U.S. patent application number 12/708991 was filed with the patent office on 2011-08-25 for armor plate.
This patent application is currently assigned to Nova Research, Inc.. Invention is credited to Raymond M. Gamache, Graham K. Hubler, Yan R. Kucherov.
Application Number | 20110203452 12/708991 |
Document ID | / |
Family ID | 44475377 |
Filed Date | 2011-08-25 |
United States Patent
Application |
20110203452 |
Kind Code |
A1 |
Kucherov; Yan R. ; et
al. |
August 25, 2011 |
ARMOR PLATE
Abstract
An armor plate includes at least four layers configured to
generate a compression wave that is dissipated in a fracture
player. The armor plate includes a deformable layer of a material
having an elongation before failure of 20% or more; a transparent
ceramic layer adjacent the deformable layer; a transparent fracture
layer adjacent the ceramic layer; and a transparent spall liner
backing the fracture layer.
Inventors: |
Kucherov; Yan R.;
(Alexandria, VA) ; Hubler; Graham K.; (Highland,
MD) ; Gamache; Raymond M.; (Indian Head, MD) |
Assignee: |
Nova Research, Inc.
Alexandria
VA
|
Family ID: |
44475377 |
Appl. No.: |
12/708991 |
Filed: |
February 19, 2010 |
Current U.S.
Class: |
89/36.02 ;
89/908 |
Current CPC
Class: |
F41H 5/0407 20130101;
B32B 17/1055 20130101; B32B 17/10119 20130101; F41H 5/0428
20130101; F41H 5/0421 20130101 |
Class at
Publication: |
89/36.02 ;
89/908 |
International
Class: |
F41H 5/04 20060101
F41H005/04 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0001] The U.S. Government has a paid-up license in this invention
and the right in limited circumstances to require the patent owner
to license others on reasonable terms as provided for by the terms
Contract No. N00173-07-C-2055 awarded by U.S. Naval Research
Laboratory.
Claims
1. An armor plate comprising: a deformable layer comprised of a
material having an elongation before failure of at least about 20%;
a ceramic layer adjacent the deformable layer; a fracture layer
adjacent the ceramic layer; and a spall liner backing the fracture
layer.
2. The armor plate as recited in claim 1, wherein the deformable
layer is comprised of polycarbonate.
3. The armor plate as recited in claim 1, wherein the deformable
layer has an elongation before failure of at least about 50%.
4. The armor plate as recited in claim 1, wherein the deformable
layer has an elongation before failure of at least about 100%.
5. The armor plate as recited in claim 1, wherein the deformable
layer has an average thickness in a range from about 1 mm to about
4 mm.
6. The armor plate as recited in claim 1, wherein the ceramic layer
is comprised of sapphire, aluminum oxynitride, spinel, AlN,
alumina, silicon carbide, boronitride, boron carbide, diamond, and
combination thereof.
7. The armor plate as recited in claim 1, wherein the ceramic layer
has an average thickness in a range from about 1 mm to about 2
mm.
8. The armor plate as recited in claim 1, wherein the fracture
layer is selected from the group consisting of glass, soda glass, a
silicate material, or a combination thereof.
9. The armor plate as recited in claim 1, wherein the fracture
layer has an average thickness in a range from about 0.5 mm to
about 5 mm.
10. The armor plate as recited in claim 1, wherein the spall liner
is comprised of a polycarbonate.
11. The armor plate as recited in claim 1, wherein the deformable
layer provides the initial impact layer for a projectile striking
the armor plate.
12. The armor plate as recited in claim 1, the deformable layer,
the ceramic layer, the fracture layer, and the spall liner have a
combined thickness in a range from about 4 mm to about 15 mm.
13. The armor plate as recited in claim 1, further comprising an
adhesive joining the deformable layer and the ceramic layer,
joining the ceramic layer and the fracture layer, and/or joining
the fracture layer and the spall liner.
14. The armor plate as recited in claim 1, wherein the deformable
layer has a thickness in a range from about 1 mm to about 4 mm, the
ceramic layer has a thickness in a range from about 1 mm to about 2
mm, and the fracture layer has a thickness in a range from about
0.5 mm to about 5 mm, and the spall liner has a thickness in a
range from about 1 mm to about 4 mm.
15. The armor plate as recited in claim 1, wherein the deformable
layer, the ceramic layer, the fracture layer, and the spall liner
are transparent.
16. A vehicle comprising a body having one or more windows
comprised of the armor plate as defined in claim 15.
17. An armored helmet including a visor comprising the armor plate
as defined in claim 15.
18. A goggle having one or more lenses comprised of the armor plate
as defined in claim 15.
19. A transparent armor plate, comprising: a transparent deformable
layer configured to receive an initial impact force of a projectile
and generate a compression wave; a fracture layer; a transparent
ceramic layer disposed between the deformable layer and the
fracture layer, the transparent ceramic layer configured to receive
the compression wave from the deformable layer and transfer the
energy thereof to the fracture layer, wherein the fracture layer is
configured to dissipate the compression wave by fracturing; and a
spall liner backing the fracture layer and configured to contain
the fractured layer after being fractured.
20. A transparent armor plate as in claim 19, wherein the
transparent deformable layer has an elongation before failure of at
least about 50%.
21. A transparent armor plate as in claim 19, wherein the
deformable layer, the ceramic layer, the fracture layer, and the
spall liner have a combined thickness in a range from about 4 mm to
about 15 mm.
22. A transparent body armor material as in claim 19, wherein the
transparent deformable layer comprises polycarbonate, the
transparent ceramic layer is selected from the group consisting of
sapphire, aluminum oxynitride, spinel, or a combination thereof,
and the transparent fracture layer includes glass, soda glass, a
silicate material, or a combination thereof.
23. A transparent armor plate consisting essentially of: a
transparent deformable layer comprised of a material having an
elongation before failure of at least 20%; a transparent ceramic
layer adjacent the deformable layer; a transparent fracture layer
adjacent ceramic layer; a transparent spall liner backing the
fracture layer; optionally an adhesive bonding two or more of the
layers of the armor plate together; and optionally a tint
coating.
24. A transparent armor plate as in claim 23, wherein the
deformable layer comprises polycarbonate.
Description
BACKGROUND OF THE INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention relates to armor plates and articles
of manufacture incorporating the armor plates.
[0004] 2. The Relevant Technology
[0005] Armor is a material or system of materials designed to
protect from ballistic threats. Transparent armor, in addition to
providing protection from the ballistic threat is also designed to
be optically transparent, which allows a person to see through the
armor and/or to allow light to illuminate the area behind the
armor.
[0006] In the general field of ballistic armors, existing armor
systems are typically comprised of many layers of projectile
resistant material separated by polymer interlayers, which bond the
projectile resistant materials. In a typical armor laminate the
strike surface is a hard layer of projectile resistant material
that is designed to break up or deform projectiles upon impact. The
interlayer materials are used to mitigate the stresses from thermal
expansion mismatches as well as to stop crack propagation into the
polymers.
[0007] For most armor plates, efforts are usually made to make the
armor plate light weight. This is particularly true of transparent
armor plates, which are often used for protective visors and
goggles. Currently existing military specification for protective
visors and goggles requires that the lens should be able to stop
0.22-caliber 17 grain FSP projectile at 550-feet per second (fps).
For comparison, most handguns give more than 1000 fps bullet
velocity and rifles up to 3000 fps. To stop bullets from handguns
one needs an inch thick polycarbonate plate and around two inches
thickness for a rifle bullet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a schematic of an armor plate according to one
embodiment of the invention and a projectile about to strike the
surface of the transparent armor plate;
[0009] FIG. 2 illustrates the schematic of FIG. 1 showing the
projectile after impact;
[0010] FIG. 3 is a graph showing the fracture energy of the soda
glass as a function of crack propagation velocity;
[0011] FIG. 4 is a graph showing the surface area of 1 cm.sup.3
material volume as a function of particle size;
[0012] FIG. 5 is a graph showing fracture energy absorbed by 1
cm.sup.3 of glass fracture as a function of particle size at 11
km/s impact;
[0013] FIG. 6 is a schematic of an armor plate with adjacent layers
of material joined using an adhesive;
[0014] FIG. 7 illustrates an armored vehicle according to one
embodiment of the invention incorporating the armor plate of FIG.
1;
[0015] FIG. 8 illustrates a helmet according to an alternative
embodiment of the invention incorporating the armor plate
illustrated in FIG. 1;
[0016] FIG. 9 illustrates a pair of goggles incorporating the armor
plate illustrated in FIG. 1; and
[0017] FIG. 10 shows a panel including a plurality of segments of
the armor plate of FIG. 1; and
[0018] FIG. 11 is a graph showing test results of armor plate
manufactured according to the present invention.
DETAILED DESCRIPTION
[0019] The present invention relates to a composite armor plate and
articles of manufacture incorporating the armor plate. The
composite armor plate typically uses at least four layers of
material that are configured to create a compression wave from the
impact of a projectile and absorb the compression wave by
fracturing one of the layers. The four-layer system of the
invention can be made comparatively lighter, stronger, and/or
thinner than armor materials using conventional laminates. In one
embodiment, the armor plate can be transparent. Transparent armor
plates can be incorporated into windows, helmets, goggles, and
similar devices where transparency and/or translucency are desired.
In other embodiments, the armor plate can include one or more
layers that are opaque.
[0020] The four-layer system of the present invention can achieve a
lighter, thinner armor by placing a deformable layer on the front
side of a ballistic-resistant ceramic layer. The ceramic layer is
in turn backed by a fracture layer and a spall liner. Upon
ballistic impact, the deformable layer creates a compression wave
that spreads out through the ceramic layer and is absorbed by the
fracture layer. The spall liner backing the fracture layer catches
the fracture layer as it disintegrates from the impact. The use of
a deformable layer in front of the strong ceramic layer allows an
intensive compression wave with a large surface area to be
generated. When the large surface area compression wave strikes the
fracture layer, the larger surface area results in comparatively
better disintegration of the fracture layer, thereby absorbing a
comparatively larger amount of energy. Depending on the plate
geometry, projectile size and speed, orders of-magnitude increase
in energy absorption can be achieved using a deformable layer and a
fracture layer with a ceramic layer in between.
[0021] FIG. 1 illustrates an example armor plate 100 according to
one embodiment of the invention. The armor plate 100 includes a
transparent deformable layer 110, a transparent ceramic layer 112,
a fracture layer 114, and a spall liner 116.
[0022] Armor plate 100 has a strike surface 117 upon which a bullet
118 or any other type of projectile impinges. Armor plate 100 also
includes a back surface 119 opposite the strike surface 117. Strike
surface 117 is configured to receive the initial impact of bullet
118 and back surface 119 is configured to be the surface closest to
the object for which the armor plate provides protection. For
example, where armor plate 100 is used as a window in an armored
vehicle, strike surface 117 is positioned outside the vehicle and
back surface 119 communicates with the interior of the vehicle.
[0023] In one embodiment, the deformable layer 110 has a first side
120 configured to be strike surface 117 upon which bullet 118
impinges. Deformable layer 110 is configured to generate a
compression wave from the impact of bullet 118. In one embodiment
the deformable layer 110 comprises a material having an elongation
before failure of at least 20%. Materials having an elongation
before failure of at least 20% typically generate an intense
compression wave upon ballistic impact. In a more preferred
embodiment, the deformable layer may include a material having an
elongation before failure of at least about 50%, even more
preferably about 100% or more. Examples of suitable transparent
materials that can be used for the deformable layer 110 include,
but are not limited to, polycarbonate, polyurethanes, elastic
acrylic polymers, and combinations of these. Examples of
nontransparent deformable materials that can be used include
aluminum, titanium, and combinations of these.
[0024] Deformable layer 110 also has a backside 122 that opposes
first side 120. Backside 122 is adjacent ceramic layer 112. As will
be discussed below in greater detail, backside 122 may be adhered
to or otherwise bonded directly to ceramic layer 112 or
alternatively backside 122 may be held in direct contact with
ceramic layer 112 without being bonded thereto. For example,
deformable layer 110 and ceramic layer 112 can be adhered using a
resin such as, but not limited to, poly(vinylbutiral) or secured
together by fixing the layers within a frame and/or clamping.
[0025] The thickness of deformable layer 110 may be selected to
enhance the generation of the compression wave. In one embodiment
the deformable layer 110 has a thickness in a range from about 0.5
mm to about 10 mm, more preferably about 1 mm to about 4 mm.
Opposing faces 120 and 122 can be disposed in parallel alignment so
that the thickness is constant where the faces can be angled
relative to each other so that the thickness varies one or both of
faces 120 and 122. Faces 120 and 122 can also be contoured, such as
curved, so that they are not planar.
[0026] In a preferred embodiment, deformable layer 110 is a single
layer of a homogeneous material. However, in some embodiments the
deformable layer 110 may be made from a plurality of sub-layers
that together are highly deformable (e.g., the sub-layers together
have an elongation before failure of at least about 20%).
[0027] Ceramic layer 112 is positioned adjacent to and between
deformable layer 110 and fracture layer 114. Ceramic layer 112 has
a front side surface 124 and an opposing backside surface 128.
Backside surface 128 is adjacent fracture layer 114. Ceramic layer
112 can be adhered to or otherwise bonded to deformable layer 110
and/or fracture layer 114 similarly to the connection between
ceramic layer 112 and deformable layer 110.
[0028] Ceramic layer 112 is made from a strong, ballistic-resistant
material having a high sound velocity. The ceramic material will
typically have a sound velocity in a range from about 2-50 km/s,
more specifically 4-30 km/s, or even more specifically 8-20 km/s.
Ceramic layer 112 may also be transparent. Examples of suitable
transparent material include sapphire, aluminum oxinitride (AlON),
spinel, AlN, alumina, and combinations of these. Nontransparent
materials can also be used. Examples of nontransparent materials
include, but are not limited to, silicon carbide, boronitride,
boron carbide, diamond, and combinations of these. These materials
and similar materials with a high sound velocity are advantageous
for allowing the compression wave generated in the deformable layer
110 to spread out as it travels through ceramic layer 112 and for
providing toughness in a thin layer.
[0029] The thickness 132 of ceramic layer 112 is typically selected
to provide maximum strength while minimizing weight. Ceramics such
as sapphire, aluminum oxynitride (AlON), and spinels typically need
to have a minimal thickness before they will outperform plastic
materials (e.g., about 0.25 mm). After this minimal thickness
ceramics tend to provide better protection than plastics, but with
increased weight, as the density of transparent ceramics are 2 to 3
times higher than the density of plastics. Thus, even where cost is
not an issue, practical weight restrictions in some cases will
limit the thickness of ceramic layers.
[0030] Even when relatively thick ceramic layers can be used, a
thick ceramic layer tends to transfer impact velocity to the
substrate (e.g. the frames of protective eyewear), which may not be
able to handle increased forces and the whole system must be
strengthened, again with weight increase. Thus in some embodiments
of the invention it is desirable to minimize the thickness of the
ceramic layer 112. In one embodiment, the thickness may be less
than 10 mm, more preferably less than about 6 mm, even more
preferably less than about 4 mm, and most preferably less than
about 2 mm. In one embodiment of thickness 132 can be in a range
from about 0.5 mm to about 6 mm, more preferably about 0.8 mm to
about 4 mm, and most preferably from about 1 mm to about 2 mm.
[0031] In one embodiment of the invention ceramic layer 112 may be
a continuous and/or homogeneous layer of the ceramic material.
However in an alternative embodiment ceramic layer 112 may include
a plurality of sub-layers of the ceramic material. The sub-layers
may be the same or different ceramic materials and may be bonded or
adhered together as previously discussed with respect to the
connection between deformable layer 110 and ceramic layer 112.
[0032] Fracture layer 114 is adjacent to and between ceramic layer
112 and spall liner 116. Fracture layer 114 has a front side 130
and an opposing backside 134. Backside 134 may be adhered to or
bonded to a front surface 136 of spall liner 116 any manner similar
to the connection between deformable layer 110 and ceramic layer
112 as discussed above.
[0033] Fracture layer 114 is configured to receive a compression
wave that has traveled through ceramic layer 112. Fracture layer
114 is configured to at least partially disintegrate upon receiving
the compression wave. Fracture layer 114 is selected to have a low
fracture toughness and high surface energy, which will maximize
fracture absorption energy, typically at the expense of impact
resistance. Typically, a lower fracture threshold will give better
energy absorption and less momentum transfer to the armor plate
supporting structure. In one embodiment, fracture layer 114 can be
made from a brittle transparent material. Examples of suitable
materials include glass, soda glass, transparent silicates, and
combinations of these. Examples of nontransparent materials include
nontransparent silicates. Within a given glass type, absorbed
fracture energy can be manipulated by tempering the glass.
[0034] Fracture layer 114 is selected to have a lower impact
resistance than ceramic layer 112. However, fracture layer 114 is
configured to absorb substantial amounts of energy through
fracturing. If desired, fracture layer 114 can even be configured
to absorb more energy than ceramic layer 112. To achieve high
energy absorption by fracture layer 114, armor plate 100 is
configured to cause a relatively large volume of fracture layer 114
to fracture into fine particles.
[0035] The energy absorbed by fracture layer 114 depends on the
velocity of the crack propagation and the fractured grain size.
FIG. 3 shows fracture energy as a function of crack propagation
velocity for soda glass (extrapolated from J. O. Atwater. "Fracture
energy of glass" DTIC report #640848, 1966). With an intense shock
wave, crack propagation velocity is pinned to the speed of sound in
the brittle material of fracture layer 114. In the case where
ceramic layer 112 is made of sapphire, the speed of sound is 11.2
kmfs and at the sapphire-glass interface crack propagation velocity
will be the same. This corresponds to 30 J/m.sup.2 surface energy
for a soda-lime glass, or almost fifteen times more than for a slow
impact event.
[0036] In order to absorb large amount of energy, fractured
particle size must be sufficiently small. The absorbed energy
increases exponentially with a decrease in the diameter of the
fractured particle size do to the increase in surface area. FIG. 4
is a graph showing surface area as a function of the particle size.
FIG. 5 shows the energy absorbed by 1 cm.sup.3 of glass fractured
at 11 km/s impact. To illustrate the potential energy absorption of
fractured glass, the energy of an AK-47 bullet is plotted on the
graph of FIG. 5. As shown in FIG. 5, 1 cm.sup.3 of glass is, in
principle, capable of absorbing all the energy from a rifle bullet
if the fractured grain size is smaller than about
1.times.10.sup.-7. The armor plate 100 of the present invention
provides for substantial energy absorption in fracture layer 114 by
generating a compression wave in deformable layer 110 and spreading
the compression wave in ceramic layer 112.
[0037] The thickness of fracture layer 114 can be selected to
provide adequate volume for absorbing a compression wave generated
in deformable layer 110. With reference now to FIG. 1, in one
embodiment the thickness 138 of fracture layer 114 can be in a
range from about 0.5 mm to about 10 mm, more specifically about 1
mm to about 5 mm.
[0038] Fracture layer 114 is backed by spall liner 116 to stop
(i.e. catch) the fractured glass particles. Spall liner 116 has a
front surface 136 that is adjacent fracture layer 114. In one
embodiment, a back surface 140 of spall liner 116 is configured to
be the back surface 119 of armor plate 110.
[0039] When a bullet strikes armor plate 100 and fracture layer 114
is pulverized, the disintegrated particles will be small, but can
still carry residual momentum. Spall liner 116 is made from a
material capable of capturing the fine particles generated from
fracture layer 114. In one embodiment spall liner 116 may have
relatively high elasticity such that spall liner 116 can expand to
absorb the momentum of the fractured particles without rupturing.
Examples of suitable materials that can be used to make spall liner
116 include polymers such as polycarbonate; woven ballistic fibers
including para-aramids (e.g., Kevlar), ultra-high strength
polyethylene fiber (e.g., Spectra and Dyneema),
poly(p-phenylene-2,6-benzobisoxazole) (PBO), and/or boron fibers;
polyurethane; and combinations of these. In one embodiment, spall
liner 116 can be made from a transparent material such as
polycarbonate or Dynema. Alternatively, spall liner 116 can be
nontransparent.
[0040] The thickness of spall liner 116 is selected to ensure
sufficient strength to withstand the residual momentum of the
fractured particles from fracture layer 114. Typically the
thickness of spall liner 116 may be in a range from about 0.5 mm to
about 10 mm, more specifically between about 1 mm and 4 mm.
[0041] FIG. 2 illustrates how armor plate 100 dissipates momentum
from bullet 118. FIG. 2 shows bullet 118 penetrating front surface
117 of armor plate 100. At the initial phase of a ballistic impact
deformable layer 110 deforms, creating the equivalent of local
compression. The compression wave then spreads out at a velocity
close to the speed of sound in ceramic layer 112. As bullet 118
moves through ceramic layer 112 it generates a lattice wave by
moving dislocations, thereby transforming an additional portion of
the projectile energy into acoustic waves. The intensity ratio of
the compression wave to the lattice waves generated by moving
dislocations depends on the thickness of the deformable layer 110
and ceramic layer 112 relative to the projectile diameter and the
properties of the materials used for deformable layer 110 and
ceramic layer 112. The approach taken in making existing body armor
typically relies on the theory that moving dislocations can last
for a relatively long time, thereby spreading total wave generation
over time and making the impact less intense. In reality this
scenario is difficult to achieve, as deformation needed to absorb
significant energy typically is outside of acceptable armor plate
thickness for most applications. Hard ceramic plates efficiently
convert impact energy into the compression wave. This compression
wave fractures a portion of the ceramic, absorbing energy. High
impact strength of the ceramics results in the energy absorption in
a fixed volume. As a result, thin ceramics do not work well. Also,
only a strong wave can fracture ceramics. Lower intensity waves go
unaffected, contributing to the momentum transfer to the substrate,
which is especially undesirable for a wearable armor.
[0042] In contrast, the proposed invention takes a counterintuitive
approach. Armor plate 100 includes a soft material in front ceramic
layer 112 (i.e., deformable layer 110). Instead of mitigating a
shock wave, deformable layer 110 and ceramic layer 112 are
amplifying the shock wave. As a projectile moves through deformable
layer 110, pressure on ceramic layer 112 builds up, effectively
accumulating the compression wave. Lattice wave generation also
lasts longer.
[0043] The speed of sound in deformable layer 110 may be selected
to be relatively small. When the compression wave reaches ceramic
layer 112, for example sapphire, it accelerates to the speed of
sound (e.g., from 3 km/s to 11 km/s), thus becoming more intense.
The compression wave also spreads out. When the compression waves
hits the fracture layer 114 it is close in intensity to the impact
point, but can be spread out over the area two orders of magnitude
larger than the projectile cross-section area.
[0044] When a brittle solid fractures, the amount of energy
absorbed depends on the grain size of the fractured material. The
fracture energy is inversely proportional to the square root of the
fractured grain size. Thus, how the layer fractures may be
important to its ability to absorb impact energy. Armor plates
manufactured according to methods known in the art tend to have a
fracture zone that look like a cone propagating from the location
of the impact, where the material closest to the impact site may
have a fine grain fracture size, but much of the fractured material
has a large grain fracture size and low energy dissipation. In
contrast, the armor plate 100 of the present invention disperses
the impact laterally, which causes fine grain fractures to occur
over a much wider surface area. This energy absorption allows the
armor plate 100 of the present invention to protect against higher
velocity projectiles compared to known armor plates with a similar
thickness.
[0045] With reference now to FIG. 6, deformable layer 110, ceramic
layer 112, fracture layer 114, and spall liner 116 can be joined
together to form plate 100 using any technique known in the art. In
one embodiment, the layers of armor plate 100 are joined together
using curable resins, heat, adhesives, and/or pressure. Preferably,
the layers are secured to each other such that armor plate 100 is
at least translucent and preferably transparent. In one embodiment
transmission values of light in the visible spectrum is at least
about 70%, more preferably at least about 80%, and even more
preferably at least about 90%.
[0046] FIG. 6 illustrates an example embodiment where deformable
layer 110, ceramic layer 112, fracture layer 114, and spall liner
116 are joined together by a plurality of intermediate layers such
as adhesive layers 142a, 142b, and 142c. Adhesive layers 142a,
142b, and 142c can be made from any material compatible with
deformable layer 110, ceramic layer 112, fracture layer 114, and/or
spall liner 116. Examples of suitable materials include polymers or
resins such as, but not limited to, polyvinyl butyral,
cyanoacrylates, epoxies, polyurethanes, acrylics, and combinations
of these. The adhesives may be transparent or nontransparent. In
one embodiment intermediate layers such as, but not limited to
adhesive layers 142, may have a thickness less than 10 mm, more
specifically less than about 2 mm, more specifically less than
about 1 mm, or even less than 100.mu.. if present, the intermediate
layers have a thickness that does not prevent a compression wave
from traveling between deformable layer 110, ceramic layer 112,
and/or fracture layer 114. For many materials, a thickness less
than 2 mm more preferably less than 1 mm can be used.
[0047] The layers of armor plate 100 can also be held together in
parallel using means other than an adhesive. For example, armor
plate 100 can have deformable layer 110, ceramic layer 112, and/or
fracture layer 114 in free contact with one another, but clamped
together using a frame or other clamping mechanism. A frame or
other substrate, such as those illustrated in the devices shown in
FIGS. 7-10, can apply a positive force on armor plate 110 to clamp
or otherwise secured the layers together.
[0048] The overall thickness of armor plate 100 will typically
depend on the amount of protection desired. Armor plates for
preventing the penetration of high momentum projectiles may be of
greater thickness than those for preventing the penetration of
lower momentum projectiles, but with increased weight. In one
embodiment the combined thickness of the deformable layer, ceramic
layer, fracture layer, and spall liner have a thickness of less
than 50 mm, more preferably less than 25 mm, even more preferably
less than 20 mm, and most preferably less than 15 mm. In an
alternative embodiment, the deformable layer, the ceramic layer,
the fracture layer, and the spall liner have a combined thickness
in a range from about 4 mm to about 25 mm, more preferably from
about 5 mm to about 20 mm, and most preferably about 6 mm to about
15 mm.
[0049] In some embodiments it may be desirable to make armor plate
100 as thin and as light as possible while achieving a desired
level of protection from projectile impact. To achieve a desired
thinness, it can be advantageous to make armor plate 100 with only
four layers (i.e., deformable layer, ceramic layer, fracture layer,
and spall liner) and optionally an adhesive between one or more of
the layers and/or a surface coating for modifying optical
transmissions (e.g., a tint).
[0050] In one embodiment, armor plate 100 may include additional
layers on front surface 117 and/or back surface 119. For example,
armor plate 100 may include coatings that modify the color and/or
light transmission through armor plate 100. In one embodiment a
tint coating may be applied to armor plate 100. For example, a tint
coating may be desirable for an armor plate used as a window to
reduce the amount of light entering through the window and/or to
inhibit people on an outside of the window to see inside.
[0051] To form armor plate 100, the layers of armor plate 100 can
be temporarily fastened together, for example, with tape, and then
placed in an autoclave, optionally under vacuum. The armor plate
100 may be pressurized and/or heated. Pressures that may be used
include atmospheric, greater than atmospheric, greater than 2 bar,
greater than 4 bar or greater than 8 bar. In some embodiments,
pressure may be applied in a pressure chamber or by mechanical
means, for instance, rollers or a press. Pressure and heat may be
applied until the adhesive layers 142 (e.g., PVB) reach a softening
point, allowing air bubbles to be expelled and allowing the
adhesive to clarify and flow.
[0052] The softening temperature of adhesives layers 142 may be,
for example, greater than 70.degree. C., greater than 100.degree.
C., greater than 150.degree. C., greater than 200.degree. C., or
greater than 250.degree. C. In some embodiments the optimum
temperature will depend on the pressure applied and the specific
adhesive material used to bind the layers. In an alternative
embodiment adhesive layers 142 can be polymerized to join the
layers of armor plate 100.
[0053] After hardening, cooling, and/or polymerizing, the layers of
armor plate 100 are securely immobilized in relation to each other
and may be mounted in a substrate. FIGS. 7-9 illustrate example
supporting structures that armor plate 100 can be incorporated
into. FIG. 7 shows an armored vehicle 150 having a first armor
plate 100a, a second armor plate 100b, and a third armor plate 103
which function in Windows on vehicle 150. Armor plates 100a and
100b are mounted in doors 152 and 154, respectively of a body 156.
Armor plate 100c functions as a front window Body 156 provides a
protective enclosure within its interior. Armor plates 100a and
100b may be transparent so as to allow personnel in the interior of
body 156 the ability to view the surroundings exterior to body 156.
Body 156 may be made from an armored material, which is typically
opaque. Armored vehicle 150 can include wheels 158 an engine cabin
160 and other features typical of vehicles for providing locomotion
(e.g., engine and drivetrain). Armored vehicle 150 can be of any
type known in the art, including but not limited to, cars, trucks,
boats, airplanes, trains, and the like.
[0054] FIG. 8 illustrates a helmet 200 that incorporates an armor
plate 100d according to the present invention. Armor plate 100d is
incorporated into a visor 202 having a curved surface secured to a
helmet structure 204 through a pair of fasteners 206 on opposing
sides of helmet structure 204. Visor 202 functions as a transparent
face shield. Helmet 200 may include one or more brackets 208 and
210 to support visor 202. Visor 202 is preferably transparent so as
to allow a person wearing helmet 200 to view their surroundings.
Armor plate 100 is particularly advantageous when used in articles
that are worn on the head of a person. The use of fracture layer
114 and armor plate 100 allows substantial percentages of the
momentum of a bullet or other object to be absorbed into fracture
layer 114 without transferring momentum to be supporting structures
such as helmet structure 204. This protects the wearer from
injuries that can be caused by rapid acceleration of helmet
200.
[0055] FIG. 9 illustrates yet another embodiment of a device that
can incorporate armor plate 100. FIG. 9 shows goggles 220 having
armor plate 100e, which function as a lens. Armor plate 100e is
mounted in frame structure 222. Armor plate 100e can be shaped to
provide a lens for correcting myopia and/or hyperopia. A strap to
24 allows goggles 220 to be worn on a person's head.
[0056] While FIGS. 6-8 illustrate specific examples of devices in
which armor plate 100 may be incorporated, those skilled in the art
will recognize that armor plate 100 may be incorporated into any
structure where a thin, armored, transparent and/or translucent
plate is desirable. For example, armor plate 100 may be used in
windows of buildings, paneling or walls in or on buildings,
including buildings where target shooting is carried out. While the
present invention is advantageous for use with devices that need to
be armored against artillery threats, the present invention is not
limited to these. Armor plate 100 can be used in any application
where a projectile could pose a threat (e.g., motorcycle helmets
designed to protect against flying debris on a road).
[0057] In one embodiment armor plate 100 can be segmented into a
panel of armor plates. FIG. 10 illustrates a panel 250 having four
segmented armor plates 100f. Segmented armor plates 100f are
mounted in a frame structure 252. Segmenting the armor plates
reduces crack propagation between portions of the armor plate. In
one embodiment, the individual segments are sized to minimize crack
propagation between segments while providing a suitable viewing
area. Minimizing crack propagation prevents one segment from being
compromised by a bullet striking an adjacent segment. In one
embodiment this segment can have a surface area in a range from
about 0.5 in.sup.2 to about 10 in, 1-4 inches.
EXAMPLES
[0058] The following examples provide formulas for making
transparent armor plates according to one embodiment of the
invention.
[0059] Example 1 describes a first type of armored plate (Type I).
Type I had a deformable layer of 0.05'' thick Lexan, followed by
0.065'' of sapphire (ceramic layer), then 0.125'' soda lime glass
(fracture layer) and 0.0935'' of Lexan (spall liner). The sandwich
was glued with a thin layer (25.mu.) of transparent
poly(vinylbutiral) resin.
[0060] Example 2 describes a second type of armor plate (Type II).
Type II sandwich was made of 0.05'' Lexan (deformable layer),
0.065'' sapphire (ceramic layer), 0.0625'' soda lime glass
(fracture layer) and 0.125'' Lexan (spall liner). The sandwich was
glued with a thin layer (25.mu.) of transparent
poly(vinylbutiral)].
[0061] Example 3 describes a third type of armored plate (Type
III). Type III was made of 0.05'' Lexan (deformable layer),
followed by 0.1425'' of sapphire (ceramic layer), then 0.075''
glass (fracture layer) and 0.1'' of Lexan (spall liner).
[0062] Example 4 describes a fourth type of armored plate (Type
IV). Type IV was made of 0.05'' Lexan (deformable layer), followed
by 0.0625'' of sapphire (ceramic layer), then 0.125'' glass
(fracture layer) and 0.1'' of Lexan (spall liner).
[0063] Example 5 describes a fifth type of armored plate (Type V).
Type V was made of 0.1'' Lexan (deformable layer), followed by
0.12'' of spinel (ceramic layer), then 0.12'' glass (fracture
layer) and 0.1'' of Lexan (spall liner).
[0064] Type III-V were bonded using an extra thick (1-1.2 mm)
adhesive layer instead of the desired 25.mu.layer. As expected,
this increase in the adhesives they are attenuated the shock wave
on the interface between the ceramic she and the fracture layer,
thereby adversely affecting armor plate performance. Nevertheless,
Examples III-V outperform traditional transparent armor plates.
[0065] Ballistic tests were conducted at the Indian Head Naval
Surface Warfare Center range. Tests were with 22-caliber 17-grain
fragment simulating projectile (FSP). This FSP is a standard
projectile for transparent armor testing. Changing propellant mass
in a cartridge varied projectile velocity. Four Ohler model 57 beam
interrupter velocity screens were used to measure the velocity. The
target system had a motor controlled positioning. The velocity data
was collected using a high-speed data acquisition system. A high
speed Phantom camera provided video recordings of the shots.
Example Test parameters are shown in Table 1 below, where PP
indicates partial sample penetration. The tests shown in Table 1
are for Type I materials. Similar tests were performed for samples
Types II-IV.
TABLE-US-00001 TABLE 1 Charge Wt Velocity Pene- Shot # Powder
Projectile (g) (rUs) tration 1. Black Powder 0.22 FSP 0.25 1281 PP
2. Black Powder 0.22 FSP 0.275 1279 PP 3. Black Powder 0.22 FSP
0.32 1369 PP 4. Black Powder 0.22 FSP 0.35 1445 PP 5. Black Powder
0.22 FSP 0.375 1519 PP 6. Black Powder 0.22 FSP 0.4 1545 PP 7.
Black Powder 0.22 FSP 0.425 1628 PP 8. Black Powder 0.22 FSP 0.425
1577 PP 9. Black Powder 0.22 FSP 0.45 1529 PP 10. Black Powder 0.22
FSP 0.475 1681 PP 11. Black Powder 0.22 FSP 0.5 1492 PP
[0066] Test results for Types I-V are shown FIG. 11 in the form of
V.sub.50 velocities versus plate weight normalized to the area
unit. FIG. 11 also shows V.sub.50 for Lexan (dotted line) and
sapphire (solid line). As shown in the data plotted in FIG. 11, all
the samples from Example 1-5 outperformed sapphire and Lexan.
Moreover, extrapolated velocities indicate better performance by
the transparent armor plates of the present invention than for any
most, if not all, existing transparent armor, even without layer
optimization.
[0067] As shown in FIG. 11, Type I samples significantly
outperformed Type II samples, providing more than 1700 Ft/s
V.sub.50. This result indicates that increasing the glass thickness
at the expense of Lexan improves armor plate performance. This is a
surprising and unexpected result since glass alone is very inferior
to Lexan. This result also confirms that a significant portion of
the projectile's momentum was absorbed in the fracturing of the
glass.
[0068] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *