U.S. patent application number 14/523606 was filed with the patent office on 2015-10-22 for composite materials and structures.
The applicant listed for this patent is Dow Corning Corporation. Invention is credited to Timothy Rex Bunce, Kenneth E. Evans, Jonathan Paul Hannington, Claire Hartmann-Thompson, Patrick Barry Hook.
Application Number | 20150298421 14/523606 |
Document ID | / |
Family ID | 9955828 |
Filed Date | 2015-10-22 |
United States Patent
Application |
20150298421 |
Kind Code |
A1 |
Hook; Patrick Barry ; et
al. |
October 22, 2015 |
COMPOSITE MATERIALS AND STRUCTURES
Abstract
The invention provides composite components, structures and
method for producing composite components. A composite component
has a negative effect Poisson's ratio and comprises a first
component and a second component. The first component and the
second component extend longitudinally relative to an axis, the
first component being provided around the second component through
one or more turns which are spaced longitudinally relative to the
axis. A variation in the tensile load on the first component causes
the radial position of the second component relative to the axis to
vary.
Inventors: |
Hook; Patrick Barry; (Devon,
GB) ; Evans; Kenneth E.; (Exeter, GB) ;
Hannington; Jonathan Paul; (Rhondda Cynon Taff, GB) ;
Hartmann-Thompson; Claire; (Midland, MI) ; Bunce;
Timothy Rex; (Vale of Glamorgan, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow Corning Corporation |
Midland |
MI |
US |
|
|
Family ID: |
9955828 |
Appl. No.: |
14/523606 |
Filed: |
October 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12467966 |
May 18, 2009 |
8916262 |
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14523606 |
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10551316 |
Jun 9, 2006 |
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PCT/GB2004/001320 |
Mar 26, 2004 |
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12467966 |
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Current U.S.
Class: |
428/34.1 ;
428/371; 57/9 |
Current CPC
Class: |
Y10T 442/637 20150401;
Y10T 428/2929 20150115; Y10T 428/2933 20150115; B32B 1/08 20130101;
B32B 2535/00 20130101; Y10T 428/2936 20150115; B32B 2605/18
20130101; Y10T 428/24942 20150115; B32B 2457/00 20130101; B32B 3/00
20130101; B32B 2605/08 20130101; B32B 2571/02 20130101; D02G 3/38
20130101; B32B 2250/02 20130101; D02G 3/24 20130101; B32B 2307/50
20130101 |
International
Class: |
B32B 3/00 20060101
B32B003/00; D02G 3/24 20060101 D02G003/24; B32B 1/08 20060101
B32B001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2003 |
GB |
0307330.1 |
Claims
1. A composite component having a negative effective Poisson's
ratio, the composite component including a first component and a
second component, the first component and the second component
extending longitudinally relative to an axis, the first component
being provided around the second component through one or more
turns, the one or more turns being spaced longitudinally relative
to the axis, wherein variation in tensile or compressive load on
the first component causing variation in radial position of the
second component relative to the axis.
2. A composite component according to claim 1, in which the first
component has a higher modulus of elasticity than the second
component.
3. A composite component according to claim 1 having the first
component arranged around the second component in a helical manner,
wherein the variation in the tensile or compressive load on the
first component causing variation in the diameter of the helix of
the first component, the variation in the diameter of the helix of
the first component causing the second component to form a helix
and/or causing variation in the diameter of the helix of the second
component, so that the diameter of the second component helix
increases as the diameter of the first component helix decreases
and the diameter of the second component helix decreases as the
diameter of the first component helix increases.
4. A composite component according to claim 1, in which the first
component is provided around the second component by applying
and/or wrapping and/or covering and/or spinning.
5. A composite component according to claim 1, in which the first
component is a fibre, rod or hollow tube of a relatively high
modulus material and the second component is a fibre, rod or hollow
tube of an intermediate or a low modulus material compared with the
first component material.
6. A composite component according to claim 1 in which the axis is
provided through a core component.
7. A composite component according to claim 3, in which the
variation in radial position is an increase in displacement of at
least a part of the second component relative to the axis when the
load is varied, with the variation being an increase when the load
is a tensile load and a decrease when the load is a compressive
load.
8. A composite component according to claim 3, in which the
variation in radial position is a decrease in displacement of at
least a part of the second component from the axis when the load is
varied, with the variation being a decrease when the load is a
tensile load and an increase when the load is a compressive
load.
9. A structure comprising two or more composite components each of
said components having a negative effective Poisson's ratio, each
composite component comprising a first component and a second
component extending longitudinally relative to an axis, the first
component being provided around the second component through one or
more turns, the one or more turns being spaced longitudinally
relative to the axis, wherein a variation in the tensile or
compressive load on the first component causes a variation in
radial position of the second component relative to the axis.
10. A structure according to claim 9, comprising at least a pair of
composite components, said composite components being arranged
adjacent to one another or in contact with one another.
11. A structure according to claim 9, wherein the structure is
formed from repeats of a unit comprising multiple composite
components.
12. A structure according to claim 9, wherein each composite
component is adjacent to or in contact with two or more other
composite components, so as to form a planar or sheet type
structure.
13. A structure according to claim 9, wherein each composite
component is adjacent to or in contact with four or more other
composite components.
14. A structure according to claim 10, wherein the first components
of the adjacent composite components are wrapped around the second
component in opposite directions to one another.
15. A structure according to claim 9, comprising one or more core
components.
16. A structure according to claim 15, in which the core component
is a fibre wherein said fibre is solid or hollow.
17. A structure according to claim 15, comprising three components
provided to allow limited movement or no movement of the components
over each other.
18. A structure according to claim 9, comprising one or more matrix
components.
19. A structure according to claim 18, in which the matrix
component resists the movement of the second component caused by
load variation and/or encourages the return of the second component
to the radial position it occupied prior to load variation.
20. A structure according to claim 9, which has energy absorbing,
impact absorbing and/or acoustic absorbing characteristics.
21. A method for producing a composite component having a negative
effective Poisson's ratio, the method comprising the steps of:
forming a first component; forming a second component; and
applying, the first component around the second component through
one or more turns, the one or more turns of the first component
being spaced longitudinally along the second component.
22. A method according to claim 21, in which the modulus of
elasticity of the first component is greater than the modulus of
elasticity of the second component.
23. A method according to claim 21, wherein the first component is
applied around the second component in a helical manner, the
tensile or compressive load on the first component is varied
causing variation in the diameter of the helix of the first
component, the variation in the diameter of the helix of the first
component causing the second component to take on the form of a
helix and/or causing variation in the diameter of the helix of the
second component, wherein the diameter of the second component
helix increases as the first component helix decreases in diameter,
and the diameter of the second component helix decreases as the
first component helix increases in diameter.
24. A method according to claim 21, wherein the applying is
provided by wrapping, spinning or covering.
Description
[0001] This invention is concerned with improvements in &
relating to composite materials and structures, particularly those
with auxetic properties (i.e. with a negative or effectively
negative Poisson's ratio), methods of producing auxetic composite
materials and applications for auxetic composite materials.
[0002] Unlike most conventional materials auxetic materials expand
perpendicular to an axis about which they are stretched. This gives
such materials a variety of useful properties. Existing auxetic
materials and the techniques for their production, such as those
detailed in WO00/53830, face significant problems in producing
auxetic materials in a reliable manner and/or on a scale suitable
for industrialisation. Additionally such prior art materials are
formed from a single material and thus have restricted properties
as a result. The present invention aims to address problems with
prior art materials and their production techniques.
[0003] The present invention has amongst its aims the provision of
improved auxetic composite materials, methods of manufacturing
auxetic composite materials and applications for auxetic composite
materials. Methods of manufacturing are envisioned that aim to be
appropriate for industrial scale production or fabrication at a
wide range of scales. The present invention has amongst its aims
the provision of auxetic composite materials and methods for
producing such materials which are reliable in their structure and
properties and which would offer a greater range of material
properties and uses.
[0004] According to a first aspect of the present invention we
provide a composite component having a negative effective Poisson's
ratio, the composite component including a first component and a
second component, the first component and the second component
extending longitudinally relative to an axis, the first component
being wrapped around the second component through one or more
turns, the one or more turns being spaced longitudinally relative
to the axis, variation in the tensile load on the first component
causing the radial position of the second component relative to the
axis to vary.
[0005] According to a second aspect of the invention we provide a
composite component having a negative effective Poisson's ratio,
the composite component including a first component and a second
component, the first component and second component extending
longitudinally relative to an axis, the first component being
wrapped around the second component through one or more turns, the
first component having a higher modulus of elasticity than the
second component, variation in the tensile or compressive load on
the first component causing the radial position of the second
component relative to the axis to vary.
[0006] According to a third aspect of the invention we provide a
composite component having a negative effective Poisson's ratio,
the composite component including a first component and a second
component, the first component and the second component extending
longitudinally relative to an axis, the first component being
wrapped around the second component in a helical manner, variation
in the tensile or compressive load on the first component causing
variation in the diameter of the helix the first component follows,
the variation in the diameter of the helix of the first component
causing the second component to take on the form of a helix and/or
causing the diameter of the helix of the second component to vary,
the diameter of the second component helix increasing as the first
component helix decreases in diameter, the diameter of the second
component helix decreasing as the first component helix increases
in diameter.
[0007] The first and/or second and/or third aspects of the
invention may include any of the features, options or possibilities
set out elsewhere in this document and particularly from amongst
the following.
[0008] The composite component and/or a structure produced there
from may have any negative value of Poisson's ratio. The system may
have a Poisson's ratio of between 0 and -5. A Poisson's ratio of
between -3 and -4 may particularly be provided.
[0009] The first component may be a fibre, rod or hollow tube
particularly of a relatively high modulus material. The first
component may be formed of carbon fibre, glass fibre, polyaramids
(e.g. Kevlar.TM.), polyamides (e.g. nylon), polyesters,
polyalkylenes, polyethyleneterepthalate (PET), metal wire, cotton
or other material. The materials from which the first component is
formed may be natural or man made, inorganic or organic. The first
component may be sealed with a cured film, for example a cured
siloxane film. In the event that the first component is a hollow
tube, the tube may contain additional materials.
[0010] The second component may be a fibre, rod or hollow tube,
particularly consisting of an intermediate or a low modulus
material. The material is preferably capable of deformation without
fracture. The second component may be formed of siloxane, liquid
silicone rubber, natural rubber, nitrile rubber or any other
elastomeric material whether natural or man-made. In the event that
the second component is a hollow tube, the tube may contain
additional materials. The additional materials may or may not be
auxetic. The additional materials may have different properties to
the tubing.
[0011] Preferably the first component is of a higher modulus than
the second component. The first component may have a diameter that
is between 0.01 and 1 times the diameter of the second component.
The first component may be between 0.001 and 1 times the
cross-sectional area of the second component.
[0012] The first component and/or second component may be formed of
a continuous material. Preferably the first component and/or second
component are elongate. The first component and/or second component
may be at least a hundred times as long as their maximum
cross-sectional dimension or extent.
[0013] The axis may be provided at the centre of a composite
component consisting of a first component and second component. The
axis may be provided between two or more components. The axis may
be provided through a core component, particularly the centre of a
core component, around which one or more first components and/or
second components are provided.
[0014] The wrapping of the first component around the second
component may be provided in the form of a covering or winding. The
wrapping of the first component around the second component may be
in the form of a spiral or a helix. The spiral or helix may have a
constant pitch along the second component. The pitch may be between
zero degrees and ninety degrees relative to the axis.
[0015] The second component may be linear with the first component
wrapped around it. The second component may also be wrapped around
the first component. The second component may be in the form of a
spiral or a helix. The pitch of the first component spiral or helix
may be the same as the pitch of the second component spiral or
helix.
[0016] The variation in the tensile or compressive load on the
first component may be a variation in the load applied along or
parallel to the axis. The variation in the load may be an increase
in the load. The variation in the load may be a decrease in the
load. The first component may have the load increased from zero to
a load value to cause the variation, or may have the load reduced
from a first value to a second lower value to cause the variation.
The load may be applied at the ends of the first component and/or
may be introduced at an intermediate location.
[0017] The radial position of the second component may be measured
perpendicular to the axis. Preferably the variation in radial
position is an increase in the displacement of at least a part of
the second component relative to the axis when the load is varied,
the variation particularly being an increase when the load is a
tensile load and a decrease when the load is a compressive load.
Preferably the variation in radial position is a decrease in the
displacement of at least a part of the second component from the
axis when the load is varied, the variation particularly being a
decrease when the load is a tensile load and an increase when the
load is a compressive load. The position of some parts of the
second component may not feature a displacement increase when the
load is varied.
[0018] Preferably a structure includes at least a pair of composite
components, each composite component including a first component
and a second component. The pair of composite components may be
arranged adjacent to one another or in contact with one another.
Contact may be between the first elements of the composite
components and/or between the second components of the composite
components. Two or more composite components may be arranged around
a core component. The first and/or second components of the
composite component may be provided adjacent to or in contact with
the core component.
[0019] A bulk structure may be formed from repeats of a unit
comprising multiple composite components. A core element may be
provided between composite components and/or between units formed
of multiple composite components. A core component may be provided
at the core of a unit with two or more composite components
provided around the core component. The composite components may be
evenly spaced around the core component. Each composite component
may be provided adjacent to, or in contact with other core
components. A bulk structure may be formed from repeats of a unit
comprising multiple composite components and multiple core
components.
[0020] A bulk structure may be provided by each composite component
being provided adjacent to or in contact with two or more other
composite components. A planar or sheet type bulk structure may be
provided by providing alongside one another repeats of a unit
formed of a first composite component, with a further composite
component to either side. A core component may be provided between
composite components in such a structure. Preferably each unit is
adjacent to or contacts two other units.
[0021] A bulk structure may be provided by each composite component
being provided adjacent to or in contact with four other composite
components. The bulk structure may be formed of units comprising
four composite components, particularly provided around a single
core component. Preferably each unit is adjacent to or contacts
four or eight other units.
[0022] A bulk structure may be provided by each composite component
being provided adjacent to or in contact with five other composite
components. The bulk structure may be formed of units comprising
five composite components, particularly provided around a single
core component. Preferably each unit is provided adjacent to or in
contact with five other units.
[0023] A bulk structure may be formed by each composite component
being provided adjacent to or in contact with six other composite
components. The bulk structure may be formed of units comprising
six composite components. A core element may be provided between
the six composite components. The six composite components may be
even spaced around the core element. Preferably each unit is
provided adjacent to or in contact with six other units.
[0024] Adjacent composite components, including those with in units
and bulk structures, may be provided with first components that are
wrapped around the second component in opposite directions to one
another.
[0025] In one preferred embodiment of the invention a structure is
provided formed of a first composite component and a further
composite component, the first composite component has a first
component wrapped around the second component in one direction and
the further composite component has a first component wrapped
around the second component in the other direction. Preferably at
least one of the composite components is wrapped clockwise and at
least one of the composite components is wrapped anti-clockwise,
ideally so that two composite components opposite each other are
the mirror image of each other. A core element may be provided
between the two or more composite components.
[0026] In an alternative embodiment of the invention a structure is
provided formed of two or more of composite components, two or
more, or even all, of the composite components having a first
component which is wrapped around the second component in identical
orientations such that they are not mirror images. A core element
may be provided between the two or more composite components.
[0027] The structure may be provided with one or more core
components, particularly core components provided between at least
two composite components. The core component may be a fibre. The
core component may be solid or hollow. The hollow core components
may contain additional materials or be filled with additional
materials. The core components and/or additional materials may be
formed from a further auxetic material. The first component and/or
the second component may be discrete from the core element. MI
three components may be discrete from one another. It is preferred
that the first and second components are provided so that there is
no movement of the components over each other. The core component
may also be provided within the composite structure such that no
movement of the core component over the first and/or second
components occurs.
[0028] The structure may include one or more matrix components. The
matrix components may be, or may include siloxane foams,
polyurethane foams or other such materials. Preferably the matrix
components are in contact with all the composite components, or at
least the first component and/or the second component. The matrix
component may be deformed by the variation in the tensile or
compressive load on the first component and/or may resist the
movement of the second component caused by load variation. The
matrix component may encourage the return of the second component
to the radial position it occupied prior to load variation. The
matrix component may amplify the negative Poisson's ratio, or
auxetic effect, of the structure and/or material.
[0029] Preferably an increase in the tensile load or a reduction in
the compressive load causes the first components to become more
linear and the second components to become less linear. Preferably
a reduction in the tensile load or an increase in the compressive
load causes the first components to become less linear and the
second components to become more linear.
[0030] The structure may be energy absorbing, for instance suitable
for impact absorption and/or acoustic absorption applications. The
structures may be formed or woven into car parts, sports equipment,
aerospace components, moulded components, Piezo-electric materials,
textiles, fabrics and the like. In particular the structures may be
formed or woven into automotive bumpers, automotive interiors,
automotive and aerospace tyres, tubing for flight suits, body
armour, biomaterials for prostheses or other medical uses, padding,
damping materials for electronic devices, including hand-held
devices, personal computers, communications equipment, cameras and
the like.
[0031] The structures may also be effective in applications
relating to strain loads where the intent is to support heavy
objects or forces across a wide surface area. The composite
structures may be formed or woven into webbings, belts and straps,
textiles, fabrics, for tyre carcass construction, etc.
[0032] According to a fourth aspect of the invention we provide a
method for producing a composite component having a negative
effective Poisson's ratio, the method comprising forming a first
component; forming a second component; applying, for instance by
wrapping and/or spinning and/or covering, the first component
around the second component through one or more turns, the one or
more turns being spaced longitudinally along the second
component.
[0033] According to a fifth aspect of the invention we provide a
method for producing a composite component having a negative
effective Poisson's ratio, the method comprising forming a first
component; forming a second component; applying, for instance by
wrapping and/or spinning and/or covering, the first component
around the second component through one or more turns, the modulus
of elasticity of the first component being greater than the modulus
of elasticity of the second component.
[0034] According to a sixth aspect of the invention we provide a
method for producing a composite component having a negative
effective Poisson's ratio, the method including forming a first
component; forming a second component; the first component and the
second component extending longitudinally relative to an axis;
applying the first component around the second component in a
helical manner, for instance by wrapping and/or spinning and/or
covering, variation in the tensile or compressive load on the first
component causing variation in the diameter of the helix the first
component follows, the variation in the diameter of the helix of
the first component causing the second component to take on the
form of a helix and/or causing the diameter of the helix of the
second component to vary, the diameter of the second component
helix increasing as the first component helix decreases in
diameter, the diameter of the second component helix decreasing as
the first component helix increases in diameter.
[0035] The fourth and/or fifth and/or sixth aspect of the invention
may include any of the features upon options or possibilities set
out elsewhere in this document and particularly from the
following:
[0036] The first component and/or the second component and/or core
component may be extruded or pultruded, e.g. by a die with or
without tension. The first component and/or the second component
and/or core component may be formed by a spinnerette or similar
spiral winding/covering device. The second component may be
stretched whilst the first component is wrapped around the second
component.
[0037] The first component and/or the second component may be
formed and then applied, for instance wrapped. The first component
may be applied around the second component as it is formed. The
first component and the second component may form a composite
component. Two or more composite components may be bundled
together. The composite components may be bundled together to form
a structure, for instance by packing them around one or more core
elements.
[0038] The method may include a matrix providing or not a void
filling step for the one or more components. The voids may be
filled with fibres and/or bulk material or matrix. Siloxane foams,
polyurethane foams, liquid silicone rubbers, natural rubber and
other synthetic or natural materials may be used to form the matrix
or act as void fillers.
[0039] The first component and the second component, or composite
components made therefrom, or structures or bundles made therefrom,
may be woven to produce structure or may be introduced to a
moulding process to form bulk structures.
[0040] Various embodiments of the invention will now be described,
with reference to the accompanying drawings in which:--
[0041] FIG. 1a is an illustration of a first prior art form of
auxetic material;
[0042] FIG. 1b is an illustration of a second prior art form of
auxetic material;
[0043] FIG. 2 illustrates an auxetic composite structure according
to the present invention in an unstrained/partially strained
state;
[0044] FIG. 3 illustrates the composite structure of FIG. 2 in a
strained state;
[0045] FIG. 4 is a schematic cross-sectional view, viewed along
axis X-X;
[0046] FIG. 5 is a schematic cross-sectional view of an alternative
auxetic composite structure according to the present invention;
[0047] FIG. 6 is a schematic cross-sectional view of an alternative
auxetic composite structure according to the present invention and
provides a body centred lattice arrangement;
[0048] FIG. 7 is a schematic view of a close packed auxetic
composite structure arrangement provided according to the present
invention;
[0049] FIGS. 8a to 8f illustrate various views of an experimental
embodiment of the present invention at various strain levels;
and
[0050] FIGS. 9a and 9b illustrate the projected angle for the first
component in an unstrained and partially strained form
respectively.
[0051] This invention is aimed at providing improved structures
& production techniques for auxetic materials, as well as
improved auxetic materials themselves. It should be noted that
where the term materials is used, it is taken that this includes
textiles and fabrics amongst other possibilities.
[0052] Auxetic materials are materials having a negative actual or
effective Poisson ratio. That is to say, when a tensile load is
applied to an auxetic material to stretch it along a first axis it
expands along a second axis perpendicular to that first axis.
Materials are also auxetic if a compressive load is applied along
the axis of a material and the compression results in a reduction
in width along a second axis perpendicular to that first axis. This
is contrary to the behaviour of most materials which exhibit a
positive Poisson ratio. A material's Poisson ratio is determined by
the ratio of the contractile transverse strain relative to the
tensile longitudinal strain.
[0053] Synthetic auxetic materials were first produced in the late
1980's by mechanical deformation of open cell polymeric foams.
Subsequent techniques have aimed to produce honeycomb style
polymeric materials or materials formed by particles linked by
fibrils.
[0054] An example of a honeycomb style auxetic polymer material is
illustrated in FIG. 1a. Applying a tensile load along axis X-X
causes stems 1 and 3 to move apart. However, this movement cause
the stems 5 and 7 to straighten and thus increase the separation of
stems 9 and 11. The result is an increase in the extent of the
material along axis Y-Y which is perpendicular to axis X-X.
[0055] An example of a particle & fibril based auxetic polymer
material is shown in FIG. 1b. This provides a series of particles
13 which are linked by fibrils 15. The fibrils 15 are generally
produced from the same material as the particles 13 by the
extrusion and/or subsequent spinning process. Again, moving
particles 13a and 13b apart along axis X-X causes the fibrils 15a,
15b to straighten and hence increase the separation of particles
13c and 13d. An increase in the materials extent along axis Y-Y,
perpendicular to axis X-X, thus occurs. Such materials have been
produced using compaction and sintering stages, or as detailed in
WO-00/53830, by partially melting and then extruding the single
polymeric material.
[0056] A variety of techniques for producing auxetic materials have
been suggested, with quite varying form and level of negative
Poisson ratio. In many cases, however, the production method is
complicated and generally suited to producing only very small
amounts of auxetic material of questionable consistency. In other
cases, the nature of the process, surface melting and extrusion to
form the material from a single material, results in an auxetic
material which is far less even in structure and properties than is
implied in the schematic representations thereof in the prior art
and FIGS. 1a and 1b of this document. Cross-linking of particles,
incomplete fibril structures, non-discrete particles and other
problems are encountered. Substantial difficulties also exist in
turning such prior art auxetic material samples into useful shapes
or forms.
[0057] The present invention seeks to address these issues and
provide an auxetic material which is relatively easy to produce, is
consistent in its structure and properties, has an appreciable and
controllable negative Poisson ratio and can readily be used to form
more complex and useful forms.
[0058] Referring to FIG. 2 the auxetic material of the present
invention is in effect a composite component made up of a number of
components. Here it is illustrated in a partially strained state.
Contrary to prior art auxetic materials the present material is
formed of a number of separate components and potentially of
separate components having different material form or
properties.
[0059] Running through the centre is a core component 20. This core
component 20 is generally linear in configuration and provides the
core for a composite structure. The core component 20 also defines
an axis of the structure, X-X. To either side of the core component
20 are first components 22a, 22b. The first components 22a, 22b are
provided in conjunction with second components 24a, 24b. In each
case, the first component 22 is wrapped around the second component
24 in a spiraling manner. That is to say, the first component 22
contacts a different part of the circumference of the second
component 24 as progress is made along the components 22, 24. As a
result of this wrapping, the first component 22 at least, has an
extent of displacement relative to the axis X-X which varies with
position along the axis X-X. Thus at location 28 the displacement
is greater than at location 26.
[0060] The extent of displacement of the other first component 22b
relative to the axis XX is of the same extent for the same position
26, 28 etc along axis X-X, but the direction of displacement may be
in the opposite direction relative to the axis X-X. Hence, parts 32
of the first component 22b are close to one another and parts 30 of
the first component 22b are relatively far apart. This is achieved
by wrapping the first components 22a, 22b around the second
components 24a, 24b in opposing directions.
[0061] In the illustrated case, both the first component 22 and
second component 24 have a displacement relative to the axis X-X
which varies with position along the axis X-X. The overall
composite component thus provides through openings 34 of a given
size.
[0062] The overall form can be seen in the schematic
cross-sectional view, viewed along axis X-X, of FIG. 4. In this
cross-sectional view the first component 22 starts at point A and
advances up and over the second component 24 to point B, before
descending the other, inside of the second component 24 to point C.
There is a mirror image on the opposite side of the core element.
The full transition of the first component 22 and full extent of
the second component 24 is not shown.
[0063] In use, FIG. 3, if a tensile load is applied, parallel to
axis X-X, to the first components 22 of the composite component
then that load straightens the first components 22 from their
helical configuration to a straighter or even straight
configuration. In FIG. 3 the core component 20 still occupies the
centre of the composite component and the first component 22 is
still wrapped around the second component 24. However, the
straightening of the first components 22 has led to an increase in
the diameter of the helix formed by the second components 24. The
level of displacement of the second component 24 away from the axis
X-X has the net effect of considerably increasing the overall
extent of the composite component along axis Y-Y. The size of the
openings 34 also significantly increases.
[0064] As an alternative to helical forms for both the first
components 22 and second components 24, a functioning composite
component could be provided using a linear second component 24 and
wrapped, displacement varying along the length, first component 22.
This form is not illustrated in the Figures. In this case, the
application of the tensile load would again straighten the first
components 22 and hence cause the second components 24 to move from
linear to helical form. Again an increase in the extent
perpendicular to the direction of the tensile load occurs.
[0065] Whilst different relative dimensions for the core component
20, first components 22 and second components 24 are illustrated in
FIGS. 2, 3 and 4, a wide variety of different sizes are possible,
both in absolute terms and in terms of the relative sizes of the
different components to one another.
[0066] In a preferred embodiment of the invention the core
component 20 is itself a further auxetic component or structure,
but may also be an elastomeric rod of intermediate or low modulus.
It is desirable that the core component be capable of deformation
without fracture. Suitable materials include siloxane, liquid
silicone rubber, natural rubber, nitrile rubber or any other
elastomeric material whether natural or man-made. In the event that
the core component is a hollow tube, the tube may contain
additional materials that may or may not be auxetic, and the
additional materials may have different properties to the tube. The
first components are desirably of high modulus of elasticity, for
instance carbon fibre, kevlar, glass fibre, or wire. The second
components are again desirably elastomeric in nature. A very wide
range of materials can be employed, however, dependant on the
desired properties, application and scale of the resultant
composite structure. Further possibilities are outlined later in
this document.
[0067] The composite component of FIGS. 2, 3 and 4 is in effect a
structure from which larger structures or articles can be
formed.
[0068] In FIG. 5 an alternative structure is illustrated in
cross-sectional end view. The structure is an expanded version of
the structure illustrated above in the FIGS. 2, 3 and 4 form of the
invention and uses similar principals. In this case, the structure
again features a central core component 20, but is provided with
six second components 24 evenly positioned around the perimeter of
the core component 20. Each of the second components 24 is provided
with a first component 22 wrapped around it. Again the extent of
the displacement of the first component from the axis running along
the centre of the structure is the same for each of the first
components at the same position along the axis. The direction of
the displacement for each component is radially away from the axis.
In the case of this structure, application of a tensile load causes
expansion in all directions radially away from the core component
20. A similar arrangement may be constructed using more or less
than six first and second component combinations.
[0069] Whilst the structures described in relation to FIGS. 2, 3, 4
and 5 offer negative Poisson ratio materials, the most useful forms
of the present invention arise from the formation of finished
articles out of such units e.g. to form fabrics, sheets, woven
articles, non-woven articles. These involve the use of multiple
structures of the type described above, or other such
structures.
[0070] In the case shown in FIG. 6, each core component 20 is
surrounded by four first components 22 and four second components
24, these being wrapped around one another to give the previously
described combinations. The four combinations are evenly positioned
around the core component 20. By providing a large number of
structures in this way a body centred lattice is formed.
[0071] In the case shown in FIG. 7, each core element 20 is
surrounded by six first component 22 and second component 24
combinations. Again the six combinations are evenly positioned
around the core component 20 and provide a close-packed arrangement
as a result. Similar arrangements may be constructed using more or
less than six first and second component combinations.
[0072] These and other packing patterns allow substantial
structures to be generated which are auxetic in behaviour. Most
importantly, when compared with prior production techniques, as the
auxetic structure is assembled from a number of components it is
highly suited to mass production using variations on existing
equipment designs that are relatively simple to implement. For
instance, it would be possible to extrude the core component and
use spinerettes to create the first component and second component
combinations. The number of first component and second component
combinations for the desired form can then be assembled around the
core component. Assembly of multiple combinations provided in this
way gives the desired bulk structure.
[0073] In addition to the material composition produced from core,
first and second components it is possible to include supplemental
materials. In a preferred form the auxetic properties of the
structure are supplemented by filling the voids in the structure
with siloxane foam, polyurethane foam or other low modulus of
elasticity materials. Further components or elastomeric rods can be
included in the voids. The introduction of such materials to the
formed product is also possible using industrial scale
processes.
[0074] It should also be noted that the FIGS. 2, 3, and 4 forms of
the invention describe a structure that is strained to increase its
extent perpendicular to the axis of strain. It is perfectly
possible for the material to be pre-strained or pre-tensioned and
exhibit its auxetic properties when the strain/tension is released
and/or when compression is applied.
[0075] In addition to mathematical calculations as to the level of
negative Poisson's ratio exhibited by such materials the applicant
has been able to experimentally demonstrate such properties.
[0076] Referring to FIG. 8a to fan experimental structure according
to the present invention is provided. The structure is formed of
two of the composite components 100 illustrated in FIG. 8a. Two
composite components 100 are provided in proximity with one another
and each include a second component 104 that has a first component
102 wound around it. The first components 102 are wound in opposing
directions. Such a structure is shown in FIG. 8b unstrained.
[0077] As a strain is applied to the structure, the auxetic
properties are visible. In FIG. 8c a longitudinal 10 mm strain
gives expansion of the gap between the components. The FIG. 8d
longitudinal 15 mm strain, FIG. 8e longitudinal 20 mm strain and
FIG. 8f longitudinal 25 mm strain give increasing gaps due to the
sideways expansion of the structure.
[0078] The effect is clearly illustrated in FIGS. 9a and 9b which
compare the projected angle of the first component relative to an
axis perpendicular to the core axis of the structure. In this
instance, in an unstrained state, an angle of 62.degree. is
observed, and in a partially strained state an angle of
74.5.degree. is observed.
[0079] As well as producing structures of this configuration using
various component forms it is possible to generate such structures
on a wide range of scales. Macro rods and fibres can be used to
form bulk composite structures suitable for a variety of uses. At
the other end of the scale various organic polymeric, inorganic
polymeric or inorganic structures may be used to achieve molecular
size auxetic materials.
[0080] The auxetic composites and structures provided by the
present invention offer a wide variety of beneficial properties. In
particular, such structures may offer enhanced shear modulus,
fracture toughness, piezoelectric properties, indentation
resistance, thermal shock resistance, impact absorption, wear
resistance and energy absorption over conventional materials.
Usefully auxetic composites and structures according to the present
invention may provide both impact and acoustic absorbing properties
in a single material. There is also potential for these structures
to display anisotropic effects where properties are different in
axial and radial directions.
[0081] Such composites and structures are seen as having particular
application as textile materials for a wide variety of purposes.
The auxetic structures of the present invention are particularly
useful in the context of textiles due to their synclastic ability
(the ability to form curves in two directions pointing in the same
way). This makes such textiles particularly well fitting to other
items they contact. This is true of both non-clothing, for instance
crash helmet linings, and clothing type applications, for instance,
comfortable body armour or clothing straps and/or belts.
[0082] Applications for such composites and structures include
situations where indentation resistance or the ability to absorb
impacts are desirable, including car bumpers, car interior
components, and moulded body parts. These properties also render
such structures useful in the area of sports equipment where impact
protection in the form of clothing or additional equipment is
desirable. Such equipment includes head protection, shin pads,
other pads and the like.
[0083] The ability to offer acoustic damping from the same material
which provides the above mentioned properties is also useful as
previously two separate materials, one aimed at each issue were
needed.
[0084] The materials in the present invention also offer benefits
in terms of their suitability for protecting hand held electronic
devices, mobile phones, cameras, videos and the like e.g. for
vibration, acoustic damping, or indentation resistance etc.
[0085] Other potential applications include use in tyres, medical
sutures, composites with enhanced properties (particularly through
reduced fibre pull-out failures), electronic sensors (especially
through the construction of pressure sensitive or optically
sensitive materials), seat belts, luggage straps, clothing straps,
doubly-curved structures, active materials (particularly filters),
active textiles, enhanced wear reduction applications, thermal
shock applications, etc.
[0086] There are many potential methods by which such materials may
be manufactured--these include braiding, knitting, spinning,
extrusion, and embroidery, as well as a variety of woven and
non-woven techniques.
* * * * *