Modern knights not only wear the same medieval steel armor worn by knights of a thousand years ago, but we also wear, under this armor, modern armor. Bullet proof vests, stab proof vests and helmets are worn when a knight is actually on guard duty - all under the steel armor.
The modern bullet-proof jacket is made of Kevlar with ceramic breast and back plates, clearly to add additional protection to the vital organs from gun shot by spreading the pressure of the impact across the entire plate.
Through the years, scientists have made many major discoveries that have impacted our society. Many of these discoveries have been a positive influence and hence have helped our society advance. One such discovery that has aided and protected our society especially the law enforcement officers is the bullet-proof vest. The discovery of the material that makes bullet-proof vests came by accident when a scientist, Stephanie Kwolek, was working with polymers. This material came to be known as KevlarTM.
In an attempt to help with a gas shortage, a chemist in the Textile Lab at
Dupont named Stephanie Kwolek began working to find new synthetic polymers.
While experimenting with two polymers that would not melt, she searched for a
solvent to dissolve them instead of melt them. The solution was not like
polymers seen before having a molasses type texture, but instead they
were almost water-like in nature. It was this property of the mixture that
lead her to research it further. In the year1964, she tried to create a
fiber that would reinforce tires, but would be lighter than steel wire, thus
saving on gasoline. While combining, heating, stirring, and spinning different
substances, Ms. Kwolek discovered a new fiber (aramid fiber) and a new substance
(liquid crystalline solutions) that was amazingly strong and stiff. The road was
long from discovery to a product that could be used through many applications.
It was not until 1975 that this fiber, now known as KevlarTM ,
was made available for sale as a material used to make bulletproof vests.
Bulletproof vests, also known as soft body armor, are most often made of the
lightweight woven material (KevlarTM) fiber. Its fibers absorb
and then dissipate a bullet’s energy. Comparing equal weights of materials,
KevlarTM is about five times stronger than steel.
The fibers, first observed by Stephanie Kwolek of DuPont, are spun from a liquid crystalline solution into a very strong and rigid crystalline fiber, which, when baked, becomes even more rigid. The resulting fiber is very crystalline, due to the polymer chains being fully stretched out and its ability to pack nearly perfectly. The ability for it to pack occurs because the polymer chain predominately assumes the trans conformation, due to steric hindrance in the cis form which can be seen below. Adjacent chains also align parallel to each other due to the pi electron interactions between the phenyl rings and hydrogen bonding between the oxygen atoms on one chain with the N-bonded hydrogen atoms on the next.
These fibers can then be used to make the bullet-proof
fibers are woven into a fabric and then the fabric is layered. Since the
fiber is very lightweight, a vest
constructed of seven layers of this fabric only weighs 2.5 pounds. This vest
has the ability to stop a .38 caliber bullet fired from a distance of ten feet.
To stop a bullet, the vest catches it with several layers of the woven material. Energy is transferred from the bullet by the propagation of stress waves that move outward through the fibers into the weave. The bullet’s tip touches thousands of individual fibers, stretching and breaking them. Most of the energy is absorbed at the points where fibers cross over each other. The bullet continues to lose energy as it travels through the layers; its end starts to flatten; and it eventually stops.
The more stiff or rigid the material, the more quickly the energy is distributed, due to the increased speed of the wave, and the faster the bullet will be stopped. But increasing a material’s stiffness often makes it more brittle, so a balance must be sought.
Software programs are available to help design vests for maximum effectiveness, especially as the hazards police and other users of these vests face change. The arrival of TeflonTM -coated “cop killer” and needle-shaped bullets on the scene necessitate the continuous redesign and improvement of bullet-proof vests.
A knight who is wearing steel THEN a bullet proof vest has the advantage of the steel flattening even 'cop killer' bullets so taht their needle-shape is flattened before the bullet hits the kevlar. So in a sense, the medieval armor actually assists the modern armor in protecting the knight against these kinds of bullets.
The higher velocity of rifle rounds requires HARD Body Armor Rifle Plates – Level III or Level IV Ballistic Steel, Ceramic or Polyethelene - usually ~10" by 12" (~25 by 30 cm.) and 3.5 to 9 lbs (1.6 - 4.1 kg.) per plate to cover the Chest or Back. SOFT Body Armor vests only offer pistol and shotgun protection (birdshot and buckshot, but not shotgun slugs). Rifle Plate information...
“When a handgun bullet
strikes body armor, it is caught in a “web” of very strong fibers. These
fibers absorb and disperse the impact energy that is transmitted to the vest
from the bullet, causing the bullet to deform or “mushroom”. Additional
energy is absorbed by each successive layer of material in the vest, until such
time as the bullet has been stopped.”
For information about this kind of modern armor see sites like: