Dating against body type

A ballistic vest helps absorb the impact from firearm -fired projectiles and shrapnel from explosions, and is worn on the torso. Soft vests are made from many layers of woven or laminated fibers and can be capable of protecting the wearer from small caliber handgun and shotgun projectiles, and small fragments from explosives such as hand grenades.

Metal or ceramic plates can be used with a soft vest, providing additional protection from rifle rounds, and metallic components or tightly-woven fiber layers can give soft armor resistance to stab and slash attacks from a knife. Soft vests are commonly worn by police forces, private citizens and private security guards or bodyguards , whereas hard-plate reinforced vests are mainly worn by combat soldiers, police tactical units and hostage rescue teams.

A modern equivalent may combine a ballistic vest with other items of protective clothing, such as a combat helmet. Vests intended for police and military use may also include ballistic shoulder and side protection armor components, and explosive ordnance disposal technicians wear heavy armor and helmets with face visors and spine protection. Limbs[ edit ] Medieval armor often offered protection for all of the limbs, including metal boots for the lower legs, gauntlets for the hands and wrists, and greaves for the legs.

Today, protection of limbs from bombs is provided by a bombsuit. Most modern soldiers sacrifice limb protection for mobility, since armor thick enough to stop bullets would greatly inhibit movement of the arms and legs. Performance standards[ edit ] Due to the various different types of projectiles, it is often inaccurate to refer to a particular product as " bulletproof " because this implies that it will protect against any and all projectiles.

Instead, the term bullet resistant is generally preferred. Around the world ammunition varies and as a result the armor testing must reflect the threats found locally. Even more astounding is that this number is on the rise. In , officers were killed, with 68 of them being killed due to a gun-related incident.

The US National Institute of Justice ballistic and stab documents are examples of broadly-accepted standards. Since the time that NIJ started testing, the lives of more than 3, officers were saved. These "model" standards are usually adapted by other countries by following the same basic test methodologies, while changing the specific ammunition tested.

This rates vests on the following scale against penetration and also blunt trauma protection deformation: Another important change is that the test-round velocity for conditioned armor will be the same as that for new armor during testing.

For example, for NIJ Standard For the NIJ Standard Armor Level Higher levels offer protection against more aggressive threats.

It is no longer part of the standard. Type IIA 9 mm ;. Conditioned armor protects against: It also provides protection against the threats mentioned in [Type I]. Type II New armor protects against: 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.

Both the clay materials and the bullets used for the test are not common. 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. 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.

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 effects on Zylon resulted in ballistic failures under standard test conditions. 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: Variability reduces the predictive power of a determination of V0. 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 the variability is known and the standard deviation can be calculated, 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. V0 is difficult to measure, so a second concept has been developed in ballistic testing called V This is the velocity at which 50 percent of the shots go through and 50 percent are stopped by the armor. US military standards [28] define a commonly used procedure for this test. The goal is to get three shots that penetrate and a second group of three shots that are stopped by the armor all within a specified velocity range.

It is possible, and desirable to have a penetration velocity lower than a stop velocity. These three stops and three penetrations can then be used to calculate a V50 velocity. A very useful concept in armor testing is the offset velocity between the V0 and V 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. Cunniff analysis[ edit ] Using dimensionless analysis, Cuniff [30] arrived at a relation connecting the V50 and the system parameters for textile-based body armors.

Under the assumption that the energy of impact is dissipated in breaking the yarn, it was shown that V.


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Total 2 comments.
#1 22.08.2018 в 06:03 Laborer75:
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#2 01.09.2018 в 06:39 Azar:
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