Note: Descriptions are shown in the official language in which they were submitted.
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Antiballistic protective helmet
* *
Description:
The invention relates to a helmet, in particular an anti-
ballistic protective helmet, consisting of a plurality of
textile fabric layers embedded in a matrix and joined to
one another via this matrix.
20
Helmets for military and police forces are normally anti-
ballistic helmets, i.e., these helmets have a retarding ~ef-
fect on bullets and fragments, thus protecting the helmet
wearer from head injuries due to projectile impact.
The protective layers of such helmets usually comprise
woven fabrics made from antiballistic fibers, such as ara-
mide fibers. Helmets containing 15 layers of aramide fab-
ric, impregnated with phenolic resins and pressed together
after being cut to a shape appropriate for helmet manufac-
ture, are encountered very frequently as antiballistic head
protection.
Normally, the protective layers of such helmets are woven
fabrics, but the use of knitted fabrics has also been pro-
posed in this case. For example, in DE-A 38 06 204 "woven
and knitted fabrics with open knit structure" are mentioned
for the manufacture of helmets. Likewise, US-A 4 343 047
mentions knitted or woven textile fabrics for helmet manu-
facture.
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Finally, in an article in a magazine of a manufacturer of
aramide fibers (Du Pont Magazine, 1988, No. 1, pp. 10-13),
"caps knitted from Kevlar~~ are cited as precursors for hel-
:mets (Kevlar is a trademark for an aramide fiber of this
:manufacturer) .
All these publications see the knitted fabric as an alter-
native to woven fabric, i.e., the teaching can be derived
from these publications that the reinforcement layers of an
antiballistic helmet are to be made from either woven or
knitted fabric. The possibility of using a combination of
' woven and knitted fabric in a helmet is not mentioned, nor
can it be inferred from these documents what type.of knit
ted fabric is considered best suited for use in a helmet.
Advancing antiballistic protective clothing, including hel-
mets, with the aim of improving the protective action
against the impact of projectiles, fragments, etc., is a
continuing task for those involved in developing such
clothing, since each step forward preserves human life and
protects against injuries. This has promoted the task of
further developing the protective action of antiballistic
helmets.
-
Surprisingly, it has been found that this succeeds particu-
larly well if the outer protective layers of the helmet,
i.e., the textile-fabric protective layers on the side away
from the wearer and thus the side initially exposed to bom-
bardment, are formed from multiaxial knitted fabric made
from antiballistic fibers.
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Textile fabrics are understood to comprise all fabrics made
from fiber materials such as woven fabrics, knitted fab-
rics, nonwoven fabrics, thread composites, etc. Of particu-
lar importance for the helmet of the invention are knitted
and woven fabrics.
Antiballistic fibers comprise all fiber materials that, in
the form of textile fabrics, stop or significantly retard
smaller objects moving at high speed, such as projectiles,
fragments, etc.
Examples of antiballistic fibers are aramide fibers, poly-
ethylene fibers spun using the gel spinning process, glass
fibers, and metal fibers. Aramide fibers are preferred for
making the helmet of the invention.
Aramide fibers, also called aromatic polyamide fibers, are
generally well known for the manufacture of protective
clothing. They are commercially available under names such
as Twaron, for example.
The aramide fibers can be present in the multiaxial knitted
. fabric and woven fabric either alone or in blends with
other fibers. In the interest of good antiballistic effec-
tiveness, it is preferred when using blends to blend ara-
mide fibers with other antiballistic fibers.
The yarns to be used for manufacturing multiaxial knitted
fabrics or woven fabrics can be filament or spun-fiber
yarns. Due to the strength attainable with filament yarns,
they are preferred. There are no restrictions with respect
to the titer of the yarns to be used, which can be between
500 and 4 000 dtex, for example.
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Multiaxial knitted fabrics are thread composites with a
plurality of axes, having at least two thread systems and~_ -
joined with each other in a knitting process by a loop
forming thread or a stitching warp. The multiaxial knitted
fabrics are usually considered to be knitted fabrics. How-
ever, the structure is on the border between knitted fabric
and thread composite. The multiaxial knitted fabric is
therefore in part also referred to as a knitted multiaxial
thread composite.
In principle it is also possible to use monoaxial struc-
tures, such as a normal warp knitted fabric, to manufacture
the helmet of the invention. Multiaxial structures have
proven better suited, however.
In the manufacture of the multi,axial knitted fabric, up to
eight thread systems can be used in the machines known in
the art. To make the helmet of the invention, a multiaxial
knitted fabric with three to four thread systems is pre-
ferred. However, the invention is not limited to a specific
type of multiaxial knitted fabric or to a specific number
of thread systems; rather, it includes all variations of
this class of materials.
In addition to the possible variations in the number of
thread systems, a multiaxial knitted fabric offers an addi-
tional possibility to configure the arrangement of the sys-
tems, which is characterized by specification of an angle.
The baseline is 0°, which forms the longitudinal axis of
the fabric in the direction of production. This 0° line,
therefore, is understood to be the axis through the center
of the web equidistant from the two edges.
a
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The arrangement of the other thread systems is given in an-
gles relative to this longitudinal axis,. or 0° line, where
the thread systems to the right of the 0° line, as viewed
5 in the fabric direction of travel, are normally designated
:by positive angles and those situated to the left by nega-
tive angles. Angles between 30° and 60° are possible. Addi-
tional thread systems can run perpendicular to the longitu-
dinal axis and thus form an angle of 90°, by which they are
designated.
The reinforcement of the thread composites produced in this
manner is effected by a so-called knitting thread, which
usually runs along the 0°, axis. If, during manufacture of
the multiaxial knitted fabrics, blends of antiballistic and
non-antiballistic fibers are used, it is practical to em-
ploy the non-antiballistic fiber material for the knitting
thread and preferably antiballistic fibers for the other
thread systems.
The manufacture of the multiaxial fabric is performed on
' . machines well known in the textile art, which are usually
referred to as warp knitting machines with multiaxial weft-
insertion systems.
The weight per unit area of the multiaxial knitted fabric
should be between 200 and 600 g/m2, a range of 300 to 500
g/m2 being preferred.
The multiaxial knitted fabric is used for layers in the
outer portion of the helmet, i.e. on the side facing away
from the wearer. In these layers, the advantages of the
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multiaxial knitted fabric are most pronounced, as will be
demonstrated in the embodiment examples.
:for example, a helmet comprises 15 layers of a textile fab-
ric made from antiballistic fibers. Of these layers, from
outside to inside, the layers 1-10 or 1-12, for example,
can be made from multiaxial knitted fabric and layers 11-15
or 13-15 from woven fabric. Both textile fabrics are made
from antiballistic fibers, such as aramide fibers. The
overall percentage of multiaxial knitted fabric in the re-
enforcement layers is 50-90~ by weight, preferably 60-80~
by weight.
It is also possible to make the helmet with portions less
than 50~, with respect to all reinforcement layers, but
better results have been obtained if the weight percentage
of the multiaxial knitted fabric layers exceeds that of the
woven fabric layers.
The woven fabric layers as well as the multiaxial knitted
fabric layers are treated with a polymer that forms the ma-
trix in the helmet. For example, this can be a phenolic
resin. The amount of matrix material applied is normally 10
to 30~, preferably 10 to 20~, with respect to the dry
weight of the textile fabric before treatment. For example,
a phenolic resin application of 55 g/m2 can be made to a
multiaxial knitted fabric with a weight per unit area of
410 g/m2, corresponding to an applied quantity of 13.4.
In addition to phenolic resin, other polymers canebe used
as matrix material for antiballistic helmets. A large num-
ber of polymers in the duromer, elastomer, and thermoplas-
tic categories are suitable. Example of usable products are
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'vinyl esters, epoxy resins, acrylic resins, unsaturated
polyesters, and alkyd resins. Because they are well suited
for antiballistic articles and are also nonflammable, phe-
:nolic resins are preferred.
As will be shown in the embodiment examples, the positiv<~
effect of the multiaxial knitted fabric is surprisingly
pronounced when this fabric is used in combination with a
conventional woven fabric in the helmet, i.e., when the
outer layers of the helmet comprise multiaxial knitted fab-
ric and the inner layers woven fabric. The antiballistic
properties are significantly better in this combination
than with helmets employing solely multiaxial knitted fab-
ric or solely woven fabric, in both cases-made from anti-
ballistic fibers.
The arrangement of the invention of-the textile fabric lay-
ers embedded in a matrix and joined with each other via
this matrix exhibits particularly good antiballistic effec-
tiveness under the bombardment of helmets by fragments. In
addition to helmets, however, other antiballistic materials
such as vehicle armor, projectile-inhibiting movable barri-
ers, etc., can be constructed in a similar manner, whereby
the multiaxial knitted fabric in each case is placed on the
side which is expected to recei~cre the projectiles or frag-
ments.
Up to now, there has not been an adequate explanation for
the quite surprising antiballistic action of the helmet of
the invention. One possible reason could be that during
bombardment of a helmet containing multiaxial knitted fab-
ric in the outer layers, the deformation waves that trans-
port the energy received by the textile fabric can propa-
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gate particularly undisturbed due to the orientation of the
thread layers. For a woven fabric, this is not possible due
to its construction resulting from the mutual enlacing
of the thread systems.
As will be shown in more detail in the embodiment examples,
a significant improvement can be attained with the helmet
of the invention compared to conventional helmets, thus
making an important contribution to the increased safety of
the wearers of such helmets.
Embodiment examples
Embodiment example 1
This example describes the manufacture of the woven fabrics
used in the trials. In this case, an aramide-fiber filament
yarn with a titer of 3 360 dtex was woven into fabric in
plain weave with a thread count of 6.2/cm each in warp and
weft. The weight per unit area of the resulting fabric was
412 g/m2.
This fabric was impregnated with a phenolic resin. The
resin application was 12~, i.e., the weight per unit area
of the impregnated woven fabric after drying was 461 g/m2.
Embodiment example 2
This example describes the manufacture of the multiaxial
' . knitted fabric. On a warp knitting machine with multiaxial
weft-insertion system, known as System Liba, aramide-fiber
filament yarn with a titer of 3 360 dtex was processed into
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a multiaxial knitted fabric. Three thread systems. were
used, at angles of +45°, -45°, and 90°. All three systems
and the knitting thread were made of the.same yarn. The
weight per unit area of the resulting fabric was 409 g/m2.
The resulting multiaxial knitted fabric was impregnated
with a phenolic resin. The resin application was 12~, i.e.,
the weight per unit area of the impregnated multiaxial
knitted fabric after drying was 458 g/m2.
Embodiment example 3
The woven fabric from embodiment example 1 and the multiax-
ial knitted fabric from embodiment example 2 were processed
together into a helmet. Cutouts suitable for helmet con-
struction were made from ll layers of the multiaxial knit-
ted fabric and 4 layers of the woven fabric. For each
layer, a so-called rose pattern was prepared. This is a
form based on the helmet shape with a round or oval middle
. 20 section and multiple side sections, for example with an ap-
proximate trapezoid shape.
The individual rose patterns are inserted in the helmet
mold such that the raw edges of the side sections are not
directly superimposed but rather the side section of the
upper layer slightly covers the raw edge of the layer un-
derneath it and thus overlaps the adjacent cutout. The in-
dividual layers are then pressed together, whereby the
polymer applied to the textile fabrics forms the matrix.
This method for making antiballistic helmets is generally
well known in the helmet industry.
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The arrangement of the individual layers was such that the
:helmet contained, from the outside to inside, 11 layers of
multiaxial knitted fabric as produced in embodiment example
2 and 4 woven-fabric layers as produced in embodiment exam-
s ple 1.
This helmet was subjected to fragment bombardment in accor-
dance with STANAG 2920. The bombardment used 1.1 g frag-
ments. The resulting V50 value was 720 m/sec. This value
~10 means that the penetration probability is 50~ at the given
bombardment speed.
Embodiment example 4
Embodiment example 3 was repeated using 10 layers of the
multiaxial knitted fabric as produced in embodiment example
2 and 5 woven-fabric layers as produced in embodiment exam-
ple 1. The helmet, manufactured as described for embodiment
example 3, therefore had, from the outside to inside, 10
layers of multiaxial knitted fabric and 5 layers of woven
fabric.
This helmet was subjected to fragment bombardment in accor-
dance with STANAG 2920. The bombardment used 1.1 g frag-
ments. The resulting V50 value was 710 m/sec.
Embodiment example 5
Embodiment example 3 was repeated using-12 layers of the
multiaxial knitted fabric as produced in embodiment example
2 and 3 woven-fabric layers as produced in embodiment exam-
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ple 1. The helmet, manufactured as described for embodiment
example 3, therefore had, from the outside to inside, 12
layers of multiaxial knitted fabric arid3 layers of woven
fabric.
This helmet was subjected to .fragment bombardment in accor-
dance with STANAG 2920. The bombardment used 1.1 g frag-
ments. The resulting V50 value was 710 m/sec.
Comparative example 1
Using the method described in embodiment example 3, a helmet
was produced with 15 layers of a woven fabric made as described
in embodiment example 1. ;
This helmet was subjected to fragment bombardment in accordance
with STANAG 2920. The bombardment used 1.1 g fragments. The
. resulting V50 value was 640 m/sec.
Comparison of the results of this example with those of
embodiment examples 3-5 shows that a helmet constructed in
accordance with examples 3-5 from a combination of woven and
multiaxial knitted fabrics has significantly better
antiballistic effectiveness than one made solely from woven
fabric .
Embodiment example 2A
15 layers of multiaxial knitted fabric as produced in
embodiment example 2 were processed into a helmet using the
method described in embodiment example 3.
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This helmet was subjected to fragment bombardment in accordance
with STANAG 2920. The bombardment used 1.1 g fragments. The
resulting V50 value was 675 m/sec.
Comparison of the results of this example with those of
embodiment examples 3-5 and comparative example 1 shows that a
helmet produced from a combination ofwoven and multiaxial
knitted fabrics according to examples~3-5 has not only a
significantly better antiballistic act=ion than one made solely
from woven fabric, but also a better antiballistic action than
one made solely from multiaxial knitted fabric.
i~omparative example 3
.An aramide-fiber filament yarn with a'titer of 3 360 dtex was
processed on a knitting machine to a knitted fabric with a
weight per unit area of 458 g/m2. Subsequently, the fabric was
impregnated with phenolic resin. After this treatment and
;subsequent drying, the knitted fabric had a weight per unit
area of 513 g/m2.
7?rom a total of 13 layers of the knitted fabric, a helmet was
~~roduced using the method described for embodiment example 3.
The number of layers was reduced compared to that in embodiment
example 3, comparative example 1, and embodiment example 2A,
. since the use of. l5 layers would have resulted in an excessive
i=otal weight and comparison would not have been possible.
The resulting helmet was subjected to fragment bombardment in
accordance with STANAG 2920. The bombardment used 1.1 g
fragments. The resulting V50 value was 465 m/sec.
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Comparative example 4
An aramide-fiber filament yarn with a titer of 3 360 dtex was
processed on a warp knitting machine to a warp knitted fabric
with monoaxial structure-and a weight per unit area of 462
g/m2. Subsequently, the fabric was impregnated with phenolic
resin. After this treatment and subsequent drying, the fabric
had a weight per unit area of 517 g/m2.
From a total of 13 layers of this warp knitted fabric, a helmet
was produced using the method described in embodiment example
3. As in comparative example 3, the number of layers was also
reduced compared to that in embodiment example 3, comparative
example 1, and embodiment example 2A, since the use of 15
layers would have resulted in:an excessive total weight.
The resulting helmet was subjected to fragment bombardment in
accordance with STANAG 2920. The bombardment used 1.1 g
fragments. The resulting V50 value was 630 m/sec.
Comparative examples 3 and 4 show that the results with other
types of knitted fabrics, as shown here with a knitted or warp
knitted fabric, cannot approach the good results obtained with
multiaxial knitted fabric (embodiment example 2A).
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The results obtained in the embodiment and comparative examples
a:re summarized in the following table:
Helmet V50
layers m/sec
Embod. example 3 11 MA+ 720
4 W
E:mbod. example 4 10 MA+ 710
W
Embod. example 5 12 MA+ 710
3 W
Comp. example 1 15 W 640
Embod. example 2A 15 MA 675
Comp. example 3 13 K 465
Comp. example 4 13 WK 630
Key: MA = multiaxial knitted fabric as produced in embodiment
example 2, W = woven fabric as produced in embodiment example
1, K = knitted fabric as described in comparative example 3, WK
- warp knitted fabric as described in comparative example 4.
