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KEVLAR: More than just the best fibre for ballistic
protection
With the "Ht", "Comfort"
and "H-shell" offerings, KEVLAR
is today's leading product family for soft
and hard ballistic protection such as bullet
and fragment resistant vests, helmets and
hard armour.
However, KEVLAR offers much more than just
lightweight protection for police and military
forces, DuPont's para-armid fibre has all
the technical properties which make KEVLAR
vests well adapted to the severe environtments
in which thyey are required to perform. These
include extrames of heat, cold and humidity
(even totally saturated) during missions which
demand full mobility and absence of discomfort
for extended periods with total retention
of protective performance.
The optimum ballistic vest is one that is
able to offer a combination of several key
properties simultaneously rather than just
one at a time. We will review some of these
properties:
1. Weight:
The lightest bullet-resistant vest can be
designed with KEVLAR
Most bullet resistant vests are designed to
counter 9 mm FMJ (Full Metal Jacket) bullets
from pistols or submachine guns. Weight and
thickness of such vests depend entirely on
the ballistic resistance of their protective
pack to this type of ammunition.
Fig. 1 compares the typical
weights of concealable vests made with KEVLAR
"Comfort", KEVLAR "Ht",
KEVLAR 29 and UHMWPE (ultra high molecular
weight polyethylene) unidirectinal sheet packs,
all intended to defeat a 9 mm FMJ Geco bullet
at 410+/- 10m/s.
Fig. 1 shows that the lightest vest to defeat
9mm FMJ Geco bullets are made of KEVLAR "Ht"
and KEVLAR "Comfort".
2. Wet performance:
The ballistic resistance of KEVLAR is pratically
unaffested by moisture
Any ballistic pack made of several layers
of material stitched together will retain
moisture after being saturated with water.
The water says between the layers and acts
as a lubricant, aiding a projectile to penetrate
the structure. For this reason, fabrics of
KEVLAR used for ballistic vests are treated
with a water-repellent according to a procedure
specialy developed for ballistic fabricsof
KEVLAR.
3. Trauma
Vests made with KEVLAR can meet the most stringent
anti-trauma requirements
A detailed casualty reduction analysis has
been conducted within the police community
in the US since 1972. During the more than
20 years of the survey, the lives of more
than 1700 policemen have been saved because
they were wearing KEVLAR vests. There was
no recorded casualty as the result of trauma
or excessive backface deformation of the vests
during impact.
There is general agreement amoung users that
44 mm is an acceptable upper limit for backface
deformation of a vest when hit by bullet.
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Solutions exist to bring backface deformation down
from 44 mm to 30 mm or even 25 mm if necessary.
Fig. 3 compares backfaces deformation of a light
and flexible 100% KEVLAR "Ht" pack without
stiching (5.4 Kg/m2 pack areal density), a 100%
UHMWPE unidirectional sheet pack (5.4 Kg/m2 pack
areal density), and 100% KEVLAR "Ht" pack
made of KEVLAR "Ht" and KEVLAR anti-trauma
pack (5.55 Kg/m2 total areal density). All three
packs defeated the 9 mm FMJ bullet at 410 +/- 10
m/s.
Fig 3 confirms
that the use of KEVLAR anti-trauma combined with
KEVLAR "Ht" brings down backface deformation
under 25 mm. Trauma is reduced from 27 mm to 23
mm with only a 2.8% weight penalty versus a 100%
KEVLAR "Ht" pack. The pack also keeps
most of its flexibility.
Contrary to most of the anti-trauma materials generally
used, such as fleece, non balistic fabrics, plastic
films or sheet, foams or honeycomb structures, KEVLAR
anti-trauma does not add thickness to the ballistic
pack.
KEVLAR anti-trauma is a KEVLAR fabric coated with
resin which contributes to the ballistic resistance
of the vest.
4. Wearlife:
KEVLAR is a durable product wwhich is not affected
by age
The durabilty of KEVLAR is due to the fibrès inherent
high mechanical, thermal and chemical resistence.
The US National Institute of Justice has tested
the ballistic of 10-year old KEVLAR vests. (NIJ,
Technology Assessment Program, August 1986, vol.1,
no.4: Old armor tests as good as new). Its conclusiions
are that "...age alone does not cause the ballistic
resistance of armor to deteriorate. Rather, the
kind of care and maintenance the garment receives
is a more important factor".
The German Police compared ballistic resistance
(V50) of 10-year old KEVLAR vests to new ones and
concluded that the fiveyears of wear did not affect
the ballistic resistance of vests (Ballistische
Haltbarkeit von Schutzwesten "Alter schützt
so gut wie neu", PVT 9/89, by Dpl.-Phys. H.-R.
Damm).
According to data collected since 1972 by the KEVLAR
Survivors Club and the International Association
of Chiefs of Police (IACP), more than 1700 officiers
live were saved by KEVLAR body armour. Only KEVLAR
aramid fibre has demonstrated more than 20 years
of flawless field performance.
We can conclude from these statistic that KEVLAR
vests can meet end-user expectations even after
10 years of wear. Nevertheless, we racommended a
regular inspection of the vests for areas of excessive
wear which could becoma damaged by accident.
5. Comfort:
KEVLAR ballistic vests are the most comfortable
The times are over when ballistic vests were stiff
and heavy. The latest KEVLAR vests and particulary
those made with KEVLAR "Comfort" are comfortable
to wear over long periods. A ballistic pack made
of KEVLAR is:
Light less heat and perspiration are generated during
intensive wear.
Thin stays cool because of higher water vapour permeability
and better evacuation of perspiration through the
ballistic pack.
stays cool because of reduced thermal barrier effect.
Flexible perfect fit to the body
100% textile soft and breathable (compared with
a stiff and sealed plastic sheet)
Conclusion
KEVLAR vests provide ballistic protection against
the most severe types of ammunition and threats,
while being the lightest, thinnest and most comfortable
vests to wear.
In addition, KEVLAR provides key advantages such
as non-flammability, heat resistance and high durability.
The KEVLAR vest is based on the latest technological
advances and demonstrated its superiority to all
other anti-ballistic materials.
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