U.S. patent application number 15/033573 was filed with the patent office on 2016-09-29 for shock absorption material.
The applicant listed for this patent is NEW AEGIS CORPORATION. Invention is credited to Ariana M. BRUNO, Paul A. BRUNO.
Application Number | 20160280880 15/033573 |
Document ID | / |
Family ID | 53005220 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160280880 |
Kind Code |
A1 |
BRUNO; Paul A. ; et
al. |
September 29, 2016 |
SHOCK ABSORPTION MATERIAL
Abstract
A composite material with an elastic modulus of less than 0.1
MPa at 100% elongation including a polymer matrix and a
non-Newtonian fluid is provided. The composite material may be
employed in shock and impact absorption applications to reduce
initial and shockwave acceleration forces. Methods of forming the
composite material and reducing acceleration forces in an impact
utilizing the composite material are also provided.
Inventors: |
BRUNO; Paul A.; (Ann Arbor,
MI) ; BRUNO; Ariana M.; (Foothill Ranch, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEW AEGIS CORPORATION |
Ann Arbor |
MI |
US |
|
|
Family ID: |
53005220 |
Appl. No.: |
15/033573 |
Filed: |
October 31, 2014 |
PCT Filed: |
October 31, 2014 |
PCT NO: |
PCT/US14/63526 |
371 Date: |
April 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 2471/02 20130101;
C08J 2433/26 20130101; A42B 3/125 20130101; C08J 2471/08 20130101;
C08J 9/42 20130101; C08J 2207/00 20130101; C08J 2383/04 20130101;
C08J 2375/04 20130101; C08J 2325/06 20130101; C08J 2375/08
20130101; C08J 2483/04 20130101 |
International
Class: |
C08J 9/42 20060101
C08J009/42; A42B 3/12 20060101 A42B003/12 |
Claims
1. A composite material comprising: a polymer foam matrix; and a
non-Newtonian fluid impregnated in the polymer foam matrix, wherein
the composite material has an elastic modulus of less than 0.1 MPa
at 100% elongation.
2. The composite material of claim 1, wherein the polymer foam
matrix has a density in the range of about 50 g/m.sup.3 to about
500,000 g/m.sup.3.
3. The composite material of claim 1 or 2, wherein the polymer foam
matrix comprises a material selected from the group consisting of
elastomers, polystyrene, polyethylene, polypropylene, polyamide,
polyurethane, ethylvinyl-acetate, polyethylene oxide, polyacrylate,
cellulose, ethylene vinyl alcohol, polybutylene, polycaprolactone,
polycarbonate, polyketone, polyester, polylactic acid, polyvinyl
chloride, polyphenylene, and copolymers thereof.
4. The composite material of any of claims 1-3, wherein the
non-Newtonian fluid is not covalently bonded to the polymer foam
matrix.
5. The composite material of any of claims 1-4, wherein the
non-Newtonian fluid comprises at least one material selected from
the group consisting of polydimethylsiloxane, substituted
polydimethylsiloxane, 1% w/v polyethylene glycol in water, 1% w/v
polyacrylamide in water, C8-silica particles in silicone oil,
silica particles in glycerol, and tin oxide particles in water.
6. The composite material of any of claims 1-5, wherein the
non-Newtonian fluid has a viscosity in the range of about 60,000
cSt to about 1,000,000 cSt.
7. The composite material of any of claims 1-6, wherein the
non-Newtonian fluid is hydrophobic.
8. The composite material of any of claims 1-7, wherein the
composite material has a density in the range of about 50 g/m.sup.3
to about 5,000,000 g/m.sup.3.
9. The composite material of any of claims 1-8, wherein the
non-Newtonian fluid is present in an amount of about 10% to about
90% of the total weight of the composite material.
10. The composite material of any of claims 1-9, wherein an initial
impact acceleration force and a shockwave acceleration force of an
impact cushioned by the composite material are less than an initial
impact acceleration force and a shockwave acceleration force of an
equivalent impact cushioned by the polymer foam matrix alone.
11. The composite material of any of claims 1-10, wherein an impact
cushioned by the composite material produces initial impact
acceleration force that is at least about 30% lower than an
equivalent impact cushioned by the polymer foam matrix alone.
12. A method of forming the composite material of any of claims
1-11, comprising: mixing a non-Newtonian fluid and a first polymer
foam matrix precursor to form a mixture; adding a second polymer
foam matrix precursor to the mixture of the non-Newtonian fluid and
the first polymer foam matrix precursor; mixing the mixture of the
non-Newtonian fluid, first polymer foam matrix precursor, and
second polymer foam matrix precursor to form a mixture; wherein
mixing the mixture of the non-Newtonian fluid, first polymer foam
matrix precursor, and second polymer foam matrix precursor results
in the foaming of the mixture and the formation of a polymer foam
matrix material, and curing the mixture of the non-Newtonian fluid,
first polymer foam matrix precursor, and second polymer foam matrix
precursor to form the composite material; and wherein the composite
material has an elastic modulus of less than 0.1 MPa at 100%
elongation.
13. The method of claim 16, further comprising disposing the
mixture of the non-Newtonian fluid, first polymer foam matrix
precursor, and second foam polymer matrix precursor in a mold prior
to curing the mixture.
14. A product for reducing acceleration forces in an impact,
comprising the composite material of any of claims 1-11.
15. The product of claim 14, wherein the product is selected from
the group consisting of a helmet, clothing, a uniform, footwear, a
glove, a case for an electronic device, a housing for an electronic
device, a vehicle seat, a vehicle headrest, a vehicle dashboard, a
vehicle door component, playground equipment, an exercise mat, a
gym mat, and a packaging material.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application No. 61/899,012, filed Nov. 1, 2013,
the entire disclosure of which is incorporated herein by
reference.
BACKGROUND
[0002] The present application relates generally to the field of
materials having utility in products and applications that provide
shock absorption properties, such as those products and
applications providing impact protection. More particularly, the
present application relates to materials that comprise a polymer
matrix impregnated with a non-Newtonian (i.e., shear thickening)
material.
[0003] Shock absorption materials have utility in a wide variety of
applications in which it is desirable to damp or mitigate
undesirable shocks to objects or to the human body (e.g., helmets,
sports padding, exercise mats, bicycle and motorcycle seats,
bumpers for movable carts and other objects, and the like). Short
term shocks (g-forces, measured in Nkg, in contrast to impact
forces, which are measured in Nm) may be induced in impacts, drops,
falls, earthquakes, and even explosions, and may also occur during
non-impact situations (e.g., during vehicle acceleration and
deceleration, airplane descent and ascent, person being
pushed/pulled, etc.). By way of reference, impacts experienced by a
football lineman may regularly result in g-forces of between
approximately 20-30 g, and may in some instances produce forces in
excess of 100 g. Jogging may produce g-forces of between
approximately 4 and 6 g, while sprinting may produce g-forces of
between approximately 8 and 10 g. The g-forces generated by impacts
and other sources of shock pose a direct threat to the well-being
and survival of humans every day, and significant resources are
devoted each year to finding new and better ways of providing shock
resistance or mitigation. Additionally, the g-forces generated by
impacts may produce long-term negative health effects, such as
chronic traumatic encephalopathy (CTE).
[0004] Certain types of relatively hard and rigid forms of
polyurethane and polystyrene foams have been used in applications
for shock absorption (e.g., in football helmets, etc.). These foams
tend to be relatively dense. While such foams have the advantage of
being able to withstand larger impacts, one disadvantage of such
foams is that they have relatively limited compressibility, and may
not optimally absorb the forces of smaller impacts experienced by
the user and may not be as comfortable as would be desirable for
certain applications. Research has shown that the cumulative effect
of smaller, sub-concussive, impacts may be long-term negative
health effects that exceed those of a limited number of large
concussive impacts. Pre-existing materials are not capable of
effectively absorbing both large impacts and small impacts, leaving
a user susceptible to injury.
[0005] It would be advantageous to produce an improved material
that may provide enhanced shock absorption and that reduces or
eliminates g-forces caused by impacts and other sources of shock.
It would also be advantageous to incorporate such a material into
products so as to provide enhanced shock protection. These and
other advantages will be apparent to those reviewing the present
disclosure.
SUMMARY
[0006] An exemplary embodiment relates to a composite material that
comprises a polymer matrix (e.g., a foam material, although
according to other exemplary embodiments, other types of polymer
matrix materials may be utilized) and a non-Newtonian fluid
(sometimes referred to as a shear thickening material or dilatant)
incorporated therein. The non-Newtonian fluid may be infused into a
pre-prepared polymeric matrix material or may be incorporated
during the synthesis or polymerization of the polymer matrix.
[0007] The composite material has an elastic modulus of less than
0.1 MPa at 100% elongation, and includes a polymer matrix in the
form of a foam and a non-Newtonian fluid impregnated in the polymer
foam matrix. The polymer foam may be an open-cell foam or a
closed-cell foam. The polymer foam may have a density in the range
of about 50 g/m.sup.3 to about 500,000 g/m.sup.3. The polymer foam
may be formed from a material selected from the group including
elastomers, polystyrene, polyethylene, polypropylene, polyamide,
polyurethane, ethylvinyl-acetate, polyethylene oxide, polyacrylate,
cellulose, ethylene vinyl alcohol, polybutylene, polycaprolactone,
polycarbonate, polyketone, polyester, polylactic acid, polyvinyl
chloride, polyphenylene, and copolymers thereof. The non-Newtonian
fluid may not be covalently bonded to the polymer foam. The
non-Newtonian fluid may include at least one material selected from
the group including polydimethylsiloxane, substituted
polydimethylsiloxane, 1% w/v polyethylene glycol in water, 1% w/v
polyacrylamide in water, C8-silica particles in silicone oil,
silica particles in glycerol, and tin oxide particles in water. The
non-Newtonian fluid may have a viscosity in the range of about
60,000 cSt to about 1,000,000 cSt. The non-Newtonian fluid may be
hydrophobic. The composite material may have a density in the range
of about 50 g/m.sup.3 to about 5,000,000 g/m.sup.3. The
non-Newtonian fluid may be present in an amount of about 10% to
about 90% of the total weight of the composite material. The
composite material may be incorporated into a product selected from
the group including a helmet, clothing, a uniform, footwear, a
glove, a case for an electronic device, a housing for an electronic
device, a vehicle seat, a vehicle headrest, a vehicle dashboard, a
vehicle door component, playground equipment, an exercise mat, a
gym mat, and a packaging material. An initial impact acceleration
force and a shockwave acceleration force of an impact cushioned by
the composite material may be less than an initial impact
acceleration force and a shockwave acceleration force of an
equivalent impact cushioned by the polymer foam alone. An impact
cushioned by the composite material may produce initial impact
acceleration forces that are at least about 30% lower than an
equivalent impact cushioned by the polymer foam alone.
[0008] Another exemplary embodiment relates to a product,
apparatus, or device (collectively referred to as "products") that
incorporates a composite material such as that described in the
preceding paragraph. Non-exclusive examples of products that may
utilize such composite materials include helmets (e.g., sports
helmets for use in football, baseball, hockey, lacrosse, or other
sports in which impacts may be experienced, motorcycle and bicycle
helmets, and any other type of helmet); padding for clothing or
uniforms (e.g., shoulder pads, shin pads, knee pads, elbow pads,
and any other type of padding worn by a human); footwear (shoe
soles, etc.); gloves (e.g., work gloves, sporting gloves such as
boxing gloves, hockey gloves, lacrosse gloves, etc.); cases or
housings for electronics such as phones, computers, tablets, and
the like; linings or padding for vehicle seats, child safety seats,
and other types of seating; vehicle headrests, dashboards, door
components, and other vehicle parts that may be impacted by a
driver or passenger in a vehicle collision; playground equipment
lining; exercise and gym mats; and packaging material for goods.
Stated differently, the composite material may be incorporated into
a helmet, clothing, a uniform, footwear, a glove, a case for an
electronic device, a housing for an electronic device, a vehicle
seat, a vehicle headrest, a vehicle dashboard, a vehicle door
component, playground equipment, an exercise mat, a gym mat, or a
packaging material.
[0009] Another exemplary embodiment relates to a method of making
the composite material and/or products made from or incorporating
the composite material. For example, an exemplary method may
include the steps of producing a non-Newtonian fluid, producing or
forming a polymer matrix, and incorporating the non-Newtonian fluid
into the polymer matrix. In another example, a method may utilize a
non-Newtonian fluid in the synthesis or polymerization of the
polymer matrix such that the non-Newtonian fluid is incorporated
into the matrix immediately upon formation of the matrix. Still
another example includes the steps of producing a composite
material that comprises a polymer matrix incorporating a
non-Newtonian fluid and incorporating the composite material into a
finished product such as those described herein.
[0010] An exemplary method of forming the composite material
includes mixing a non-Newtonian fluid and a first polymer foam
matrix precursor to form a mixture, adding a second polymer foam
matrix precursor to the mixture of the non-Newtonian fluid and the
first polymer foam matrix precursor, mixing the mixture of the
non-Newtonian fluid, first polymer foam matrix precursor, and
second polymer foam matrix precursor to form a mixture; wherein
mixing the mixture of the non-Newtonian fluid, first polymer foam
matrix precursor, and second polymer foam matrix precursor results
in the foaming of the mixture and the formation of a polymer foam
matrix material, and curing the mixture of the non-Newtonian fluid,
first polymer foam matrix precursor, and second polymer foam matrix
precursor to form the composite material. The formed composite
material has an elastic modulus of less than 0.1 MPa at 100%
elongation. The method may further include disposing the mixture of
the non-Newtonian fluid, first polymer foam matrix precursor, and
second foam polymer matrix precursor in a mold prior to curing the
mixture.
[0011] A method of reducing acceleration forces in an impact may
include disposing a composite material between an impact object and
an impact surface. The composite material has an elastic modulus of
less than 0.1 MPa at 100% elongation and includes a polymer foam
matrix and a non-Newtonian fluid impregnated in the polymer foam
matrix. An initial impact acceleration force and a shockwave
acceleration force of the impact may be less than an initial impact
acceleration and a shockwave acceleration of an equivalent impact
with the polymer foam alone disposed between the impact object and
the impact surface. The impact may produce an initial impact
acceleration force that is at least about 30% lower than an
equivalent impact with the polymer foam alone disposed between the
impact object and the impact surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1-3 are graphs illustrating comparative test results
for drop tests performed at 5, 7.5, and 11 inches,
respectively.
[0013] FIG. 4 is a graph illustrating expected shock absorption
profiles for normal impacts as compared to cushioned impacts.
[0014] FIG. 5 is a pair of graphs comparing shock absorption
profiles of polyurethane and polystyrene foams.
[0015] FIG. 6 is a pair of graphs comparing shock absorption
profiles of polystyrene and polystyrene impregnated with water.
[0016] FIG. 7 is a pair of graphs comparing shock absorption
profiles of polystyrene impregnated with two different
non-Newtonian fluids.
[0017] FIGS. 8(a)-8(d) illustrate a series of graphs summarizing
the shock absorption behavior of polystyrene impregnated with
select non-Newtonian fluids.
[0018] FIG. 9 provides a description of a polymerization process
incorporating a non-Newtonian fluid according to an exemplary
embodiment.
[0019] FIG. 10 is a graph comparing the shock absorption
performance of polyurethane form to that of PDMS-impregnated
polyurethane foam.
[0020] FIGS. 11(a) and 11(b) are graphs comparing the shock
absorption profiles of polyurethane foam by itself and
PDMS-impregnated polyurethane foam, respectively.
[0021] FIG. 12 is a graph comparing the impact drop test results of
an unmodified helmet and a helmet modified to utilize a
polyurethane foam-non-Newtonian fluid composite material.
[0022] FIGS. 13(a)-13(c) illustrate various perspective views of an
impact drop test rig, according to an exemplary embodiment.
[0023] FIGS. 14(a)-14(c) depict graphs comparing the acceleration
forces of an impact in a drop test of polyurethane foam, a
polyurethane and non-Newtonian fluid composite material with an
elastic modulus of greater than 0.1 MPa at 100% elongation, and a
polyurethane and non-Newtonian fluid composite material with an
elastic modulus of less than 0.1 MPa at 100% elongation,
respectively.
DETAILED DESCRIPTION
[0024] According to an exemplary embodiment, a shock absorption
material includes a polymer matrix (e.g., a polymer foam such as a
polystyrene or polyurethane foam, although other materials may be
used according to other exemplary embodiments as described herein,
including copolymers of various types) impregnated with a
non-Newtonian fluid to provide enhanced shock absorption
characteristics for the material and products incorporating such a
material. A wide variety of non-Newtonian fluids may be utilized,
either alone or in combination with each other, depending on the
particular performance characteristics, manufacturing
considerations, and other factors.
[0025] A non-Newtonian fluid is a fluid that is characterized by
the fact that its shear viscosity increases with applied shear
stress. A non-Newtonian fluid may sometimes be referred to as a
shear thickening material or dilatant, and for purposes of the
present disclosure, the three terms will be used interchangeably.
For example, a non-Newtonian fluid may exhibit the properties of a
liquid when the material is at rest, but when a force or stress is
applied to the material, the material begins to essentially
"thicken" and adopt some properties of a solid material. One
well-known example of a non-Newtonian fluid is a mixture of
cornstarch and water sometimes referred to as "oobleck," which
exhibits certain shear-thickening characteristics when a stress is
applied to the material.
[0026] According to an exemplary embodiment, the composite material
may be formed of a relatively soft foam matrix (e.g., a polystyrene
foam, a polyurethane foam, etc.) having a non-Newtonian fluid
incorporated therein. A soft foam matrix may refer to a matrix
material that is highly compressible. One advantageous feature of
such a composite material is that the material may act as a soft
foam under normal conditions in which little or no forces/stresses
are applied to the material, and when larger forces/stresses are
applied, the material increase in stiffness and/or hardness to
better absorb the shock or impact. Because the softening/hardening
effect is reversible, the composite material will return to its
original soft-foam-like behavior, such that the material can be
used for relatively long periods of time while retaining its
shock-absorbing effectiveness in response to applied
forces/stresses. The composite material is capable of providing
impact protection over a larger range of forces than is typical of
pre-existing foam materials.
[0027] The polymeric matrix may be formed from any of a wide
variety of materials, including, for example, natural and synthetic
elastomers (e.g., cis-polyisoprenes, trans-polyisoprenes,
polybutadiene, neoprene, butyl rubber (both halogenated and
unhalogenated), nitrile, silicone rubber, fluorosilicone rubber,
and polyacrylonitrile), polystyrene, polyethylene (high density and
low density), polypropylene, polyamide, polyurethane,
ethylvinyl-acetate, polyethylene oxide, polyacrylate, cellulose,
ethylene vinyl alcohol, polybutylene, polycaprolactone,
polycarbonate, polyketone, polyester, polylactic acid, polyvinyl
chloride, and polyphenylene. According to other exemplary
embodiments, the polymer matrix may include any combination of the
polymers as a copolymer (including alternating, periodic, random,
block and graft copolymers). According to other exemplary
embodiments, the polymer matrix may include fluorinated versions of
any of the foregoing polymers or any of the foregoing polymers that
have been substituted with other branched alkyl, aryl, or
halogenated substitutions.
[0028] According to a particular exemplary embodiment, the polymer
matrix is formed of a relatively soft polystyrene foam. In general,
polystyrene tends to be less dense than polyurethane, which makes
it more suitable for absorbing the impact forces of small objects
as compared to polyurethane, while the increased density of
polyurethane allows it to be more capable of absorbing forces of
large impacts as compared to polystyrene (additionally,
polyurethane may be better in certain applications where water and
sweat are present, since it is less susceptible to water vapor
absorption and mold growth than polystyrene). Both polystyrene and
polyurethane (and other polymers, such as those described above)
may be formed into relatively soft foams, and the inventors have
advantageously incorporated a non-Newtonian fluid into relatively
soft foams to provide enhanced shock absorption properties for the
foam. As will be described in more detail below, the incorporation
of a non-Newtonian fluid into the polystyrene foam may dramatically
alter the overall shock absorption capabilities of the material,
making it far more suitable for use in shock absorption
applications.
[0029] According to an exemplary embodiment, the polystyrene foam
has a density of between approximately 50 g/m.sup.3 and
approximately 500,000 g/m.sup.3, such as between approximately
50,000 g/m.sup.3 and approximately 500,000 g/m.sup.3 and, according
to a particular exemplary embodiment, approximately 100,000
g/m.sup.3. Of course, other types of foam and other densities may
be utilized according to other exemplary embodiments.
[0030] According to other exemplary embodiments, the polymer matrix
may be formed from any of the other materials described herein, and
may have differing materials properties that may be tailored or
selected for a particular application as desired.
[0031] The non-Newtonian fluid may be selected from any of a
variety of materials that exhibit shear thickening behavior,
non-exclusive examples of which include polydimethylsiloxanes, 1%
w/v polyethylene glycol in water, 1% w/v polyacrylamide in water,
or polydimethylsiloxanes with other alkyl, alkenyl, alkynyl,
phenyl, or halogenated substitutions in place of the methyl group.
Other possibilities include C8-silica particles in a silicone oil,
silica particles in glycerol, and tin oxide particles in water.
According to one embodiment, the non-Newtonian fluid is not
covalently bonded to the polymer foam matrix. Covalent bonds
between the polymer foam matrix and the non-Newtonian fluid may
constrain the movement of the non-Newtonian fluid in response to an
impact, preventing the effective absorption of impact energy and
the effective reduction of impact energy acceleration forces.
Covalent bonds between the polymer foam matrix and the
non-Newtonian fluid may also undesirably change the properties of
the polymer foam, such as by increasing the density of the polymer
foam.
[0032] According to an exemplary embodiment, the non-Newtonian
fluid may have a viscosity in the range of between approximately
60,000 cSt and approximately 1,000,000 cSt. According to other
exemplary embodiments, the non-Newtonian fluid may have a viscosity
of between approximately 100,000 cSt and approximately 500,000
cSt.
[0033] According to an exemplary embodiment, the composite material
(i.e., the foam having the non-Newtonian fluid incorporated
therein) may have a density in the range of between approximately
50 g/m.sup.3 and approximately 5,000,000 g/m.sup.3, such as between
approximately 50 g/m.sup.3 and approximately 3,000 g/m.sup.3 or
between approximately 15,000 g/m.sup.3 and approximately 400,000
g/m.sup.3. According to other exemplary embodiments, the composite
may have a density of between approximately 5,000 g/m.sup.3 and
approximately 5,000,000 g/m.sup.3, while in still other exemplary
embodiments, the density may be between approximately 50,000
g/m.sup.3 and approximately 500,000 g/m.sup.3. According to a
particular exemplary embodiment, the composite may have a density
of approximately 100,000 g/m.sup.3. The density of the composite
material may be directly correlated to the elastic modulus of the
composite material, such that lower density composite materials may
have lower elastic moduli. Low density composite materials may also
reduce the weight of products including the composite
materials.
[0034] The composite material may have an elastic modulus at 100%
elongation of less than approximately 0.1 MPa. According to a
particular exemplary embodiment, the composite material may have an
elastic modulus at 100% elongation of between approximately 0.001
MPa and approximately 0.1 MPa, such as between approximately 0.01
MPa and approximately 0.05 MPa. The elastic modulus indicates the
elastic behavior of the composite material. A low elastic modulus
indicates a highly compressible material, and highly compressible
materials are well suited to reducing impact acceleration forces in
small impact events. Additionally, composite materials with elastic
moduli below approximately 0.1 MPa are capable of reducing the
shockwave acceleration forces in an impact event. Shockwave
acceleration forces are the acceleration forces produced as a
result of an impact after the initial impact acceleration forces,
as shown in FIG. 4.
[0035] According to an exemplary embodiment, the non-Newtonian
fluid may be provided at a level of between approximately 10
percent and approximately 90 percent of the total weight of the
composite material. According to a particular exemplary embodiment,
the non-Newtonian fluid may be approximately 30 percent of the
weight of the composite material. According to other exemplary
embodiments, the weight percentage of the non-Newtonian fluid in
the composite material may be varied depending on the particular
performance criteria desired and other factors.
[0036] Any of a variety of methods may be used to incorporate the
non-Newtonian fluid into the polymeric matrix. For example,
according to an exemplary embodiment, the composite could be made
by incorporating the non-Newtonian fluid before the
polymerization/foaming process of elastomer by adding the
non-Newtonian fluid to one of the precursor materials used to form
the polymer matrix. According to another exemplary embodiment, the
composite can be made by adding the non-Newtonian fluid to a
polymerized/foamed elastomer using injection or absorption methods.
According to one embodiment, the non-Newtonian fluid is uniformly
or homogenously dispersed in the polymer foam matrix.
[0037] Experimental testing was performed to determine the efficacy
of incorporating non-Newtonian fluids into polymer matrices for
enhancing the shock absorption properties thereof. Two
non-Newtonian fluids were used in the testing: (1) a
polyacrylamide/water non-Newtonian fluid characterized as having a
generally linear polymer chain, a molecular weight of greater than
1,000,000, and minimal hydrogen bonding, and (2) a polyethylene
glycol/water non-Newtonian fluid characterized as having a
generally linear polymer chain, a molecular weight of greater than
4,000,000, and a large degree of hydrogen bonding.
[0038] Five series of samples were produced to assess shock
absorption performance: (1) polyurethane foam with no incorporated
non-Newtonian fluid (PU), (2) polystyrene foam with no incorporated
non-Newtonian fluid (PS), (3) polystyrene foam with water
incorporated therein (PS-H.sub.2O); (4) polystyrene foam with a
polyacrylamide/water non-Newtonian fluid incorporated therein
(PS-PA), and (5) polystyrene foam with a polyethylene glycol/water
non-Newtonian fluid incorporated therein (PS-PEO). Additional
information regarding the five samples is provided below in Table
1.
TABLE-US-00001 TABLE 1 Foam Foam Foam Composite Foam volume Weight
Density Material Material Fluid (cm.sup.3) (g) (g/cm.sup.3) PU
Polyurethane none 135 4 0.02962963 PS Polystyrene none 135 4
0.02962963 PS-H.sub.2O Polystyrene H.sub.2O 135 34 0.251851852
PS-PA Polystyrene polyacrylamide/ 135 34 0.251851852 H.sub.2O
PS-PEO Polystyrene polyethylene 135 34 0.251851852
glycol/H.sub.2O
[0039] To test the shock absorption performance of the materials,
each of the samples was placed on a flat surface and an impact
object weighing 1.5 pounds that was fitted with an accelerometer
was dropped onto each of the samples from three different heights.
FIGS. 1-3 graphically illustrate the g-forces experienced by the
samples when objects were dropped from heights of 5 inches, 7.5
inches, and 11 inches, respectively. Multiple drops were performed
for each sample, and the numbers illustrated graphically represent
the average results from the multiple tests. As illustrated in FIG.
1, all of the polystyrene-based materials appear to better absorb
g-forces at a relatively low drop height as compared to
polyurethane foam, this may be a function of higher compressibility
of the polystyrene-based materials. Each composite material
exhibited a reduction in g-forces of greater than about 60% in
comparison to the polyurethane foam. Additionally, it appears that
each composite material (i.e., polystyrene impregnated with water
or a non-Newtonian fluid) outperforms polystyrene foam by itself.
From this data, it appears that the addition of both water and a
non-Newtonian fluid may improve the shock absorption performance of
the polystyrene foam.
[0040] FIG. 2 graphically illustrates the shock absorption
performance of the polystyrene foam and polystyrene foam composites
when dropped from a height of 7.5 inches. In this case, it appears
that the water-impregnated polystyrene is marginally better at
absorbing g-forces than polystyrene by itself (nearly an 8%
reduction), while the addition of non-Newtonian fluids into the
polystyrene foam both decrease the amount of g-forces experienced
by more than 15%, suggesting a significant improvement through the
addition of non-Newtonian fluids into the polymer matrix.
[0041] FIG. 3 graphically illustrates the shock absorption
performance of the polystyrene foam and polystyrene foam composites
when dropped from a height of 11 inches. At this height, a
difference between the two different non-Newtonian fluids became
apparent, with the polyacrylamide-impregnated polystyrene foam
showing similar performance as the water-impregnated polystyrene
foam (suggesting that the polyacrylamide-impregnated foam has
exceeded its damping capability at this height), while the
polyethylene glycol impregnated polystyrene foam significantly
outperformed the other foams. One possible explanation for the
differing performance of the two different non-Newtonian fluids may
be the difference in the extent of the hydrogen bonding between the
two materials, with the polyethylene glycol having significantly
more hydrogen bonding as compared to the polyacrylamide.
[0042] Next, the shock absorption profiles of the different
materials were measured to understand the differences between them.
FIG. 4 illustrates shock absorption profiles for typical and
cushioned impacts, while FIGS. 5-7 illustrate the shock absorption
profiles for the various materials discussed above. FIG. 5
illustrates that polystyrene foam absorbs impact over a longer
period of time in comparison to polyurethane, as demonstrated by
the broader peaks observed for the polystyrene material. This data
indicates that the polystyrene material appears to be more
compressible than the polyurethane material. Each of the
impregnated polystyrene foams have a different shock profile than
the non-impregnated polyurethane and polystyrene foams, with the
secondary shockwave after initial impact being significantly
diminished in the impregnated foams as compared to the
non-impregnated foams. FIG. 8 summarizes the initial results. The
polyethylene glycol impregnated polystyrene foam demonstrates a
moderate decrease in g-forces experienced compared to
water-impregnated polystyrene and non-impregnated polystyrene
(.about.13% reduction) and greatly attenuates the g-forces
experienced compared to polyurethane foam (>70% reduction), as
shown in FIGS. 8(a) and 8(b), respectively. The material also
adopts a shock absorption profile as shown in FIG. 8(d) that is
consistent with absorption of g-force over increased time as well
as a greatly diminished shockwave after initial impact in
comparison to the shock absorption profile of the polyurethane foam
as shown in FIG. 8(c).
[0043] Notably, after each drop, it was apparent that the foams
impregnated with non-Newtonian fluid returned to their pre-drop
states having a relatively soft foam-like-behavior. This suggests
that the enhanced dampening and shock absorption of the impregnated
foams was the result of a temporary shear thickening of the
non-Newtonian fluid, which reversibly transitioned back to its
pre-stress state in repeatable fashion. As a result, it would be
expected that in normal use (i.e., before shock is applied to the
material) the foams would have a relatively soft and cushioned
feel, and that the application of shock will case a temporary and
reversible hardening of the material to absorb the shock, after
which the foam will return to its original state. Advantageously,
this may provide a soft and cushioned feel for a user in certain
applications (e.g., helmets, gloves, etc.) to provide improved user
comfort during normal use. The composite material is therefore
capable of absorbing both small impacts when acting as a soft foam
and large impacts upon hardening, providing protection against a
larger range of impacts than pre-existing foam materials which are
directed to absorbing either small impacts or large impacts.
[0044] Because non-Newtonian fluids such as polyacrylamide and
polyethylene glycol are water soluble, it is possible that their
effectiveness at absorbing shock in applications where water
exposure is present may be limited. Under certain circumstances,
evaporation and environmental effects may also play a role in
diminishing the effectiveness of the non-Newtonian fluid
impregnated polymer matrices. Accordingly it may be advantageous
for certain applications to encase the composites in a polymer
coating or "skin" to control environmental impact on the
effectiveness of the material.
[0045] According to another exemplary embodiment, the effect of the
surrounding environment may be mitigated by utilizing a hydrophobic
material in place of a water-based non-Newtonian fluid and/or
incorporating the non-Newtonian fluid prior to polymerization of
the polymer matrix in an effort to "trap" the non-Newtonian fluid
within the foam and combat evaporation and other
environment-related concerns.
[0046] FIG. 9 provides an overview of a process for preparing a
composite material that involves adding a non-Newtonian fluid (in
this case, high molecular weight polydimethylsiloxane, otherwise
referred to as PDMS) to the components used in synthesizing a
polymer (polyurethane) foam (in this case, a low molecular weight
polyol (polyether chain) and methylene-diphenyl-diisocyanate
(MDI)). After the components are mixed, the polyol and MDI begin to
polymerize, incorporating the PDMS during the polymerization
process. Excess MDI releases CO.sub.2, foaming the material. The
PDMS is inert during the polymerization process, such that the PDMS
is not covalently bonded to the polymer foam matrix. The resulting
polyurethane foam has a far lower density than the polyurethane
foam discussed in the context of FIGS. 1-8, and more closely
resembles the feel and density of the polystyrene foams discussed
previously.
[0047] According to other exemplary embodiments, different
non-Newtonian fluids and foam precursors may be used, depending on
the desired performance characteristics of the composite material,
manufacturing considerations, and/or other factors. It bears noting
that the PDMS was found to be soluble in the polyol, which was
found to aid in the complete dispersion or homogenization of the
non-Newtonian fluid throughout the resulting composite material.
The polyol, MDI, and PDMS were then polymerized together while the
non-Newtonian fluid was in solution, which allowed for the
production of a composite material with a fully incorporated and
"trapped" non-Newtonian fluid within the polymer foam matrix. One
particularly advantageous feature of using relatively long-chain
PDMS is that it does not evaporate during normal use, thereby
providing enhanced non-Newtonian fluid properties and being water
resistant.
[0048] FIGS. 10, 11(a) and 11(b) depict the shock absorption
performance of non-impregnated and PDMS-impregnated low-density
polyurethane foams, the shock absorption profile of non-impregnated
low-density polyurethane foam, and the shock absorption profile of
PDMS-impregnated low-density polyurethane foam, respectively.
Because the low-density polyurethane foam has a higher density than
the polystyrene foams described above, the weight of the object
used in the 3.5 inch drop tests was increased to 15 pounds.
Additionally, the use of an object weighing 15 pounds better
simulates the effects on impacts to human heads, as a typical high
school student's head weighs approximately 15 pounds.
[0049] The composite material exhibited a roughly 30% improvement
in shock absorption compared to the greater than 20 g acceleration
experienced by the non-impregnated foam. The shock absorption
profile of the composite material also showed a higher degree of
secondary shock wave reduction as compared to the non-impregnated
material, thus providing further evidence of the improvement in
shock absorption performance of the polymer containing a
non-Newtonian fluid. It is also expected that the manufacturing
process used in the creation of the composite material will provide
for more consistent shock reduction performance over a wide range
of use conditions, since the incorporated non-Newtonian fluid would
be expected to be less susceptible to adverse impact from local
environmental conditions (e.g., moisture, evaporation, etc.)
because of its incorporation during the polymerization process for
the foam. Additionally, incorporation of the non-Newtonian fluid
during the polymerization process of the foam allows the
non-Newtonian fluid to be incorporated in to closed-cell foams and
the production of composite materials in which the non-Newtonian
fluid is uniformly and homogeneously distributed in the polymer
foam matrix. The use of a closed-cell foam may allow the
non-Newtonian fluid to be fully encapsulated within the foam,
preventing the leaching of the non-Newtonian fluid from the
composite material and rendering the composite material waterproof
and unaffected by environmental contaminants, such as sweat.
[0050] According to a variety of exemplary embodiments, the
composite materials herein may be incorporated into a wide variety
of products, apparatuses, or devices (collectively referred to as
"products"). Non-exclusive examples of products that may utilize
such composite materials include helmets (e.g., sports helmets for
use in football, baseball, hockey, lacrosse, or other sports in
which impacts may be experienced, motorcycle and bicycle helmets,
and any other type of helmet); padding for clothing or uniforms
(e.g., shoulder pads, shin pads, knee pads, elbow pads, and any
other type of padding worn by a human); footwear (shoe soles,
etc.); gloves (e.g., work gloves, sporting gloves such as boxing
gloves, hockey gloves, lacrosse gloves, etc.); cases or housings
for electronics such as phones, computers, tablets, and the like;
linings or padding for vehicle seats, child safety seats, and other
types of seating; vehicle headrests, dashboards, door components,
and other vehicle parts that may be impacted by a driver or
passenger in a vehicle collision; playground equipment lining;
exercise and gym mats; and packaging material for goods.
[0051] Although the present disclosure contemplates a wide variety
of composite materials and methods of making the same, the
following examples are provided by way of illustration, and are not
intended as limiting with respect to the present disclosure and the
scope of the inventions described herein. Accordingly, it should be
understood that other materials and combinations of materials, and
methods of making the same, are contemplated by the present
disclosure and are intended to be a part hereof.
Example 1
Polyacrylamide/Polystyrene Composite Material
[0052] In a first example, a polyacrylamide/polystyrene composite
material may be produced according to the following procedure.
[0053] For the non-Newtonian fluid, 1.5 grams of polyacrylamide
(molecular weight >1,000,000) is added to a mixing container,
and 150 mL of water is added to the container with the
polyacrylamide. To aid in the dissolving of the polyacrylamide, the
solution is slowly poured back and forth between two containers
until the polyacrylamide is completely dissolved. Once the
polyacrylamide is completely dissolved, the process of pouring the
solution back and forth between the two containers is continued for
between approximately 5 and 10 minutes, after which the solution is
allowed to rest for between approximately 1 and 2 hours. To ensure
correct mixing, the solution is then checked to confirm that the
solution has the ability to self-siphon (Self-siphoning fluids tend
to be solutions of long chain polymers, and self-siphoning refers
to the ability of the solution to "pull" the solution over the
crest of the container without any added force; once the fluid goes
past the crest of the container, the fluid that has made it over
the crest will simply pull the rest of the solution out of the
container with no additional force; this is sometimes referred to
as a "tubeless siphon"). The resulting non-Newtonian fluid is a 1%
w/w solution of polyacrylamide in water (e.g., 150 grams of
non-Newtonian fluid solution would include 1.5 grams of
polyacrylamide and 148.5 grams of water).
[0054] To incorporate the non-Newtonian fluid into a polymer
matrix, a preferred size of polystyrene foam (e.g., sized for a
particular product or application) is cut or otherwise formed, and
the desired amount of non-Newtonian fluid (in this case,
polyacrylamide in water) is measured out. The non-Newtonian fluid
is then dispersed across the top of the foam and is absorbed into
the foam. According to an exemplary embodiment, the absorption
process may take approximately five minutes, although according to
other exemplary embodiments, the amount of time for absorption may
differ depending on a variety of factors, including the amount of
non-Newtonian fluid and size/shape of foam, the types of
non-Newtonian fluid and foam used, and other factors). After the
absorption is complete, the foam is repeatedly compressed and
decompressed for a suitable amount of time to ensure that the
non-Newtonian fluid is uniformly dispersed throughout foam.
Example 2
Polyethylene Glycol/Polystyrene Composite Material
[0055] In a second example, a polyethylene glycol/polystyrene
composite material may be produced according to the following
procedure.
[0056] For the non-Newtonian fluid, 4 grams of polyethylene glycol
(molecular weight of approximately 4,000,000) are added to a mixing
container. Approximately 40 mL of ethanol, isopropanol, or acetone
are then added to the polyethylene glycol while stirring rapidly to
ensure that aggregation does not occur. Stirring continues until
the solution is completely homogenous (e.g., for approximately 10
minutes, although the time may differ depending on the solvent
selected). During the stirring process, 400 mL of water is slowly
added to avoid aggregation within the solution. The solution is
then slowly poured back and forth between two containers until the
solution is completely homogenous, after which the solution may be
checked to ensure that it self-siphons. The solution may then be
allowed to rest for a suitable time (e.g., approximately 4 hours)
to allow the alcohol to evaporate. The resulting non-Newtonian
fluid is a 1% w/v solution of polyethylene glycol.
[0057] To incorporate the non-Newtonian fluid into a polymer
matrix, a preferred size of polystyrene foam (e.g., sized for a
particular product or application) is cut or otherwise formed, and
the desired amount of non-Newtonian fluid (in this case,
polyethylene glycol) is measured out. The non-Newtonian fluid is
then dispersed across the top of the foam and is absorbed into the
foam. According to an exemplary embodiment, the absorption process
may take approximately five minutes, although according to other
exemplary embodiments, the amount of time for absorption may differ
depending on a variety of factors, including the amount of
non-Newtonian fluid and size/shape of foam, the types of
non-Newtonian fluid and foam used, and other factors). After the
absorption is complete, the foam is repeatedly compressed and
decompressed for a suitable amount of time to ensure that the
non-Newtonian fluid is uniformly dispersed throughout foam.
Example 3
Polydimethylsiloxane/Polyurethane Composite Material
[0058] In a third example, a polydimethylsiloxane/polyurethane
composite material may be produced according to the following
procedure.
[0059] An appropriate amount of non-Newtonian fluid (e.g.,
polydimethylsiloxane) is measured out for a desired w/w percentage
for a given application. For example, a 30% w/w composite of
polydimethylsiloxane in urethane would require 10 grams of
polydimethylsiloxane for 32 grams composite (other 22 grams is the
polyurethane foam matrix). Once the polydimethylsiloxane is
measured out, the appropriate amount of monomer A (16.5 grams
polyol) is weighed and added to the previously-measured
polydimethylsiloxane. These components are then mixed together
until completely homogenous. An isocyanate cross linker (11 grams)
is added to the polyol-polydimethylsiloxane solution mixture and
mixed until homogenous. According to an exemplary embodiment, the
mixing is completed in a relatively short time frame (e.g.,
approximately 30 seconds), at which point the polymerization and
foaming process begins to take place. According to an exemplary
embodiment, the ratio of monomer A (polyol) to monomer B
(isocyanate) is 60:40. This can be adjusted appropriately for the
desired application; however, there must be excess isocyanate
present (determined by molar equivalents of isocyanate to polyol)
to produce the CO.sub.2 needed for foaming (otherwise an additional
foaming agent will need to be introduced). The composite material
is then allowed to cure for approximately 24 hours at room
temperature. According to other exemplary embodiments, the curing
may be performed at approximately 60 degrees Celsius, such as by
disposing the foam in a mold heated to a consistent temperature by
an oven or water bath. According to still other exemplary
embodiments, the curing time and temperature may vary according to
other exemplary embodiments depending on the constituents used and
other factors.
Example 4
Polydimethylsiloxane/Polyurethane Composite Material
[0060] In a fourth example, a polydimethylsiloxane/polyurethane
composite material may be produced according to the following
procedure.
[0061] A mixture was formed by adding 60 parts by weight of a
polyol solution and 35 parts by weight of polydimethylsiloxane
(PDMS) 300,000 cSt to a mixing container. The polyol and PDMS
mixture was then mixed with a drill mixer attachment at greater
than 1,000 revolutions per minute (RPM), producing a blended
mixture that was white in appearance, frothy, and bubbly. An
isocyanate solution in an amount of 40 parts by weight was then
added to the blended polyol and PDMS mixture, and the
isocyanate/polyol/PDMS mixture was then mixed with a drill mixer
attachment at greater than 1,000 RPM for approximately 15-20
seconds until the blended mixture started to foam. The foaming
mixture was then quickly transferred to an aluminum mold that was
pre-treated with an anti-stick coating, and the top cover of the
mold was secured over the mold cavity and fastened with clamps.
After curing for approximately 4-24 hours, the PDMS/polyurethane
composite material was removed from the mold.
Example 5
Silicone Foam Composite Material
[0062] In a fifth example, a silicone foam composite material may
be produced according to the following procedure.
[0063] A mixture was formed by adding 40 parts by weight of a
polyorganosilane solution and 30 parts by weight of
polydimethylsiloxane (PDMS) 300,000 cSt to a mixing container. The
polyorganosilane and PDMS mixture was then mixed with a drill mixer
attachment at greater than 1,000 revolutions per minute (RPM),
producing a blended mixture that was white in appearance, frothy,
and bubbly. A siloxane catalyst solution in an amount of 80 parts
by weight was then added to the blended polyorganosilane and PDMS
mixture, and the mixture was then mixed with a drill mixer
attachment at greater than 1,000 RPM for approximately 15-20
seconds until the blended mixture started to foam. The foaming
mixture was then quickly transferred to an aluminum mold that was
pre-treated with an anti-stick coating, and the top cover of the
mold was secured over the mold cavity and fastened with clamps.
After curing for approximately 20 minutes, the silicone foam
composite material was removed from the mold and allowed to cure
for an additional 24 hours to allow the composite to achieve full
strength.
Example 6
Helmet Impact Tests
[0064] Helmet impact tests were carried out utilizing an impact
drop rig 100 of the type shown in FIGS. 13(a)-13(c). The helmet
drop rig 100 was analogous to a NOCSAE twin wire, frictionless drop
assembly, and was outfitted with a hybrid III dummy head
neck/assembly 110. The hybrid III dummy head/neck assembly 110 was
secured to the base of the drop carriage 120 such that the
head/neck assembly would contact an impact target 130 during an
impact drop test, and the head neck assembly 110 was outfitted with
an accelerometer located at the center of gravity of the dummy
head. The accelerometer was configured to measure the acceleration
forces produced during a helmet drop test in when the head/neck
assembly 110 contacts the impact target 130.
[0065] A Riddell Speed Classic Helmet was then modified by
stripping the foam provided by the manufacturer and replaced with
the polyurethane foam composite material produced in Example 4. The
polyurethane foam composite material utilized in the modified
helmet had the same shape and thickness as the manufacturer
supplied foam. For the sake of comparison, an unmodified helmet was
subjected to impact drop tests in parallel with the modified
helmet. Drop heights of 6, 12, 24, 36, and 48 inches were employed
utilizing the helmet drop rig 100 with the helmet mount on the
dummy head/neck assembly 110, and peak acceleration forces were
measured using the accelerometer. The mean and standard deviation
of five iterations of each test for the modified and unmodified
helmet are provided in Table 2, and depicted in FIG. 12. The data
demonstrates that the composite material produced lower average
peak impact acceleration forces than the manufacturer supplied
foam, indicating that the composite material provided better
protection against all impacts. Thus, the composite material
provides better protection against injuries and long-term negative
health effects produced by impact acceleration forces than the
manufacturer supplied foam.
TABLE-US-00002 TABLE 2 Drop G-forces experienced by Riddell Helmet
G-Forces Experienced by Modified Helmet Height Standard N Standard
N (in) Mean Deviation (replicates) Mean Deviation (replicates) 6
20.8282 1.754533 5 15.9226 0.620869 5 12 37.6054 1.609977 5 24.2386
1.228886 5 24 51.155 0.8165865 5 34.1872 0.4493214 5 36 62.5
1.629793 5 42.0762 1.054014 5 48 79.5898 2.252049 5 66.8108
0.4535093 5
Example 7
Polydimethylsiloxane/Polyurethane Composite Material
[0066] Polyurethane and polydimethylsiloxane (PDMS) composite
materials were produced with a modulus of elasticity at 100%
elongation of 0.105 MPa and 0.032 MPa, to determine the effect of
modulus of elasticity on the ability of the composite materials to
reduce impact acceleration forces. The composite materials included
30% by weight PDMS. The composite materials were subjected to
impact drop tests from a height of 3.5 inches with a 25 pound
weight. A polyurethane foam that was not impregnated with a
non-Newtonian fluid was also subjected to the impact drop tests as
a control.
[0067] The acceleration forces produced by the impact drop tests
are shown in FIGS. 14(a)-14(c) for the polyurethane with no
non-Newtonian fluid, the composite material with a modulus of
elasticity of 0.105 MPa, and the composite material with a modulus
of elasticity of 0.032 MPa, respectively. The data demonstrates
that composite material with a modulus of elasticity of 0.032 MPa
effectively reduces both the initial impact acceleration forces and
the shockwave acceleration forces in comparison to the polyurethane
with no non-Newtonian fluid. By contrast the composite material
with a modulus of elasticity of 0.105 MPa increased shockwave
acceleration forces in comparison to the polyurethane with no
non-Newtonian fluid, and exhibited a minimal reduction of the
initial impact acceleration forces. Thus, the composite material
with a modulus of elasticity at 100% elongation of 0.032 MPa
effectively reduced both the initial acceleration forces and the
shockwave acceleration forces, indicating that the modulus of
elasticity of the composite materials at least in part determines
the impact acceleration performance of the material.
[0068] As utilized herein, the terms "approximately," "about,"
"substantially," "essentially," and similar terms are intended to
have a broad meaning in harmony with the common and accepted usage
by those of ordinary skill in the art to which the subject matter
of this disclosure pertains. It should be understood by those of
skill in the art who review this disclosure that these terms are
intended to allow a description of certain features described and
claimed without restricting the scope of these features to the
precise numerical ranges provided. Accordingly, these terms should
be interpreted as indicating that insubstantial or inconsequential
modifications or alterations of the subject matter described and
claimed are considered to be within the scope of the disclosure as
recited in the appended claims.
[0069] It should be noted that the term "exemplary" as used herein
to describe various embodiments is intended to indicate that such
embodiments are possible examples, representations, and/or
illustrations of possible embodiments (and such term is not
intended to connote that such embodiments are necessarily
extraordinary or superlative examples).
[0070] It is important to note that the exemplary embodiments are
illustrative only. Although only a few embodiments have been
described in detail in this disclosure, those skilled in the art
who review this disclosure will readily appreciate that many
modifications are possible (e.g., variations in values,
manufacturing processes, etc.) without materially departing from
the novel teachings and advantages of the subject matter described
herein. The order or sequence of any process or method steps may be
varied or re-sequenced according to alternative embodiments. Other
substitutions, modifications, changes and omissions may also be
made in the design, operating conditions and arrangement of the
various exemplary embodiments without departing from the scope of
the present disclosure.
* * * * *