U.S. patent application number 12/682642 was filed with the patent office on 2010-09-16 for helmet containing polyethylene fibers.
Invention is credited to Hen H. Hoefnagels, Roelof R. Marissen.
Application Number | 20100229271 12/682642 |
Document ID | / |
Family ID | 39135121 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100229271 |
Kind Code |
A1 |
Marissen; Roelof R. ; et
al. |
September 16, 2010 |
HELMET CONTAINING POLYETHYLENE FIBERS
Abstract
An anti-ballistic helmet (1) having a shell (2) containing
mono-layers of uni-directional ultrahigh molecular weight
polyethylene (UHMwPE) fibers, the shell is at its rim being
connected to a reinforcing profile (3).
Inventors: |
Marissen; Roelof R.; (Born,
NL) ; Hoefnagels; Hen H.; (Hulsberg, NL) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
39135121 |
Appl. No.: |
12/682642 |
Filed: |
October 9, 2008 |
PCT Filed: |
October 9, 2008 |
PCT NO: |
PCT/EP08/08525 |
371 Date: |
April 12, 2010 |
Current U.S.
Class: |
2/2.5 |
Current CPC
Class: |
A42B 3/062 20130101;
F41H 1/08 20130101 |
Class at
Publication: |
2/2.5 |
International
Class: |
F41H 1/04 20060101
F41H001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 12, 2007 |
EP |
07020033.2 |
Claims
1. An anti-ballistic helmet having a shell containing mono-layers
of uni-directional ultrahigh molecular weight polyethylene (UHMwPW)
fibers, characterized that at its rim the shell is connected to a
reinforcing profile.
2. A helmet according to claim 1, wherein the shell further
comprises a binder.
3. A helmet according to claim 1, wherein the reinforcing profile
is U-shaped.
4. A helmet according to claim 1, wherein the profile is made from
a metal.
5. A helmet according to claim 1, wherein the reinforcing profile
exists of composite containing fibers, and a second binder.
6. A helmet according to claim 5, wherein the reinforcing profile
contains ceramic fibers, glass fibers, basalt or silicon carbide
fibers.
7. A helmet according to claim 6, wherein the reinforcing profile
contains carbon fibers
8. A helmet according to claim 5, wherein the reinforcing profile
has at least two fiber orientations.
9. A helmet according to claim 5, wherein the U-ring has at least
three fiber orientations.
10. A helmet according to claim 9, wherein one fiber orientation is
in the profile direction and two other orientations are at +45
degree and -45 degree with the profile direction.
11. A helmet according to claim 1, wherein the sum of the weight of
the shell and the reinforcing profile is at most 1.2 kg.
12. A helmet according to claim 1, wherein the reinforcing profile
has a compressive yield stress of at least 2 times the compressive
yield stress of the shell as measured by ASTM D 6641.
13. A helmet according to claim 1, wherein the part of the
reinforcing rim that overlaps with the lateral side of the shell of
the helmet has a length of preferably at least 0.5 times the
thickness of the shell.
Description
[0001] The invention relates to an anti-ballistic helmet having a
shell containing mono-layers of uni-directional ultrahigh molecular
weight polyethylene (UHMwPE) fibers.
[0002] An anti-ballistic helmet, unless otherwise specified
hereinafter simply called helmet, is known from U.S. Pat. No.
4,613,535. In U.S. Pat. No. 4,613,535 shaped parts are described
containing mono-layers of uni-directional UHMwPE fibers and a
binder. Examples of the shaped parts include ballistic articles
like helmets. The shaped parts are provided with at least one
additional rigid layer on a major surface of the parts, to produce
a part having increased rigidity.
[0003] One of the main problems in developing helmets is to obtain
weight reduction. In view of known steel helmets, the introduction
of a composite helmet was an important step forward in weight
reduction. Improvements in the design and the materials used have
brought further weight reductions. However there is still a need
for further weight reduction, without sacrificing on ballistic
protection, service life and damage tolerance of the helmet. For
example for air born troops it is very important to keep the total
head-load below acceptable limits, while in the same time troopers
are more and more equipped with for example communication
equipment, night viewer etc., attached to their helmets which
consequently add weight.
[0004] In most instances the way of finding the solution was in
providing complex composite structures, combining different types
of layers. One example is the above-mentioned U.S. Pat. No.
4,613,535. Another example is the helmet disclosed in WO961478 and
also in `Hybridized thermoplastic aramids enabling material
technology for future force headgear` by S. M. Walsh, B. R. Scott,
D. M. Spagnuolo and J. P. Wolbert of the US Army Research
Laboratory Weapons & Materials Research Directorate Aberdeen
Proving Ground as presented at the SAMPE 2005 conference, wherein
it is said that the most promising structure is a shell containing
an aramid composite layer as base layer and a hard layer as a skin
containing carbon fibers and epoxy.
[0005] Aim of the invention is to provide a helmet having a low
total weight and yet providing adequate protection against
ballistic impacts, while furthermore this helmet has a good
durability.
[0006] Surprisingly this aim is fulfilled by a helmet having a
shell containing mono-layers of uni-directional UHMwPE fibers and
preferably a binder, wherein at its rim the helmet shell is
connected to a reinforcing profile. The function of the binder is
to hold the fibers together. However, instead of applying a binder,
the fibers can also be connected by pressing with a sufficiently
high pressure at sufficiently high temperature.
[0007] It is unexpected that by applying a reinforcing profile to
the rim of the shell adequate ballistic protection is obtained
against impacts in parts of the helmet remote from the rim, so that
it is possible to produce a helmet having a low weight and still a
good durability. Although a helmet having an additional rigid layer
over the surface of its shell is not excluded from the scope of the
present invention, it is even possible to produce a helmet without
this rigid layer that is often applied in composite helmets.
[0008] A safety helmet having an inner rigid layer provided with a
reinforcing rim and an outer layer which is preferably made of high
density foam is known from Australian Patent Application No.
2005/202254 A1. However, the safety helmet disclosed therein is
only suitable as a construction or sports helmet and is clearly not
suitable as an anti-ballistic helmet. The protection mechanisms
provided by such a helmet construction is obviously not suitable to
be used against bullets where other mechanisms of dissipating the
bullet energy are needed. Although the inner rigid layer is
provided with a reinforcing rim, the referred application mentions
no advantages which directly or even remotely associate the
presence of the reinforcing rim to anti-ballistic properties.
[0009] The invention is further explained in the drawings, without
being limited to the embodiments exemplified in these drawings. In
these drawings,
[0010] FIG. 1 shows a side view of helmet according to the
invention.
[0011] FIG. 2 shows an intersection of a helmet according to the
invention.
[0012] FIG. 3 shows a view on the helmet from the bottom.
[0013] FIG. 1 shows a helmet (1), containing a shell (2), the shell
containing the mono-layers of uni-directional fibers and preferably
a binder. At its rim the shell is connected to a reinforcing
profile (3). The profile has a preferred fiber orientation with
fibers in the profile direction and fibers in an angle of
45.degree. and -45.degree. with the profile direction.
[0014] FIG. 2 shows an intersection of a helmet (1) according to
the invention, containing a shell (2) and a reinforcing profile
(3), the reinforcing profile being U-shaped. The shell fits between
the legs of the U-shaped profile and is connected to the profile at
the surfaces (3.1), (3.2) and (3.3) of the profile.
[0015] FIG. 3 shows a helmet (1) according to the invention having
a shell (2) and a reinforcing profile (3).
[0016] Preferably, the shell of the helmet of the invention
comprises mono-layers of unidirectional UHMwPE fibers and a
binder.
[0017] According to the invention the term mono-layer of
unidirectional UHMwPE fibers and preferably a binder refers to a
layer of a fibrous network of unidirectional oriented UHMwPE fibers
and preferably a binder that basically holds the fibers together.
The term unidirectional oriented fibers refer to fibers in one
plane that are essentially oriented in parallel.
[0018] The term fiber comprises not only a monofilament but, inter
alia, also a multifilament yarn or a tape. Width of the tape
preferably is between 2 mm and 100 mm, more preferably between 5 mm
and 60 mm, most preferably between 10 mm and 40 mm. Thickness of
the tape preferably is between 10 .mu.m and 200 .mu.m, more
preferably between 25 .mu.m and 100 .mu.m.
[0019] The UHMwPE fibers in the mono-layers of the helmet of the
invention preferably have a tensile strength of at least about 1.2
GPa and a tensile modulus of at least 40 GPa. The fibers more
preferably have a tensile strength of at least 2 GPa, even more
preferably at least 2.5 GPa or most preferably at least 3 GPa. The
advantage of these high strength fibers is that they are very
suitable for use in lightweight ballistic-resistant articles.
[0020] Good results are obtained if linear UHMwPE is used. Linear
UHMwPE is herein understood to mean polyethylene with less than 1
side chain per 100 C atoms, and preferably with less than 1 side
chain per 300 C atoms; a side chain or branch generally containing
at least 10 C atoms. The linear polyethylene may further contain up
to 5 mol % of one or more other alkenes that are copolymerisable
therewith, such as propene, butene, pentene, 4-methylpentene,
octene. Preferably, the linear polyethylene is of high molar mass
with an intrinsic viscosity (IV, as determined on solutions in
decalin at 135.degree. C. according to the test method presented
hereinafter) of at least 4 dl/g; more preferably of at least 8
dl/g. Intrinsic viscosity is a measure for molecular weight that
can more easily be determined than actual molar mass parameters
like M.sub.n and M.sub.w. There are several empirical relations
between IV and M.sub.w, but such relation is highly dependent on
molecular weight distribution. Based on the equation
M.sub.w=5.37.times.10.sup.4 [IV].sup.1.37 (see EP 0504954 A1) an IV
of 4 or 8 dl/g would be equivalent to M.sub.w of about 360 or 930
kg/mol, respectively.
[0021] UHMwPE fibers prepared by a gel spinning process, such as
described, for example, in GB 2042414 A or WO 2001/73173 are
preferably used. This results in a very good
ballistic-protection/weight performance. A gel spinning process
essentially consists of preparing a solution of a linear
polyethylene with a high molar mass, spinning the solution into
filaments at a temperature above the dissolving temperature,
cooling the filaments to below the gelling temperature, such that
gelling occurs, and stretching the filaments before, during or
after the removal of the solvent.
[0022] In a preferred embodiment of the invention, the shell of the
helmet comprises mono-layers of unidirectional oriented UHMwPE
fibers, said mono-layers being grouped in at least two sheets. A
sheet preferably contains at least two mono-layers. The mono-layers
in a sheet may be positioned at an angle with respect to each
other, the angle varying from 0 to 90.degree.. The sheets may also
be positioned at an angle with respect to each other.
[0023] The term binder refers also to a material that binds or
holds the uni-directional fibers together in the sheet comprising
mono-layers of unidirectional oriented fibers and a binder, the
binder may enclose the fibers in their entirety or in part, such
that the structure of the mono-layer is retained during handling
and making of preformed sheets. The binder may be applied in
various forms and ways; for example as a film (by melting hereof at
least partially covering the UHMwPE fibers), as a transverse
bonding strip or as transverse fibers (transverse with respect to
unidirectional fibers), or by impregnating and/or embedding the
fibers with a matrix material, e.g. with a polymer melt, a solution
or a dispersion of a polymeric material in a liquid. Preferably,
matrix material is homogeneously distributed over the entire
surface of the mono-layer, whereas a bonding strip or bonding
fibers may be applied locally. Suitable binders are described in
e.g. EP 0191306 B1, EP 1170925 A1, EP 0683374 B1 and EP 1144740
A1.
[0024] In a preferred embodiment, the binder is a polymeric matrix
material, and may be a thermosetting material or a thermoplastic
material, or mixtures of the two. The elongation at break of the
matrix material is preferably greater than the elongation of the
fibers. The binder preferably has an elongation of 2 to 600%, more
preferably an elongation of 4 to 500%. Suitable thermosetting and
thermoplastic matrix materials are enumerated in, for example, WO
91/12136 A1 (pages 15-21). In the case the matrix material is a
thermosetting polymer vinyl esters, unsaturated polyesters, epoxies
or phenol resins are preferably selected as matrix material. In the
case the matrix material is a thermoplastic polymer polyurethanes,
polyvinyls, polyacrylics, polyolefins or thermoplastic elastomeric
block copolymers such as
polyisopropene-polyethylene-butylene-polystyrene or
polystyrene-polyisoprene-polystyrene block copolymers are
preferably selected as matrix material. Preferably the binder
consists of a thermoplastic polymer, which binder preferably
completely coats the individual filaments of said fibers in a
mono-layer, and which binder has a tensile modulus (determined in
accordance with ASTM D638, at 25.degree. C.) of at least 75 MPa,
more preferably at least 150 MPa and even more preferably at least
250 MPa, most preferably of at least 400 MPa. Preferably the binder
has a tensile modulus of at most 1000 MPa. The binder should be
chosen such to result in a high flexibility of the sheet comprising
mono-layers, while the shell compressed from said sheets have a
high enough stiffness.
[0025] Preferably, the amount of binder in the mono-layer is at
most 30 mass %, more preferably at most 25, 20, or even at most 15
mass %. This results in the best anti-ballistic performance.
[0026] Good results are obtained if the direction of orientation of
the fibers in adjacent mono-layers is at an angle of between 5 and
90.degree., preferably between 45 and 90.degree., most preferably
between 75 and 90.degree..
[0027] Very good results for the helmet of the invention are
obtained when the direction of orientation of the UHMWPE fibers in
the mono-layers is at an angle towards the rim of the helmet.
Preferably, the direction of orientation of the fibers in
mono-layers in the shell are at an angle of between +30 and +60
respectively -30 .degree. and -60.degree. towards the rim of the
helmet. More preferably this angle is between +40 and +50.degree.,
respectively -40 and -50.degree., most preferably +45.degree. or
about 45.degree., respectively -45.degree. or about
-45.degree..
[0028] The shell may still contain a hard top layer, e.g. a metal
or ceramic strike face, or a hard composite top layer, e.g. a woven
glass fiber fabric impregnated with a thermosetting resin. However,
preferably such a layer is not present, so that the most optimal
helmet with respect to weight, anti-ballistic protection and
durability is obtained. The term durability will be explained
below.
[0029] The reinforcing profile may be produced from all kind of
light-weight materials having a high stiffness and strength. Good
examples include metals like steel, titanium, aluminum, magnesium
and their alloys. Preferably the reinforcing profile is produced
from a composite, containing reinforcing fibers and a second
binder. The composite may contain all kind of reinforcing fibers,
for example organic fibers such as aramid fibers. More preferable
the composite contains inorganic fibers as e.g. ceramic fibers,
glass fibers, basalt or silicon carbide fibers. In general, such
fibers contain at least 15% silicon. Most preferably the composite
contains carbon fibers. If a composite is chosen, the number
orientations of the reinforcing fiber are at least two. More
preferred are at least three fiber orientations. Suitable
orientations may be 0.degree., 90.degree., +45.degree., and
-45.degree. with the direction of the reinforcing profile, as is
illustrated in FIG. 1, item (3). Most preferably the fibers are
orientated at 0.degree., +45.degree., and -45.degree. with the
profile direction. The fibers in the composite may be woven or
unidirectionally aligned, according to the mentioned fiber
directions.
[0030] The second binder in the composite of the reinforcing
profile should preferably show a reasonable adhesion to the fibers
and a modulus of preferably at least 1400 MPa. The amount of second
binder is preferably between 20 and 70% by volume, more preferably
between 35 and 55% by volume.
[0031] Preferably the reinforcing profile has a compressive yield
stress of at least 2 times the compressive yield stress of the
shell, more preferably at least 4 times, most preferably at least 6
times the compressive yield of the shell. The compressive yield
stress is measured by ASTM D 6641(issued in 2001). In case of a
reinforcing rim comprising elongated reinforcing elements, e.g.
fibers, the compressive yield stress must be measured in the
direction of those said reinforcing elements which are positioned
along the rim. It was observed that by a reinforcing rim having the
required compression yield stress provides the helmet of the
invention with improved anti-ballistic properties, in particular
the anti-ballistic properties at locations remote from the rim are
improved. Another advantage is that such a helmet has even further
improved durability.
[0032] The reinforcing profile may have a cross section with all
kind of shapes as for example L-shaped or U-shaped. Preferably the
reinforcing profile has a U-shape. Furthermore the U-shaped profile
may be connected easy and secure to the shell, if the shell fits
into the U-shaped profile.
[0033] The reinforcing profile is connected to the shell of the
helmet at the rim of said shell. By connected is herein understood
that the reinforcing profile is fixated onto the shell of the
helmet such that forces acting on the shell can be effectively
transferred to and attenuated by the reinforcing profile and
vice-versa.
[0034] The reinforcing profile may be connected to the shell of the
helmet according to any known method in the art. A suitable example
include gluing with a suitable adhesive, fixation by heat or simply
by approaching the lateral sides of a U-shaped profile until a good
fixation on the shell is achieved.
[0035] Good connections are achieved when the part of the
reinforcing rim that overlaps with the lateral side of the shell of
the helmet has a length of preferably at least 0.5 times the
thickness of the shell, said thickness being measured at the bottom
of the shell of the helmet, more preferably at least 1 times, most
preferably at least 2 times said thickness of the shell. Such
helmet shows even further improved durability as well as improved
anti-ballistic properties in particular at locations remote from
the rim.
[0036] Preferably, the part of the reinforcing rim that overlaps
with the lateral side of the shell of the helmet has a thickness
small enough not to cause an unnecessary increase in the thickness
of the bottom of the helmet. It is preferred that the increase in
the thickness of the helmet at its bottom is less than 30%, more
preferably less than 20%, most preferably less than 10%. Such a
helmet shows good anti-ballistic properties while being
lightweight. Also it has an increased versatility.
[0037] The skilled person knows how to select suitable production
processes for the preparation of the parts of the helmet and the
helmet itself. The shell of the helmet may be produced by a process
containing the steps of forming a stack of sheets containing cross
plied mono-layers of unidirectional aligned UHMwPE fibers and
preferably a binder, placing the stack in a mould and closing the
mould to form and consolidate the stack of layers into a shell of a
helmet shape. Such a process is described in WO2007/107359.
[0038] The reinforcing profile may be a machined or molded light
weight metal part. Preferably however the reinforcing profile is a
carbon fiber composite that is laminated along the rim of the
helmet.
[0039] Preferably the sum of the weight of the shell and the
reinforcing profile of the helmet according to the invention is at
most 1.2 kg, more preferably at most 1.1 kg, even more preferably
at most 1.0 kg.
[0040] The invention is further illustrated in the example and
comparative experiments.
[0041] The helmets produced in the comparative experiments and in
the example were subjected to two types of tests. The first test
was a shooting test with 17 grain fragment simulating projectiles
(FSP). The second test was a so called durability test.
Shooting Test
[0042] The shooting test was performed by clamping the helmet in a
suitable clamping device in front of a gun. The clamping device was
made in such a way that the helmet could be rotated and
subsequently fixed rigidly again. In this way, the helmet was
rotated after each shot and fixated again so that about eight shots
could be fired at each helmet. The projectiles are 17 grain
Fragment Simulating Projectiles (FSP).
[0043] The first shot is fired at an anticipated speed at which it
is expected that 50% chance of perforation was present, so at an
expected so-called V.sub.50 value. The speed of all projectiles was
measured at a short distance before impact. Measurement was
performed with an optical device. If a perforation occurred, the
next FSP was fired at a speed that was anticipated to be 10% lower
than that of the previous projectile. Again the speed was measured
at short distance before impact. If a projectile was stopped
without perforation, the next projectile was fired at an
anticipated speed being 10% larger than the previous projectile. It
is always assured that the distance between the impact locations is
sufficiently large to prevent overlap of the trauma areas (impact
affected areas). In general about eight shots were possible this
way for each helmet. The experimental V.sub.50 value was obtained
from the average speeds of the three highest speeds at which a stop
occurred and the three lowest speeds at which a perforation
occurred. In case only two stops or only two perforations are
obtained, V.sub.50 is obtained from the two highest stops and two
lowest perforations. The intrinsic kinetic energy U is obtained as
the kinetic energy of an FSP at V.sub.50, so 0.5 m V.sub.50.sup.2.
The mass m of a 17 grain FSP is equal to m=0.0011 kg. The
performance of a helmet is related to the intrinsic kinetic energy
U at V.sub.50 and to the helmet mass M. Therefore a performance
parameter P is derived as P=U/M.
Durability Test
[0044] The helmet is subjected to a compressive force on 2 opposing
positions at its rim, at the position of the ears of a wearer. The
places where the compressive force acts are chosen to be just above
the reinforcing rim, therefore preventing compressing the
reinforcing rim as well. The change of the shape of the helmet as a
function of the compressive force is measured.
[0045] The displacement caused in the shell of the helmet at a
force of 1500 N (about twice the bodyweight of a human) is
considered a representative quality parameter and hereafter is
referred to as `displacement`.
[0046] After unloading the compressive force and 5 minutes
recovery, the change of the shape of the helmet is measured again.
This value is referred to as `deformation`.
[0047] It should be noted that the force at which delamination of
the helmet shell, or plasticity occurs should be well above this
force of 1500 N.
[0048] In case the deformation at 1500 N is sufficiently small,
this load is repeated 24 times and the displacement evolution is
recorded: this is referred to as `damage tolerance` or simply as
`durability`.
Other Test Methods
[0049] Side chains: the number of side chains in a UHPE sample is
determined by FTIR on a 2 mm thick compression moulded film, by
quantifying the absorption at 1375 cm.sup.-1 using a calibration
curve based on NMR measurements (as in e.g. EP 0269151); [0050] IV:
the Intrinsic Viscosity is determined according to method PTC-179
(Hercules Inc. Rev. Apr. 29, 1982) at 135.degree. C. in decaline,
the dissolution time being 16 hours, with DBPC as anti-oxidant in
an amount of 2 g/l solution, by extrapolating the viscosity as
measured at different concentrations to zero concentration [0051]
Tensile strength (or strength) is defined and determined on
multifilament yarns as specified in ASTM D885M, using a nominal
gauge length of the fibre of 500 mm, a crosshead speed of 50%/min
and Instron 2714 clamps, of type Fibre Grip D5618C. For calculation
of the strength, the tensile forces measured are divided by the
titre, as determined by weighing 10 meters of fibre; values in GPa
are calculated assuming a density of UHMwPE of 0.97 g/cm.sup.3.
Comparative Experiment A.
[0052] A helmet was produced from a stack of 50 layers of cross
plied sheet comprising two monolayers of with 80 w % unidirectional
aligned UHMwPE fibers having a tensile strength of 3.5 GPa and a
thermoplastic binder. The fibre orientations of the two monolayers
in a cross plied sheet are about perpendicular. The helmet was
produced by putting the stack in an open mould with the shape of a
helmet, followed by closing the mould at a temperature of
130.degree. C. and after consolidation at a pressure of 8 MPa (i.e.
pressing force divided by projected helmet surface) during one
hour, the helmet was cooled, demolded and trimmed to the desired
size. The average helmet mass M was 0.876 kg. The helmet was tested
and the test results are given in Table 1.
[0053] Comparative Experiment B.
[0054] A helmet was produced from a stack of 42 instead of 50
layers of Comparative Experiment A while using the same process.
The pressure during moulding was similar to that of Comparative
Experiment A. After demoulding and trimming, the average mass was
0.737 kg. Subsequently, after demoulding and trimming, the helmet
was subjected to a laminating process with a fabric of carbon
fiber. Four layers of twill weave carbon fibre fabric with an
aerial density of 0.12 kg/m2 were laminated at the outside of the
helmet, using a standard commercial epoxy resin. The resin could be
cured at room temperature. Nevertheless, a post curing in an oven
at 40.degree. C. was performed after 2 days of curing in ambient
air. Post curing was performed to ensure optimal hardening of the
epoxy at all locations of the helmet. Thus a helmet was made with a
hard outer skin of carbon epoxy composite. The thickness of the
helmet was similar to that of the helmet of reference example 1.
However, the average mass of the helmets after adding the hard
outer skin was 0.946 kg. The helmet was tested and the test results
are given in Table 1.
Example According to the Invention.
[0055] Helmets were produced in the same way as described in
comparative experiment A. However, after demoulding and trimming, a
carbon fiber epoxy composite layer was laminated around the rim of
the helmet and cured in the same way as described for comparative
experiment B. The carbon fiber epoxy [amount of expoxy was 40% by
volume.] composite layer consists of a tape fabric with a width of
80 mm and three fibre orientations as shown in FIG. 1. (3). Areal
density of the tape fabric was 600 g/m.sup.2. One fibre orientation
is in the length direction of the tape. The two other fibre
orientations are at +45 degrees and -45 degrees with the tape
direction. Only one tape was laminated along the rim of the helmet
as illustrated in the drawings with tape begin and end overlapping
each other for 3 cm. The mass of the helmet with the rim was 0.940
kg. The helmet was tested and the test results are given in Table
1.
TABLE-US-00001 TABLE 1 Example according to Property Comp. exp. A.
Comp. exp. B. the invention V.sub.50 683 633 687 [m/sec] U 256 220
259 [J] P 293 233 276 [J/kg] Displacement >150 (1) 32 8 (2) at
1500 N, [mm] Deformation, 145 12 0.5 after unloading and recovery
[mm] Damage tolerance, Not performed Failure 6 after 24 cycles of
1500 N because load (excessive [mm] can not be deformation reached
after 12 cycles) (1) test stopped at a force of 600 N in view of
excessive deformation (2) a force of 4000 N could be reached with
35 mm displacement
[0056] The result shows that a helmet made entirely from UHMwPE
monolayers shows a good helmet performance parameter P against
impact of FSP. However, the durability is low. Only a low
transverse compressive load can be sustained, and the resulting
deformation is large. Addition of a hard outer layer improves the
shell deformation, however its durability is still sub optimal.
Displacements are large and only partial recovery occurs. Moreover,
antiballistic performance, as expressed by the parameter P
decreases considerably.
[0057] The helmet according to the invention however, shows
excellent durability combined with limited displacement and almost
no deformation. It is also surprisingly shows an increase in
V.sub.50 and therefore having improved anti-ballistic properties
when compared to known helmets.
* * * * *