Kinetic energy, bulletproof, knife guard or syringe shield ... everyone knows what a bulletproof vest is. But on what physical principle does a "fabric" or a rigid plate stop a ball or a knife and what is the material that forms a screen between you and a penetrating body? What ergonomics, what weight and what benefit / risk ratio for the user? What is the life span (optimal) for the protection material? In short, a quick overview to help you choose the right protection and take into account the constraints that come with it!
We will begin by defining the essential (for those who get bored by the article), what is kinetic energy? We will make it simple and concise

  • It is the energy of a moving body (in this case the bullet, the knife or the syringe). This energy will depend on the mass of the body in question, and its speed. Kinetic energy is expressed in joule. In the case of a ball - which will be the simplest and most telling example - it is the kinetic energy released which determines its power of penetration (with a set of other factors such as the caliber of the ball, its shape, its material, the power of the explosion that will allow to print the initial force - setting in motion of the ball, and the length of the barrel - which will allow the accumulation of the energy up to its mouth ).
  • To calculate the kinetic energy of a bullet (or other object) the following formula must be applied:
  • Ec = 0,5 × m × v 2
  • Ec: Kinetic energy
  • m: mass - expressed in kilos
  • v: speed (squared) - expressed in meters (per second, minute ...)
    • So for a ball of 9x19mm, with a weight of 8 grams (0,008 Kg) and projected at a speed of 350 m / s it gives:
      • 0,5 × 0,008 (mass expressed in Kg): 0,004
      • 350 × 350 (the speed squared of the ball in m / s): 122500
      • So: 0,004 × 122500: 490 joules
  • The fascinating thing about energy is that it can not be lost, only transferred. Once out of the barrel - and thus once in the air - the energy of a bullet undergoes friction (by dilating the air precisely) and it transfers some of it, until the impact on that target . At impact, the remaining energy will be transferred in its entirety (depending obviously on the nature of the target) and cause the damage that goes well on tissues, bones, organs ...This is where the bulletproof material will do the job!
The general idea is to absorb (stop net the projectile is tempting but ... you remember that the energy does not undergo a loss, simply a transfer - I let you imagine where it will go if the material of protection stopped the projectile without absorbing energy eh ...) energy transfer of the projectile on a surface (the widest possible) other than your body. The complication is that the tip of a knife or the cone of a ball have relatively small impact surfaces while concentrating phenomenal energy!

kinetic energy comparison

Ballistic Steel, Kevlar, Goldflex, polyethylene, dyneema, ceramic... Before presenting the mechanical properties of protective materials, a small list of those used in all vests on the market (I voluntarily exclude nanotechnology materials, biosteel - the famous bristles of spiders - or cellular changes of the artist Jalila Essaïdi):

  • Fibers (declined in flexible plates):
    • The para-aramids
      • Twaron (Teijin company)
      • Kevlar (Dupont company)
      • Goldflex (Honeywell company)
    • Polyethylenes
      • Spectra (Honeywell company)
      • Dyneema (DSM company)

Of all its fibers one retains the Goldflex (capacity of increased resistance, optimal behavior to the torsion - more expensive to the production) and the Dyneema (report weight / resistance higher than its competitors and a remarkable resistance to the moisture, abrasion and UV).

Again we pass on the manufacturing process and the different stages of transformation of the fibers, the weavings used as well as on the physical properties of each material or their variations (for information there are 6 different types of Kevlar, without counting the types of Dyneema, obtained according to a different protocol of manufacture - I miss time to write a book ... But if you are interested, send us a message, we will send you the documentation).

You find one of these fibers in all flexible plates currently available on the market. They have more or less the same mechanical capabilities - absorption capacity in joules per m2 - with variations in resistance to moisture, exposure to UV and abrasion. Obviously some will be "better" than others but anyway it must be considered that a damaged plate (following the absorption of a shot, exposure to a chemical agent, a tear ...) must imperatively to be replaced.

ballistic fiber dyneema

  • Steels (broken down into hard plates or specific cuts for the protection of a vehicle or a building):
    • Armor or Armox 500 - depending on the manufacturer
      • Without going into detail a steel with the specific structure, used for the manufacture of hard ballistic plates and bulletproof structures for vehicles, modular buildings ... Decline in variable thickness depending on the need.
      • The 500 indication refers to the hardness index (Brinell scale)
      • We pass on the steels having an index of 550 or more, they are not used for the manufacture of individual protection elements.
  • Ceramics - or rather a composite material including ceramics (available in hard plates or balls, exclusively for bullet-proof use):
  • Composed mostly of a first layer of epoxy or fiberglass - protection of the plate against splinters, scratches, blunt shocks ... - ceramic (alumina, boron carbide ...), then layers of polyethylene UHMWPE (ultra high molecular weight polyethylene) or a flexible ballistic fiber (see above) that will ensure the dispersion of energy over the entire surface of the plate. This is what gives the famous SAPI (Small Arms Protective Insert) ballistic plate
  • The three ceramic formulas used (most commonly) for the manufacture of a ballistic protection plate:
    • Aluminum oxide (Al2O3 - commonly known as Alumina)
      • It is the most economical formula (at the cost of manufacture and the volume of material to be used to obtain an optimal level of protection) and the one with the highest density - depending on the purity of the final product - its manufacturing process must display a purity of 90 at 99,95% and a porosity of less than 2%
    • Boron carbide (B4C)
      • 2 times harder than alumina, but also of a lower density, it is the ideal material to "stop" a ball ... except that it is expensive to produce, extremely brittle to "tear" - which is the characteristic of a perforating bullet for example - and that it requires a different manufacturing process depending on which one wants to obtain optimal protection for the absorption of one or more. To exploit its exceptional performance, boron carbide is generally used in conjunction with silicon carbide.
    • Silicon carbide (SiC)
      • We find, grosso merdo, the same physical capacities as boron carbide, with however a higher density. The combination of a hardness almost similar to alumina and boron carbide with its density - depending on the manufacturing process - more or less high make it the ideal choice for (or against rather) the balls at very high speed or piercing.
    • It should be noted that the ceramic component, by nature, is "brittle" and that the ceramic shield will invariably suffer significant damage to the impact - this is even partly what ensures the energy transfer and the stopping the projectile. We will discuss further the difference between "single" and "multi" hits (plate that has the ability to absorb the energy of one or more projectiles) but, as noted in the introduction to the chapter "ceramic", ensure the consistency of the material, allow it to retain its ballistic properties and avoid the projection of brilliance, through the addition of a composite material (cover - epoxy, polyester fiber resin carbon) and a ballistic material (to polyethylene fiber base or aramid for example - allowing the reduction of microcracks of the ceramic plate and optimal absorption of kinetic energy). Most ceramic plates also have a layer of material (phenolic foam) for its fire resistance and thermal insulation properties.

In a nutshell, the more rigid the ceramic plate (and made in conjunction with a "blanket" and "reinforced" with a ballistic fiber), the harder the ceramic used is - harder than the material of the ball - better c 'is !

  • The high performance polyethylene (UHMWPE - ultra high molecular weight polyethylene) in its laminated composite form (in its fiber version the UHMWPE is - in particular - the ballistic protection materials Dyneema and Spectra in the form of flexible ballistic plates) - the still the material will be operated in the form of individual plates or cutting for protection of vehicle or aircraft. We will make simple: to date it is the most resistant thermoplastic compound (shock, solvents, abrasion) and it absorbs virtually no moisture. Composed of a repetition of monomer units (roughly the repetition of the structure of a macromolecule - thousands of times, polymerization), the UHMWPE can be manufactured according to several processes (with the impregnation of a thermostatic matrix , with a number of filaments more or less high or of a more or less wide section, with a particular spinning ...) and the protective plate may have a variable number of leaves (the "sheet" of UHMWPE manufactured by DSM Dyneema ® SB71 for example), but in the case of a hard plate it will always be presented in composite form. Its very low density and exceptional resistance make it the ideal material for an optimal protection / weight ratio.
  • You will find the UHMWPE in the composition of most ballistic shields and visors - especially because it allows transparency and therefore an optimal vision for the wearer.
  • A UHMWPE plate can not be used for protection against a perforating bullet or at very high speed (a test set has demonstrated) but will be an excellent additive to the ceramic plate to allow a species of individual plate "sandwich" - The ceramic and composite plate as presented above - which will provide protection against most light gauge (excluding some specific ammunition, the .50 BMG, .408 CheyTac, basically all that can also serve as anti-vehicle caliber ).

ceramic arrangement

Great ! But how does it work? Relatively simple! whether it's a fiber, steel or ceramic, the important thing is:

  1. That the molecular structure of the material has a maximum energy absorption capacity.
  2. That the absorption of energy is done on the widest possible surface.
  3. In the case of a bullet-proof vest, the force of the impact on the protective material allows the deformation (and thus reduces the energy concentration by allowing the bullet to expand) or the burst of the projectile.

For the proposed "soft" protection materials (kevlar, goldflex, spectra or dyneema):

For the sake of popularization I voluntarily exclude the structural differences between para-aramids and polyethylene. Imagine a net of tennis court (or the goal net of a football field). When a ball (or ball) touches the net it deforms conically and the strings that make up the net absorb the energy at 360 ° until it is fully absorbed and the ball stops . The "soft" textile material of a bullet-proof plate will act in exactly the same way, except that the trauma caused by a very powerful conical penetration - and on a very small surface - towards the inside of the body may be just as deadly as if the projectile actually penetrated the body. The difference lies therefore in a mesh of fiber much tighter than the mesh of a sports net. This very fine mesh will allow the dispersion of the energy on the whole surface of the plate and thus the reduction of the conical deformation that the projectile imposes on it (one will come back to it in the chapter of the various official standardizations).

To allow this dispersion of the energy and the complete stopping of the projectile before penetration, it is necessary:

  • The succession of textile layers that act individually as a net
  • A mesh of each layer which is sufficiently fine for a maximum dispersion of the energy on all its surface
  • That at impact the energy transfer acts on the projectile itself by "crushing" it to remove some of the penetration due to the conical shape of the bullets - and thus by helping to increase the "grip" surface in charge of the ball
  • That the fiber used has exceptional tensile strength properties
  • The special case of knife-protection plates or syringe-guards:
  • The difference in velocity (speed) of a blow carried with a knife (or a pick, or a syringe) is much lower than that of a bullet (even of very small caliber). In fact the manufacturers (the first standardization of anti-knife plates date from ... 1993) had to adapt the mechanical strength of the fibers usually used to stop the bales.
  • The fibers used have the same trade names - Dyneema or Kevlar - but the manufacturing process differs to obtain a mesh capable of absorbing and stopping the progression of a blade or a syringe in the surface of the plate.
  • We will come back to this later but it is the English (damn roast beef) that have (in 1993, therefore), via the HOSDB (Home Office Scientific Development Branch - the scientific institute of the Ministry of the Interior what) develop a specific standard designed for protection against knife blades or syringes (ballistic capabilities, test protocol, efficiency levels, etc.)
  • It is noted that a knife guard plate may be worn in conjunction with a bullet-proof plate

For the proposed "hard" protection materials (ceramics & UHMWPE):

The process is slightly different! A hard plate is intended to protect the wearer from the mechanical damage of a much faster ammunition (potentially with a design designed for increased penetration or the concentration of kinetic energy on a restricted surface). The behavior of a "smaller" caliber bullet (or with a smaller initial explosion) when it hits a "textile" plate can not be identical in the case of a faster and more "bullet". powerful ". On the one hand because the kinetic energy released could allow the projectile to penetrate the protective surface without any problem - and continue its trajectory in the body of the wearer - and secondly because even in case of absorption of energy mechanically imposed conical deformation would cause potentially life-threatening physiological damage if there was no protection at all. It is therefore imperative that the plate lasts:

  • It is composed of a material harder than the one that is opposed to it (the ball that tries to penetrate)
  • That the absorption of energy is done (as for soft plates) on the largest possible area
  • That on impact (always as for soft plates) the projectile crashes or disintegrates to the maximum
  • The special case of "multi-hits" (the plate able to absorb the energy of several projectiles as a result):
  • Nothing too complicated - refer to the chapter "Ceramics - or rather a composite material including ceramic" which details the structure of a plate made of different layers (protective coating - epoxy, ceramic, composite ballistic material and potentially a layer of phenolic foam).
  • It is this composition in "sandwich" that will allow to retain mainly the properties of ceramics (which, as indicated above will fragment at the first impact). Even in "piece" the ceramic material, from the moment when the design in "sandwich" retains its initial structure - in short, the piece ceramic remains compressed in its gangue (before the first impact), will retain its mechanical properties. Composite ballistic material will continue to perform its role of absorbing energy.
  • In addition to the "sandwich" composition, the type of structure used for the ceramic surface is involved. According to the tests mentioned below it is essential that the ceramic is arranged not in one piece but in several "tiles". This tiling makes it possible to preserve intact the protection capacities of the tiles adjacent to the tile that absorbs the first impact. Logic what.
  • Based on a V50 (velocity 50 - see below) comparative test conducted by Messrs. Horsfall and Buckley and Watson et al (have a look at google if their tests are of interest to you) with intact plates and plates the result indicates (depending on the velocity of the bullet on impact / with 7,62 ammunition / on alumina SAPI plates) a decrease in performance from 3 to 8%. This still allows to note that the material retains a capacity of 24 12% higher than the requirements of the standard.
  • Caution : even if the material does the job, it will not be able to protect you against dozens of impacts! In two words covered fissa!
  • The particular case of "stand-alone" plates (the plate that provides the level of protection it indicates - according to the standard chosen for its test - without being used in conjunction with another (flexible) protection plate:
  • Again it is a protective plate (hard) that has benefited from a manufacturing process or structure that allows its use alone, without being worn in conjunction with the support of a flexible plate (typically a protective plate carried in a vest AND a hard plate carried on top in a compartment provided for this purpose). In a nutshell, you can use this plate in a tactical "plate holder" - which will reduce the volume and weight of the combination vest with flexible plate + hard plate and the comfort of movement of the wearer. Obviously this also reduces the area of ​​protection, but if you are about to deal with shots caliber more powerful than those "treated" by a flexible plate ... so do not be bored - think anyway at the risk of bursts of shrapnel ...
  • The "anti-trauma" plaque:
  • Simple: it is an additional flexible plate (usually made of fiber, but it existed in steel or aluminum) which is packaged in a much thinner format than the conventional bullet-proof flexible plate (but in the same material, therefore). The idea is not to propose a protection "in addition" but to limit the conical deformation to the impact (and the resulting physiological trauma) by optimizing the surface of dispersion of the energy and the crushing of the projectile at impact.

But then what kind of plates stop what kind of templates or chips?

Each industrialized country - France, USA, Germany, China, Russia, England ... defined, at one time or another, a test protocol that defines the protection capabilities (for shrapnel, ammunition, blast effect and knives) of each material used. The various protocols all offer (depending on the constraints required for the tests) a scale which makes it possible to determine which product is the most adapted to the risk that one wants to treat.

Well, we start with us, huh? That's the lesser of it ! The French protocol and scale of evaluation therefore:

  • Well, there is a slight problem: AFNOR (French Association of Standards) does not propose a specific protocol for bullet-proof materials used for personal protection or vehicle
  • It will be noted however:
    • NF A36-800-2 and NF A50-800-2 standards (Hot-rolled weldable steel sheets for shielding - Part 2: fire test method)
    • The standard NF P 78-401 (replaced by the European standard EN 1063 - Glass in building - Safety glazing - Testing and classification of resistance to attack by bullet
    • The NF EN 1522 / 1523 standard (Windows, doors, closures and blinds - Bulletproof - Prescriptions and classification)
    • In short, no comment ...

The protocol and the American evaluation scale:

  • You all know the standard defined by the NIJ. But the Ricans like to do things big! So it gives:
  1. The standards defined by the NIJ (National Institute of Justice - the US federal standardization and scientific research body):

NIJ Standard 0101.07 - Ballistic Resistance (draft)
NIJ Standard 0101.06 - Ballistic Resistance
NIJ Standard 2005 Interim Requirements for Ballistic Resistance
NIJ Standard 0101.04 - Ballistic Resistance
NIJ Standard 0101.04 Revision A - Ballistic Resistance
NIJ Standard 0101.03 - Ballistic Resistance
NIJ Standard 0115.00 - Stab Resistance
NIJ 0104.02 Standard - Riot Helmets and Face Shields
NIJ Standard 010600 - Helmets
NIJ Standard 0117.00 - Public Safety Bomb Suit Standard
NIJ Standard 0108.01 - Ballistic Protective Materials
FBI body armor 2008 test protocol
HP White 401-01b Helmet Testing Procedure

  1. The standards defined by the US military:

MIL-STD-662F, STANDARD MILITARY: V50 BALLISTIC TEST FOR ARMOR

The protocol and the German evaluation scale:

  • With my apologies, can not find a version of the documents in French or in English, so I give you the original version in German - you still have to use google translate huh ...
  1. The German certification body (Vereinigung der Prüfstellen für angriffshemmende Materialien und Konstruktionen) defines the following standards:

VPAM KDIW2004 Stand: 18.05.2011
VPAM KDIW 2004 Stand: 12.05.2010
VPAM HVN 2009 Booth: 12.05.2010
VPAM APR 2006 Edition: 2009-05-14
VPAM BSW 2006 Stand: 14.05.2009

The Russian protocol and scale of evaluation:

  • The GOST (for those interested in a translation of the document send me a message, we know how to do it internally).

GOST R 50744 95

Protocol and Rating Scale English:

  • It is recalled that the English scientific institute first defined a specific protocol for materials manufactured for protection against knives and 2013 syringes.
  1. English certification body - HOSDB Home Office Scientific Development Branch) defines the following protocols:

HOSDB Body Armor Standards for UK Police (2007)
HOSDB Body Armor Standards for UK Police (2007) 1 Part: General Requirements
HOSDB Body Armor Standards for UK Police (2007) Part 2: Ballistic Resistance
HOSDB Body Armor Standards for UK Police (2007) Part 3: Knife and Spike Resistance

The Chinese protocol and scale of evaluation:

  • I hope you have some notions of English, this is the only version I found - excluding Chinese and Mandarin of course ...
  1. The standard is defined as:

GA 141 2010

NATO Protocol and Rating Scale (STANAG) - for vehicles and aircraft exclusively:

  • This protocol is expressed in 2 volumes (NATO AEP-55 STANAG 4569 1 flight and 2 flight)
  • It is not intended for personal protection elements but exclusively for vehicles and aircraft
  1. The table of the standard is available here:

NATO AEP-55 STANAG 4569

Protocol and Scale of Australia and New Zealand:

  • It should be noted that this protocol only takes into account handguns and hunting caliber .12
  1. The standard is defined as:

AS / NZS 2343: 1997

HERE A SUMMARY TABLE OF STANDARDS FOR INDIVIDUAL PROTECTIONS AND PROTECTIONS FOR VEHICLES AND AIRCRAFT

SMALL ADVICE BEFORE (AND AFTER) PURCHASE:

  • Think about mobility and comfort of movement - to be still under enemy fire is to be dead
  • No protective material guarantees you that a projectile will not penetrate. Have confidence in your material but in a reasoned way, do not expose yourself in a useless way
  • When a plate (flexible or rigid) has suffered a significant impact or degradation ... it is no longer operational!
  • When you evaluate the weight of your vest or your plates take into account the carriage of your bag, your ammunition, your weapons ...
  • Acquire "anti-trauma" plates. The cost is less and in any case lower than the pain and the lethal risk following the physiological damage caused by the internal deformation of your soft plates at impact.
  • Remember that the effectiveness of materials has a life time! Beyond the warranty provided by the seller or the manufacturer, you must consider that the material is no longer operational
  • Observe the maintenance and protection instructions (humidity, UV exposure, exposure to solvents, etc.) indicated by the seller or the manufacturer
  • Practice handling your weapons and accessories carried with your vest or plate holder on the back! It will improve your feelings like your reflexes

Good luck, and as usual, stay safe, be blessed!

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