Bullet Proof Glass

Bullet Proof Materials
Fall 2011
By Kevin Helms, Josh Borrajo, Karan Kanagasabapathy, Raghid Mardini
Bullet Proof Glass
Bulletproof glass is an optically transparent material that is
resistant to being penetrated by bullets.
It’s better referred to as bullet resistant glass, because it’s not
completely impenetrable.
It has applications in places where you need the protection
of a bullet resistant material, without sacrificing the
advantage of optical clarity.
For example it has uses in the military, defense and security,
and in transaction windows at places like banks, gas
stations, and other business that have a high probability of
being robbed.
It’s made out of multiple materials layered and joined
together, because no one material has the properties needed
to stop a bullet.
Polycarbonate is a thermoplastic polymer.
Polymers are large molecules composed of repeating structural
units in long chains.
There are both natural and synthetic polymers. Examples of
natural polymers include wood, rubber, cotton, wool, leather,
and silk. Synthetic examples include polycarbonate, plexiglass,
and PVC.
Thermoplastic polymers are a type of polymer than liquefy
when heated and harden when cooled, a process that is
completely reversible and may be repeated.
Polycarbonate has an ideal application in bulletproof glass, in
that it has a very high strength, and is also optically
Polycarbonate is often used as the “soft” material in
bulletproof glass because it can flex back while holding shards
of broken glass in place.
Polycarbonate is 30x stronger than acrylic, which is 17x
stronger than a sheet of glass of equal thickness.
Laminated Glass
Laminated Glass is a type of safety glass that holds together
when shattered.
Laminated glass is treated with a layer of polyvinyl butyral
that holds the pieces together when it’s shattered.
Polyvinyl butyral is a resin that can provide a strong bond
between two layers of material. It’s tough and ductile,
which when bonded between two layers of glass, prevents
the brittle cracks from passing from one side of the
laminate to the other.
This makes the glass stronger, and also prevents it from
breaking into large sharp pieces when it does fracture.
It’s commonly used in windshields in cars.
How It’s Made
The two (or more) materials are then layered and
molded together under heat and pressure to create
a solid block of bullet resistant material.
Most often it’s just layers of glass, PVB(the
material they laminate glass to make it laminated
glass), and polycarbonate.
However different manufacturers have different
formulas for making their own brands of bullet
proof glass which could differ by layering, materials
used or both.
Depending on how it’s made and the thickness of
the final product, the glass is rated on the level of
protection it offers.
How It Works
Glass is brittle and it does not have a good orderly crystalline
structure. If it did, it would be like a metal steel, where it
dents and deforms instead of shattering.
This allows the glass to absorb the bullet’s energy by
transferring the kinetic energy of the bullet into shattering
the glass.
The softer plastic layer reinforces the glass by holding it in
place and allowing the glass to flex back as it absorbs the
The polycarbonate and laminate also spreads the force of the
bullet laterally across the entire glass surface.
Layering these in multiple sheets allows the window to use
properties of both materials more effectively; such as the glass
on the backside shattering while the undamaged Plexiglas
holds together the window. This also allows the glass to stop
more that one bullet.
Since polycarbonate is very strong, and it does not shatter like
glass it’s an excellent candidate for bulletproofing.
Our Experiment
Originally wanted to test different materials, of different
thicknesses, in different series of layers.
We also wanted to test with two types of guns and multiple shots.
However too expensive, and time consuming.
Small scale experiment with BB gun.
We decided to use Plexiglas (acrylic) and regular glass.
Wanted to test how well these materials stood up to bullets, and
put the current technique to the test to try and understand how
hard and soft layering works.
Our Experiment (Small Scale)
First we tested method using a
BB gun
Used basic concept of bullet
proof glass and layered hard
material (aluminum foil) and
soft material (saran wrap).
Projectile penetrated differently
based on layer combinations
Results of BB gun testing
(Went through)
(Went through)
(Went through)
(Went through)
(Went through first four layers)
(Only went through first layer of Aluminum)
It took 4 layers of Aluminum foil alone to stop the BB
or and 8 layers of only plastic wrap to stop BB.
Large Scale Set Up
Used Plexiglas and standard glass in the place of
polycarbonate and tempered glass.
¼ inch thickness
More affordable, but much weaker.
Used .22 mm rifle.
Fired 1 bullet at each of the 7 different set-ups from
about 10 meters away.
1 layer of acrylic
AA: 2 layers of acrylic
GG: 2 layers of glass
GA: 2 layers (glass/acrylic)
4 layers (glass/acrylic/glass/acrylic)
4 layers (acrylic/glass/acrylic/glass)
4 layers (glass/glass/acrylic/acrylic)
The bullet went through the backboard, which means AA is too weak to stop the bullet.
Bullet bounced off wood, which means that GG is more effective than AA.
Bullet bounce off backboard, with less damage to the window. The ‘A’ layer supported the glass
Stopped the bullet, but the back glass shattered; not practical.
Stopped the bullet with no interior damage.
Stopped the bullet. Same concept as GA, but we had to increase thickness to stop bullet.
What we found out
Karan likes guns!
Alternating layers is more effective.
Having the hard material first was much more effective.
Acrylic instead of polycarbonate still allowed us to stop
a bullet, but we had to increase thickness
Glass shattering absorbs most of the impact, and in
most trials the Plexiglas was unaffected.
Other applications!
Bullet proof glass in aircrafts
Partitioning followed
by integration
Bullet-proof glass used on fighter aircraft initially had a serious defect.
When a bullet hits the glass a network of cracks would form and obstruct
Now the windows are formed of smaller panes of glass, cemented to an
acrylic plastic sheet. Transparent adhesive is used to join the edges of the
glass panes. When a bullet hits, only the affected pane is covered by
Think about possible nanotechnology applications!
ALON is a special variant of alumina (aluminum oxynitride). A white chalk-like
powder is heated to thousands of degrees in a furnace and treated with nitrogen in
a process that allows the ALON to turn into a transparent material which - similar
to other ceramics - has a rigid crystalline structure that gives it strength.
When polished to remove tiny surface defects, the ALON material resembles
sapphire - a gem prized for its hardness and resistance to scratches.
ALON has proven to be a remarkable bullet-resilient material. In tests, a
"sandwich" of transparent ALON, glass and a polymer laminate survived multiple
hits from .30-caliber armor.
The difference: The ALON laminate provides the same antiballistic performance at
half the weight comparing it with traditional bulletproof glass materials.
One-way Bulletproof Glass
What is it made of?
One-way bullet-resistant glass is manufactured by
creating a brittle layer coated with a flexible material
only on one side.
Another method is by making a series of:
glass layers merged in a special manufacturing process
Held together by special glue
How does it work
Polycarbonate material compresses, acrylic
Bullet passes through soft polycarbonate
layer and into acrylic layer which weakens as
it stretches
Bullet shatters acrylic, continuing with no
loss of velocity or deflection
When bullet strikes the acrylic outer layer
(brittle, but very strong when compressed), it
compresses, denses/strengthens, and
absorbs/distributes the energy.
The polycarbonate layer, which has flexible
characteristics, stretches as it dissipates the
remaining bullet energy with no full penetration
Spider webbing occurs on impact side, but
inside glass remains smooth and undamaged.
More Applications!
Gaddafi’s dictator auditorium!
Special Thanks
Arch’s Glass
Tap Plastics

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