U.S. patent application number 10/299987 was filed with the patent office on 2004-05-20 for method of making a protective material and articles made therefrom.
This patent application is currently assigned to Integrity Testing Laboratory Inc.. Invention is credited to Efim, Litovsky, Kleiman, Jacob I., Tatyana, Litovsky.
Application Number | 20040094026 10/299987 |
Document ID | / |
Family ID | 32297821 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040094026 |
Kind Code |
A1 |
Efim, Litovsky ; et
al. |
May 20, 2004 |
Method of making a protective material and articles made
therefrom
Abstract
A method of preparing a protective material is shown. In one
aspect the method includes the steps of providing a powder mixture
of solid particles having a size in the range of colloidal up to
100 .mu.m. The particles have a ceramic or mineral composition.
Then a liquid is provided to form an external phase of a suspension
when mixed with the powder, to yield a solids volume concentrating
greater then 0.5. The solid powder liquid mixture forms a
thixotropic-dilatant liquid material. The rheological curve of the
TDLM is adjusted to suit the application, resulting in thixotropic
properties at low strain rates and dilatant properties at higher
strain rates to yield a material that solidifies upon impact. The
rheological curve is adjusted by one or more of additives, material
composition and gravity mixing. In another aspect protective
articles made from TDLM are provided.
Inventors: |
Efim, Litovsky; (Richmond
Hill, CA) ; Tatyana, Litovsky; (Richmond Hill,
CA) ; Kleiman, Jacob I.; (Thornhill, CA) |
Correspondence
Address: |
VIDAS, ARRETT & STEINKRAUS, P.A.
6109 BLUE CIRCLE DRIVE
SUITE 2000
MINNETONKA
MN
55343-9185
US
|
Assignee: |
Integrity Testing Laboratory
Inc.
Markham
CA
|
Family ID: |
32297821 |
Appl. No.: |
10/299987 |
Filed: |
November 19, 2002 |
Current U.S.
Class: |
89/36.02 |
Current CPC
Class: |
F41H 5/0414
20130101 |
Class at
Publication: |
089/036.02 |
International
Class: |
F41H 005/02 |
Claims
We claim:
1. A method of preparing a protective material comprising the steps
of: providing a powder mixture of solid particles having a particle
size in the range of colloidal size up to 100 .mu.m, said solid
particles being of ceramic and/or mineral composition; providing a
liquid to form an external phase of a suspension when mixed with
said powder with a solids volume concentration of greater than 0.5;
mixing said powder and said liquid together to form a
thixotropic-dilatant liquid material TDLM; adjusting the
rheological curve of said material; and producing a TDLM having a
dependence of viscosity on strain rate which is thixotropic or
constant at lower strain rates and dilatant at higher strain rates
wherein said TDLM solidifies on impact.
2. A method as claimed in claim 1 wherein said solid particles in
the powder mixture are selected from the group of fused silica,
silica, quartz, alumina, vermiculate, mica or other crystalline
and/or amorphous materials.
3. A method as claimed in claim 1 further including adding
admixtures of alkaline and/or acid substances, or industrial
surfactants.
4. A method as claimed in claim 1 wherein said step of providing
said powder further comprises wet grinding said solid particles in
a suspension.
5. A method as claimed in claim 1 wherein said step of wet grinding
the solid particles results in a particle size distribution in the
range from colloidal to 100 .mu.m with a solid particles volume
concentration of C.sub.V>0.80 and colloidal fractions content of
C.sub.V>0.005, all having a specific surface of >0.5
m.sup.2/g (larger than 0.5 m.sup.2/g).
6. A method as claimed in claim 4 further including the step of
drying said suspension.
7. A method as claimed in claim 1 wherein said step of mixing said
liquid and said powder comprises gravitational mixing.
8. A method as claimed in claim 1 further including adding organic
fluids to permit applications of said TDLM to be used at
temperatures below 0.degree. C.
9. A method as claimed in claim 7 wherein said step of
gravitational mixing/treatment comprises slowly rotating a volume
of said material in a rotating volume with rotational velocity of
1-60 revolutions/min for at least 12 hours.
10. A method as claimed in claim 1 wherein said step of adjusting
the rheological curve further comprises adjusting the solids volume
concentration of said material by adjusting the proportions of said
powder or said liquid in said material.
11. A method as claimed in claim 1 wherein said step of adjusting
the Theological curve further comprises extending a period of
gravitational mixing/treatment by at least 24 hours.
12. An armour material comprising: at least two layers including an
outer layer and an inner layer; the outer layer consisting of a
thixotropic-dilatant liquid material having a first rheological
curve; the inner layer consisting of a thixotropic-dilatant liquid
material having a second Theological curve; wherein the first
rheological curve has a critical shear stress at a higher shear
rate than the second curve.
13. An armour material comprising: a layer of thixotropic-dilatant
liquid material; and a projectile resistant material that is not
rigidly fixed, in contact with said layer, to disperse and
redistribute shear forces caused by a projectile across an area
within said layer.
14. An armour material as claimed in claims 12 or 13 further
including at least one containment structure for containing said
layers of thixotropic-dilatant liquid material therein.
15. An armour material as claimed in claims 12 or 13 wherein the
layers containing TDLM are hermetically enclosed to prevent liquid
evaporation and changes of rheological properties.
16. An armour material as claimed in claim 14 further including a
valve on said containment structure for controlled pressure release
of gasses arising in the containment structure.
17. An armour material as claimed in claim 12 comprising cells with
rigid walls containing the said TDLM structures wherein side walls
of cells are made of hard and strong materials and are rigidly
fixed to increase armour protection.
18. An armour material as claimed in claim 12 wherein the front
wall has a coating with a coefficient of heat emission <0.3
(e.g. Ni, etc.) to reflect heat radiation.
19. An armour material as claimed in claim 12 wherein some layers
are made of metal and carbon containing materials to improve
protection from ioning radiation.
20. A method for long term storage of the protective materials as
claimed in claims 12 or 13 comprising slowly rotating or otherwise
gravitational stirring said material while said materials are being
tested.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to the field of material
sciences and more specifically to liquid materials which exhibit
non-linear changes in shear strength with changes in shear rate.
More particularly this invention relates to materials which when
properly formulated may be used for antiballistic protective
applications and other mechanical applications and to methods of
making, using, and storing such materials.
BACKGROUND OF THE INVENTION
[0002] It is well known that certain liquid materials exhibit a
non-linear increase of shear strength with an increase in shear
rate. This property is referred to as dilatancy. Typically such
materials are concentrated suspensions of a solid material in a
liquid. The solid may be an organic material or an inorganic
material, and the liquid may be water or an organic liquid.
Examples of known solid materials include polyvinyl chloride,
polymethyl methacrilate, polystyrene, titanium dioxide, various
pigments, kaolin, silica and others.
[0003] Dilatants have been proposed for use in many applications,
including personal armour. For example, U.S. Pat. No. 3,649,426
proposes flexible fluid dilatant armour for the insulation and
protection of personnel and equipment from intense sound rays,
heat, light, and high velocity projectile impacts. The patent
teaches mixing a dilatant fluid and powder solid mixture containing
over 75% solid particles of for example silica, having a particle
size of from colloidal to about 100 mesh size, with a continuous
liquid phase and encasing the mixture in a container. However, the
patent fails to teach the rheological properties of the
mixture.
[0004] U.S. Pat. No. 5,854,143 teaches a material for use in
antiballistic clothing comprising a single layer or multilayer
package or laminate including at least one layer of a flat
structure containing an organic dilatancy agent. This patent
teaches that an organic agent can be used to improve the
antiballistic effect. This patent further states that the stopping
power of the material proposed in U.S. Pat. No. 3,649,426 is too
low, thereby requiring excessively thick layers. Again however,
this patent fails to teach the rheological properties of the
dilatant material comprising the package.
[0005] To date neither prior art approach of U.S. Pat. Nos.
3,649,426 or 5,854,143 has achieved any significant commercial
success.
[0006] It is also well known that certain materials have a property
opposite to dilatancy, in which the liquid material becomes less
viscous with a higher rate of shear. This property is known as
thixotropy, and materials having this property include asphalt,
emulsions, ceramic suspensions and many food products.
SUMMARY OF THE INVENTION
[0007] What is needed is a protective material for personnel
protection which is both comfortable and lightweight and yet
exhibits superior stopping power to projectile impacts. What is
further required is a material which is relatively viscous in its
undisturbed shape, which becomes less viscous under slight to
moderate shear and which exhibits a non-linear increase of shear
strength when subjected to high shear rates. Such a material
therefore exhibits thixotropic properties for low shear rates and
dilatant properties for high shear rates and may be referred to as
a thixotropic-dilatant liquid material ("TDLM").
[0008] What is further needed is a method of formulating such a
material to achieve such preferred properties and a method of
storing an article made from such a material to retain such
preferred properties.
[0009] Therefore, according to the present invention there is
provided a method of preparing a protective material comprising the
steps of:
[0010] providing a powder mixture of solid particles having a
particle size in the range of colloidal size up to 100 .mu.m, said
solid particles being of ceramic and/or mineral composition;
[0011] providing a liquid to form an external phase in the form of
a suspension when mixed with said powder with a solids volume
concentration of greater than 0.5;
[0012] mixing said powder and said liquid together to form a
thixotropic-dilatant liquid material having a Theological
curve;
[0013] adjusting the Theological curve; and
[0014] producing a material having dependence of viscosity on
strain rate which is thixotropic or constant at lower strain rates
and dilatant at higher strain rates wherein said TDLM solidifies on
impact.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Reference will now be made, by way of example only, to
preferred embodiments of the present invention in which:
[0016] FIG. 1 is a graph showing the rheological curve for the
present invention at various pH values;
[0017] FIG. 2 is multilayered protective structure;
[0018] FIG. 3 is a diagram of a protective structure -according to
one aspect of the invention; and
[0019] FIG. 4 is a sealed protective structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The present invention is directed to the formulation of a
thixotropic-dilatant liquid material (TDLM) which has use in
protective armour as well as in various mechanical applications.
The first step in the method is to provide a powder mixture of
solid particles having a particle size range from colloidal size up
to about 100 .mu.m. While ceramic solids are preferred various
forms of ceramic and/or mineral compositions can be used. Some
examples include fused silica, silica, quartz, alumina,
vermiculate, mica, crystalline substances and amorphous materials.
Other materials may also be suitable as will be understood by those
skilled in the art. Essentially what is required in the TDLM is
that the material exhibit the property of non-linear increase in
shear strength in response to an increase in shear rate when placed
in a liquid suspension.
[0021] The preferred method of obtaining the powder is to wet grind
the solid particles. An important aspect of the invention is the
particle size distribution. What is preferred is to carefully
control the wet grinding conditions, such as rate and duration,
until the volume content of solids in the suspension is over 50%,
preferably reaches over 75% and most preferably is over 80%.
Another desired property of the powder according to the present
invention is that it has, in suspension, a specific surface area of
greater than 0.5 m.sup.2 per gram that corresponds to a content of
colloidal fraction >0.5%. Other methods to control the colloidal
particle content are also available, for instance, centrifugal
separation.
[0022] The next step is either to use the prepared suspension
directly, or if a different external liquid is preferred, to dry
the suspension to yield a powder with the required particle size
distribution and which, when mixed in the correct proportions with
the liquid, provides the specific surface properties as
aforesaid.
[0023] The next step is to select an appropriate liquid to mix with
the dried powder, if the powder has been dried. Then the liquid and
powder must be mixed, with the liquid being the external phase and
so a step of gravitational mixing to form a suspension is
preferred. The gravitational mixing is most preferably in the form
of a slow rotational mixing of the suspension which helps to
establish the rheological properties of the mixture. Such mixing
according to the present invention is to increase the stability of
the suspension to resist sedimentation, to permit gas to escape,
and thus to generally increase the density of the material.
[0024] One form of gravitational mixing that has yielded
satisfactory results is the use of a slowly rotating container in
which the liquid suspension is contained. Most preferably such
mixing is gentle enough that turbulence, which would otherwise
introduce extra gas and voids into the mixture is avoided. Speeds
of between 1 and 60 revolutions per minute are preferred with about
20 to 40 revolutions per minute being the most preferred. One of
the aspects of the present invention is that the duration of the
gravitational mixing has an effect on the rheological properties of
the material. For example, mixing for a period of at least 12 hours
is desired to achieve a relatively stable and dense material.
However, by mixing the suspension as described for over 24 hours,
changes to the rheological curve can be made, as described in more
detail below in the examples. Thus, the present invention
contemplates that one method to adjust the rheological curve is to
control the duration of the gravitational mixing step.
[0025] A further aspect of the present invention is to use
additives to adjust the Theological curve. These additives can
include acids, acid salts, alkaline, or industrial surfactant
materials. Thus, one aspect of the invention is to adjust the
Theological properties of the TDLM by changing the pH of the
material. In addition the liquid selected can be from the range of
organic liquids that have low freezing temperatures, such as
alcohol and glycerine and the like. In this aspect the present
invention provides for low temperature applications for the
materials.
EXAMPLE 1
Control of Rheological Curve of TDLM
[0026] One aspect of the present invention is to control the
rheological curve of TDLM by selecting a preferred pH which will
yield a Theological curve having desired attributes. Thus one
realization of the present invention is that the rheological
properties can be varied with pH to adjust the negative slope of
the curve of change in shear strength for change in shear rate
(thixotropy) as well as the positive slope of the same curve at
higher shear rates (dilatancy). As well, it is also possible to
adjust the position of the inflection point. These discoveries are
demonstrated by a test performed on a quartz glass suspension with
water in the external liquid.
[0027] A basic suspension of quartz glass (SiO2=99.8%) in water was
prepared by wet grinding in a ceramic mill with alumina balls. The
solid particle sizes making up the suspension varied from 0.01
.mu.m to 60 .mu.m. A BET specific surface was measured at 2
m.sup.2/g. After grinding the suspension was gravitationally mixed
(without balls) for 36 hours to stabilize the rheological
properties. The rheological properties were measured by a rotary
viscosimeter in a range of angular velocities from 0.7 to 700 1/sec
at 20.degree. C., and the pH was varied to generate different
rheological curves as set out in FIG. 1. FIG. 1 shows generally the
relationship of viscosity to shear rate (in, for example,
revolutions per minute of a mixing container). It will be
understood by those skilled in the art that the shear rate is
related, in a complex way to the strain rate arising in the
material. Thus, at high shear rates, shear thickening is desired to
prevent a projectile, for example, from passing through the
material.
[0028] In addition, the mixtures were tested by applying a load to
the mixture. After load removal, relaxation of the solidified
material occurred, the suspension regained its fluidity, and shear
stress dropped to zero within 1-2 sec or less. Sometimes solidified
agglomerates (blocks) could be observed in the material after
testing, which then slowly dispersed over time.
EXAMPLE 2
Pistol Shooting Test
[0029] A bullet was fired from a pistol (velocity about 500 m/sec)
towards an open surface of a suspension, prepared in accordance
with example 1 having a pH of 10. The suspension was carried in a
small cup about 5 cm in diameter and 3 cm wall thickness. The
stopping distance for the bullet was about 1.5 cm.
EXAMPLE 3
Automatic Rifle Shooting Test
[0030] Another test was carried out with a Kalashnikov automatic
rifle from a distance of 10 m. A plastic container was used to
contain the suspension, with an open surface, having an amount of
suspension of 120 cm.sup.3. The suspension consisted of a TDLM as
prepared in example 1 having a pH of 10. After shooting the bullet
into the volume, the whole volume was solidified, and the resulting
solid was cracked and broken. It was concluded that for such a
powerful weapon composite materials, such as a high strength solid
thin first layer may be required together with the TDLM.
EXAMPLE 4
Impact Test
[0031] A measurement of the mechanical properties of the suspension
of example 1 at high strain rates was carried out in an impact test
system. The suspension was placed into cylindrical tank. A rigid
rod with a metallic ball or cylindrical tip mounted on its end was
mounted to the tank in such a way that it could freely move inside
suspension in a vertical direction. The diameter of the probing
ball or cylindrical tip was varied from 5 to 50 mm. An impact force
was applied to the upper end of the rigid rod by an impactor. The
impactor was in the form of a half-sphere with radius of 12.7 mm,
and a total falling mass was 1.33 kg. The velocities of the
impactor were measured by photocell, and the acceleration of the
impactor was measured by precision accelerometer. The output
signals from the photocell and accelerometer were monitored by
oscilloscope and transferred to computer for data processing.
[0032] In the impact test the impactor's acceleration versus time
was determined during dynamic loading. The instant velocity and
displacement of the impactor were computed by subsequent
integration of the acceleration over time. The system thus measured
the drag forces, acting on the probing ball moving in the
suspension.
[0033] An anomalous energy dissipation in the suspension was
demonstrated. Essentially the fluid suspension behaves as a rigid
solid during the loading. After unloading, a fast dissipation of
energy occurs, which is the characteristic feature of an extremely
viscous liquid. Such behaviour characterizes a material with high
potential for use as an armour material.
[0034] A second type of impact test was made. In this case a rod 5
mm in diameter and weighing 2.3 kg was dropped from a height of 4 m
onto an open surface of the material. The surface of the TDLM (the
same in example 1) solidified instantly and the rod did not
penetrate into the liquid. After impact the solidified surface was
absolutely smooth and unfigured.
EXAMPLE 5
Organic Liquid Based Suspensions
[0035] In this example a highly dilatant suspension based on
glyceraol was formulated. At the first stage it was prepared
according to example 1 by milling in water. Then, the mixture was
subjected to the gravity mixing process for in excess of 24 hours
to form a stable suspension. Then water based suspension was dried
again during gravity mixing to prevent sedimentation of suspension
during evaporation. The organic component in this example glycerin,
was then added during gravity mixing until the mixture met the
required concentration.
EXAMPLE 6
Impact Test
[0036] The same impact tests as in example 4 were carried out for
the suspension of example 5, namely, C.sub.V=85% fused silica, 10%
glycerol and 4% water, admixture of sodium silicate up to pH=9. The
liquid also solidified instantly and the rod did penetrate past the
surface of the material but only just barely. After impact an
impression was visible of about 1-3 mm deep for about 2-3 sec.
[0037] As a result of conducting the tests as described above, a
table was developed which identifies the recommended solids volume
concentration C.sub.V, pH and time of gravitational mixing for
different applications. Below, Table 1 presents the information in
accordance with the present invention.
1 TABLE 1 Application C.sub.V pH GM, hour Armour (first layer)
>0.75 2-7 >24 Armour (second layer) >0.75 4-13 >24
Armour Composite (with >0.70 7-10 >12 super solid surface
layer) Velocity regulators >0.70 1-7 >6 Brakes, viscoelastic
>0.75 7-13 >6 dampers, packing materials Amusement devices
>0.55 1-14 >0
[0038] From the above-noted table it is noted that adding
water-soluble polymers such as methylcellulose provides an increase
of viscosity in the thixotropic part of the rheological curve. On
the other hand, a decrease in the viscosity of the thixotropic part
of the rheological curve can be provided by extending the
gravitational mixing process for longer periods, such as 24 hours
for instance.
[0039] Other additives can be used to control the separation of the
solids from the liquid, such as alkaline additives, or other
materials containing colloidal silica fractions of 1-2 nm, for
example, sodium silicate solution. Such additives control the
sedimentation stability of the material. In addition, as will be
noted from FIG. 1 and Table 1, improved workability of a TDLM can
be obtained by providing a pH in the range of 2 to 3. In this case
improved workability means that the material flows fast making it
easy to fill different types of containers. Thus, according to the
present invention, the material can be provided with one pH on
fabrication, to facilitate being placed inside containers, and then
the pH adjusted to improve the rheological characteristics once in
the container, such as to optimize the thixotropic dilatancy curve
for personnel armour protection from projectile impacts.
[0040] The present invention therefore comprehends using TDLM as an
armour material in various embodiments and configurations. The
liquid ceramic materials can be modified for use in protection of
various engines, compartments and other crucial and strategic
places in trucks, tanks, armoured personnel carriers, etc. from
high temperature-sudden impact conditions (explosion, fire hazard).
Various ways of designing such protection enclosures (portable
flexible bags, screens etc.) are comprehended by this
invention.
[0041] In one embodiment of the present invention, as shown in FIG.
2, there is provided a protective material which comprises an
exposed face 10, a rear face 12, and side walls 11 which
encapsulate or encase a layer of TDLM 13. A hard strong thin plate
14 such as a dense ceramic plate, Kevlar plate or even metal plate,
which is not rigidly fixed to the rigid container, but is simply
floating in the TDLM material is also shown. The side walls 11 of
the container can be also prepared from rigid and strong materials
and the front and rear walls 10, 12 can be of flexible materials.
Such a thin plate material 14 will tend to distribute the impact
force across the layer 14 and therefore will enhance the armour
properties of the layer. Thus, the present invention contemplates
the presence of a separate element 14 within the TDLM 13 which acts
to distribute impact shear through the material 13, to spread the
impact force to reduce impact shear from being passed through the
layer to the item being protected.
[0042] In the embodiment of FIG. 3, the armour material has a
multilayer structure where each layer 15, 16, 17 of the structure
preferably has different rheological curves. For example, an outer
layer 15, which would first receive the impact energy 16, would
preferably have a critical shear stress that starts at very high
rates and a high dilatancy. Subsequent layers 16, 17 can have lower
critical shear stresses. It is believed that such a layered
structure would operate to distribute the projectile impact from
the local area of the impact more broadly across the first layer
and subsequently more broadly across each of the layers below the
first layer.
[0043] In a further embodiment, as shown in FIG. 4, the present
invention contemplates that each layer of a multilayer protective
material be hermetically sealed or enclosed to prevent any liquid
evaporation over time. As noted above, changes in the solids volume
concentration arising by reduction in the liquid affects the
rheological properties of the TDLM. Therefore, to prevent any such
rheological changes occurring, the present invention comprehends
hermetically sealing the TDLM 19 into the armour container 18. Of
course, a consequence of a large impact is the generation of heat.
Due to the presence of the external liquid phase, generation of
heat can cause significant pressure peaks within the hermetically
sealed container. Therefore, the present invention further
contemplates a pressure release valve or valves 20, 21 to permit
the controlled release of pressure in the event of a sudden
pressure build up due to projectile impact or heat radiation.
[0044] A further aspect of the present invention relates to the use
of rigid lateral or side walls to increase the armour protection.
Use of rigid lateral side walls will help absorb energy, laterally
transferred by the TDLM material and will likely improve armour
characteristics.
[0045] In the alternative, the present invention also contemplates
flexible side walls for free deformation of the material without
damage upon ballistic impact.
[0046] In a further embodiment, the present invention contemplates
the exterior wall of the armour material having a coating with a
coefficient of heat emission less than or equal to 0.3 to reflect
heat radiation. Nickel metal would be appropriate for such an
external coating. In addition, the layers may contain materials to
improve protection against ionizing radiation, such as various
types of metal and carbon.
[0047] In a further aspect of the present invention, long term
storage of the armour and protective materials can be achieved
using slow rotation or other type of movement for continual
gravitational mixing or stirring. Such long term mixing or stirring
will prevent settling of the suspension in the liquid and the
subsequent change or loss of desirable Theological properties.
[0048] In summary therefore, it can be understood that the present
invention contemplates that for a number of armour purposes,
control of the rheological curve is very important for specific
applications. Control of the properties of the TDLM suspensions can
be achieved by small chemical additives and/or by gravitational
mechanical treatment. Other aspects affect or control the
Theological properties to increase storage time, increase
flexibility and alter the critical shear rate or solidification
point. Thus, the present invention teaches that the rheological
curve of TDLM can be engineered for this purpose of optimizing the
material for the application of armour and mechanical
properties.
[0049] The present invention is therefore directed to preparing
TDLM suspensions for armour and other applications all in
accordance with the foregoing.
[0050] It will be appreciated by those skilled in the art that
while mention has been made of various preferred alternatives, the
present invention is not limited to the forms and embodiment
discussed above. Rather, the scope of the invention is to be
determined by the scope of the attached claims.
* * * * *