of some tank brigades. The SN armor protected wearers from 9 mm bullets fired by a MP-40 at around 50 meters, which made it useful in urban battles such as the Battle of Stalingrad. However, the SN's weight made it impractical for infantry on foot in an open outdoor setting.
The United States developed a vest using Doron Plate, a fiberglass-based laminate. These vests were first used in the Battle of Okinawa in 1945.
1950s-1970s
During the Korean War several new vests were produced for the United States military, including the M-1951, which made use of fibre-reinforced plastic or aluminium segments woven into a nylon vest. These vests represented "a vast improvement on weight, but the armor failed to stop bullets and fragments very successfully," although officially they were claimed to be able to stop 7.62x25mm Tokarev pistol rounds at the muzzle. Developed by Natick Laboratories and introduced in 1967, T65-2 plate carriers were the first vests designed to hold hard ceramic plates, making them capable of stopping 7 mm rifle rounds. These "Chicken Plates" were made of either boron carbide, silicon carbide, or aluminium oxide. They were issued to the crew of low-flying aircraft, such as the UH-1 and UC-123, during the Vietnam War.
In 1969, American Body Armor was founded and began to produce a patented combination of quilted nylon faced with multiple steel plates. This armor configuration was marketed to American law enforcement agencies by Smith & Wesson under the trade name "Barrier Vest." The Barrier Vest was the first police vest to gain wide use during high threat police operations.
In the mid-1970s, DuPont introduced Kevlar synthetic fiber, which was woven into a fabric and layered. Immediately Kevlar was incorporated into a National Institute of Justice (NIJ) evaluation program to provide lightweight, concealable body armor to a test pool of American law enforcement officers to ascertain if everyday concealable wearing was possible. Lester Shubin, a program manager at the NIJ, managed this law enforcement feasibility study within a few selected large police agencies, and quickly determined that Kevlar body armor could be comfortably worn by police daily, and would save lives.
In 1975 Richard A. Armellino, the founder of American Body Armor, marketed an all Kevlar vest called the K-15, consisting of 15 layers of Kevlar that also included a 5" X 8" ballistic steel "Shok Plate" positioned vertically over the heart and was issued US Patent #3,971,072 for this innovation. Similarly sized and positioned "trauma plates" are still used today on the front ballistic panels of most concealable vests, reducing blunt trauma and increasing ballistic protection in the center-mass heart/sternum area.
In 1976, Richard Davis, founder of Second Chance Body Armor, designed the company's first all-Kevlar vest, the Model Y. The lightweight, concealable vest industry was launched and a new form of daily protection for the modern police officer was quickly adapted. By the mid to late 1980s, an estimated 1/3 to 1/2 of police patrol officers wore concealable vests daily. By 2006, more than 2,000 documented police vest "saves" were recorded, validating the success and efficiency of lightweight concealable body armor as a standard piece of everyday police equipment.
1990s-2000s
Kevlar soft armor had its shortcomings because if "large fragments or high velocity bullets hit the vest, the energy could cause life-threatening, blunt trauma injuries" in selected, vital areas. Ranger Body Armor was developed for the American military in 1991. Although it was the second modern US body armor that was able to stop rifle caliber rounds and still be light enough to be worn by infantry soldiers in the field, it still had its flaws: "it was still heavier than the concurrently issued PASGT (Personal Armor System for Ground Troops) anti-fragmentation armor worn by regular infantry and ... did not have the same degree of ballistic protection around the neck and shoulders." The format of Ranger Body Armor (and more recent body armor issued to US special operations units) highlights the trade-offs between force protection and mobility that modern body armor forces organizations to address.
Newer armor issued by the United States military to large numbers of troops includes Interceptor Body Armor, the United States Army's Improved Outer Tactical Vest and the more advanced United States Marine Corps Modular Tactical Vest. All of these systems are designed with the vest intended to provide protection from fragments and pistol rounds. Hard ceramic plates such as the Small Arms Protective Insert as used with Interceptor Body Armor, are worn to protect the vital organs from higher level threats. These threats mostly take the form of high velocity and armor piercing rifle rounds. Similar types of protective equipment have been adopted by modern armed forces the world over.
Since the 1970s, several new fibers and construction methods for bulletproof fabric have been developed besides woven Kevlar, such as DSM's Dyneema, Honeywell's Gold Flex and Spectra, Teijin Twaron's Twaron, Pinnacle Armor's Dragon Skin, and Toyobo's Zylon (now controversial, as new studies report that it degrades rapidly, leaving wearers with significantly less protection than expected). These newer materials are advertised as being lighter, thinner and more resistant than Kevlar, although they are much more expensive. The US military has developed body armor for the working dogs who aid GIs in battle.
According to dog handler Petty Officer Michael Thomas, the "new vests are an upgrade" from the previous vests, which only offered stab protection. The new vests also offer protection from bullets.
Performance standards
Due to the various different types of projectile, it is often inaccurate to refer to a particular product as "bulletproof" because this implies that it will protect against any and all threats. Instead, the term bullet resistant is generally preferred.
Body armor standards are regional. Around the world ammunition varies and as a result the armor testing must reflect the threats found locally. Law enforcement statistics show that many shootings where officers are injured or killed involve the officer's weapon. As a result each law enforcement agency or para-military organizations will have their own standard for armor performance if only to ensure that their armor protects them from their own weapon. While many standards exist a few standards are widely used as models. The US National Institute of Justice ballistic and stab documents are examples of broadly accepted standards, In addition to the NIJ, the UK Home Office Scientific Development Branch (HOSDB - formerly the Police Scientific Development Branch (PSDB)) standards are used by a number of other countries and organizations. These "model" standards are usually adapted by other counties by incorporation of the basic test methodologies with modification of the bullets that are required for test.
NIJ Standard-0101.06 has specific performance standards for bullet resistant vests used by law enforcement. This rates vests on the following scale against penetration and also blunt trauma protection (deformation):
| Armor Level | Protection |
|---|
Type I
(.22 LR; .380 ACP) | This armor would protect against 2.6 g (40 gr) .22 Long Rifle Lead Round Nose (LR LRN) bullets at a velocity of 329 m/s (1080 ft/s ± 30 ft/s) and 6.2 g (95 gr) .380 ACP Full Metal Jacketed Round Nose (FMJ RN) bullets at a velocity of 322 m/s (1055 ft/s ± 30 ft/s). It is no longer part of the standard. | Type IIA
(9 mm; .40 S&W) | New armor protects against 8 g (124 gr) 9x19mm Parabellum Full Metal Jacketed Round Nose (FMJ RN) bullets at a velocity of 373 m/s ± 9.1 m/s (1225 ft/s ± 30 ft/s) and 11.7 g (180 gr) .40 S&W Full Metal Jacketed (FMJ) bullets at a velocity of 352 m/s ± 9.1 m/s (1155 ft/s ± 30 ft/s). Conditioned armor protects against 8 g (124 gr) 9 mm FMJ RN bullets at a velocity of 355 m/s ± 9.1 m/s (1165 ft/s ± 30 ft/s) and 11.7 g (180 gr) .40 S&W FMJ bullets at a velocity of 325 m/s ± 9.1 m/s (1065 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Type I]. | Type II
(9 mm; .357 Magnum) | New armor protects against 8 g (124 gr) 9 mm FMJ RN bullets at a velocity of 398 m/s ± 9.1 m/s (1305 ft/s ± 30 ft/s) and 10.2 g (158 gr) .357 Magnum Jacketed Soft Point bullets at a velocity of 436 m/s ± 9.1 m/s (1430 ft/s ± 30 ft/s). Conditioned armor protects against 8 g (124 gr) 9 mm FMJ RN bullets at a velocity of 379 m/s ±9.1 m/s (1245 ft/s ± 30 ft/s) and 10.2 g (158 gr) .357 Magnum Jacketed Soft Point bullets at a velocity of 408 m/s ±9.1 m/s (1340 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Types I and IIA]. | Type IIIA
(.357 Sig; .44 Magnum) | New armor protects against 8.1 g (125 gr) .357 SIG FMJ Flat Nose (FN) bullets at a velocity of 448 m/s ± 9.1 m/s (1470 ft/s ± 30 ft/s) and 15.6 g (240 gr) .44 Magnum Semi Jacketed Hollow Point (SJHP) bullets at a velocity of 436 m/s (1430 ft/s ± 30 ft/s). Conditioned armor protects against 8.1 g (125 gr) .357 SIG FMJ Flat Nose (FN) bullets at a velocity of 430 m/s ± 9.1 m/s (1410 ft/s ± 30 ft/s) and 15.6 g (240 gr) .44 Magnum Semi Jacketed Hollow Point (SJHP) bullets at a velocity of 408 m/s ± 9.1 m/s (1340 ft/s ± 30 ft/s). It also provides protection against most handgun threats, as well as the threats mentioned in [Types I, IIA, and II]. | Type III
(Rifles) | Conditioned armor protects against 9.6 g (148 gr) 7.62x51mm NATO M80 ball bullets at a velocity of 847 m/s ± 9.1 m/s (2780 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Types I, IIA, II, and IIIA]. | Type IV
(Armor Piercing Rifle) | Conditioned armor protects against 10.8 g (166 gr) .30-06 Springfield M2 armor piercing (AP) bullets at a velocity of 878 m/s ± 9.1 m/s (2880 ft/s ± 30 ft/s). It also provides at least single hit protection against the threats mentioned in [Types I, IIA, II, IIIA, and III]. |
In addition to the NIJ and HOSDB standards, other important standards include: German Police TR-Technische Richtlinie, Draft ISO prEN ISO 14876, Underwriters Laboratories (UL Standard 752)
Textile armor is tested for both penetration resistance by bullets and for the impact energy transmitted to the wearer. The "backface signature" or transmitted impact energy is measured by shooting armor mounted in front of a backing material, typically oil-based modelling clay. The clay is used at a controlled temperature and verified for impact flow before testing. After the armor is impacted with the test bullet the vest is removed from the clay and the depth of the indentation in the clay is measured.
The backface signature allowed by different test standards can be difficult to compare. Both the clay materials and the bullets used for the test are not common. In general the British, German and other European standards allow 20-25 mm of backface signature, while the US-NIJ standards allow for 44 mm, which can potentially cause internal injury. The allowable backface signature for body armor has been controversial from its introduction in the first NIJ test standard and the debate as to the relative importance of penetration-resistance vs. backface signature continues in the medical and testing communities.
In general a vest's textile material temporarily degrades when wet. Neutral water at room temp does not affect para-aramid or UHMWPE but acidic, basic and some other solutions can permanently reduce para-aramid fiber tensile strength. (As a result of this, the major test standards call for wet testing of textile armor ). Mechanisms for this wet loss of performance are not known. Vests that will be tested after ISO type water immersion tend to have heat sealed enclosures and those that are tested under NIJ type water spray methods tend to have water resistant enclosures.
From 2003-5, a large study of the environmental degradation of Zylon armor was undertaken by the US-NIJ. This concluded that water, long-term use, and temperature exposure significantly affect tensile strength and the ballistic performance of PBO or Zylon fiber. This NIJ study on vests returned from the field demonstrated that environmental affects on Zylon resulted in ballistic failures under standard test conditions.
Ballistic testing V50 and V0
Measuring the ballistic performance of armor is based on determining the kinetic energy of a bullet at impact. (KE= ½ mv2) Because the energy of a bullet is a key factor in its penetrating capacity, velocity is used as the primary independent variable in ballistic testing. For most users the key measurement is the velocity at which no bullets will penetrate the armor. Measuring this zero penetration velocity (V0) must take into account variability in armor performance and test variability. Ballistic testing has a number of sources of variability: the armor, test backing materials, bullet, casing, powder, primer and the gun barrel, to name a few. Variability reduces the predictive power of a determination of V0. If for example, the V0 of an armor design is measured to be with a 9 mm FMJ bullet based on 30 shots, the test is only an estimate of the real V0 of this armor. The problem is variability. If the V0 is tested again with a second group of 30 shots on the same vest design, the result will not be identical. Only a single low velocity penetrating shot is required to reduce the V0 value. The more shots made the lower the V0 will go. In terms of statistics, the zero penetration velocity is the tail end of the distribution curve. If you know the variability and can calculate the standard deviation, one can rigorously set the V0 at a confidence interval. Test Standards now define how many shots must be used to estimate a V0 for the armor certification. This procedure defines a confidence interval of an estimate of V0. (See "NIJ and HOSDB test methods".)
V0 is difficult to measure, so a second concept has been developed in ballistic testing called V50. This is the velocity at which 50 percent of the shots go through and 50 are stopped by the armor. US military standards define a commonly used procedure for this test. The goal is to get 3 shots that penetrate that are slower than a second group of 3 shots that are stopped by the armor. These 3 high stops and 3 low penetrations can then be used to calculate a V50 velocity. In practice this measurement of V50 requires 1-2 vest panels and 10-20 shots. A very useful concept in armor testing is the offset velocity between the V0 and V50. If this offset has been measured for an armor design, then V50 data can be used to measure and estimate changes in V0.
For vest manufacturing, field evaluation and life testing both V0 and V50 are used. However, as a result of the simplicity of making V50 measurements, this method is more important for control of armor after certification.
Military testing: fragment ballistics
After the Vietnam War, military planners developed a concept of “Casualty Reduction”. The large body of casualty data made clear that in a combat situation, fragments, not bullets, were the most important threat to soldiers. After WWII vests were being developed and fragment testing was in its early stages . Artillery shells, mortar shells, aerial bombs, grenades, antipersonnel mines are all fragmentation devices. They all contain a steel casing that is designed to burst into small steel fragments or shrapnel, when their explosive core detonates. After considerable effort measuring fragment size distribution from various NATO and Soviet bloc munitions, a fragment test was developed. Fragment simulators were designed and the most common shape is a Right Round Cylinder or RCC simulator. This shape has a length equal to its diameter. These RCC Fragment Simulation Projectiles (FSPs) are tested as a group. The test series most often includes 2 grain (0.13g), 4 grain (0.263g), 16 grain (1.0g), and 64 grain (4.2g) mass RCC FSP testing. The 2-4-16-64 series is based on the measured fragment size distributions.
The second part of “Casualty Reduction” strategy is a study of velocity distributions of fragments from munitions . Warhead explosives have blast speeds of 20,000 to . As a result they are capable of ejecting fragments at very high speeds of order 1000m/s(3330 ft/s), implying very high energy (where the energy of a fragment is ½ mass x velocity2, neglecting rotational energy). The military engineering data showed that like the fragment size the fragment velocities had characteristic distributions. It is possible to segment the fragment output from a warhead into velocity groups. For example 95% of all fragments from a bomb blast under have a velocity of or less. This established a set of goals for military ballistic vest design.
The random nature of fragmentation required the military vest specification to tradeoff mass vs. ballistic-benefit. Hard vehicle armor is capable of stopping all fragments, but military personnel can only carry a limited amount of gear and equipment, so the weight of the vest is a limiting factor in vest fragment protection. The 2-4-16-64 grain series at limited velocity can be stopped by an all-textile vest of approximately 5.4 kg/m2 (1.1lb/ft2). In contrast to the design of vest for deformable lead bullets, fragments do not change shape; they are steel and can not be deformed by textile materials. The FSP (the smallest fragment projectile commonly used in testing) is about the size of a grain of rice; such small fast moving fragments can potentially slip through the vest, moving between yarns. As a result fabrics optimized for fragment protection are tightly woven, although these fabrics are not as effective stopping lead bullets.
Backing materials for ballistic testing
One of the critical requirements in soft ballistic testing is measurement of "back side signature" (i.e. energy delivered to tissue by a non-penetrating projectile) in a deformable backing material placed behind the targeted vest. The majority of military and law enforcement standards have settled on an oil/clay mixture for the backing material, known as Roma Plastilena . Although harder and less deformable than human tissue, Roma represents a “worst case” backing material when plastic deformations in the oil/clay are low (less than 20 mm). (Armor placed over a harder surface is more easily penetrated.) The oil/clay mixture of "Roma" is roughly twice the density of human tissue and therefore does not match its specific gravity, however "Roma" is a plastic material that will not recover its shape elastically, which is important for accurately measuring potential trauma through back side signature.
The selection of test backing is significant because in flexible armor, the body tissue of a wearer plays an integral part in absorbing the high energy impact of ballistic and stab events. However the human torso has a very complex mechanical behavior. Away from the rib cage and spine, the soft tissue behavior is soft and compliant. In the tissue over the sternum bone region, the compliance of the torso is significantly lower. This complexity requires very elaborate bio-morphic backing material systems for accurate ballistic and stab armor testing. A number of materials have been used to simulate human tissue in addition to Roma. In all cases, these materials are placed behind the armor during test impacts and are designed to simulate various aspects of human tissue impact behavior.
One important factor in test backing for armor is its hardness. Armor is more easily penetrated in testing when backed by harder materials, and therefore harder materials, such as Roma clay, represent more conservative test methods .
| Backer type | Materials | Elastic/plastic | Test type | Specific gravity | Relative hardness vs gelatin | Application |
|---|
| Roma Plastilena Clay #1 | Oil/Clay mixture | Plastic | Ballistic and Stab | >2 | Moderately hard | Back face signature measurement. Used for most standard testing | | 10% gelatin | Animal protein gel | Visco-elastic | Ballistic | ~1 (90% water) | Baseline | Good simulant for human tissue, hard to use, expensive. Required for FBI test methods | | HOSDB-NIJ Foam | Neoprene foam, EVA foam, sheet rubber | Elastic | Stab | ~1 | Slightly harder than gelatin | Moderate agreement with tissue, easy to use, low in cost. Used in stab testing | | Silicone gel | Long chain silicone polymer | Visco-elastic | Biomedical | ~1.2 | Similar to gelatin | Biomedical testing for blunt force testing, very good tissue match | | Pig or Sheep animal testing | Live tissue | Various | Research | ~1 | Real tissue is variable | Very complex, requires ethical review for approval | |
Backing materials for stab armor testing
Stab and spike armor standards have been developed using 3 different backing materials. The Draft EU norm calls out Roma clay, The California DOC called out 10% ballistic gelatin and the current standard for NIJ and HOSDB calls out a multi-part foam and rubber backing material.
- Using Roma clay backing, only metallic stab solutions met the 109 joule Calif. DOC ice pick requirement
- Using 10% Gelatin backing, all fabric stab solutions were able to meet the 109 joule Calif. DOC ice pick requirement.
- Most recently the Draft ISO prEN ISO 14876 norm selected Roma as the backing for both ballistics and stab testing.
This history helps explain an important factor in Ballistics and Stab armor testing, backing stiffness affects armor penetration resistance. The energy dissipation of the armor-tissue system is Energy = Force x Displacement when testing on backings that are softer and more deformable the total impact energy is absorbed at lower force. When the force is reduced by a softer more compliant backing the armor is less likely to be penetrated. The use of harder Roma materials in the ISO draft norm makes this the most rigorous of the stab standards in use today.
Rifle resistant armor
Because of the limitations of the technology a distinction is made between handgun protection and rifle protection. See NIJ levels 3 and 4 for typical requirements for rifle resistant armor. Broadly rifle resistant armor is of two basic types: ceramic plate-based systems and hard fiber-based laminate systems. Many rifle armor components contain both hard ceramic components and laminated textile materials used together. Various ceramic materials types are in use, however: Aluminum Oxide, Boron Carbide and Silicon Carbide are the most common. The fibers used in these systems are the same as found in soft textile armor. However, for rifle protection high pressure lamination of ultra high molecular weight Polyethylene with a Kraton matrix is the most common. The Small Arms Protective Insert SAPI and the enhanced SAPI plate for the US DOD generally has this form . Because of the use of ceramic, plates for rifle protection these vests are 5-8 times as heavy on an area basis as handgun protection. The weight and stiffness of rifle armor is a major technical challenge. The density, hardness and impact toughness are among the materials properties that are balanced to design these systems. While ceramic materials have some outstanding properties for ballistics they are not strong under tensile loads. Failure of ceramic plates by cracking must also be controlled . For this reason many ceramic rifle plates are a composite. The strike face is ceramic with the backface formed of laminated fiber and resin materials. The hardness of the ceramic prevents the penetration of the bullet while the tensile strength of the fiber backing helps prevent tensile failure.
Armor Piercing Ammunition Core Hardness and Protection
There is no simple distinction for rifle bullets which can be considered armor piercing. A few points are clear. Lead core copper jacketed bullets are too deformable to penetrate hard materials. At the other end of the spectrum rifle bullets manufactured with very hard “exotic” core materials like tungsten carbide are engineered to have maximum penetration effect on hard armor .
Explosive protection
Bomb disposal officers often wear heavy armor designed to protect against most effects of a moderate sized explosion, such as bombs encountered in terror threats. Full head helmet, covering the face and some degree of protection for limbs is mandatory in addition to very strong armor for the torso. An insert to protect the spine is usually applied to the back, in case an explosion blasts the wearer. Visibility and mobility of the wearer is severely limited, as is the time that can be spent working on the device. Armor designed primarily to counter explosives is often somewhat less effective against bullets than armor designed for that purpose. The sheer mass of most bomb disposal armor usually provides some protection, and bullet-specific trauma plates are compatible with some bomb disposal suits.
Stab armor and combination stab-ballistic armor
Early “Ice Pick” test
In the mid-1980s the state of California Department of Corrections issued a requirement for a body armor using a commercial ice pick as the test penetrator. The test method attempted to simulate the capacity of a human attacker to deliver impact energy with their upper body. As was later shown by the work of the former British PSDB, this test over stated the capacity of human attackers. The test used a drop mass or sabot that carried the ice pick. Using gravitational force, the height of the drop mass above the vest was proportional to the impact energy. This test specified 109 joules (81 ft-lbs) of energy and a 7.3 kg (16.1 lb) drop mass with a drop height of 153 cm (60 inches). The ice pick has a 4 mm (0.16”) diameter with a sharp tip with a 5.4m/s (17ft/s) thermal velocity in the test. The California standard did not include knife or cutting edge weapons in the test protocol. The test method used the oil/clay (Roma Plastilena) tissue simulant as a test backing. In this early phase only Titanium and Steel plate offerings were successful in addressing this requirement. Point Blank developed the first ice pick certified offerings for CA Department of Corrections in shaped titanium sheet metal. Vests of this type are still in service in US corrections facilities as of 2008.
Beginning in the early '90s, an optional test method was approved by California which permitted the use of 10% ballistic gelatin as a replacement for Roma clay. The transition from hard, dense clay-based Roma to soft low-density gelatin allowed all textile solutions to meet this attack energy requirement. Soft all textile “ice pick” vests began to be adopted by California and other US states as a result of this migration in the test methods. It is important for users to understand that the smooth, round tip of the ice pick does not cut fiber on impact and this permits the use of textile based vests for this application. The earliest of these “all” fabric vests designed to address this ice pick test was Warwick’s TurtleSkin ultra tightly woven para-aramid fabric with a patent filed in 1993. Shortly after the TurtleSkin work, in 1995 DuPont patented a medium density fabric that was designated as Kevlar Correctional. It should be noted that these textile materials do not have equal performance with cutting-edge threats and these certifications were only with ice pick and were not tested with knives.
Knife standards developed by PSDB
Parallel to the US development of “ice pick” vests the British police, PSDB, was working on standards for knife resistant body armor. Their program adopted a rigorous scientific approach and collected data on human attack capacity. Their ergonomic study suggested three levels of threat: 25, 35 and 45 joules of impact energy. In addition to impact energy attack, velocities were measured and were found to be 10-20 m/s (much faster than the California test). Two commercial knives were selected for use in this PSDB test method. In order to test at a representative velocity, an air cannon method was developed to propel the knife and sabot at the vest target using compressed air. In this first version, the PSDB ’93 test also used oil/clay materials as the tissue simulant backing. The introduction of knives which cut fiber and a hard-dense test backing required stab vest manufactures to use metallic components in their vest designs to address this more rigorous standard.
Combination stab and ballistic vests
Vests that combined stab and ballistic protection were a significant innovation in the 1990s period of vest development. The starting point for this development were the ballistic-only offerings of that time using NIJ Level 2A, 2, and 3A or HOSDB HG 1 and 2, with compliant ballistic vest products being manufactured with areal densities of between 5.5–6 kg/m3 (1.1-1.2 lb/ft2). However police forces were evaluating their “street threats” and requiring vests with both knife and ballistic protection. This multi threat approach is common in England and Europe and is less popular in the USA. Unfortunately for multi-threat users, the metallic array and chainmail systems that were necessary to defeat the test blades offered little ballistic performance. The multi-threat vests have areal densities are close to the sum of the two solutions separately. These vests have mass values in the 7.5-8.5 kg/m2 (1.55-1.75lb/ft2) range. Ref (NIJ and HOSDB certification listings). Rolls Royce Composites -Megit and Highmark produced metallic array systems to address this HOSDB standard. These designs were used extensively by the London Metropolitan Police Service and other agencies in the United Kingdom.
Standards update US and UK
As vest manufactures and the specifying authorities worked with these standards, the UK and US Standards teams began a collaboration on test methods.A number of issues with the first versions of the tests needed to be addressed. The use of commercial knives with inconsistent sharpness and tip shape created problems with test consistency. As a result, two new “engineered blades” were designed that could be manufactured to have reproducible penetrating behavior. The tissue simulants, Roma clay and gelatin, were either un-representative of tissue or not practical for the test operators. A composite-foam and hard-rubber test backing was developed as an alternative to address these issues. The drop test method was selected as the baseline for the updated standard over the air cannon option. The drop mass was reduced from the “ice pick test” and a wrist-like soft linkage was engineered into the penetrator-sabot to create a more realistic test impact. These closely related standards were first issued in 2003 as HOSDB 2003 and NIJ 0015. (PSDB was renamed Home Office Scientific Development Branch in 2004)
Stab and spike vests
These new standards created a focus on Level 1@25J, Level 2@35J, Level 3@45 joules protection as tested with the new engineered knives defined in these test documents. The lowest level of this requirement at 25 joules was addressed by a series of textile products of both wovens, coated wovens and laminated woven materials. All of these materials were based on Para-aramid fiber. The co-efficient of friction for ultra high molecular weigh polyethylene (UHMWPE) prevented its use in this application. The TurtleSkin DiamondCoat and Twaron SRM products addressed this requirement using a combination of Para-Aramid wovens and bonded ceramic grain. These ceramic-coated products do not retain the flexibility and softness of un-coated textile materials. For the higher levels of protection L2 and L3, the very aggressive penetration of the small, thin P1 blade has resulted in the continued use of metallic components in stab armor. In Germany, Mehler Vario Systems have developed sophisticated hybrid vests of woven para-aramid and chain mail their solution was selected the London Metro Police. Another German company BSST, in cooperation with Warwick Mills, has developed a system to meet the ballistic-stab requirement using Dyneema laminate and an advanced metallic-array system, TurtleSkin MFA. This system is currently implemented in Holland. The trend in multi threat armor continues with requirements for needle protection in the Draft ISO prEN ISO 14876 norm. In many countries there is also an interest to combine military style explosive fragmentation protection with bullet-ballistics and stab requirements.
Vest sizing, carriers and encapsulation
In order for ballistic protection to be wearable the ballistic panels and hard rifle resistant plates are fitted a special carrier. The carrier is the part of a ballistic vest that we see. The most basic carrier includes the pockets to carry the ballistic panels and the straps for mounting the carrier on the user. There are two major types of carriers, military or tactical carriers that are worn over the shirt and covert law enforcement type carriers that are worn under the shirt.
Military carriers
The military type of carrier, English police waistcoat carrier, or police tactical carrier most typically has a series of webbing, hook and loop and snap type connectors on the front and back face. This permits the wearer to mount various gear to the carrier in a flexible way. This load carriage feature is an important part of uniform and operational design for police weapons teams and the military. In addition to load carriage, this type of carrier may include pockets for neck protection, side plates, groin and backside protection. Because this style of carrier is not close fitting sizing in this system is straight forward for both men and women and custom fabrication is not necessary.
Concealable carriers
Law enforcement carriers in some countries are concealable. The carrier holds the ballistic panels close to the wearers body and the uniform shirt is worn over the carrier. This type of carrier must be designed to conform closely to the officers body shape. For concealable armor to conform to the body the fit is important. Many programs specify full custom measurement and manufacturing of armor panels and carriers to ensure good fit and comfort for concealable armor. Officers who are either female or obese have more difficulty in getting accurately measured and having comfortable armor fabricated.
Vest slips
Between the carrier and the ballistic components is a third layer of textile. The ballistic panels are covered in a coated pouch or slip. This slip provides the encapsulation of the ballistic materials. Slip are manufactured in two types, heat sealed hermetic slips and simple sewn slips. For some ballistic fibers the slip is a critical part of the system. The slip prevents moisture from the user body from saturating the ballistic materials. This protection from moisture cycling increases the useful life of the armor.
Research
Progress in fiber science
In recent years advances in material science have opened the door to the old idea of a literal "bulletproof vest" that will be able to stop handgun and rifle bullets with a soft textile vest without the assistance of heavy and cumbersome extra metal or ceramic plating. In fact the progress in fibers materials is quite slow by comparison to the rate of change in some other technical disciplines. The most recent offering from Kevlar called Protera was released in 1996. Current soft body armor can stop most handgun rounds which has been the case for perhaps 15 years. However armor plates are needed to stop rifle rounds and steel core handgun rounds such as 7.62x25. The para-aramids have not progressed beyond the limit of 23 grams/denier in fiber tenacity. Modest ballistic performance improvements have been made by new producers of this fiber type. Much the same can be said for the UHMWPE material; the basic fiber properties have only advanced to the 30-35g/d range. Improvements in this material have been seen in the development in cross-plied non-woven laminate eg Spectra Shield. The major ballistic performance advance of fiber PBO is perhaps a classic cautionary tale in materials science.. This fiber permitted the design of handgun soft armor that was 30-50% lower in mass as compared to the aramid and UHMWPE materials. However this higher tenacity was delivered with a well-publicized weakness in environmental durability. Akzo-Magellen (now DuPont) teams have been working on fiber called M5, however its announced startup of its pilot plant has been delayed more than 2 years. Data suggests if the M5 material can be brought to market, its performance will be roughly equivalent to PBO. In May 2008, the Teijin Aramid group announced a “super-fibers” development program. The Teijin emphasis appears to be on computational chemistry to define a solution to high tenacity without environmental weakness. The materials science of second generation “super” fibers is complex, requires large investments, and represent significant technical challenges. Research aims to develop artificial spider silk which could be super strong, yet light and flexible. Other research has been done to harness nanotechnology to help create super-strong fibers that could be used in future bulletproof vests.
Textile wovens and laminates research
Finer yarns and lighter woven fabrics have been a key factor in improved ballistic results. The cost of ballistic fiber goes up dramatically as yarn size goes down, so it is unclear how long this trend can continue. The current practical limit of fiber size is 200 denier with most wovens limited at the 400 denier level. Three-dimensional weaving with fibers connecting flat wovens together into a 3D system are being considered for both hard and soft ballistics. Team Engineering Inc is designing and weaving these multi layer materials. Dyneema DSM has developed higher performance laminates using a new, higher strength fiber designated SB61, and HB51. DSM feels this advanced material provides some improved performance, however the SB61 “soft ballistic” version has been recalled . At the Shot Show in 2008, a unique composite of interlocking steel plates and soft UHWMPE plate was exhibited by TurtleSkin. In combination with more traditional woven fabrics and laminates a number of research efforts are working with ballistic felts. Tex Tech has been working on these materials. Like the 3D weaving, Tex Tech sees the advantage in the 3-axis fiber orientation.
Developments in ceramic armor
Ceramic materials, materials processing and progress in ceramic penetration mechanics are significant areas of academic and industrial activity. This combined field of ceramics armor research is broad and is perhaps summarized best by The American Ceramics Society. The ACS has run an annual armor conference for a number of years and complied a proceedings 2004–2007 An area of special activity pertaining to vests is the emerging use of small ceramic components. Large torso sized ceramic plates are complex to manufacture and are subject to cracking in use. Monolithic plates also have limited multi hit capacity as a result of their large impact fracture zone These are the motivations for new types of armor plate. These new designs use 2 and 3 dimensional arrays of ceramic elements that can be rigid, flexible or semi-flexible. Dragon Skin body armor is one these systems. European developments in spherical and hexagonal arrays have resulted in products that have some flex and multi hit performance. The manufacture of array type systems with flex, consistent ballistic performance at edges of ceramic elements is an active area of research. In addition advanced ceramic processing techniques arrays require adhesive assembly methods. One novel approach is use of hook and loop fasteners to assembly the ceramic arrays.
Nanomaterials in ballistics
Currently, there are a number of methods by which nanomaterials are being implemented into body armor production. The first, developed at University of Delaware is based on nanoparticles within the suit that become rigid enough to protect the wearer as soon as a kinetic energy threshold is surpassed. These coatings have been described as shear thickening fluids. These nano-infused fabrics have been licensed by BAE systems however as of mid 2008, no products have been released based on this technology. In 2005 an Israeli company, ApNano, developed a material that was always rigid. It was announced that this nanocomposite based on tungsten disulfide nanotubes was able to withstand shocks generated by a steel projectile traveling at velocities of up to 1.5 km/s. The material was also reportedly able to withstand shock pressures generated by the impacts of up to 250 tons per square centimeter. During the tests, the material proved to be so strong that after the impact the samples remained essentially unmarred. Additionally, a recent study in France tested the material under isostatic pressure and found it to be stable up to at least 350 tons/cm². As of mid-2008, spider silk bulletproof vests and nano-based armors are being developed for potential market release. Both the British and American militaries have expressed interest in a carbon fiber woven from carbon nanotubes that was developed at Cambridge University and has the potential to be used as body armor. In 2008, large format carbon nanotube sheets began being produced at Nanocomp.
Legality
Body armor is legal in most countries, one exception being Australia, where body armor has been prohibited for some time. The late 19th century Australian outlaw and folk hero Ned Kelly is famous for his iconic home-made armor, which he used with mixed results. While the steel armor worn by Kelly defeated the soft lead, low velocity bullets fired by police Martini-Henry rifles, it greatly restricted his movement.
United States law restricts possession of body armor for convicted violent felons. Many US states also have penalties for possession or use of body armor by felons. In February 1999, Russell Jones was arrested in California for possession of body armor by a convicted felon. In other states, such as Kentucky, possession is not prohibited, but probation or parole is denied for a person convicted of certain violent crimes while wearing body armor and carrying a deadly weapon.
Canadian legislation makes it legal to wear and to purchase body armor such as ballistic vests. However, there are current proposals to the legislation to make it illegal to wear such body armor during the commission of a criminal offense.
See also
External links
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