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 Bulletproofing is a big business and therefore an
ever-developing area of focus for materials science. Erm, perhaps we'll call it
bullet resistance from here on out, because eventually any material will be
punctured by a bullet big enough and with enough force, so it's arguable
'bulletproof' is a misnomer.
Throughout history there have been some notable, and also
peculiar, methods of protecting individuals from those who attempt to do them
harm with firearms. Dr.
George E. Goodfellow of Tombstone, Arizona Territory, had much particular
interest, as he made a significant living treating the gun shot wounds of
lawmen and outlaws, including the Earp brothers after the infamous gunfight at
O.K. Corral. Goodfellow found a few cases where silk apparel had saved the
lives of gunshot victims and wrote an article about his findings in an early
medical journal. In short course, gangsters were buying $800 (with inflation: $18,000)
silk vests as bullet armor.
It's true that silk has some rudimentary bullet-stopping
properties, due to its elongation and strength. A 2014
study found that Archduke Franz Ferdinand's life, and possibly all those
lost in the ensuing war, would have been saved had the Archduke elected to wear
his silk armor on June 28, 1914. Spider silk is considered the premier source
of silk for bulletproofing, and there is hope it could
one day be integrated into body armor for soldiers and police, though it's
difficult to harvest in amounts needed for scaled manufacturing.
 Other bulletproofing technologies have ranged from mystical garments to plates
of metals, polymers, and ceramic integrated into apparel. In the 1970s Kevlar
was developed, and virtually every item of ballistics body armor utilizes
aramid fibers today, usually in conjunction with plating. While this type of
armor is much more effective than silk, it also fails when bullets hit near
each other, and can be defeated by certain types of firearms or rounds. It's
also quite heavy, which tires and reduces the mobility of its wearer.
But could a truly bulletproof material be on the way?
Graphene is often heralded as a breakthrough material, but
reports on the material typically focus on its electric properties. A 2014 study laser-fired
miniscule (1/10th the width of a human hair) bullets at 3 km/second
at layers of graphene stacked up to 300 layers thick. Researchers found that
the graphene stretched and slowed down the bullet, thanks to the way graphene
distributes kinetic energy. Tensile
stress travels through graphene at a speed of 22.2 km/second, faster than any
other material. Graphene performs twice as well as Kevlar, and ten
times better than steel in comparable ballistics tests.
 Meanwhile, Afsaneh Rabiei, an engineering professor at North
Carolina State University, has been working on composite metal foams
(CMFs).Metal foams include gaseous pores within the material, and are
manufactured by bubbling gas through molten metal or casting metallic alloy
around metal spheres. Because of this construction they are incredibly
lightweight. In ballistics tests, a 7.62 x 63 mm armor-piercing round was fired at a CMF mass according to body armor
standards established by the National Institute of Justice. The result was that
the bullet completely disintegrated upon impact, and the CMF was indented only
8 mm, while NIJ standards allows up 44 mm of indentation.
Will either graphene or CMFs become the material
of choice for the next Popemobile? It's unknown. However, significant research
into the ballistics resistance of these two materials can be expected, because
governments will be eager to protect leaders, soldiers, police and everyone in
between.
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Re: Can a Material be Truly 'Bulletproof'?
