Peter fabian ACE with the evolution of Windshield

1. Bullet resistance & civilian vehicles, is this
possible?
Evolution of the windshield:
Auto glass has changed dramatically over the years. When first introduced early
1905, windshields were flat. So too were the side and rear windows. The glass
construction was sufficient to block the wind and rain. No further thought was give to
the auto glass until a series of lawsuits led up to the development of stronger
windshields. The most notable example of this is the Pane vs. Ford case of 1917 that
decided against Pane in that he was only injured through impaired driving. They
were replaced with windshields made of toughened glass and were fitted in the
frame using a rubber or neoprene seal. The hardened glass shattered into many
mostly harmless fragments when the windshield broke.
These windshields, however, could shatter from a simple stone chip. In 1919, The
Ford Motor Company solved the problem of flying debris by using the new French
technology of glass laminating. Windshields made using this process were two layers
of glass with a cellulose inner layer. This inner layer held the glass together when it
fractured. Between 1919 and 1929, Ford ordered the use of laminated glass on all of
his vehicles.
Modern, glued-in windshields contribute to the vehicle's rigidity, but the main force
for innovation has historically been the need to prevent injury from sharp glass
fragments. Almost all nations now require windshields to stay in one piece even if
broken, except if pierced by a strong force. Properly installed automobile windshields
are also essential to safety; along with the roof of the car, they provide protection to
the vehicle's occupants in the case of a roll-over accident.

2. Over time aerodynamics and auto styling changed this and glass took on various
shapes and sizes.
In 1921, German inventor Edmund
Rumpler created the Rumpler-
Tropfenauto, which translates into
"tear-drop car." Based on the most
aerodynamic shape in nature, the
teardrop, it had a Cd of just .27, but
its unique looks never caught on with
the public. The German design
changed not only the body but too the
glass.
On the American side, one of the
biggest leaps ahead in aerodynamic
design came in the 1930s with the
Chrysler Airflow. Inspired by birds in
flight, the Airflow was one of the first
cars designed with aerodynamics in
mind however major changes began
in the mid forties and fifties with
pickup and cars having an X-Y curve
introduced.
Looking at this example you can see
that the windshield has an ‘X’ (flat)
straight line in the vertical and the ‘Y’
axis has a severe curve wrapping
around the sides providing a stylistic
aerodynamics. All of these
construction present unique issues
should the requirement be to retro fit
a product onto it that would resist
bullets of any speed or threat.
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3. In modern times auto glass is still a challenge in order to take a off the market
civilian piece of auto glass and retro fit a product that will adhere sufficiently enough
to resist projectiles. Auto glass has changed once again beginning in the 1980’s with
windshields that adopted a third axis, the ‘C’ curve. As illustrated below, auto glass
has three curvatures, the X,Y,Z.
In order to apply or retro fit a soft plastic bullet resistant material without creating
any serious visible distortion a low level small arms fire solution exists whereby when
applying the ASLX vertical seems (butt joints) are incorporated in order to track the
surface of the glass without interruption on the horizontal plane. As thick P.E.T.
cannot be heat shrunk satisfactorily, the only other method to adhering would be to
custom tailor the ASLX Security Laminate to fit the specimen allowing room for
thermodynamic reactions to the air conditioning and heating system in the vehicle,
along with exterior weather and temperate changes.
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4. Side glass in automobiles
Side glass in cars, SUV’s, pick-ups, Vans, etc,… for the vast majority pose little or no
problem as they are either flat or are limited to the X-Y curvatures.
The depth of the curvature at times
will pose a problem for the installer,
however as of 2010, we have not
encountered any reason to install
ACE’s ASLX security laminates
imposing a horizontal seam or butt
joint.
When installing the ASLX on side glass
the glass must be removed. Installing
the security laminate as if it was a
window tint would be dangerous. The
auto-glass goes deep into the door,
and if you were to install in a ‘line of
sight’ fashion you would have it that
once the window is hit from the first
projectile that window would fold right
at the edge of the door where the
glass and door meet, leaving the
occupant at risk.
In addition by installing the security
laminate to the whole surface of the
glass, you have added an addition
security feature that protects the lower
abdomen, and thighs of the occupants.
Removing the glass from a door is a
relatively easy task, it a matter of
removing the panel and 2 screws that
hold the window into the winding
mechanism referred to as the
‘regulator’.
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5. Summary:
Small arms fire, projectiles traveling less than 1000 feet per second can be
successfully resisted on auto-glass. As each make and model of car differs so too
does the style, thickness and quality of tempering differ.
It is ACE’s recommendation that before anyone proceeds to retro-fit a vehicle with
ACE’s ASLX that a pre-test (given the threat risk) and verify if in fact that this
product meets with your criteria and tolerance.
It was by doing this that the Federal Police in Mexico went a head using ACE, and so
to the Military Police in Guatemala protecting their officers out on patrol, and more
recently the Indian Military protecting their soldiers from close range high powered
weapons. Amour Vehicles, US and Canadian APC’s in Afghanistan/Iraq are using
ACE’s ASLX ensuring their people are safe and secure.
Glass/
UL Threat Stopped
Security Laminates P.E.T.
Protection Level (example) Thickness inch
I 9 mm .25 PASS
II .357 Magnum .40 PASS
III 44 Magnum .43 PASS
IV 30 Calibre N/A
V 30 Calibre N/A
VIII 7.62 mm N/A
IMPORTANT: When it
comes to defending
yourself, using
traditional bullet proof
glass that was not an
option, however, the
smart design of the
ASLX allows security
forces from within the
vehicle the ability to
shoot first, or return
fire. All the while what
was once a window of
vulnerability not
becomes your shield of
defence!
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6. How Can I Determine If Glass Is Tempered?
Tempered glass, or safety glass, is formed by sealing two pieces of glass together
with a clear resin. Instead of shattering into shards upon breakage like normal glass,
tempered glass is designed to hold together under light breakage conditions or
shatter into very small pieces during severe breakage conditions. Due to these
qualities, tempered safety glass is used in such products as automobile windows,
shower doors, microwaves and stained glass windows.
You can try polarized sunglasses. If you look at the piece of glass while
wearing them, you might see various rainbow patterns in the glass, obscuring
your view. This is why polarized lenses are not recommended for driving; the
side windows on cars are tempered
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7. Tempered safety glass is a single piece
of glass that gets tempered using a
process that heats, and then quickly
cools, the glass to harden it. The
tempering process increases the
strength of the glass to five to 10
times that of untempered glass.
Tempered safety glass breaks
differently than regular clear glass.
When tempered safety glass is struck
it does not break into sharp jagged
pieces of shrapnel-like glass as normal
window panes or mirrors do. Instead,
it breaks into little pebble-like pieces,
without sharp edges. It is used in the
side and rear windows of automobiles.
When certain high grade ballistics
laminates or Ceramic laminates are
applied to glass, a rainbow effect
occurs in lower quality of tempered
glass or tempered glass that has not
reached its full heat treatment when
being processed. The greater
contraction of the inner layer during
manufacturing induces compressive
stresses in the surface of the glass
balanced by tensile stresses in the
body of the glass.
For glass to be considered toughened, this compressive stress on the surface of the
glass should be a minimum of 69 MPa.
For it to be considered safety glass, the surface compressive stress should exceed
100 MPa. The greater the surface stress, the smaller the glass particles will be when
broken.
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8. It is this compressive stress that gives the toughened glass increased strength. This
is because any surface flaws tend to be pressed closed by the retained compressive
forces, while the core layer remains relatively free of the defects which could cause a
crack to begin. However, the toughened glass surface is not as hard as annealed
plate glass and is therefore somewhat more susceptible to scratching. To prevent
this, toughened glass manufacturers may apply various coatings and/or laminates to
the surface of the glass.
Toughened glass is made from annealed plate glass via a thermal tempering process.
The glass is placed onto a roller table, taking it through a furnace that heats it above
its annealing point of about 720 °C. The glass is then rapidly cooled with forced air
drafts while the inner portion remains free to flow for a short time.
An alternative chemical process involves forcing a surface layer of glass at least
0.1mm thick into compression by ion exchange of the sodium ions in the glass
surface with the 30% larger potassium ions, by immersion of the glass into a bath of
molten potassium nitrate. Chemical toughening results in increased toughness
compared with thermal toughening, and can be applied to glass objects of complex
shape.
Advantages
The term toughened glass is generally used to describe fully tempered glass but is
sometimes used to describe heat strengthened glass as both types undergo a
thermal 'toughening' process.
There are two main types of heat treated glass, heat strengthened and fully
tempered. Heat strengthened glass is twice as strong as annealed glass while fully
tempered glass is typically four to six times the strength of annealed glass and
withstands heating in microwave ovens. The difference is the residual stress in the
edge and glass surface. Fully tempered glass in the Canada and the US is generally
rated above 65 MPa (9427 psi) in pressure-resistance while Heat Strengthened glass
is between 40 and 55 megapascals (5801 and 7977 psi respectively).
It is important to note that the tempering process does not change the stiffness of
the glass. Annealed glass deflects the same amount as tempered glass under the
same load, all else being equal. But Tempered glass will take a larger load, and
therefore deflect further at break.
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9. Disadvantages
Toughened glass must be cut to size or pressed to shape before toughening and
cannot be re-worked once toughened. Polishing the edges or drilling holes in the
glass is carried out before the toughening process starts. Because of the balanced
stresses in the glass, damage to the glass will eventually result in the glass
shattering into thumbnail-sized pieces.
The glass is most susceptible to breakage due to damage to the edge of the glass
where the tensile stress is the greatest, but shattering can also occur in the event of
a hard impact in the middle of the glass pane or if the impact is concentrated (for
example, striking the glass with a point). Using toughened glass can pose a security
risk in some situations because of the tendency of the glass to shatter completely
upon hard impact rather than leaving shards in the window frame.
The surface of tempered glass does exhibit surface waves caused by contact with the
rollers. This waviness is a significant problem when applying solar control or ceramic
films to tempered glass.
Key Quality Areas
1. Optical Distortion – Heat-strengthened glass that is manufactured in a
horizontal tempering furnace may contain slight surface waves caused by contact
with the rollers. This waviness or roller distortion can be detected when viewing
reflected images from a distance. Orientation of the glass in the furnace is critical
in order to minimize the appearance of the roll wave distortion. It is
recommended that the roller wave be oriented parallel to the horizontal glass
dimension.
2. Flatness – Heat-strengthened glass products are not as flat as flat as annealed
glass due to processes used in manufacturing . For heat–treated glass products,
the deviation for flatness is a function of thickness. Width, length and other
factors. Usually, increasing thickness yields flatter products.
3. Strain Pattern - For heat-strengthened, a strain pattern or iridescence, which is
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10. not normally visible, can become visible under certain light conditions especially
polarized sky conditions. This is an inherent characteristics of heat –processed
glass and should not be mistaken as discoloration or non uniform tint or color.
Strain pattern is a result of air quenching (cooling) of the glass and is not
considered a defect.
4. Bow & Warp- Since heat-strengthened are reheated to their softening points
and rapidly cooled, a certain amount of wrap and bow is associated with each
glass piece due to the resulting stress. Although warp and bow is not generally a
significant factor to the design professional , it may appear as distorted reflected
images under certain viewing conditions. For instances, it will be more noticeable
in reflective glass. And, it is an inherent characteristics of heat-treated glass and
is not considered a defect.
7. Scratches – Inspect glass from a distance of 10 ft.(3 m). Scratches up to 3”
(76mm) are allowed. Scratches from 3” to 5” (76 mm to 127 mm) are only
allowed within 3” (76 mm) from the edge of the glass. Concentrated scratches or
abraded areas are not allowed.
8. Fragmentation:- Heat Strengthened glass breaks in similar fashion as an
annealed glass breaks so it is not possible to gauge the quality of Heat
Strengthened glass by doing a fragmentation test.
9. Spontaneous Breakage:- Heat Treated glass on rare occasion shatters for no
apparent reason. The main reason for this are the presence of a microscopic
inclusion known as Nickel Sulfide (NiS). NiS in annealed float glass do not pose
an treat to the glass because during annealing the NiS gets sufficient time to
loose its energy and reach its stable condition. Once the raw glass containing NiS
is tempered the NiS stone gains energy and become unstable. So when it is
installed at site it get impetus with temperature difference and various pressure
to release its energy and break. Many research is done to eliminate the NiS stone
from the float tank but till this time it is impossible to remove it from the raw
material. Spontaneous breakage don’t depend upon the quality of tempering, if
there is a presence of NiS in tempered glass then there is a possibility of
breakage.
Typically the NiS induced breakage
will be in the first 2-3 years and then
the rate drastically reduce. Research
reveals that 1 to 2 % of tempered
glass panes break due to NiS
inclusions. NiS induced fracture
reduces by the factor of 20 for heat
strengthen glass as the cooling rates
is slower allowing NiS particles to
return back to their stable state.
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11. Properties & specification
1. Density (approximate) : 2.42-2.52 g/cubic cm
2. Tensile Strength : 120 to 200 N/sq .mm
3. Compressive Strength : 1000 N/sq.mm
4. Modulus of Elasticity : 70Gpa-
5. Coefficient of linear expansion : 9 x 10-^6 m/Mk
6. U Value : 5.7 W/sq .m.K for 6mm thick clear.
7. SF for 6 mm clear 81 %
8 Shading coefficient of 6 mm clear .93
9 Selectivity 1
10 Visible light transmission of 6 mm clear 87 %
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