Kinetic energy, bullet proof, knife or needle shield… everyone knows what a bullet proof vest is. But on what physical principle does a "cloth" or a rigid plate stop a bullet or a knife and what is the material that shields you from a penetrating body? What ergonomics, what weight and what benefit / risk ratio for the user? What (optimal) lifespan for the protective material? in short, a quick overview to help you choose the right protection and take into account the constraints that go with it!
We will start by defining the essential (for those who piss off, go on to the rest of the article), what is kinetic energy? We will keep 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 ball (or of another object) it will be necessary to apply the following formula:
  • Ec = 0,5 × m × v 2
  • Ec: Kinetic energy
  • m: mass - expressed in kilos
  • v: speed (squared) - expressed in meters (per second, minute, etc.)
    • So for a 9x19mm bullet, with a weight of 8 grams (0,008 Kg) and projected at a speed of 350 m / s it gives:
      • 0,5 × 0,008 (the mass expressed in Kg): 0,004
      • 350 × 350 (the squared speed 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 therefore to absorb (stopping the projectile dead it's 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 its energy eh…) the energy transfer of the projectile on a surface (as large as possible) other than your body. Where it gets complicated is that the tip of a knife or the cone of a bullet have relatively “small” impact surfaces while concentrating a 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 the vests on the market (I deliberately exclude materials from nanotechnologies, biosteel - the famous spider bristles - or cellular modifications of artist Jalila Essaïdi):

  • Fibers (available in flexible sheets):
    • 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 will find one of these fibers in all the flexible sheets currently available on the market. They have more or less the same mechanical capacities - absorption capacity in joules per m2 - with variations in resistance to humidity, UV exposure and abrasion. Obviously some will be "better" than others but in any case it will be necessary to consider that a damaged plate (following the absorption of a shot, an exposure to a chemical agent, a tear ...) must imperatively be replaced.

ballistic fiber dyneema

  • Steels (available in hard plates or specific cutouts 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 bullet ... 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 whether 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 protection plate will invariably suffer significant damage on impact - this is even in part what ensures the transfer of energy and l stopping the projectile. We will discuss the difference between “single” and “multi” hits (plate which presents the possibility of absorbing the energy of one or more projectiles) but, as noted in the introduction to the “ceramic” chapter, to ensure the consistency of the material, allowing it to retain its ballistic properties and avoid the projection of splinters, involves the addition of a composite material (in cover - epoxy, polyester carbon fiber resins) and a ballistic material (to polyethylene or aramid fiber base for example - allowing the reduction of micro-cracks in the ceramic plate and optimum absorption of kinetic energy). Most ceramic plates also have a layer of material (phenolic foam) for its fire resistance and thermal insulation properties.

In short, the stiffer the ceramic plate (and made in conjunction with a "blanket" and "reinforced" with ballistic fiber), the "harder" the ceramic used - harder than the material of the bullet - the better it is. 'East !

  • High performance polyethylene (UHMWPE - ultra high molecular weight polyethylene) in its laminated composite form (in its fiber version, UHMWPE is - in particular - Dyneema and Spectra ballistic protection materials in the form of flexible ballistic plates) - again the Material will be tapped in the form of individual plates or cut to size for vehicle or aircraft protection. Let's keep it simple: to date, it is the most resistant thermoplastic compound (to impacts, solvents, abrasion) and it hardly absorbs moisture. Composed of a repetition of monomer units (roughly the repetition of the structure of a macromolecule - thousands of times. Polymerization), UHMWPE can be made in 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 protection plate can have a variable number of sheets (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 capacity 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 cannot be used for protection against a perforating bullet or at very high speed (a test set has shown this) but will be an excellent additive to the ceramic plate to allow a kind of individual plate in "sandwich" - the ceramic and composite plate as presented above - which will provide protection against most light calibers (excluding certain specific ammunition, the .50 BMG, .408 CheyTac, basically anything that can also serve as an anti-vehicle caliber ).

ceramic arrangement

Great ! So how does it actually work? Relatively simple! whether it is 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 “flexible” protective materials (kevlar, goldflex, spectra or dyneema):

For the sake of popularization I voluntarily exclude the structural differences between para-aramids and polyethylene. Imagine a tennis court net (or a football field goal net). When a ball (or a ball) hits the net it deforms conically and the strings that make up the net absorb the energy at 360 ° until it is totally absorbed and the ball comes to a stop . The "soft" textile material of a bulletproof 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 - into the interior of the body can be. just as deadly as if the projectile actually penetrated the body. The difference therefore lies in a mesh of the fiber much tighter than the mesh of a sports net. This very fine mesh will allow the dispersion of the energy over the entire surface of the plate and therefore the reduction of the conical deformation imposed on it by the projectile (we will come back to this in the chapter on the various official standardizations).

To allow this dispersion of 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 on impact the transfer of energy acts on the projectile itself by "crushing" it to eliminate part of the penetration due to the conical shape of the bullets - and thus by contributing to increase the surface of "catch". in charge 'of the ball
  • That the fiber used has exceptional tensile strength properties
  • The specific case of knife or syringe guard plates:
  • 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” protective materials (ceramics & UHMWPE):

The process is slightly different! The purpose of a hard plate is to protect its wearer from the mechanical damage of a much faster ammunition (potentially with a design designed for increased penetration or concentration of kinetic energy in a small area). The behavior of a bullet of a more “modest” caliber (or with a smaller starting explosion) when it hits a “textile” plate will absolutely 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 problem - and continue its trajectory in the body of the wearer - and on the other hand because even in the event of absorption of the energy the mechanically imposed conical deformation would cause physiological damage potentially as fatal as if there were 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 particular case of "multi-hits" (the plate able to absorb the energy of several projectiles in a row):
  • Nothing very complicated - see the chapter "Ceramic - or rather a composite material including ceramic" which details the structure of a plate made up of different layers (protective coating - epoxy, ceramic, composite ballistic material and potentially a layer of phenolic foam).
  • It is this “sandwich” composition which will make it possible to retain mainly the properties of the ceramic (which, as indicated above, will fragment from the first impact). Even as a “piece” ceramic material, from the moment the “sandwich” design retains its initial structure - in short, the piece ceramic remains compressed in its matrix (before the first impact), will retain its mechanical properties. The composite ballistic material will continue to fulfill its role of absorbing energy.
  • In addition to the "sandwich" composition, there is the type of structure used for the ceramic surface. According to the tests cited below, it is essential that the ceramic be placed not in one piece but in several "tiles". This tiling keeps intact the protective capacities of the tiles adjacent to the tile which absorbed the first impact. Logical 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.
  • Warning : even if the material does the job, it won't be able to protect you against dozens of impacts! In short, cover fissa!
  • The particular case of “stand-alone” plates (the plate which provides the level of protection it indicates - depending on the standard chosen for its test - without being used in conjunction with another (flexible) protection plate:
  • Again it is a protective plate (hard) which will have benefited from a manufacturing process or a structure that allows its use alone, without being worn in conjunction with the support of a flexible plate (conventionally a protective plate worn in a vest AND a hard plate worn over it in a compartment provided for this purpose). In short, you can use this plate in a tactical "plate holder" - which will reduce the volume and weight represented by the combination of the vest with soft plate + hard plate as well as the comfort of movement of the wearer. Obviously this also reduces the protective surface, but if you are more or less sure to face shots of caliber more powerful than those "treated" by a flexible plate ... you might as well not get bored - just think about the risk of damage. shards of shrapnel ...
  • The "anti-trauma" plate:
  • Simple: it is an additional flexible plate (generally in fiber, but it existed in steel or aluminum) which is packaged in a much thinner format than the classic flexible bulletproof plate (but in the same material therefore). The idea is not to offer an "additional" protection but to limit the conical deformation on impact (and the physiological trauma which results from it) by optimizing the surface of energy dispersion and the crushing of the projectile. at impact.

But then what type of plates stops what type of gauges or chips?

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

Well, we start with home, eh? That's the lesser of it ! The French protocol and assessment scale therefore:

  • Well, there is a slight problem: AFNOR (Association Française de Normalization) does not offer a specific protocol for bulletproof materials used for personal protection or on vehicles.
  • Note, 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 American protocol and rating scale:

  • You all know the standard set by the NIJ. But the Ricans like to do it big! This therefore gives:
  1. The standards defined by the NIJ (National Institute of Justice - the American federal scientific research and standardization 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:


The German protocol and rating 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) defined 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 rating scale:

  • 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

The English protocol and assessment scale:

  • 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) defined 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 assessment scale:

  • 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 under the name:

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:


Australia and New Zealand protocol and rating scale:

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

AS / NZS 2343: 1997



  • Think about mobility and comfort of movement - to be stationary 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 undergone an impact or significant 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 ...
  • Purchase "anti-trauma" plates. The cost is lower and in any case lower than the pain and the consequent lethal risk of physiological damage caused by the internal deformation of your flexible plates on impact
  • Remember that efficient materials have a lifetime! Beyond the guarantee 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 the accessories you carry with your vest or your plate holder on your back! It will improve your sensations as your reflexes

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

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