U.S. patent application number 14/085095 was filed with the patent office on 2014-05-29 for infusible unidirectional fabric.
This patent application is currently assigned to Milliken & Company. The applicant listed for this patent is Milliken & Company. Invention is credited to Ryan W. Johnson, Xin Li, Joseph E. Rumler.
Application Number | 20140147620 14/085095 |
Document ID | / |
Family ID | 50773547 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140147620 |
Kind Code |
A1 |
Li; Xin ; et al. |
May 29, 2014 |
INFUSIBLE UNIDIRECTIONAL FABRIC
Abstract
An infusible, unidirectional fabric containing a plurality of
unidirectional fibers spaced uniformly in the unidirectional
fabric, a plurality of bridges, and a plurality of void spaces
between the unidirectional fibers. Each bridge is connected to at
least 2 unidirectional fibers and at least 70% by number of fibers
have at least one bridge connected thereto forming a bridged
network of unidirectional fibers. The void spaces are
interconnected and the fabric has a volume fraction of voids of
between about 8 and 70%, a volume fraction of fibers of between
about 35 and 85%, and at least 50% by number of the bridges have a
bridge width minimum less than about 2 millimeters.
Inventors: |
Li; Xin; (Boiling Springs,
SC) ; Johnson; Ryan W.; (Moore, SC) ; Rumler;
Joseph E.; (Greenville, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Milliken & Company |
Spartanburg |
SC |
US |
|
|
Assignee: |
Milliken & Company
Spartanburg
SC
|
Family ID: |
50773547 |
Appl. No.: |
14/085095 |
Filed: |
November 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61730677 |
Nov 28, 2012 |
|
|
|
Current U.S.
Class: |
428/114 ;
416/230; 427/373; 427/389.9; 428/221 |
Current CPC
Class: |
D04H 3/004 20130101;
D06M 15/51 20130101; D06M 15/564 20130101; Y10T 428/24132 20150115;
B29C 70/226 20130101; F01D 5/282 20130101; D04H 3/12 20130101; B29B
15/12 20130101; B29C 70/20 20130101; Y10T 428/249921 20150401 |
Class at
Publication: |
428/114 ;
428/221; 427/389.9; 427/373; 416/230 |
International
Class: |
D06M 15/51 20060101
D06M015/51; F01D 5/28 20060101 F01D005/28 |
Claims
1. An infusible, unidirectional fabric having an upper inner
surface and a lower inner surface comprising: a plurality of
unidirectional fibers having a diameter and a length, wherein the
unidirectional fibers are spaced uniformly in the unidirectional
fabric; a plurality of bridges, each bridge being connected to at
least 2 unidirectional fibers and wherein at least 70% by number of
fibers comprise at least one bridge connected thereto forming a
bridged network of unidirectional fibers, wherein the bridges
comprise a bridging polymer, wherein between the unidirectional
fibers the bridges each have a width and a bridge width minimum,
and wherein at least 50% by number of the bridges have a bridge
width minimum less than about 2 millimeters; and, a plurality of
void spaces between the unidirectional fibers, wherein the void
spaces are interconnected, wherein the fabric has a volume fraction
of voids of between about 8 and 70%, and wherein the fabric has a
volume fraction of fibers of between about 35 and 85%.
2. The infusible unidirectional fabric of claim 1, wherein the
bridged network of unidirectional fibers have a tensile strength of
at least 200 Pa in the direction perpendicular to the
unidirectional fibers.
3. The infusible, unidirectional fabric of claim 1, wherein the
bridging polymer forms between about 0.1 and 30% of the effective
cross-sectional area of the infusible, unidirectional fabric.
4. The infusible, unidirectional fabric of claim 1, wherein the
unidirectional fibers comprise a material selected from the group
consisting of glass, carbon, aramid, polyethylene, polyester,
polyamide, and mixtures thereof.
5. The infusible, unidirectional fabric of claim 1, wherein the
infusible, unidirectional fabric does not comprises any stitching
fibers or yarns.
6. An infused, unidirectional composite comprising: at least one
unidirectional fabric having an upper inner surface and a lower
inner surface, the unidirectional fabric comprising a plurality of
unidirectional fibers having a diameter and a length, wherein the
unidirectional fibers are spaced uniformly in the unidirectional
fabric; a plurality of bridges, each bridge being connected to at
least 2 unidirectional fibers and wherein at least 70% by number of
fibers comprise at least one bridge connected thereto forming a
bridged network of unidirectional fibers, wherein the bridges
comprise a bridging polymer, wherein between the unidirectional
fibers the bridges each have a width and a bridge width minimum,
and wherein at least 50% by number of the bridges have a bridge
width minimum less than about 2 millimeters; and, a cured resin
between the unidirectional fibers, wherein the cured resin is
continuous through the composite, wherein the composite has a
volume fraction of cured resin of between about 8 and 70%, and
wherein the composite has a volume fraction of fibers of between
about 35 and 85%.
7. The infused, unidirectional composite of claim 6, wherein the
bridging polymer forms between wherein the bridging polymer forms
between about 0.1 and 30% of the effective cross-sectional area of
the infused, unidirectional composite.
8. The infused, unidirectional composite of claim 6, wherein the
composite comprises at least two or more adjacent unidirectional
fabrics.
9. A structure comprising the infused, unidirectional composite of
claim 6.
10. The structure of claim 9, wherein the structure is selected
from the group consisting of wind turbine blades, bridges, boat
hulls, boat decks, rail cars, pipes, tanks, reinforced truck
floors, pilings, fenders, docks, reinforced wood beams, retrofitted
concrete structures, aircraft structures, reinforced extrusions and
injection moldings.
11. A wind turbine blade comprising an infused, unidirectional
composite in a section of the wind turbine blade selected from the
group consisting of spar section, a root section, leading edge,
trailing edge, wherein the infused, unidirectional composite
comprises: a plurality of unidirectional fibers having a diameter
and a length, wherein the unidirectional fibers are spaced
uniformly in the unidirectional fabric; a plurality of bridges,
each bridge being connected to at least 2 unidirectional fibers and
wherein at least 70% by number of fibers comprise at least one
bridge connected thereto forming a bridged network of
unidirectional fibers, wherein the bridges comprise a bridging
polymer, wherein between the unidirectional fibers the bridges each
have a width and a bridge width minimum, and wherein at least 50%
by number of the bridges have a bridge width minimum less than
about 2 millimeters; and, a cured resin between the unidirectional
fibers, wherein the cured resin is continuous through the
composite, wherein the composite has a volume fraction of cured
resin of between about 8 and 70%, and wherein the composite has a
volume fraction of fibers of between about 35 and 85%.
12. A process of forming infusible, unidirectional fabric
comprising: arranging a plurality of unidirectional fibers into a
unidirectional fabric, wherein the unidirectional fibers are spaced
uniformly within the unidirectional fabric; forming an emulsion or
suspension of a solvent, a bridging polymer, and a film-forming
preventing agent, wherein the bridging polymer is dissolvable or
dispersible in the solvent, wherein the film-forming preventing
agent is dissolvable or dispersible; applying the emulsion or
suspension to the unidirectional fabric; removing the solvent;
removing the film-forming preventing agent to form an infusible,
unidirectional fabric, wherein the infusible, unidirectional fabric
comprises: a plurality of unidirectional fibers having a diameter
and a length, wherein the unidirectional fibers are spaced
uniformly in the unidirectional fabric; a plurality of bridges,
each bridge being connected to at least 2 unidirectional fibers and
wherein at least 70% by number of fibers comprise at least one
bridge connected thereto forming a bridged network of
unidirectional fibers, wherein the bridges comprise a bridging
polymer, wherein between the unidirectional fibers the bridges each
have a width and a bridge width minimum, and wherein at least 50%
by number of the bridges have a bridge width minimum less than
about 2 millimeters; and, a plurality of void spaces between the
unidirectional fibers, wherein the void spaces are interconnected,
wherein the fabric has a volume fraction of voids of between about
8 and 70%, wherein the fabric has a volume fraction of fibers of
between about 35 and 85%.
13. The process of claim 12, wherein the solvent is water.
14. The process of claim 12, wherein the film-forming preventing
agent is a liquid.
15. The process of claim 12, further comprising infusing and curing
a resin into the infusible, unidirectional fabric.
16. The process of claim 12, wherein the infusible, unidirectional
fabric does not comprises any stitching fibers or yarns.
17. The process of claim 12, wherein the bridging polymer forms
between about 0.1 and 30% of the effective cross-sectional area of
the infusible, unidirectional fabric.
18. A process of forming infusible, unidirectional fabric
comprising: arranging a plurality of unidirectional fibers into a
unidirectional fabric, wherein the unidirectional fibers are spaced
uniformly within the unidirectional fabric; forming an emulsion or
suspension of a solvent, a bridging polymer, a blowing agent, a
foaming agent and a gelling agent, wherein the bridging polymer is
dissolvable or dispersible in the solvent; applying the emulsion or
suspension to the fabric; activating the blowing agent forming
bubbles in the emulsion and suspension, wherein the foaming agent
and gelling agent stabilize the bubbles; removing the solvent
forming an infusible, unidirectional fabric, wherein the infusible,
unidirectional fabric comprises: a plurality of unidirectional
fibers having a diameter and a length, wherein the unidirectional
fibers are spaced uniformly in the unidirectional fabric; a
plurality of bridges, each bridge being connected to at least 2
unidirectional fibers and wherein at least 70% by number of fibers
comprise at least one bridge connected thereto forming a bridged
network of unidirectional fibers, wherein the bridges comprise a
bridging polymer, wherein between the unidirectional fibers the
bridges each have a width and a bridge width minimum, and wherein
at least 50% by number of the bridges have a bridge width minimum
less than about 2 millimeters; and, a plurality of void spaces
between the unidirectional fibers, wherein the void spaces are
interconnected, wherein the fabric has a volume fraction of voids
of between about 8 and 70%, wherein the fabric has a volume
fraction of fibers of between about 35 and 85%.
19. The process of claim 18, further comprising infusing and curing
a resin into the infusible, unidirectional fabric.
20. The process of claim 18, wherein the infusible, unidirectional
fabric does not comprises any stitching fibers or yarns.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. provisional
application 61/730,677, filed Nov. 28, 2012, the contents of which
are incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to infusible,
unidirectional fabrics.
BACKGROUND
[0003] The development of more structurally efficient composite
materials enables higher performance and more cost competitive
solutions across a range of markets which use these materials. The
traditional forms used for introducing dry fibers such as glass
roving or carbon tow into a composite system are fabrics such as
woven fabrics (having crimping) or multi-axial knit fabrics (with
minimal crimping). These fabric forms typically impart performance
penalties on the final composite system.
[0004] Composites reinforced with woven fabrics are known to
exhibit lower modulus and strength due to the extensive fiber
crimping which occurs as opposing direction fibers cross over each
other. In the case of multi-axial knits, the layers of reinforcing
fibers do not interpenetrate each other. The knitting process
employs a stitch yarn which is looped around the reinforcing fibers
tying the fibers together and providing stability to the fabric.
The stitch yarn creates local deviations in yarn direction and
imparts a subtle waviness along the fiber axis direction. The
stitch yarns typically create a separation or gap between rovings
or tows within a fabric and between layers of fabric while not
offering any improvement in mechanical properties. Furthermore, the
gaps created by the presence of the stitch yarns reduce the maximum
achievable fiber volume fraction of a composite made with such
reinforcement. Finally, the fiber waviness negatively impacts
several structural properties of composites reinforced with such
systems such as tensile modulus and compression strength.
[0005] There is an opportunity to develop infusible composite
fabrics that offer high fiber volume fractions, a high degree of
fiber alignment and straightness with excellent fiber distribution
uniformity. These fabrics should be convertible into composite
parts through common composite molding operations such as vacuum
infusion or resin transfer molding. These characteristics enable
superior structural properties while preserving the cost advantages
of well-established resin infusion processing. A new approach for
delivering a composite preform with these attributes is
described.
BRIEF SUMMARY
[0006] An infusible, unidirectional fabric containing a plurality
of unidirectional fibers spaced uniformly in the unidirectional
fabric, a plurality of bridges, and a plurality of void spaces
between the unidirectional fibers. Each bridge is connected to at
least 2 unidirectional fibers and at least 70% by number of fibers
have at least one bridge connected thereto forming a bridged
network of unidirectional fibers. The void spaces are
interconnected and the fabric has a volume fraction of voids of
between about 8 and 70%, a volume fraction of fibers of between
about 35 and 85%, and at least 50% by number of the bridges have a
bridge width minimum less than about 2 millimeters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional illustrative view of one
embodiment of an infusible, unidirectional fabric.
[0008] FIG. 2 is a cross-sectional illustrative view of one
embodiment of an infused, unidirectional composite.
[0009] FIG. 3 is a photographic, cross-sectional image of one
embodiment of an infusible, unidirectional fabric.
[0010] FIG. 4 is a photographic, cross-sectional image of one
embodiment of an infused, unidirectional composite.
[0011] FIG. 5A is a micrograph of one embodiment of the
unidirectional fabric along the length of the fibers showing
bridges.
[0012] FIG. 5B is an illustration of FIG. 5A.
[0013] FIG. 6 illustrates the method for determining uniformly
spaced fibers.
[0014] FIG. 7 is an illustrative view of a wind turbine.
[0015] FIGS. 8-12 are illustrative views of a turbine blade.
DETAILED DESCRIPTION
[0016] FIG. 1 is an illustration of one embodiment of an infusible,
unidirectional fabric 10. The infusible, unidirectional fabric 10
contains a bridged network of unidirectional fibers 100 which
contain a plurality of fibers 110 and a plurality of bridges 200.
The infusible, unidirectional fabric 10 also contains void spaces
120 surrounding the fibers 110. The bridged network of
unidirectional fibers 100 has an upper inner surface 10a and a
lower inner surface 10b. The upper and lower inner surfaces are
defined as the boundaries which contain between them essentially
all of the fibers within the bridged network of unidirectional
fibers excluding any unique features occurring only near the edges
or edge effects. Edge effects might include a polymer rich skin or
a region of non-uniform fiber spacing. FIG. 3 is a micrograph image
of one embodiment of the infusible, unidirectional fabric.
[0017] The unidirectional fabric may be any suitable width and in
any suitable shape. In some embodiments where the width of the
fabric is smaller, typically between about 2 and 300 mm, the fabric
may be referred to as a unidirectional tape or fabric band.
[0018] Once the infusible, unidirectional fabric 10 is infused with
resin and cured, an infused, unidirectional composite 400
illustrated in FIG. 2 is formed. In the infused, unidirectional
composite, the resin 300 coats and at least partially infuses into
the bridged network of unidirectional fibers 100 and cures at least
partially filling the void space 120 in the bridged network of
unidirectional fibers 100. This forms the infused, unidirectional
composite 400 containing bridged network of unidirectional fibers
100 which contains fibers 110, bridges 200, and resin 300. FIG. 4
is a micrograph image of one embodiment of an infused,
unidirectional composite.
[0019] A fabric with the above described structure will be
infusible in vacuum assisted resin transfer molding (also called
vacuum assisted resin infusion) process. The word "infusible", in
this invention, refers to fabrics having the following
characteristics: The fabrics can be used to make fiber reinforced
polymer composites having a thickness greater than 2 mm by using a
standard vacuum assisted resin transfer molding (also called vacuum
assisted resin infusion) method and low viscosity infusion grade
thermoset resin. The infusion process has a typical processing time
scale ranging from minutes to hours. Preferably, the finished
composite with the infusible fabric typically has a void content as
measured by a standard test such as ASTM D2734 of less than 5%,
more preferably less than 2%.
[0020] A simple method to predict whether a fabric is infusible or
not can be described as follows. Several water droplets with 0.01%
water soluble color dye (for example, Acid Blue 9) are dropped on
the surface of fabric by using a 5 mL transfer pipette. The time
duration required for the droplets to completely infuse into the
fabric is used as an indication of infusibility. By definition, in
this method, "completely infuse into the fabric" means that more
than 99% by mass of the water from the original droplet has been
absorbed between the upper inner surface and lower inner surface of
the fabric. By definition, a fabric is considered "infusible" in
this invention if the average water droplet infusion time is less
than 1 minute. This method is a method to indicate that the fabric
is "infusible", if the average water droplet infusion time is
longer than 1 minute, it is not necessary to mean that the fabric
is not resin infusible due to the hydrophobic nature of most
thermoset resin. This test method may not be accurate if there is
coating strong hydrophobic tendencies on the fabric.
[0021] Preferably, the infusible, unidirectional fabric 10 is
self-supporting. "Self-supporting", in this invention, means that
the fabric is dimensionally stable, and the fibers in the fabric
will not fall apart due to their own weight under gravity. The
fabric has a well-defined width and thickness. Additional
components may be attached to the fabric but are not required.
Preferably, additional stabilizing means such as stitching, scrims,
films, and the like are not needed to handle and convey the
infusible, unidirectional fabric 10.
[0022] Within the infusible, unidirectional fabric 10, the void
spaces are interconnected and the fabric has a void fraction of
preferably between about 8 and 70%, more preferably between about
10 and 70%. The infusible, unidirectional self-supporting fabric
preferably has a fiber volume fraction between 35% and 85%,
preferably between 45% and 80%, more preferably between 50% and
80%. A fiber volume fraction less than about 30% may make the fiber
reinforcement less practical as a composite reinforcement. A fiber
volume fraction greater than 85% could have negative consequences
as it may slow down the resin infusion process, reduce the
mechanical properties perpendicular to the fiber direction, or
reduce the fatigue durability of the composite. If the void spaces
are not interconnected, there may be to too few channels for resin
infusion. If there is not enough void content in the fabric, resin
infusion may be very slow and difficult.
[0023] The fiber volume fraction can be measured using a first
method (for fabric made by inorganic fibers) where one measures the
total mass (m.sub.0), thickness (D), width (W), and length (L) of
given piece of fabric, and then calculates the total volume
(V.sub.0) of the given piece of fabric by
V.sub.0=D.times.W.times.L. Next, the sample (piece of fabric) is
placed in an oven, heated at 700.degree. C. for 4 hours to burn off
all organic content in the fabric, and the mass of inorganic
component is measured (mass (m.sub.f)) after this burn off step.
The fiber volume fraction (V.sub.f%) is calculated by
V.sub.f%=(m.sub.f/.rho..sub.f)/V.sub.0, where .rho..sub.f is the
density of the material which made the fiber. .rho. can be measure
by any suitable density measurement methods, or obtained from
technical data sheet of the fiber material. The method works only
when there is no or very small amount (less than 1%) other
inorganic component such (for example, silica nanoparticles) in the
fabric.
[0024] Another method to measure the void content in the fabric can
be described as the following: use the infusible unidirectional
fabric to make a fiber reinforced composite material by using
vacuum assisted resin infusion method (detail description of this
method is described in the Example section below) and do a SEM or
optical imaging to a typical cross section of the composite, where
the cross section is perpendicular to the fiber direction. The void
content can be calculated by measuring the total cross section area
of infused resin, divided by the total cross section area of the
composite. To help identifying the infused resin area, about 0.01%
to 0.1% by weight of color dye or fluorescent dye can be added into
the resin before resin infusion.
[0025] The infusible, unidirectional self-supporting fabric also
comprises polymer bridges, where the volume ratio of polymer
bridges to fibers is between 1:370 and 1:2, more preferably between
1:40 and 1:4, more preferably between 1:12 and 1:4. The polymer
bridges are a main source of support to the fabric structure and
help prevent fibers fall apart due to gravity. The overall polymer
bridge structure will not be strong enough to support the fabric
structure if there are too few polymer bridges in the fabric. If
there is too much polymer in the fabric, there may not be enough
void space for resin infusion. The total volume of polymer bridges
can be calculated by knowing how much mass (m.sub.p) polymer bridge
material(s) have been added into the fabric during manufacturing,
or using a burn off test (Described in the first method above for
measuring fiber volume) to estimate the mass of polymer bridges by
m.sub.p=(m.sub.0-m.sub.f). The volume of polymer bridges (V.sub.p)
is calculated by V.sub.p=m.sub.p/.rho..sub.p, where .rho..sub.p is
the density of polymer material.
[0026] The infusible, unidirectional fabric 10 (and composite 400)
contains a bridging polymer which forms bridges 200 between and
connected to at least a portion of the fibers 110. This is shown in
both FIGS. 1 and 2. Preferably, each bridge is connected to at
least 2 unidirectional fibers forming bridged fibers. In one
embodiment, at least 70% by number, at least 80% by number, or at
least essentially all of the fibers 110 are bridged to at least one
other fiber 110 somewhere along the length of the fiber.
"Essentially all", this this context means that enough of the
fibers are attached such that there are no loose fibers, therefore
the fabric acts as a unit not like a yarn. In another embodiment,
at least about 90% by number of the fibers 110 are bridged to at
least one other fiber 110 somewhere along the length of the fiber.
As the % connected by number of fibers is anywhere along the length
of the fiber, in a typical single cross-section, fewer connections
will be seen.
[0027] Therefore, in a given cross-section, preferably between
about 10 and 100% by number of fibers contain bridges to one or
more fibers within the bridged network of unidirectional fibers 100
(composite 400). In another embodiment, between about 15 and 100%
by number of fibers in a given cross-section contain bridges to one
or more fibers, more preferably between about 50 and 100%, more
preferably between about 60 and 100% more preferably between about
75 and 100% by number of fibers in a given cross-section.
[0028] Within the bridged network of unidirectional fibers 100,
there are a plurality of bridges 200 between and connected to at
least a portion of fibers 110. The bridging between fibers 110
helps control the position of the fibers 110 relative to other
fibers and the fabric. The bridging attaches the fibers together
and creates a stable fabric form. These bridges are connected and
adhered to the surface of the fibers 110. A bridging polymer that
extends between at least two fibers 110 but is not attached to at
least two fibers 110 is not a bridge as defined in this
application. The bridging increases the interaction between fibers
110 while still allowing resin to flow between and around the
fibers 110. The bridging polymer preferably has an elasticity which
is characterized as elongation at break at least about 50%, more
preferably higher than 100%, and more preferably higher than 300%.
The elasticity of the bridges helps the fabric remain flexible
(able to conform to curved mold shapes) and helps the bridges
survive bending or folding of the fabric.
[0029] The bridging polymer may be physically or chemically bonded
(through there may be in some embodiments a thin layer between
anchoring surface and fiber surface, for example, a coating layer
or sizing) to the surface of the fiber 110 through interactions
including but not limited to hydrogen bonding, van der Waals
interactions, ionic interactions, electrostatic interactions,
mechanical interlocking, or a portion of the anchoring surface may
chemically react with the surface of the fiber 110 to form covalent
bonds between the fiber and the anchoring surface. The anchoring
surface may be physically or chemically bonded to a coating or
sizing that was previously applied to the fiber, through
interactions including hydrogen bonding, van der Waals
interactions, ionic interactions, electrostatic interactions, or a
portion of the anchoring surface may chemically react with the
coating or sizing on the surface of the fiber to form covalent
bonds between the coating or sizing on the fiber surface and the
anchoring surface. If the fiber or coating or sizing on the fiber
is porous or if the precursors to the bridge can diffuse or
penetrate into the surface of the fiber, then the anchoring surface
may interpenetrate with the fiber surface on a nanometer or
micrometer length scale. It is important that the bridging polymer
has good adhesion to fiber surface, because all the fibers in the
unidirectional fabric structure are held together by the
bridges.
[0030] In one embodiment, at least a number of the bridges contain
a width gradient, where the width of the bridge is greatest at the
anchoring surface and decreases in a gradient away from the
anchoring surface. The greater width at the anchoring surface helps
increase the strength of the adhesion between the bridge and the
fiber, and a narrower width away from the anchoring surface leaves
more void space in the fabric 10 for resin infusion. An optimized
system is preferred which has sufficient strength for maintaining
fabric integrity during handling while minimizing the time required
to infuse the structure with resin.
[0031] Additionally, preferably at least 50% of the bridges have a
bridge width minimum narrower than 2 mm, more preferably narrower
than 0.5 mm, more preferably narrower than 0.2 mm. The bridge width
minimum is defined as the minimum width of the bridge (in the
direction of fiber length) from surface of the first fiber to the
surface of the second connected fiber. In one embodiment, the
bridges typically have approximately the same width along the fiber
direction from the surface of one fiber to the connected fiber. In
this case, the bridge width is approximately constant in the
bridge. In another embodiment, the bridge is wider where the bridge
attaches to the fibers and is the narrowest (and has the minimum
width) between the two fibers.
[0032] The width of the bridges in fiber direction can be measured
by optical microscopic image or SEM image. In this measurement, dry
fabric (before resin infusion) is preferred to be used to take
images. The images are taken from the cross section which is
parallel to fiber direction. FIGS. 5A and 5B show some typical
bridges in the unidirectional fabric and composites. FIG. 5A is a
micrograph image and FIG. 5B is an illustration of the photograph
of FIG. 5A. FIGS. 5A and 5B show some typical bridges. If the width
of the bridges in the fiber direction is too wide (and therefore
the bridge width minimum is too large), the resin is less able to
infuse through the fabric in the thickness direction.
[0033] In one embodiment, the bridges 200 preferably form between
about 0.1 and 60% of the effective cross-sectional area of the
infusible, unidirectional fabric 10 (and infused, unidirectional
composite 400). In another embodiment, the bridges 200 form between
about 0.1 and 30% of the effective cross-sectional area of the
fabric and composite, more preferably between about 0.3% and 10%,
more preferably between about 0.5% and 5%. "Effective
cross-sectional area", in this application, is measured by taking a
cross-sectional image of the fabric and calculating the area of
bridge. If the cross-sectional area of bridges is less than about
0.1%, there may not be enough bridges to enhance the mechanical
properties of the composite. If the cross-sectional area of bridges
is larger than 30%, there may not be enough porosity in the fabric
for resin infusion leading to lower performance due to dry spots or
voids in the composite systems.
[0034] Where bridging occurs in the fabric 10 depends on a number
of factors including but not limited to the type of bridging
polymer, solvent, film forming preventing agent, surface chemistry
of fiber, separation distance between fibers, coating process
conditions, drying conditions, post mechanical treatment during and
after drying. The time required for bridging to occur also depends
on concentration of bridging polymer, concentration of
co-stabilizer, concentration of surfactant, surface chemistry of
fiber, initial size of dispersed phase in the emulsion,
temperature, solidification time of the bridging polymer,
separation distance between adjacent fibers, and coating process
conditions,
[0035] In one embodiment, the bridging polymer forms between about
1% and 20% by weight of the infusible, unidirectional fabric. In
another embodiment, the cross sectional area of the fibers is
between 30% and 80% of the total cross sectional area of the
fabric, and the ratio by cross sectional area of polymer:void is
between 1:0.5 and 1:93.
[0036] The anchoring surfaces of bridges cover less than 100% of
the fiber surfaces (this includes all of the surface area of the
fiber). The uncovered fiber surfaces can bond to the resin directly
in composites and increase the interaction between fibers and
infused resin in composite. In one embodiment, the anchoring
surfaces of bridges cover about 10% to 99% of the fiber surface.
Preferably the anchoring surfaces of bridges cover about 30% to 90%
of the fiber surface.
[0037] The bridges in the infusible, unidirectional fabric are
formed from a bridging polymer including but not limited to
thermoset resin, thermoplastic resin, ionomer, dendrimer, and
mixtures thereof. Thermoset resins, such as epoxy, polyurethane,
acrylic resin, rubbers, and phenolic, are liquid resins which
harden by a process of chemical curing, or cross-linking, which
takes place during the coating process. Thermoplastic resins, such
as polyethylene, polypropylene, polyolefin copolymer elastomer,
thermoplastic polyurethane, polyvinyl alcohol (PVA), PET and PEEK,
are liquefied by the application of heat prior to coating and
re-harden as they cool within the fabric. Preferably, the bridging
polymer has good adhesion on fiber surface. Preferably, the
bridging polymer (or the polymer in organic solvent solution, or
the chemicals that form polymer during process) can be uniformly
dispersed in water before coating. In one embodiment, the bridging
polymer is ethylene vinyl acetate (EVA) copolymer, styrene
butadiene rubber (SBR), water borne polyurethane, polyolefin
elastomer (POE), or a mixture thereof. SBR and polyurethane are
preferred due to its moderate cost, good mechanical properties, and
good adhesion to fibers.
[0038] In one embodiment, the polymer bridges are formed beginning
with a polymer in water dispersion or polymer water solution. SBR
latex or water borne polyurethane are preferred due to its moderate
cost, good mechanical properties, good adhesion to fibers.
Film-forming preventing agents are preferred to be added in to the
polymer water dispersion or polymer water solution, because the
film-forming preventing agents can create void space and channels
between fibers by preventing the polymer forming continuous
film.
[0039] In one embodiment, the film-forming preventing agent is
solid or liquid particles which can be dispersed or dissolved in
the polymer in water dispersion or polymer water solution. This
type of film forming preventing agent will be removed from the
fabric after the polymer solidified. Silica particles are one of
the examples. In one embodiment, the film-forming preventing agent
is water soluble material, which can phase separate from the
polymer and form continuous phase during water evaporation. One
requirement of the water soluble materials is that they don't make
the polymer in water dispersion or polymer water solution unstable.
In one embodiment, sugar or other water soluble non-ionic materials
are preferred. In another preferred embodiment, glycerin or
propylene carbonate is used as a film forming preventing agent to
create the void space. After water evaporation and polymer
solidified, the film forming preventing agent rich phase will be
removed from the fabric, leaving voids and channels in the
fabric.
[0040] In one embodiment, the film-forming preventing agents are a
combination of blowing agents, and frothing agents or foaming
agents. The blowing agent can be any suitable material that can
create bubbles during coating process. In one embodiment, the
blowing agent is water. Water can quickly evaporate under heat and
creates bubbles. In another embodiment, the blowing agent is carbon
dioxide that has dissolved in water. In another embodiment, the
blowing agent is low boiling point organic liquid. In another
embodiment, the blowing agent can chemically decompose and release
gas under heat. This type of blowing agent includes but not limit
to NaHCO.sub.3, azodicarbonamide, and p-p'-oxbis (benzensulfonyl
hydrazide). The frothing agents or foaming agents include but not
limited to ionic surfactant such as sodium dodecyl sulfate (SDS),
sodium dodecylbenzenesulfonate (NaDDBS), or non-ionic block
copolymer such as ethylene oxide and propylene oxide copolymer. One
example of the block copolymer is Pluronic.RTM. from BASF. A
gelling agent is also preferred to be added to stabilize the
polymer foam. The gelling agent includes but not limited to acacia,
alginic acid, bentonite, carbomers, carboxymethylcellulose.
ethylcellulose, gelatin, hydroxyethylcellulose, hydroxypropyl
cellulose, magnesium aluminum silicate (Veegum.RTM.),
methylcellulose, Pluronics.RTM., polyvinyl alcohol, sodium
alginate, tragacanth, and xanthan gum. A gelling agent with lower
critical solution temperature (LCST) is preferred because it is
soluble in cold water and gels in hot water. One example of the
gelling agent with LCST characteristic is Pluronics.RTM. F-127.
[0041] In one embodiment, sugar is used as the film-forming
preventing agent. The polymer solid content is between about 1% and
60% of the polymer in water dispersion or polymer in water
solution. More preferably the polymer solid content is between
about 3% and 20%. The sugar to polymer solid content ratio by
weight is between about 0.5:1 and 10:1, more preferably between 1:1
and 5:1. Too little sugar cannot prevent polymer forming films and
cannot create enough void space and channels in the fabric; Too
much sugar makes the polymer bridges weak.
[0042] In one embodiment, glycerin is used as the film-forming
preventing agent. The polymer solid content is between about 1% and
60% of the polymer in water dispersion or polymer in water
solution. More preferably the polymer solid content is between
about 3% and 20%. The glycerin to polymer solid content ratio by
weight is between about 0.5:1 and 20:1, more preferably between 1:1
and 10:1. Too little glycerin cannot prevent polymer forming films
and cannot create enough void space and channels in the fabric; too
much glycerin makes polymer dispersion unstable and the polymer
bridges are weak.
[0043] In another embodiment, foaming agents and gelling agents are
used as the film-forming preventing agent. The polymer solid
content is between about 1% and 60% of the polymer in water
dispersion or polymer in water solution. More preferably the
polymer solid content is between about 3% and 20%. The frothing
agent is between about 0.1% and 20% of the total weight, more
preferably between about 1% and 10% of the total weight. The
gelling agent is between about 0.1% and 40% of the total weight,
more preferably between 1% and 10% of the total weight. In one
embodiment, Pluronics.RTM. F-127 is used as a foaming agent and
also a gelling agent, preferably between 1% and 15% by weight in
the coating mixture, more preferably between 3% and 10% by weight
in the coating mixture.
[0044] In one embodiment, the bridging polymer and the resin 300
have different chemical compositions. Having a different chemical
composition, in this application, means that materials having a
different molecular composition or having the same chemicals at
different ratios or concentrations. Having different chemical
compositions may be able to help redistribute stress in composites.
In another embodiment, the bridging polymer and the resin 300 have
the same chemical compositions. Having the same compositions may
make the infusing resin wet the fabric more easily.
[0045] The bridged network of unidirectional fibers 100 may be any
suitable fibers for the end product. "Unidirectional fibers", in
this application means that the majority of fibers aligned in one
direction with the axis along the length of the fibers being
generally parallel. The composite 400 may contain a plurality of
fibers in a bundle (the bundles may be part of a textile layer
including but not limited to a woven textile, non-woven textile
(such as a chopped strand mat), bonded textile, knit textile, a
unidirectional textile, and a sheet of strands.) In one embodiment,
the bridged network of unidirectional fibers 100 are formed into
unidirectional strands such as rovings and may be held together by
bonding, knitting a securing yarn across the rovings, or weaving a
securing yarn across the rovings. In the case of woven, knit, warp
knit/weft insertion, non-woven, or bonded the textile can have
fibers that are disposed in a multi- (bi- or tri- or quadri-) axial
direction. In one embodiment, the bridged network of unidirectional
fibers 100 contains an average of at least about 2 fibers, more
preferably at least about 20 fibers. The fibers 110 within the
fabric 10 generally are aligned and parallel, meaning that the axes
along the lengths of the fibers 110 are generally aligned and
parallel. Each fiber has a fiber surface defined to be the outer
surface of the fiber and a fiber diameter.
[0046] Preferably, the infusible, unidirectional fabric 10 contains
unidirectional fibers 110 that are spaced uniformly in the
unidirectional fabric 10. "Spaced uniformly" or "uniformly spaced",
in this application, means that in a typical fabric cross section,
within the bridged network of unidirectional fibers, there is no
clear boundary of any fiber bundle, yarn, roving, or tow.
[0047] For the purpose of this invention, fiber distribution
uniformity can be measured by the following method. A typical cross
section image of the unidirectional fabric or composite made
thereof is prepared by standard microscopy mounting and imaging
techniques. Unidirectional fabrics are typically encapsulated in a
polymer such as mounting epoxy and cut with a diamond wafer saw
orthogonal to the fiber direction through the sample. Composites
can often be sectioned without requiring mounting because the
fibers are already stabilized by the composite matrix polymer.
[0048] After sectioning, the surface of the cross section to be
viewed is ground and polished to enable unobstructed viewing of the
sample through optical or electron microscopy. The polishing
process is repeated until the contrast between fiber and matrix in
the images at the target resolution is sufficient to compute the
fiber area fraction within the cross section. The perimeter of each
fiber should be clearly distinguishable.
[0049] For measuring fiber distribution uniformity via the fiber
area ratio method described herein, the image must be of a
sufficient size scale to encompass the entire thickness of at least
one layer of the fabric. An example image of a composite reinforced
with two layers of unidirectional fabric, 501 and 501, comprising
glass fibers is shown in FIG. 6. Within the layer to be analyzed,
501, the upper inner surface, 10a, and lower inner surface, 10b,
are located. The distance between the upper inner surface and the
lower inner surface is defined as the bulk thickness, t.sub.b.
[0050] Within the unidirectional region of the cross section image
located between the upper inner surface and the lower inner
surface, a grid of squares is overlaid onto the image, 510. The
grid contains a square pattern of non-overlapping connected squares
which share edges and corners, 520. Each square in the grid has
sides of length t.sub.b/2. The image must be of sufficient size to
contain at least four such squares. The number of grid squares
should be the maximum possible within the cross section area of the
fabric where each sub-region remains fully within the fabric cross
section. Each area of the image within the borders of each square,
521, is defined as a sub-region.
[0051] For each sub-region, the fiber area fraction is computed.
The fiber area fraction for a sub-region is the ratio of the area
within the sub-region that is occupied by fiber divided by the
total area of the sub-region. This calculation is readily done by
standard image processing algorithms based on the image contrast or
color difference between the fiber and the matrix region.
[0052] After all sub-regions of the typical cross section image
have been analyzed, the overall average fiber area ratio can be
computed. A uniform distribution is defined as one in which at
least 85% of the sub-regions have a fiber area ratio value that
falls within the range defined by .+-.15% of the overall average
fiber area ratio. More preferably the distribution is characterized
by at least 95% of the sub-regions having a fiber area ratio value
within the range defined by .+-.15% of the overall average fiber
area ratio. Most preferably, the distribution is characterized by
at least 98% of the sub-regions having a fiber area ratio value
within the range defined by .+-.15% of the overall average fiber
area ratio.
[0053] In some embodiments, a composite contains more than one
fabric or a group of fabrics. The same definition of "uniform
distribution" can be applied across cross section images containing
regions of more than one unidirectional fabric. A grid as described
above is created within one layer of the reinforcement, and then
extended to encompass the entire unidirectional region of the
composite less any residual area that does not fit within a full
square defined by the grid. Fiber area ratios are computed within
each sub-region. After all sub-regions of the typical cross section
image have been analyzed, the overall average fiber area ratio can
be computed. A uniform distribution is defined as one in which at
least 85% of the sub-regions have a fiber area ratio value that
falls within the range defined by .+-.15% of the overall average
fiber area ratio. More preferably the distribution is characterized
by at least 95% of the sub-regions having a fiber area ratio value
within the range defined by .+-.15% of the overall average fiber
area ratio. Most preferably, the distribution is characterized by
at least 98% of the sub-regions having a fiber area ratio value
within the range defined by .+-.15% of the overall average fiber
area ratio.
[0054] A composite comprising multiple layers of conventional
unidirectional fabrics may not be considered to have a uniform
fiber distribution if the gaps created between the unidirectional
yarns or rovings or tows within the fabric or the gaps created
between the layers of fabric are large enough to prohibit
satisfying the criteria requiring at least 85% of the sub-regions
have a fiber area ratio value that falls within the range defined
by .+-.15% of the overall average fiber area ratio.
[0055] In this definition, a fabric having yarns or threads woven
into the unidirectional fibers in the direction perpendicular to
the unidirectional fibers would fall under the definition of spaced
uniformly as typically the gap between rovings or bundles are about
4 times of the fiber diameter. If a typical bundle of rovings is
used, then the unidirectional fibers are grouped into bundles where
the fibers in those bundles are held closer together and there is
typically a space between bundles where little to no fibers reside.
Preferably, there are no additional fibers or yarns holding the
unidirectional fibers together.
[0056] The strength and free-standing nature of the bridged network
of unidirectional fibers 100 is due mostly to the bridges 200.
Preferably, the bridged fibers (containing no additional
reinforcements besides the bridges) have enough tensile strength to
be handled in a manufacturing process without any additional
reinforcement fabrics or layers. In another embodiment, the bridged
fibers have a tensile strength of at least 200 Pa in the direction
perpendicular to the length direction of the unidirectional fibers.
In another embodiment, the bridged fibers have a tensile strength
of at least 700 Pa, more preferably higher than 10 kPa in the
direction perpendicular to the length direction of the
unidirectional fibers. The tensile strength of the fabric is
measured by gripping two ends of a rectangular piece fabric in a
tensile strength test machine (for example, Instron), while the
tensile test direction is perpendicular to the unidirectional fiber
direction. The fabric is then stretched under a constant speed
(typically about 1.about.10 cm/minute). The tensile strength is
calculate by measuring the maximum tensile force before fabric is
broken, divided by the area of cross section of the fabric. In
another embodiment, the fabric does not suffer significant
structural damage under a peel strength of 0.25 lbf/inch (0.44
N/cm) in a peel strength test between the fabric and an adhesive
tape. In this test, a piece of adhesive tape about 6.about.10 inch
long is adhered to the fabric surface in the fiber direction at
room temperature, and the peel strength between the tape and fabric
is tested. The details of peel strength test can be found in ASTM
D5170. "Not suffer significant structural damage", in this
invention, means that most fibers are still keeping their relative
position in the fabric during peel strength test, and after the
peel strength test, less than 20 fibers, preferably less than 10
fibers, more preferably zero fiber, are sticking on the adhesive
tape. The fibers (if there is any) which are sticking on the
adhesive tape are originally located on the surface of the fabric.
This means that the interface between the tape and the fabric
failed before the fabric cohesively failed. In one embodiment, the
fabric contains no additional stitching fibers, reinforcement
layers, or reinforcement fabrics such as stitching yarns or scrims.
Thus, the infusible unidirectional fabric has enough strength to be
used as a stand-alone fabric, for example allowing the fabric to be
placed in the mold before infusion with resin. Because additional
stitching fibers, reinforcement layers, or reinforcement fabrics
usually creates gap or space with very few fibers, as a result, the
fibers may not be spaced uniformly.
[0057] The fibers 110 may be any suitable fiber for the end use.
"Fiber" used herein is defined as an elongated body and includes
yarns, tape elements, and the like. The fiber may have any suitable
cross-section such as circular, multi-lobal, square or rectangular
(tape), and oval. The fibers may be monofilament or multifilament,
staple or continuous, or a mixture thereof. Preferably, the fibers
have a circular cross-section which due to packing limitations
intrinsically provides the void space needed to host the bridges.
The fibers 110 can have an average length of at least about 3
millimeters. In another embodiment, the fiber length is at least
about 100 times the fiber diameter. In another embodiment, the
average fiber length is at least about 10 centimeters. In another
embodiment, the average fiber length is at least about 1 meter.
Preferably, the fibers are continuous. The fiber lengths can be
sampled from a normal distribution or from a bi-, tri- or
multi-modal distribution depending on how the fabrics are
constructed. The average lengths of fibers in each mode of the
distribution can be selected from any of the fiber length ranges
given in the above embodiments.
[0058] The fibers 110 can be formed from any type of fiberizable
material known to those skilled in the art including fiberizable
inorganic materials, fiberizable organic materials and mixtures of
any of the foregoing. The inorganic and organic materials can be
either man-made or naturally occurring materials. One skilled in
the art will appreciate that the fiberizable inorganic and organic
materials can also be polymeric materials. As used herein, the term
"polymeric material" means a material formed from macromolecules
composed of long chains of atoms that are linked together and that
can become entangled in solution or in the solid state. As used
herein, the term "fiberizable" means a material capable of being
formed into a generally continuous or staple filament, fiber,
strand or yarn. In one embodiment, the fibers 110 are selected from
the group consisting of carbon, glass, aramid, boron, polyalkylene,
quartz, polybenzimidazole, polyetheretherketone, basalt,
polyphenylene sulfide, poly p-phenylene benzobisoaxazole, silicon
carbide, phenolformaldehyde, phthalate and napthenoate,
polyethylene. In another embodiment, the fibers are metal fibers
such as steel, aluminum, or copper.
[0059] Preferably, the fibers 110 are formed from an inorganic,
fiberizable glass material. Fiberizable glass materials useful in
the present invention include but are not limited to those prepared
from fiberizable glass compositions such as S glass, S2 glass, E
glass, R glass, H glass, A glass, AR glass, C glass, D glass, ECR
glass, glass filament, staple glass, T glass and zirconium oxide
glass, and E-glass derivatives. As used herein, "E-glass
derivatives" means glass compositions that include minor amounts of
fluorine and/or boron and most preferably are fluorine-free and/or
boron-free. Furthermore, as used herein, "minor amounts of
fluorine" means less than 0.5 weight percent fluorine, preferably
less than 0.1 weight percent fluorine, and "minor amounts of boron"
means less than 5 weight percent boron, preferably less than 2
weight percent boron. Basalt and mineral wool are examples of other
fiberizable glass materials useful in the present invention.
Preferred glass fibers are formed from E-glass or E-glass
derivatives.
[0060] The glass fibers of the present invention can be formed in
any suitable method known in the art, for forming glass fibers. For
example, glass fibers can be formed in a direct-melt fiber forming
operation or in an indirect, or marble-melt, fiber forming
operation. In a direct-melt fiber forming operation, raw materials
are combined, melted and homogenized in a glass melting furnace.
The molten glass moves from the furnace to a forehearth and into
fiber forming apparatuses where the molten glass is attenuated into
continuous glass fibers. In a marble-melt glass forming operation,
pieces or marbles of glass having the final desired glass
composition are preformed and fed into a bushing where they are
melted and attenuated into continuous glass fibers. If a pre-melter
is used, the marbles are fed first into the pre-melter, melted, and
then the melted glass is fed into a fiber forming apparatus where
the glass is attenuated to form continuous fibers. In the present
invention, the glass fibers are preferably formed by the
direct-melt fiber forming operation.
[0061] In one embodiment, when the fibers 110 are glass fibers, the
fibers contain a sizing. This sizing may facilitate processing of
the glass fibers into textile layers and enhances fiber--polymer
matrix interaction. In another embodiment, the fibers 110 being
glass fibers do not contain a sizing. The non-sizing surface may
help to simplify the coating process and give better control of
polymer--fiber interaction. Fiberglass fibers typically have
diameters in the range of between about 10-35 microns and more
typically 17-19 microns. Carbon fibers typically have diameters in
the range of between about 5-10 microns and typically 7 microns,
the fibers (fiberglass and carbon) are not limited to these
ranges.
[0062] Non-limiting examples of suitable non-glass fiberizable
inorganic materials include ceramic materials such as silicon
carbide, carbon, graphite, mullite, basalt, aluminum oxide and
piezoelectric ceramic materials. Non-limiting examples of suitable
fiberizable organic materials include cotton, cellulose, natural
rubber, flax, ramie, hemp, sisal and wool. Non-limiting examples of
suitable fiberizable organic polymeric materials include those
formed from polyamides (such as nylon and aramids), thermoplastic
polyesters (such as polyethylene terephthalate and polybutylene
terephthalate), acrylics (such as polyacrylonitriles), polyolefins,
polyurethanes and vinyl polymers (such as polyvinyl alcohol).
[0063] In one embodiment, the fibers 110 preferably have a high
strength to weight ratio. Preferably, the fibers 110 have strength
to weight ratio of at least 0.7 GPa/g/cm.sup.3 as measured by
standard fiber properties at 23.degree. C. and a modulus of at
least 69 GPa.
[0064] Textiles or other assemblies of the infusible,
unidirectional fabric 10 can be further processed to create
composite preforms. One example would be to wrap the fabric 10
around foam strips or other shapes to create three dimensional
structures. These intermediate structures can then be formed into
composite structures 400 by the addition of resin in at least a
portion of the void space 120 in the fabric 10.
[0065] The infusible, unidirectional fabric 10 can be further
processed into an infused, unidirectional composite 400 as
illustrated in FIG. 2 with the addition of resin in at least a
portion of the void space 120 in the fabric 10, preferably filling
up approximately all of the void space within the fabric 10.
[0066] The infusible, unidirectional fabric 10 is impregnated or
infused with a resin 300 which flows, preferably under differential
pressure, through the fabric 10 at least partially filling the void
space creating the infused, unidirectional composite 400. The
infused, unidirectional composite 400 could also be created by
other wetting or composite laminating processes including but not
limited to hand lay-up, filament winding, and pultrusion.
Preferably, the resin flows throughout the infusible,
unidirectional fabric 10 (and all of the other reinforcing
materials such as reinforcing sheets, skins, optional stabilizing
layers, and strips) and cures to form a rigid, composite 400.
[0067] It is within the scope of the present invention to any type
of hardenable resin to infuse or impregnate the porous and fibrous
reinforcements of the cores and skins. Thermoset resins, such as
unsaturated polyester, vinyl ester, epoxy, polyurethane, acrylic
resin, and phenolic, are liquid resins which harden by a process of
chemical curing, or cross-linking, which takes place during the
molding process. Thermoplastic resins, such as polyethylene,
polypropylene, PET and PEEK, are liquefied by the application of
heat prior to infusing the reinforcements and re-harden as they
cool within the panel. In one embodiment, the resin 300 is an
unsaturated polyester, a vinylester, an epoxy resin, a polyurethane
resin, a bismaleimide resin, a phenol resin, a melamine resin, a
silicone resin, or thermoplastic PBT or Nylon or mixtures thereof.
Unsaturated polyester and epoxy are preferred due to their moderate
cost, good mechanical properties, good working time, and cure
characteristics.
[0068] In some commercial applications, the epoxy based resins have
higher performance (fatigue, tensile strength and strain at
failure) than polyester based resins, but also have a higher cost.
The uniformly spaced fibers in the fabric 10 may increase the
performance of a composite 400 using an unsaturated polyester resin
to levels similar to the performance levels of the epoxy resin
composite, but with a lower cost than the epoxy resin system.
[0069] Having the resin 300 flow throughout the infusible,
unidirectional fabric 10 under differential pressure may be
accomplished by processes such as vacuum bag molding, resin
transfer molding or vacuum assisted resin transfer molding (VARTM).
In VARTM molding, the components of the composite are sealed in an
airtight mold commonly having one flexible mold face, and air is
evacuated from the mold, which applies atmospheric pressure through
the flexible face to conform the composite 400 to the mold.
Catalyzed resin is drawn by the vacuum into the mold, generally
through a resin distribution medium or network of channels provided
on the surface of the panel, and is allowed to cure. Additional
fibers or layers such as surface flow media can also be added to
the composite to help facilitate the infusion of resin. A series of
thick yarns such as heavy rovings or monofilaments can be spaced
equally apart in one or more axis of the reinforcement to tune the
resin infusion rate of the composite.
[0070] As an alternate to infusion of the infusible, unidirectional
fabric 10 with liquid resin, the fabric may be further
pre-impregnated (pre-pregged) with partially cured thermoset
resins, thermoplastic resins, or intermingled with thermoplastic
fibers which are subsequently cured (or melted and solidified) by
the application of heat.
[0071] The infused, unidirectional composite 400 may be used as a
structure or the composite 400 have additional processes performed
to it or have additional elements added to form it into a
structure. It may also be bonded to other materials to create a
structure including incorporation into a sandwich panel. In one
embodiment, skin sheet materials such as steel, aluminum, plywood
or fiberglass reinforced polymer may be added to a surface of the
composite 400. This may be achieved by adding the additional
reinforcement layers while the resin cures or by adhesives.
Examples of structures the composite may be (or be part of) include
but are not limited to wind turbine blades, boat hulls and decks,
rail cars, bridge decks, pipe, tanks, reinforced truck floors,
pilings, fenders, docks, reinforced beams, retrofitted concrete
structures, aircraft structures, reinforced extrusions or injection
moldings or other like structural parts. In many of the above
mentioned structures, fatigue life is an important consideration.
The infused, unidirectional composite 400 may improve the fatigue
performance of these structural parts.
[0072] Composites incorporating a bridged network of unidirectional
fibers 100 can realize higher fiber volume fractions compared to
those made with conventional reinforcements. Higher fiber volume
fractions increase the modulus and strength of the composites,
particularly in the direction of the fiber axis. The uniformity of
fiber distribution and lack of fiber crimp due to stitching or
off-axis fibers enables higher compression strength and enhanced
fatigue durability. Composites with these characteristics are also
resistant to delamination and therefore provide significant damage
tolerance. These benefits can allow for longer, lighter, more
durable and/or lower cost structures in numerous applications
including wind turbine blades.
[0073] One benefit of the fabric with infusible uniformly spaced
fibers is the opportunity to utilize the fabric in specific
subsections of the structure where the demonstrated performance
benefit is most applicable.
[0074] Wind turbine blades are an example of a large composite
structure that can benefit from use of infusible, unidirectional
fabrics in specific areas. The loading patterns on wind turbine
blades are complex, and the structure is designed to satisfy a
range of load requirements. For example, wind turbine blades are
designed using at least four different design criteria. The blade
must be stiff enough to not strike the turbine tower, strong enough
to withstand the maximum expected wind gust loads, durable enough
to tolerate hundreds of millions of cycles due to the rotation of
the generator, and sufficiently resistant to buckling to avoid
collapsing when flexed under the combined stress induced by the
blade itself and the wind loads.
[0075] FIG. 7 is a schematic of a wind turbine 1700 which contains
a tower 1702, a nacelle 1704 connected to the top of the tower, and
a rotor 1706 attached to the nacelle. The rotor contains a rotating
hub 1708 protruding from one side of the nacelle, and wind turbine
blades 1710 attached to the rotating hub.
[0076] FIG. 8 is a schematic of a wind turbine blade 1710. The
blade represents a type of airfoil for converting wind into
mechanical motion. The airfoil 1800 extends from a root section
1802 at one end along a longitudinal axis to the tip section 1804
at the opposing end.
[0077] Sectional view A-A in FIG. 9 from FIG. 8 shows a typical
blade cross section and identifies four functional regions around
the perimeter of the wind turbine blade air foil. The leading edge
1806 and trailing edge 1808 are the regions at the ends of the line
extending along the maximum chord width W. The leading and trailing
edge regions are connected by two portions of a blade shell, a
suction side shell 1810 and a pressure side shell 1812. The blade
shells are connected via a shear web 1814 which helps stabilize the
cross section of the blade during service.
[0078] The blade shells generally consist of one or more
reinforcing layers 1816 and may include core materials 1818 between
the reinforcing layers for increased stiffness.
[0079] FIG. 9 also identifies two primary structural elements or
spar caps 820 located within both the pressure side and suction
side shell regions which both extend along the longitudinal axis of
the blade as shown in FIGS. 10 and 11. FIG. 10 represents a plan
view of a blade as viewed from either the pressure side or suction
side of the blade while FIG. 10 is the sectional view B-B as
illustrated in FIG. 8. FIG. 9 also identifies a leading edge spar
1822 structural element within the leading edge region, and an
additional trailing edge spar 1824 structural element within the
trailing edge region. FIG. 12 is a view along the length of the
blade showing a piece of the blade shell with various layers.
[0080] During the wind turbine blade design process, different
sections of the structure are optimized based on the most critical
design criteria for that section. For example, in blades using
fiberglass reinforced spar caps, the size of the spar caps can be
based on the stiffness requirements to avoid hitting the turbine
tower or the fatigue requirements over which the spar cap can be
expected to remain intact over hundreds of millions of load cycles.
The nature of the design process and the requirements imposed on
the various sections of the blade can benefit from materials which
offer the opportunity to be deployed locally within that section. A
spar cap reinforcement material with improved fatigue resistance
could allow more optimized wind turbine blades when fatigue
performance dictates the size and weight of the spar caps.
[0081] The infusible, unidirectional fabric 10 may be formed by any
suitable manufacturing method. One method to form the infusible,
unidirectional fabric begins with forming the fabric, or fiber
tows. The fabric contains a plurality of fibers and void space
between the fibers. Preferably the fabric then goes through one or
multiple fiber tow spreading devices, which spread a fiber bundle
into a fabric sometimes in the form of a fiber tape or fiber band.
This step can break the binder which has already existed in the
fiber bundle and re-distribute fiber space more uniformly. The tow
spreading device can be any suitable design. In one preferred
embodiment the tow spreading device(s) comprising several
football-shaped rolls, and the fabric is spread when it is pushed
against the football shaped rolls. In another embodiment, the
fabric is spread by blowing air to the bundle. In another
embodiment, the fabric is spread by immersing into water and nipped
under pressure.
[0082] After spreading, preferably the fabric is then combined with
other spread bundles of fibers in the fiber direction to form a
heavier or wider unidirectional fiber tape, fiber sheet, fiber
band, or fabric. In one embodiment, two 9600 Tex (Tex is a unit of
measure for the linear mass density of fibers and is defined as the
mass in grams per 1000 meters) bundles of fibers are spread
independently and then combined together to form a 25.4 mm wide
fabric or tape. In one embodiment, eight 9600 Tex bundles of fibers
are combined together to form an approximately 500 gsm, 150 mm wide
fabric. In another embodiment, multiple 9600 Tex bundles of fibers
are combined together to form an approximately 1000 gsm, 400 mm
wide fabric. In another embodiment, multiple 4800 Tex bundles of
fibers are combined together to form the unidirectional fabric.
[0083] The fabric (in the form of a fiber tape, fiber band or
fabric) is then coated with a coating liquid that contains the
bridge polymer or the chemicals that can react and make the bridge
polymer. In one embodiment, the polymer bridges are formed
beginning with a polymer in water dispersion or polymer water
solution. Preferably the polymer in water dispersion is an
emulsion. The emulsion contains both a continuous solvent phase and
a discontinuous dispersed liquid phase. The two phases are chosen
so that the discontinuous dispersed phase is sufficiently stable
that it does not agglomerate or solidify on the time scale required
for emulsion preparation and coating at typical emulsion
preparation and coating temperatures. This typically requires the
resin to be stable for a period of at least several minutes. SBR
latex or water borne polyurethane are preferred due to their
moderate cost, good mechanical properties, good adhesion to fibers.
In one embodiment, the average size of the particles in the
dispersed phase (called dispersed particles or micelles or referred
to as the discontinuous phase) in the emulsion is less than 50
.mu.m, preferably less than 10 .mu.m. These dispersed particles
make up at least about 0.5% by weight of the emulsion, more
preferably at least about 1% by weight, more preferably at least
about 3% by weight. In another embodiment, the emulsion contains
between about 3 and 10% by weight of dispersed particles. The
continuous phase of the emulsion can contain an aqueous, a
non-aqueous liquid, or a mixture of both. Preferably the solvent is
aqueous or polar because of the cost and environmental concerns,
wettability of the fiber, flammability issues and ability to create
an emulsion with the dispersed phase. The solvent may also contain
a surfactant, which may improve the stability of the dispersed
phase after emulsification or may make emulsification a more
reliable and efficient process.
[0084] In one embodiment, it is preferred to add film-forming
preventing agents in to the polymer water dispersion or polymer
water solution, because the film-forming preventing agents are able
to create void space and channels between fibers by preventing the
polymer forming a continuous film.
[0085] In one preferred embodiment, the film-forming preventing
agent is a water soluble material, which can phase separate from
the polymer and form solid or liquid phase during water
evaporation. Preferably, the water soluble materials do not make
the polymer in water dispersion or polymer water solution unstable.
Sugar (solid or in liquid form) or other water soluble non-ionic
materials are preferred. After water evaporation and polymer
solidified, this type of film forming preventing agent will
typically be removed from the fabric, leaving voids and channels in
the fabric.
[0086] In one embodiment, sugar is used as the film-forming
preventing agent. In this embodiment, the polymer solid content is
between about 1% and 60% of the polymer in water dispersion or
polymer in water solution. More preferably the polymer solid
content is between about 3% and 20%. The sugar to polymer solid
content ratio by weight is between about 0.5:1 and 10:1, more
preferably between 1:1 and 5:1. Too little sugar may not prevent
the polymer from forming films and may not create enough void space
and channels in the fabric; too much sugar may make the polymer
bridges weak.
[0087] In another embodiment, glycerin is used as the film-forming
preventing agent. In this embodiment, the polymer solid content is
between about 1% and 60% of the polymer in water dispersion or
polymer in water solution. More preferably the polymer solid
content is between about 3% and 20%. The glycerin to polymer solid
content ratio by weight is between about 0.5:1 and 20:1, more
preferably between 1:1 and 10:1. Too little glycerin may not
prevent the polymer from forming films and may not create enough
void space and channels in the fabric; too much may make the
polymer bridges weak.
[0088] The polymer in water dispersion or polymer in water solution
may be applied to the fiber bundles by any suitable coating method
that results in the coating liquid filling the void spaces between
the fibers and wetting the surface of the fibers. The fiber tape,
fiber band or fabric is then treated to cause solidification of the
bridge polymer and forming phase separation between bridge polymer
and this type of film forming preventing agent. The bridge polymer
chemical(s) can solidify by undergoing chemical reaction, cooling
below its(their) melt point, precipitating, crystallizing, or
evaporation of a portion of the mixture. In one preferred
embodiment, this phase change occurs because of evaporation of
water. In another preferred embodiment, this phase change occurs
because of a chemical reaction, such as polymerization or
crosslinking of mixture that may contain monomers, oligomers,
cross-linkers, and initiators; these are commonly available as
thermosetting resins that are paired with either a hardener or
initiator. The liquid may also contain catalysts which may affect
the rate of solidification of the polymer. It may also contain
other solvents that affect the stability of emulsion, the rate of
solidification. After the bridge polymer rich phase has solidified,
the fiber tape, fiber band or fabric is treated to remove the film
forming preventing agent phase and leave an infusible,
unidirectional fiber tape, fiber band or fabric.
[0089] In another preferred embodiment, the film-forming preventing
agents are a combination of blowing agents and frothing agents (or
foaming agents). When the combination of blowing agents and
frothing agents are used, preferably a gelling agent is also added
to stabilize the polymer foam. The blowing agents may be any
suitable materials that can generate small air bubbles when exposed
to a stimulus after coating the polymer in water dispersion or
polymer in water solution onto the fabric. Frothing agents or
foaming agent in the coating liquid help stabilize the air bubbles,
making the bubbles stable for longer periods of time and also
allowing them to grow bigger (with the help from the blowing
agents). During or after the foaming stage, bridge polymer
chemical(s) start to solidify by undergoing chemical reaction,
cooling below its melt point, precipitating, crystallizing, or
evaporation of a portion of the mixture. In one preferred
embodiment, this phase change occurs because of evaporation of
water. In another preferred embodiment, this phase change occurs
because of a chemical reaction, such as polymerization or
crosslinking of mixture that may contain monomers, oligomers,
cross-linkers, and initiators; these are commonly available as
thermosetting resins that are paired with either a hardener or
initiator. The liquid may also contain catalysts which may affect
the rate of solidification of the polymer. It may also contain
other solvents that affect the stability of emulsion, the rate of
solidification, the structure of the resulting bridges, or the
surface of the bridges. The gelling agent can increase the
viscosity of the liquid, transfer the solvent from liquid state to
a gel state. It can help to further stabilize the bubbles and
polymer foam, and locks the phase structure of the coating material
during the polymer solidify step.
[0090] In one embodiment, the blowing agent is water. Water can
quickly evaporate under heat and creates bubbles. In another
embodiment, the blowing agent is carbon dioxide that has dissolved
in water. In another embodiment, the blowing agent is low boiling
point organic liquid. The frothing agents or foaming agents include
but not limited to ionic surfactant such as sodium dodecyl sulfate
(SDS), sodium dodecylbenzenesulfonate (NaDDBS), or non-ionic block
copolymer such as ethylene oxide and propylene oxide copolymer. One
example of the block copolymer is Pluronic.RTM. from BASF. A
gelling agent is also preferred to be added to stabilize the
polymer foam. The gelling agent includes but not limited to acacia,
alginic acid, bentonite, carbomers, carboxymethylcellulose.
ethylcellulose, gelatin, hydroxyethylcellulose, hydroxypropyl
cellulose, magnesium aluminum silicate (Veegum.RTM.),
methylcellulose, Pluronics.RTM., polyvinyl alcohol, sodium
alginate, tragacanth, and xanthan gum. A gelling agent with lower
critical solution temperature (LCST) is preferred because it is
soluble in cold water and gels in hot water. One example of the
gelling agent with LCST characteristic is Pluronics.RTM. F-127. In
one embodiment, foaming agents and gelling agents are used as the
film-forming preventing agent. The polymer solid content is between
about 1% and 60% of the polymer in water dispersion or polymer in
water solution. More preferably the polymer solid content is
between about 3% and 20%. The frothing agent is between about 0.1%
and 20% of the total weight, more preferably between about 1% and
10% of the total weight. The gelling agent is between about 0.1%
and 40% of the total weight, more preferably between 1% and 10% of
the total weight. In one embodiment, Pluronics.RTM. F-127 is used
as a foaming agent and also a gelling agent, preferably between 1%
and 15% by weight in the coating mixture, more preferably between
3% and 10% by weight in the coating mixture.
[0091] The coating mixture with the blowing agent, frothing agent
(or foaming agent) and gelling agent can be applied to the fiber
tape, fiber band or fabric through many coating methods that are
typically used to apply coating mixture to fiber bundles or
fabrics. The emulsion can be applied using dip, nip, roll, kiss
transfer, spray, slot, slide, die, curtain, or knife coating
processes among others. The coating should be applied so that it
fills the void spaces within the fiber bundles and so that it does
not destabilize the coating mixture during the coating process.
Mechanical action, such as passing over a series of rollers,
passing over a roller with a patterned surface, pumping the
emulsion through the fiber bundles, repeated saturation of the
bundles with the emulsion, sonication or oscillating the fiber
bundle tension may aid in homogeneously filling the void spaces
between fibers within the fiber bundle. The amount of applied
coating mixture can be metered using routinely practiced metering
methods available for the aforementioned coating methods.
[0092] After coating the fabric, the blowing agent is activated by
exposing to a stimulus to generate bubbles. In one preferred
embodiment, water is used as the blowing agent. The coated fiber
tape, fiber band or fabric is exposed to heat, resulting rapid
vaporization of water and bubble formation in water. Preferably the
wet fibers are directly contact on a hot surface. Preferably the
temperature of the hot surface is at least 100.degree. C., more
preferably the temperature of the hot surface is at least
120.degree. C., more preferably the temperature of the hot surface
is at least 150.degree. C. The bubbles that are generated by the
blowing agent are stabilized by the frothing agent or foaming
agent, and are further stabilized by the gelling agent. In one
preferred embodiment, Pluronics.RTM. F-127 is used as a foaming
agent and also a gelling agent, preferably between 1% and 15% by
weight in the coating mixture, more preferably between 3% and 10%
by weight in the coating mixture. During or after the activating
the blowing agent, the chemicals in the coating mixture is
solidified to form the bridge structure. This bridge forming
process has been shown to impact the formation of the bridge
structure. An important part of the bridge forming process is to
allow enough heat to transfer to the blowing agent rapidly to
generate enough bubble before polymer has had time to solidify. And
another important part of the bridge forming process is to
stabilize the foam during polymer solidification. The size of the
void space or channel in the fiber tape, fiber band or fabric, is
controlled by the concentration of the polymer in the coating
mixture, the concentration of the film-forming preventing agents,
and the method to dry the fibers. The more effective of the
activating the blowing agent, the better bridge structure can be
made. The foaming agent and gelling agent is critical to prevent
the polymer forming a film. If the blowing agent is not functioning
well before the polymer has solidified, the polymer will want to
form a continuous film on and between fibers. If the foam structure
is not stable enough and breaks before the polymer has solidified,
the polymer will also want to form a continuous film on and between
fibers.
[0093] Likewise, if the water is removed from the system before the
polymer has solidified, the polymer will want to spread out onto
the functionalized glass fibers. This favorable surface interaction
will cause the polymer to form films on and between the fibers,
greatly reducing the ability of the fabric to be infused into a
composite material using standard resin infusion techniques.
[0094] During or after the discontinuous phase has solidified, the
coated fabric may be dried to remove the residual solvent. The
drying process has been shown to impact the performance of the
infusible, unidirectional fabric in composite. To increase the
production rate it is preferable to dry the fiber bundles at a
temperature above room temperature, preferably at or above the
boiling point of the solvent, provided that the drying temperature
and time are below a temperature and time combination that causes
the structure of the bridges to change, for example by decomposing
the material forming the bridges, causing them to flow, or causing
the bridges to become significantly less fatigue resistant.
[0095] In one embodiment, the coated fabric is dried at a
temperature between about 80 and 150.degree. C. for a time of
between about 3 and 60 minutes. In one particular embodiment, the
coated fabric is dried at temperature of 150.degree. C. for 3
minutes. In another embodiment, the surface temperature of fiber
bundles immediately after drying is at least 110.degree. C. The
energy imparted to the fabric is sufficient to remove at least 90%
of the solvent by weight, preferably at least 99.7% by weight.
After drying in one embodiment, the solvent content in the fabric
is preferably less than 1% by weight, more preferably less than
about 0.1% by weight.
[0096] Mechanical action may also be used during various steps of
production. Mechanical action may be used only once in the process,
or many times during different steps of the process. Mechanical
action may be in the form of sonication, wrapping the fabric around
a roller under tension, moving the fabric normal to its uniaxial or
machine direction in the coating bath, compressing/relaxing fabric,
increasing or reducing the tension of the fabric, passing it
through a nip, pumping the coating liquor through the fabric, using
rollers in the process with surface patterns. These surface
patterns can have similar characteristic dimensions to the diameter
of the fiber, the outside diameter of the fiber bundle, or the
width of the fabric. It has been found that the addition of
mechanical action during production of the infusible,
unidirectional fabric may temporarily increase or decrease the
space between fibers either once or multiple times, provide a
pressure gradient to increase flow of the emulsion or suspension
into, throughout and out of the bundle, and homogenize the
distribution of dispersed polymer phase within the bundle. In one
embodiment, the coated fabric is subjected to mechanical action
after the coating step. In another embodiment, the coated fabric is
subjected to mechanical action during the drying step. In another
embodiment, the coated fabric is subjected to mechanical action
after the drying step. The mechanical action may help to soften the
fabric and create additional discontinuity in the coating by
breaking large polymer bridges into smaller pieces.
[0097] After the infusible, unidirectional fabric is formed, it may
be further processed into a bridged composite using the infusing
the infusible, unidirectional fabric with resin as described
previously.
EXAMPLES
[0098] The invention will now be described with reference to the
following non-limiting examples, in which all parts and percentages
are by weight unless otherwise indicated.
Fatigue Testing Method
[0099] During testing, fatigue loads are normally characterized by
an R value which is defined as the ratio of minimum to maximum
applied stress. By convention, compressive stress is taken to be a
negative number and tension stress is taken as a positive number.
Full characterization of fatigue performance involves testing over
a range of R values such as R=0.1, -1, and 10, which corresponds to
tension-tension, tension-compression, and compression-compression
fatigue cycles respectively. Tension-tension fatigue with R=0.1 is
a key metric of fatigue performance and was used to quantify the
fatigue behavior of composite systems herein.
[0100] The fatigue performance of the composite materials made with
the fusible, unidirectional fabric was measured using a standard
tension-tension fatigue test. After composite panels were infused,
composite tabs (1.6 mm thick) were bonded to the surfaces of the
panels in the appropriate locations to establish the specimen gage
length. Specimen details and dimensions were similar to those
specified in ISO 527-5 with straight sided specimens 25 mm
wide.
[0101] The specimens were environmentally conditioned for 40 hours
at 23.degree. C.+/-3.degree. C. and 50%+/-10% relative
humidity.
[0102] Using a servohydraulic test machine equipped with hydraulic
wedge grips, the specimens were gripped using the minimum pressure
required to avoid slipping. The machine was programmed to load the
specimen in sinusoidal fashion using a specified frequency, mean
load, and load amplitude. Cyclic loading continued until the
specimen failed.
[0103] Typical schemes employ testing at a given R value with peak
stress values chosen for the different tests of 80%, 60%, 40%, and
20% of the quasi-static strength. Test frequency is chosen to
accelerate testing while ensuring the specimen temperature does not
increase significantly (less than 35.degree. C. for room
temperature testing). This means that lower stress level testing
can be done at higher frequencies than higher stress level
tests.
[0104] The output of a typical fatigue testing regimen at a given R
value is known as an S-N curve which relates the number of cycles a
material can survive to specified loading conditions. S-N curves
provide the most common comparison tool for basic fatigue
performance evaluation. S-N curves for well-defined conditions are
frequently used to compare the fatigue performance of different
composite systems under similar loading. Improvement in R=0.1
fatigue testing, generally indicates a significant change in the
fatigue behavior of a composite material.
[0105] Wind blades are generally designed to withstand over
10.sup.8 loading and unloading cycles, however testing materials to
such extremes is an impractical exercise. Comparisons are often
made among materials at intermediate points such as the one million
or 10.sup.6 cycle performance. In order to screen samples, a
specific peak loading level of 800 N/mm of specimen gage section
width was applied with an R value of 0.1 (tension-tension fatigue)
and the number of cycles to failure was measured for each sample.
This loading was chosen to balance the amount of time required to
perform an experiment with the reliability of the data for
predicting fatigue performance at more typical levels of strain.
The same loading levels of 800 N/mm were also applied to a control
composite samples made from traditional reinforcing fabrics.
Sample Layup Procedure
[0106] The layup procedure was to stack the layers on top of a flat
glass tool prepared with a mold release and covered with one layer
of release fabric (peel ply). A laser crosshair was used to provide
a fixed reference for alignment of the fibers in each layer. Both
pieces of fabric were placed so that the fibers on the top surfaces
ran in the same direction. Then a 900 layer of the unidirectional
fabric was aligned with the crosshair and placed with the
unidirectional tows up. This was followed with a 090 layer of
unidirectional fabric that was aligned and placed with the
unidirectional side down. The next 900 layer of unidirectional
fabric was placed with the unidirectional tows up and a final 090
layer was placed with the unidirectional tows facing down. The last
two layers of .+-.45 fabric were placed so that the fibers on their
top surface ran perpendicular to the fibers on the top surface of
the .+-.45 fabric on the bottom two layers of the fabric stack.
Finally, the laminate stack was covered with another layer of
release fabric (peel ply).
[0107] The vacuum infusion molding process was used to impregnate
the laminates with resin. On top of the release fabric for each
laminate, a layer of flow media was used to facilitate resin
flowing into the reinforcement plies. The entire laminate was
covered with a vacuum bagging film which was sealed around the
perimeter of the glass mold. Vacuum was applied to the laminate and
air was evacuated from the system. Resin was then prepared and
pulled into the reinforcement stack under vacuum until complete
impregnation occurred. After the resin was cured, the composite
panel was removed from the mold and placed in an oven for
post-curing.
Example 1
[0108] An unsaturated polyester control sample was made using the
sample layup procedure using the 090 fabric and the .+-.45 fabric.
The stacked textiles were infused in a standard vacuum infusion
apparatus at a vacuum of less than 50 mbar with unsaturated
polyester resin (Aropol Q67700 available from Ashland) and 1.5
parts per hundred resin (phr) methyl ethyl ketone peroxide (MEKP).
The resin flow direction was along the 0.degree. direction of the
090 fabric. The panel was cured at room temperature for more than 8
hours and further post cured at 80.degree. C. for more than 4
hours. Fatigue testing of the unmodified glass reinforced
unsaturated polyester composite at R=0.1 with a load of 1450 N/mm
of specimen gage section width measured a lifetime of approximately
1.times.10.sup.4 cycles.
[0109] Example 2 to Example 7 showed how the film forming
preventing agents affect the infusibility of the fiber fabric. The
fiberglass fabrics used in Examples 2-6, and 8 were in small widths
so will be referred to herein as fiberglass tapes.
Example 2
[0110] A fiberglass tape was made in the following manner. First, a
9600 Tex fiberglass tow from PPG (HYBON.RTM. 2026) was spread into
a 20 mm wide tape by a fiber tow spreading device. Next, four of
the 20 mm wide tapes were combined and aligned in the same
direction to form a 40 mm wide tape with twice the original tape
thickness. A SBR latex (GENCAL.RTM. 7555 from OMNOVA) was mixed
with water at a SBR latex to deionized water ratio of 1:4. The
fiber tape was then dipped in the coating mixture and dried in an
oven at 150.degree. C. for 30 minutes. Next, the fiber tape was
washed using deionized water and dried in oven at 150.degree. C.
for 15 minutes.
Example 3
[0111] A 40 mm wide, fiberglass tape was made using the same
fiberglass materials and process as Example 2. A SBR latex
(GENCAL.RTM. 7555 from OMNOVA) was mixed with water and glycerin at
a SBR latex to deionized water to glycerin ratio of 1:2:2. The
fiber tape was dipped in the coating mixture and dried in an oven
at 150.degree. C. for 30 minutes. Next, the fiber tape was washed
by deionized water and dried in oven at 150.degree. C. for 15
minutes.
Example 4
[0112] A 40 mm wide, fiberglass tape was made using the same
fiberglass materials and process as Example 2. A SBR latex
(GENCAL.RTM. 7555 from OMNOVA) was mixed with glycerin at a SBR
latex to glycerin ratio of 1:4. The fiber tape was dipped in the
coating mixture and dried in an oven at 150.degree. C. for 30
minutes. Next, the fiber tape was washed by deionized water and
dried in oven at 150.degree. C. for 15 minutes.
Example 5
[0113] A 40 mm wide, fiberglass tape was made using the same
fiberglass materials and process as Example 2. A SBR latex
(GENCAL.RTM. 7555 from OMNOVA) was mixed with water and glycerin at
a SBR latex to water to glycerin ratio of 1:1:8. The fiber tape was
then dipped in the coating mixture and dried in an oven at
150.degree. C. for 30 minutes. Next, the fiber tape was washed by
deionized water and dried in oven at 150.degree. C. for 15
minutes.
Example 6
[0114] A 40 mm wide, fiberglass tape was made using the same
fiberglass materials and process as Example 2. A waterborne
polyurethane (SYNTEGRA.RTM. YM 2000 from Dow Chemical) was mixed
with water at a YM 2000 to deionized water ratio of 1:6. The fiber
tape was then dipped in the coating mixture and dried in an oven at
80.degree. C. for 4 hours. Next, the fiber tape was washed by
deionized water and dried in oven at 80.degree. C. for 12
hours.
Example 7
[0115] A fiberglass tape was made in the following manner. First, a
4800 Tex fiberglass tow from PPG (HYBON.RTM. 2002) was wrapped on a
piece of plastic to form a roughly 1000 gsm fabric. A waterborne
polyurethane (SYNTEGRA.RTM. YM 2000 from Dow Chemical) was mixed
with sugar and water at a YM 2000 to sugar to deionized water ratio
of 1:2.7:6. The fiber tape was then dipped in the coating mixture
and dried in an oven at 80.degree. C. for 4 hours. Next, the fiber
tape was washed by deionized water for 2 days and dried in oven at
80.degree. C. for 12 hours.
[0116] The infusibility of the fiber tape for Examples 2-7 were
characterized in the following manner: Several water droplets with
0.01% water soluble color dye Acid Blue 9 were dropped on the
center surface of fiber fabric by using a 5 mL transfer pipette,
and the time that how long it took for the droplets to completely
infuse into the fabric was used as an indication of infusibility of
the fiber tape. In this method, "completely infuse into the fiber
fabric" means that more than 99% water from original droplets is
staying between the upper inner surface and lower inner surface of
the fabric.
[0117] For the fiber tape in Example 2, the droplets stayed on the
surface of the tape and cannot infuse into the tape. For the tape
in Example 3, the droplets took about several seconds to infuse
into the tape. For the tape in Example 4 and 5, the droplets
immediately infused into the tape. The differences between these
three examples showed how the film forming preventing agent
(glycerin in Example 2, 3 and 4) affected the infusibility of the
final article.
[0118] For the fiber tape in Example 6, the droplets stayed on the
surface of the tape and did not infuse into the tape. For the tape
in Example 7, the droplets took about half minute to infuse into
the tape. The differences between these two examples showed how the
film forming preventing agent (sugar in Example 6) affected the
infusibility of the final article.
[0119] An optical microscope image of the SBR coating in Example 5
was taken and determined that most of the bridges had a bridge
width narrower than 60 microns.
Example 8
[0120] A fiberglass tape was made in the following manner. A
waterborne polyurethane (SYNTEGRA YM 2000), a blocked isocyanate
based cross-linking agent (Milliken MRX), sugar and water were
mixed at a mass ratio of 103:5.6:277:620. A fiber roving (PPG
HYBON.RTM. 2002) was spread to form a roughly 500 gsm fabric
(sometimes referred to as a tape as it is has a low width). Then
the fiber tape was dipped into the coating mixture. The fabric was
dried at 80.degree. C. for 4 hours and washed by water for 12
hours. Next, the fiber tape was dried in oven at 80.degree. C. for
12 hours.
[0121] The FIG. 3 shows an SEM image of the cross section of the
fabric. One can see the polymer bridges connecting fibers.
Example 9
[0122] A fiberglass fabric was made in the following manner. 7.6 g
waterborne polyurethane (BONDTHANE J-884-A from Bond Polymers
International), 0.2 g crosslinking agent (Milliken MRX), 9 g sugar
and 100 g water was mixed to made the coating solution. A total
mass of about 150 g fiber rovings (HYBON.RTM. 2002) from PPG were
uniformly fixed on an 8'' by 24'' plate by holing ends of rovings
under tension. A piece of SPUNFAB lightweight adhesive web was put
on top of the rovings. The coating mixture was pulled onto the
rovings and a rubber roller was used to apply uniform coating and
nip the excess liquid. The 8'' by 24'' plate together with rovings
was dried at 80.degree. C. overnight. Next, the whole fabric was
removed from the plate and immersed in water for 24 hours and then
dried at 80.degree. C.
Example 10
[0123] A stack of textiles was formed in order: Two (2) layers of
the infusible fabric of Example 9, the fibers in the two layers
were parallel. The side having SPUNFAB web was on the outer side.
The stacked textiles were infused in a standard vacuum infusion
apparatus at a vacuum of -25 in. Hg (about 169 mbar) with 98.77% wt
unsaturated polyester resin (Aropol G300 available from Ashland)
and 1.33% wt methyl ethyl ketone peroxide (MEKP 925H available from
Norox). The resin flow direction was along the fibers. The panel
was cured at room temperature more than 8 hours and further post
cured at 80.degree. C. for more than 4 hours forming the composite.
FIG. 4 shows a cross section view of the composite. One can see
that the fiber location distribution is more uniform than Example
1. The tensile modulus of the composite is 5% higher than Example 1
which comprises traditional stitched unidirectional fabric. The
peak stress and peak strain in static tensile test of the composite
is about 20% higher than Example 1.
Example 11
[0124] A fiberglass fabric was made in the following manner. 8 g
waterborne polyurethane (SYNTEGRA YM 2000 from Dow Chemical), 0.5 g
crosslinking agent (Milliken MRX), 13.5 g sugar and 150 g water was
mixed to made the coating solution. A total mass of about 260 g
fiber rovings (HYBON.RTM. 2002) from PPG were uniformly fixed on an
14'' by 24'' plate by holing ends of rovings under tension. A piece
of SPUNFAB lightweight adhesive web was put on top of the rovings.
Another total mass of about 260 g fiber rovings (HYBON.RTM. 2002)
from PPG were uniformly put on top of the SPUNFAB lightweight
adhesive web and fixed on the same 14'' by 24'' plate by holding
ends of rovings under tension. In both layers, all fibers are in
the same direction. The coating mixture was pulled onto the rovings
and a rubber roller was used to apply uniform coating and nip the
excess liquid. And then the whole 14'' by 24'' plate together with
rovings was dried at 80.degree. C. overnight. Next, the whole
fabric was removed from the plate, immersed in water for 24 hours,
and then dried at 80.degree. C.
Example 12
[0125] The fabric in Example 11 was infused in a standard vacuum
infusion apparatus at a vacuum of 25 in. Hg (about 169 mbar) with
98.77% wt unsaturated polyester resin (Aropol G300 available from
Ashland) and 1.33% wt methyl ethyl ketone peroxide (MEKP 925H
available from Norox). The resin flow direction was along the
fibers. The panel was cured at room temperature more than 8 hours
and further post cured at 80.degree. C. for more than 4 hours. This
formed the composite. The tensile modulus of the composite is 5%
higher than Example 1 which comprises traditional stitched
unidirectional fabric. The peak stress and peak strain in static
tensile test of the composite is about 20% higher than Example 1.
In the R=0.1 tensile fatigue test, the cycles to failure of this
composite is about 12 times of the control which comprises
traditional stitched unidirectional fabric.
[0126] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0127] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0128] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *