American culture heavily prizes the right to bear arms. While the interpretation of the 2nd Amendment is a controversial topic, guns remain an everyday reality. Bulletproof materials are used in times of war and peace, just as guns are. Bulletproof materials serve to protect law enforcement, while keeping the lives of service members overseas safe. Most often, when used as body armor, bulletproof materials take the form of vests. Bulletproof materials are also commonly found in armored vehicles and businesses in the form of bulletproof glass. Bulletproof materials such as those used in bulletproof vests and bulletproof glass are an important aspect in the protection of law enforcement and citizens daily.
Bulletproof materials are an important aspect of our daily lives. They reduce injuries and death, as well as helping people feel more safe. Those who we credit with our daily safety especially benefit through these materials. It is estimated that 3,000 police officers between the mid-70s to 2012 have been saved by the wearing of bulletproof vests. Bulletproof vests are items of personal armor that are designed to help absorb the impact and mitigate or prevent penetration to the body from projectiles shot from firearms and shrapnel from explosives. Bulletproof vests are not actually “bulletproof”. More accurately, they are often called bullet-resistant vests. The reality is that these vests do not protect the user from every threat. Some bullets, such as those that have serrated edges, still can penetrate the vest and cause harm to the wearer.
Bullet-resistant vests can come in soft body as well as hard body armor. Soft body armor, as the name suggests, is softer and more flexible than hard body armor, though what it is made of can still be many times stronger than steel. Soft armor is often made with fabric-like material with extreme strength. These include materials, most commonly Kevlar. Because it is not as bulky and cumbersome as hard body armor, it is more likely to be worn underneath a uniform. However, at the cost of being lighter and easier to wear, it does not protect the user from high-caliber rounds and is only able to effectively protect the wearer from pistol-caliber ammunition.
Hard body armor, on the other hand is heavier and less flexible, but far more effective at protecting its user from projectiles than soft body armor. Hard body armor is made of a soft armor shell but has the added benefit of having plates. These plates can be made of extremely strong materials such as ballistic steel or ceramic. These plates may also be coated in strong protective material for increased protection. By sacrificing flexibility hard body armor is better able to protect its user from high-caliber ammunition and is what is typically worn by those serving in the military.
Bullet-resistant vests are designed to dispel a round’s force as well as to deform the bullet to minimize blunt force trauma. They do this by being made of extremely strong materials that can withstand the force of projectiles. Kevlar, the most common material used in bulletproof vests, is an incredibly durable fiber than is found in many of today’s bullet-resistant vests. Kevlar can stop bullets and other projectiles because of its molecular structure. It is a polyacrylamide plastic fabric with an extremely high tensile strength (5 times that of steel relative to its weight) while remaining relatively light.
Within a bullet-resistant vest, there are many strings and layers of interlinked Kevlar. A bullet fired from a gun has kinetic energy and momentum due to its mass and the velocity at which it travels. When a bullet hits the vest, the bullet tries to penetrate through the material. To do this however, it must push the layers of Kevlar fibers apart. Because of its high tensile strength, the layers of Kevlar are effectively able to resist the momentum of the bullet. A bullet-proof vest accepts the energy from the bullet and dissipates it so that only a small portion is passed on to the actual target, the person who is wearing the vest. The momentum of the bullet is then ultimately rendered into a stretching force on the fibers.
It is helpful to think of a soccer ball being kicked into a soccer goal when understanding how bulletproof vests and Kevlar works. The lateral tension of the net spreads the energy of the impact of the ball across the net and stops the ball. In other words, in the same way a soccer goal’s net absorbs the soccer ball’s energy and diffuses it out across the many ropes of the net, effectively slowing and then stopping the soccer ball’s momentum into the net, the tightly woven and flexible fibers of a bulletproof vest such as Kevlar “catch” the bullet and deprives it of its kinetic energy and momentum before it can penetrate the wearer and cause injury or death.
Just as a bulletproof vest is not truly bulletproof, neither is bulletproof glass. To add to the misnomer, glass itself is not always present in bulletproof glass. Instead, these sheets can be made with acrylic or layered polycarbonate. While normal glass would shatter when impacted by a projectile, such as a bullet, bulletproof glass works to absorb the energy of the projectile. Normal glass shatters by its inability to absorb the energy, in part due to its inability to move. The inflexibility of glass prevents it from bending around the projectile, so the momentum of the projectile is hardly affected. Bulletproof glass, thus, is made of a more flexible material able to spread the energy throughout the pane. The projectile’s momentum is significantly decreased, which is why, despite a bullet at times being able to pass through a pane of bulletproof glass, we still refer to it as such. The force of a bullet after passing through bulletproof glass is comparatively small and innocuous.
There are several different variations of bulletproof glass, but it is commonly made by layering polycarbonate materials between pieces of glass in a processed called lamination. Lamination produces glass-like materials that are thicker and much stronger than normal glass. Projectiles attempting to penetrate a sheet of bulletproof glass will pierce the outside layer of the glass, but the layered polycarbonate-glass material will be able to absorb the projectile’s kinetic energy and slow it down or stop it before it exits the final layer. What is happening is that the force of the bullet is distributed along the surface of the material. By having multiple layers, the effect is compounded and the glass class can withstand larger and more powerful rounds.
There are four forms of bulletproof glass: bulletproof laminate, acrylic, polycarbonate, and glass-clad polycarbonate. Bulletproof laminate is an outdated form of bulletproof glass, made of layers of resin in between glass. The rigid structure of this makes it difficult to cut, and these panes tend to be rather heavy. Bulletproof laminate is similar to the glass used in the windshield of a car, as they both utilize this stacking process to withstand the impact of projectiles, rather it be a rock while you are driving or bullets while in a war zone. The resin also prevents shards of glass from scattering upon impact. Monolithic acrylic is becoming more popular with bulletproof glass, as it is easier to cut. The single, nonlayered panes of acrylic are preferred for the versatility that comes with being easier to cut and install. Unique to bulletproof glass, layering is not necessary in creating the energy absorbing quality. While most acrylic sheets are not layered, they can be fortified by being placed in between polycarbonate sheets.
Polycarbonate bulletproof glass is made by layering the plastic. This is necessary, as polycarbonate is a softer substance than acrylic. Glass-clad polycarbonate is the most commonly thought of bulletproof glass, as it utilizes the glass layering technique of traditional bulletproof laminate. It is the strongest of all bulletproof glasses, and can be made even stronger by multiplying the layers used. Bulletproof glass is regulated by a rating system scaled from 1 to 7. A bulletproof glass with a rating of 1 only be able to withstand something like the fire from a handgun, while 7 would be a large caliber rifle.
One of the newest forms of bullet-resistant glass available is one-way bulletproof glass. This type of bulletproof glass is commonly utilized in armored vehicles and has two sides: one side which is able to stop bullets and the other side which allows bullets to pass through unaffected. This effectively enables the person inside the vehicle that is being shot at the ability to shoot back and defend him or herself.
One-way bulletproof glass is made by laminating a brittle sheet of material in conjunction with a flexible material. The outside layer that is faced towards the threat is made with the brittle glass. A bullet that impacts the brittle external layer causes the glass to break inward towards the flexible polycarbonate material. The glass that breaks is able to absorb a considerable amount of the bullet’s kinetic energy by spreading that force over a larger area and ultimately the flexible polycarbonate layer is able to mitigate the penetration, if not stop the bullet.
Bullets that are shot from the inside of the armored vehicle with one-way bullet resistant glass are able to penetrate the from the inside because they strike the polycarbonate layer first with much more focused energy. Because the bullet’s force is much more concentrated on a smaller area, this causes the material to flex. As the bullet passes through, the brittle glass layer then breaks outward allowing the bullet to penetrate with minor kinetic energy loss.
The most commonly regarded use of bulletproof glass is on armored vehicles, such as those used to transport money or dignitaries. Bulletproof glass is also used around most modern buildings. Businesses typically have windows made of bulletproof glass to reduce crimes, particularly robbery through forced entry. Bulletproof glass, similarly to bulletproof vests, is used for more than what its name suggests. The energy absorbing qualities of bulletproof glass mean it can withstand harsh weather conditions, such as hurricanes and tornados, because it will be able to withstand any projectiles the wind may pick up. As previously mentioned, it is good for use in security because it can better withstand impact than traditional glass.