Ballistic vest

From Wikipedia, the free encyclopedia

This article does not cite any references or sources. (March 2007) Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.

A ballistic vest is an item of protective clothing that absorbs the impact from gun-fired projectiles and explosive fragments fired at the torso. Soft vests made from layers of tightly-woven fibres protect wearers from projectiles fired from handguns, shotguns, and shrapnel 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. 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 armor for more protection and leg armor for protection against grenade blasts.

Contents 1 Overview 2 History 2.1 1800s-1930s 2.2 World War II 2.3 1960s-1970s 2.4 1990s-2000s 3 Performance standards 3.1 Ballistic Testing V50 and V0 3.2 Military testing: Fragment Ballistics 4 Rifle Resistant Armor 4.1 Armor Piercing Ammunition Core Hardness and Protection 5 Explosive protection 6 Stab Armour and Combination Stab-Ballistic Armour 6.1 Early “Ice Pick” Test 6.2 Knife Standards developed by PSDB 6.3 Combination Stab and Ballistic Vests 6.4 Standards Update US and UK 6.5 Stab and Spike Vests 7 Research 7.1 Progress in Fiber Science 7.2 Textile Wovens and Laminates Research 7.3 Developments in Ceramic Armour 7.4 Nanomaterials in Ballistics 8 Legality 9 External links 10 References

[edit] Overview

Vests may be augmented with metal (steel or titanium), ceramic or polyethylene plates that provide extra protection to vital areas. These hard armour plates have proven effective against all handgun bullets and a range of rifles. These "tactical body armour" vests have become standard in military use, as soft body armour vests are ineffective against most military rifle rounds. The CRISAT NATO (Collaborative Research Into Small Arms Technology-North Atlantic Treaty Organization) standard for body armour specifies the use of titanium backing. This titanium plate may be removable or sewn in.

A vest does not protect the wearer by deflecting bullets. Instead, the layers of material catch the bullet and spread its force over a larger portion of the body, absorbing energy more quickly and hopefully bringing it to a stop before it can penetrate into the body. This tends to deform the bullet, further reducing its ability to penetrate. While a vest can prevent bullet wounds, the wearer still absorbs the bullet's energy, which can cause blunt force trauma. The majority of users experience only bruising, but impacts can still cause severe internal injuries.

Most vests offer little protection against arrows, ice picks, stabbing knife blows, bullets with their points sharpened or armour-piercing rounds. As the force is concentrated in a relatively small area with bladed weapons and armour-piercing rounds, they can push through the weave of most bullet-resistant fabrics. Specially-designed vests which protect against bladed weapons and sharp objects are often used in vests for prison guards and other law enforcement officers. Some materials like Dyneema offer considerable protection against bladed weapons and slash attacks.

Most ballistic vests may provide little or no protection against rifle ammunition or even against handgun ammunition fired from a pistol-caliber carbine, the exception being .22 LR ammunition, which can usually be stopped by these vests even when fired from a rifle. However, vests of type III and up are built to be resistant to rifle and armour piercing rifle fire. These vests are usually protective against handgun ammunition fired from handguns of all calibers, depending on the armour level of the vest.

[edit] History

[edit] 1800s-1930s

The first ballistic armour known is Myunjebaegab invented in Korea in 1860s. It was invented right after the French Campaign against Korea, 1866. Heungseon Daewongun ordered development of bullet-proof armor because of increasing threats from western army. Kim Gi-Doo and Gang Yoon found that cotton could protect from bullets through many experiments, and invented bullet-proof vests made of 30 folds of cotton. The vests were used in battles when the US Navy attached Ganghwa Island in Korea in 1871 (United States expedition to Korea). The US army captured one of the vests and took it to the US, and it was stored in the Smithsonian Museum until 2007. Now this vest went to Korea, and it became known to public.

One of the early instances of ballistic armour being used was in Australia in 1879, when Ned Kelly's "Kelly Gang" made armour from scrap metals which covered their torsos, upper arms, and upper legs. Along with the helmet, the home-made suit weighed 44kg (96lbs), which made Kelly clumsy and unwieldy when he wore the armour 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 which and they resembled medieval padded jacks, 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, Illinois 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, which is equivalent to about $16,886 in 2008 dollars. On 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. However, the vest did not protect him, because he was shot in the neck above the vest with a .32 ACP bullet fired by Gavrilo Princip using a handgun. A similar vest was made by Jan Szczepanik in 1901 saved the life of Alfonso XIII of Spain when he was shot at 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, .25, S&W .32 Long, S&W .32, .380 ACP, and .45 ACP traveling at slower speeds of up to approximately 1000 ft/s (300 m/s). To overcome these vests, law enforcement agents such as the FBI began using the new, more powerful .357 Magnum cartridge.

[edit] 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. These armor vests were often incompatible with existing equipment as well. The military diverted its research efforts to developing "flak jackets" for aircraft crews. These flak jackets were made of nylon fabric and capable of stopping flak and shrapnel, but not designed to stop bullets.

The British Army issued Medical Research Council body armour, as did the Canadian Army, in north-west 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 they 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 armour, 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 the German MP-40 9 mm bullet at around 100-125 meters, which made it useful in urban battles (Stalingrad). However, the SN's weight made it impractical for infantry on foot in an open outdoor setting.

[edit] 1960s-1970s

During the Korean War several new vests were produced for the United States military, including the M-1951, which made use of fiberglass or aluminum 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 a standard Soviet 7.62x25 pistol round at the muzzle. The Vietnam war era vests were simply updated versions of the Korean models and were still not capable of stopping rifle rounds.

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 the Smith & Wesson gun company 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, the DuPont Corporation 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, comprised of 15 layers of Kevlar that also included a 5" X 8" ballistic steel "Shok Plate" positioned vertically over the heart and was issued U.S Patent #3,971,072 for this ballistic vest 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 this company's first all-Kevlar vest, named 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 the year 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.

[edit] 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. So the Ranger Body Armor was developed for the American military in 1994. 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.

The newer armor issued by the United States military to large numbers of troops is known as the Interceptor Multi-Threat Body Armor System. The Kevlar Interceptor vest is intended mainly to provide shrapnel protection, but is rated for threats up to and including 9mm sub machine gun fire. Small Arms Protective Insert (SAPI) plates, made of ceramic materials, are worn front and back and protect the vital organs from threats up to and including 7.62x51mm NATO rifle rounds.

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 GoldFlex 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.^[1] 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.

[edit] Performance standards

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 American National Institute of Justice ballistic and stab documents are examples of broadly accepted standards, In addition to US NIJ the English Home Office Scientific Development Branch (HOSDB)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. The United States National Institute of Justice (NIJ Standard 0101.04) have specific performance standards for bullet resistant vests used by law enforcement. The US NIJ rates vests on the following scale against penetration and also blunt trauma protection (deformation) (Table from NIJ Standard 0101.04):

Armor Level	Protects Against
Type I (.22 LR; .380 ACP)	This armor protects against 22 calibre Long Rifle Lead Round Nose (LR LRN) bullets, with nominal masses of 2.6 g (40 gr) at a reference velocity of 329 m/s (1080 ft/s ± 30 ft/s) and .380 ACP Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 6.2 g (95 gr) at a reference velocity of 322 m/s (1055 ft/s ± 30 ft/s)
Type IIA (9 mm; .40 S&W)	This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 341 m/s (1120 ft/s ± 30 ft/s) and .40 S&W calibre Full Metal Jacketed (FMJ) bullets, with nominal masses of 11.7 g (180 gr) at a reference velocity of 322 m/s (1055 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Type I].
Type II (9 mm; .357 Magnum)	This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 367 m/s (1205 ft/s ± 30 ft/s) and 357 Magnum Jacketed Soft Point (JSP) bullets, with nominal masses of 10.2 g (158 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Types I and IIA].
Type IIIA (High Velocity 9 mm; .44 Magnum)	This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s) and .44 Magnum Semi Jacketed Hollow Point (SJHP) bullets, with nominal masses of 15.6 g (240 gr) at a reference velocity of 436 m/s (1430 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)	This armor protects against 7.62 mm Full Metal Jacketed (FMJ) bullets (U.S. Military designation M80), with nominal masses of 9.6 g (148 gr) at a reference velocity of 847 m/s (2780 ft/s ± 30 ft/s) or less. It also provides protection against the threats mentioned in [Types I, IIA, II, and IIIA].
Type IV (Armour Piercing Rifle)	This armor protects against .30 caliber armour piercing (AP) bullets (U.S. Military designation M2 AP), with nominal masses of 10.8 g (166 gr) at a reference velocity of 878 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 NIJ and HOSDB some 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 Back-Face-Signature or transmitted impact energy is measured by shooting armor mounted on a tissue simulant material. Sculpture modeling oil-clay materials are most commonly used for this testing. 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.^[2]

The allowable Back-Face-Signature between different test standards can be difficult to compare. Both clay materials and the bullets used for the test are not common. However in general English, German and other European standards allow 20-25 millimeters of Back-Face-Signature. US-NIJ standards allow for 44 millimeters, which can potentially cause internal injury (^[3]). The allowable Back-Face-Signature for body armor has been controversial from its introduction under the first NIJ test standard. The debate as to the relative importance of Penetration-Resistance vs. Back-Face-Signature continues in medical and test communities.

In general a vest's textile material must not get wet, because it will have reduced protective capability until dry again. Neutral water at room temp does not affect para-armid or ultra-high-molecular-weight-polyethylene, however acid, base and other solutions can permanently impact para-arimid fiber tensile strength (^[4] . Because all ballistic materials can loose ballistic performance when wet the major test standards call for wet testing of textile armor ^[5]) 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.

In 2003-5 a large effort to study environmental degradation of Zylon armor was under taken by the US-NIJ. This study concluded that water, use and temperature exposure significantly affect tensile strength and 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. ^[6]

[edit] Ballistic Testing V50 and V0

Measuring the ballistic performance of armour is based on determining the energy of a bullet at impact which is ½ mass x velocity². 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 armour performance and test variability. Ballistic testing has a number of sources of variability: the armour, 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 1600fps with a 9mm 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 armour certification. This procedure defines a confidence interval of an estimate of V0. see (NIJ and HOSDB test methods)

Because V0 is difficult to measure 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 armour. US military standards ^[7] 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 armour. 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 armour testing is the offset velocity between the V0 and V50. If this offset has been measured for an armour 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 Armour after certification.

[edit] Military testing: Fragment Ballistics

After the Vietnam War, military planners developed a concept of “Casualty Reduction”^[8]. . The large body of casualty data made clear that in a combat situation, fragments not bullets were the most important threat to solders. After WWII vests were being developed and fragment testing was in its early stages ^[9]. 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 block 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 Projectile RCC FSP 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 ^[10]. Warhead explosives have blast speeds of 20,000 to 30,000fps. As a result they are capable of ejecting fragments at very high speeds of order 1000m/sec(3330 fps). Noting again that the energy of a fragment is ½ * mass * Velocity2. 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 4 grains have a velocity of 3000fps or less. This established a set of goals for military ballistic vest design.

The random nature of fragmentation required the military vest specification to take a mass vs. ballistic-benefit approach. Only hard vehicle armor is capable of stopping all fragments. Solders can only carry a limited mass of gear and equipment so vest fragment protection is a limited by carry mass. The 2-4-16-64 grain series at limited velocity can be stopped by an all-textile vest of approximately 5.4kg/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 2-grain FPS is about the size of a grain of rice, small fast moving fragments can slip through the vest moving between yarns. As a result fabrics designed for fragment protection are tightly woven. These wovens are not as effective on lead bullets and are optimized for this fragment requirement.

[edit] 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 conponents 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.^[11] 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 ^[12]. 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 ^[13]. 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.

[edit] 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 ^[14]. However most rifle bullets are outside these two extremes, perhaps the most common rifle bullet on the planet is the 7.62x39mm M43 standard cartridge for the AK47 rifle. This bullet has a steel core, depending on where the bullet is made this steel can range from Rc35 mild steel up to Rc45 medium hard steel (Indentation hardness). Many other rifle bullets have steel cores and have hardness that fall into this range. The US Department of Defense has taken two approaches to this continuum of rifle bullet core hardness. To protect for the more challenging ammunition US DOD has the Enhanced SAPI specification. Ceramic composite plates that meet this requirement have a areal density of 35-45kg/m2 (7-9lbs/ft2). The earlier SAPI plates has a mass 20-30kg/m2 (4-5lbf/ft2). The eSAPI was designed to stop bullets like the 7.62 x 63 AP(M2) with an engineered hard core. The penetration mechanics for armor piercing bullets can be over simplified to some useful concepts. The harder the steel in the core the more ceramic must be used. Like the soft ballistics the ceramic hardness is required to damage these hard core materials. In the case of the AP rounds the bullet core is eroded rather than deformed. Cercom, now BAE systems, CoorsTek, Ceradyne, Tencate, Honeywell, DSM, Pinnacle Armor and a number of other engineering companies develop and manufacture the materials for composite ceramic rifle armor.

[edit] 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 may be severely limited.

[edit] Stab Armour and Combination Stab-Ballistic Armour

[edit] Early “Ice Pick” Test

In the mid 1980’s the state of California Dept. 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 it was later shown by the work of the British Police Scientific Development Branch (PSDB) that this test over stated the capacity of human attackers. The test created 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 7.3kg (16.1 lb) drop mass with a drop height of 153cm (60 inches). The ice pick has a 4mm (0.16”) diameter with a sharp tip with a 5.4m/sec (17ft/sec) 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 90’s 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 filled in 1993^[15]. Shortly after the TurtleSkin work, in 1995 DuPont patented a medium density fabric that was designated as Kevlar Correctional^[16]. It should be noted that these textile materials do not have equal performance with cutting-edge threats and theses certifications were only with ice pick and were not tested with knives.

[edit] 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^[17]. 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/sec (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 canon 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.

[edit] Combination Stab and Ballistic Vests

Vests that combined stab and ballistic protection were a significant innovation in the 1990’s 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 Home Office Scientific Development Branch (HOSDB) HG 1 and 2, with compliant ballistic vest products being manufactured with aerial 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 chain Chainmail systems that were necessary to defeat the test blades offered little ballistic performance. The multi-threat vests have aerial densities are close to the sum of the two solutions separately. These vests have mass values in the 7.5-8.5kg/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 London Metro Police and other agency in Great Britain.

[edit] Standards Update US and UK

As vest manufactures and the specifying authorities worked with these standards, the English and US Standards teams began a collaboration on test methods^[18].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 stimulants, 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 canon 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^[19])

[edit] 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 armour. 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. In Holland, BSST-Warwick have developed a system to meet the ballistic-stab requirement using Dyneema laminate and an advanced metallic-array system, TurtleSkin MFA. The trend in multi threat armour 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.

[edit] Research

[edit] 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 armour 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. ^[20] 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 tail in materials science.^[21]. 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.^[22]. 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^[23]. Other research has been done to harness nanotechnology to help create super-strong fibers that could be used in future bulletproof vests.

[edit] 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 ^[24]. At the Shot Show in 2008, a unique composite of interlocking steel plates and soft UHWMPE plate was exhibited by TurtleSkin^[25]. 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. These materials may offer lower cost ballistic solutions based on their lower fiber cost.

[edit] Developments in Ceramic Armour

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 a annual armour conference for a number of years and complied a proceedings 2004-2007^[26] 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^[27]. 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^[28].

[edit] Nanomaterials in Ballistics

Currently, there an number of methods by which nanomaterials are being implemented into body armor production. The first 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^[29]. These nano-infused fabrics have been licensed by BAE systems however as of mid 2008, no products have been released based on the this technology. In 2005 an American company, ApNano, developed a material that was always rigid. It was announced that this nanocomposite based on Tungsten Disulfide was able to withstand shocks generated by a steel projectile traveling at velocities of up to 1.5 km/second^[30]. 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. Cambridge University has developed a carbon fibre woven from carbon nanotubes and the researchers predict that it will find practical application as body armour, and both the British and American militaries have expressed interest^[31]. In 2008, large format carbon nanotube sheets are being produced at Nanocomp. These long tube materials may find there way into advanced ballistic armor.

[edit] Legality

Body armor is legal in most countries. One exception is Australia, where body armor has been prohibited for some time.^[32] This ban may have its origins in the late 19th century, when the iconic Australian outlaw and folk hero Ned Kelly used home-made armor 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 of 1999, the late Russell Jones a.k.a. "Ol' Dirty Bastard" 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.

Recently (2006-2007) Hungary outlawed the unsolicited use of body armor by the general public. This was done in response to the heavy riots during the 50th celebration (2006.10.23) of the Revolution of '56.

[edit] External links

• How Stuff Works - Body Armor

[edit] References