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Common Types of Woven Fabric
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Basic weave structures
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Woven Structure
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Orientations in a Woven Fabric Machine direction = "warp" or "end" Perpendicular direction = "fill" or "weft"
or "pick" or "woof” Frequently the warp direction
corresponds with the 0°, or longitudinal direction
And fill with the 90° or transverse directionHowever - this is not necessarily the case
and should be carefully noted.
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Woven Fabrics
Generally characterized by two sets of perpendicular yarns systems
One set is raised and lowered to make “sheds” (these are warp yarns)
The other set is passed through these sheds, perpendicular to the warp yarns (these are fill, or pick or weft yarns)
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Woven Fabrics
The structure of the woven fabric is the pattern of interlacing between the warp and weft yarns
Yarns can “float”, or not interlace for some distance within a woven fabric
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Crimp in Weaves The crimp is defined as one less than the
ratio of the yarn's actual length to the length of fabric it traverses.
Crimp levels influence fiber volume fraction, thickness of fabric, and mechanical performance of fabric.
High crimp leads toReduced tensile and compressive propertiesIncreased shear modulus in the dry fabric and
the resulting compositeFewer regions for localized delamination
between individual yarns.
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Crimp
Crimp is defined as the ratio of excess length of yarn in a fabric to the length of the fabricC = ly/ lf - 1
lf
ly
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Crimp
Crimp is determined by the texture of the weave and the yarn size
Generally, in weaving, the warp yarns have most of the crimp, the fill very littleThis is a direct result of the warp yarns lifting
during weaving and the filling yarn being inserted along a straight path
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Crimp
Various models of crimp exist, the most rigorous developed by Pierce in the 1930s.
Dd 2
θ1
θ1
p 2
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Crimp○ pi = (lj – D θj) cos θjD sin θj
○ hi = (li – D θi)sin θi + D(1 - cos θi)
○ ci = (li/pj) - 1
○ h1 + h2 = d1 + d2 = D
Where pi =Thread spacing; li = Modular length; ci = Yarn crimp; di = Yarn diameter; hi = Modular height; θi = Weave angle D = Scale factor; sum of warp and weft diameters
i,j = warp and weft directions.
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Crimp
Simplified crimp calculations: assume triangle wave shape
○ tan θ= (tf + tw) pf
○ C= 1/cos θ - 1
θ
pf
tf + tw
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Crimp
0.0%
0.2%
0.4%
0.6%
0.8%
1.0%
1.2%
1.4%
1.6%
1.8%
2.0%
8 10 12 14 16 18 20 22 24
Ends per inch
22T - 12K 12K - 22B 22T - 6K
5HS - 6K 4HS - 12K 4HS - 3K
22T - 3K 44T - 3K 8HS - 3K
3K 6K 12K
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Thickness
Thickness is a difficult parameter to measure.
Thickness is dependent on applied transverse pressure to the fabric
Predictions of thickness show variation throughout the unit cell
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Thickness
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Theoretical Predictions of Thickness Consider yarns to be ellipses with major
axes ai and minor axes bi.
Thickness is between 4bw + 2bf ≤ t ≤ 2bw + 2bf
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Theoretical Predictions of Thickness
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Areal Density
Areal density is a measure of the weight per unit area of the fabricUsually expressed in g/m2 or oz/yd2.
Areal density is a more reliable experimental metric for fabrics than thickness
Areal density can be correlated to volume fraction
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Areal Density
Areal density can be calculated asA = [l (1+Cw) nw Lw + w (1+Cf) nf Lf]/(w l)
Where Ci = crimp of the i yarn, ni = number of i yarns per unit length, Li = linear density of the i yarn, w = width, l = length, and I=warp or weft.
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Areal Density
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Woven Structures3D Woven
Double Cloth
Twill
Satin
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Mechanical behavior: The Effect of Yarn Crimp
Intro to composites, Hull & Clyne
Plain weave
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T. Norman et al. FiberTex ‘92
Mechanical behavior: The Effect of Yarn Crimp
Angle Interlock weave
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Mechanical behavior: The Effect of Yarn Crimp
XYZ orthogonal weave
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3D Weaves
Layer-to-layer Through thickness
XYZ
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Doubly Stiffened Woven Panel
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Variations in Weave Design If large yarns are used in the warp direction
and small yarns are infrequently spaced in the weft direction, the resulting fabric resembles a unidirectional material.
Weaves can be formed with gradients in a single or double axis by changing yarn size across the width or length
Complex shapes can be achieved through “floating” and cutting yarns to reduce total number of yarns in some section of the part
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Gradations through yarn size
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Shape through floats
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Issues with shaping woven fabrics Tailoring the cross-section of a woven
fabric will generally result in a change in weave angle, a change in the distribution of longitudinal,
weaver, and fill, and a change in fiber volume fraction in
consequence to the change in thickness. Some fiber volume fraction effects can be
controlled by tooling. The tailoring occurs in a discrete manner, using individual yarns, whereas most tooling will be approximately continuous.
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Example of single taper weave Consider a tapered panel where
gradation in thickness is achieved by changing yarn size/count across the width
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Design of tapered woven panel
Pick count is constant, warps and wefts per dent are modified to taper
Z yarn path changes to accommodate the weave.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
Dent
Number
Pick Columns per inch Picks per column
Warp per dent
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40%
42%
44%
46%
48%
50%
52%
54%
56%
58%
60%
0.000 0.500 1.000 1.500 2.000 2.500
Distance from Thin Edge (in)
FiberVolumeFraction
Calculated
Target
Variation in Fiber Volume Fraction
This variation in yarn packing results in variations in Vf for the resulting composite.
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Variation in weave angle
The weave angle will also change throughout the width of the part due to varying warp yarn count and part thickness.
25 °
30 °
35 °
40 °
45 °
50 °
55 °
0.0 0.5 1.0 1.5 2.0 2.5
Distance from Thin Edge (in)
WeaveAngle
Calculated
Target
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Yarn Distributions
The distribution of warp, weft, and Z yarn will also vary throughout the part.
15%
20%
25%
30%
35%
40%
45%
50%
55%
60%
0.0 0.5 1.0 1.5 2.0 2.5Distance from Thin Edge (in)
YarnDistribution % Z % Warp % Fill
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Variations in Modulus All mechanical properties will vary
throughout the part
0
2
4
6
8
10
12
14
0.0 0.5 1.0 1.5 2.0 2.5
Distance from Thin Edge (in)
TensileModulus(Msi)
E11 E22 E33
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Volume Fraction
Volume fraction is the percent of fiber contained within a given volume (usually the composite in question)
Volume fraction can be calculated from areal densityVf = A / t
Where Vf = fiber volume fraction, A = areal density, = density of the fibers, and t = composite thickness
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Process Control and Variability Processing Errors
Damaged yarnsMisplaced yarns
Sources of errorMachinery malfunctionMachinery variabilityBad control parametersPost-manufacturing deviations
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Distortions in Woven Fabrics
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On-line Monitoring of Manufacturing Realtime feed-back from shedding and
insertion mechanisms Visual scan of fabric surfaces Xray or neutron scan of fabric interior
Using tracer yarns
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Three Dimensional Weaving Uses "standard" weaving technology Complexity of weave is limited by
number of independent shedding devices
Some limitations on maximum thickness of fabric due to shed size and beatup limitations
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Types of 3-D Woven Fabrics XYZ Layer-to-layer Through-thickness
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3-D Weaving
shed
warp
filling insertion
weaver
fabric movement
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XYZ 3-D Woven Fabrics
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Layer-to-layer 3-D Woven Fabrics
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Through thickness 3-D Woven Fabrics
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Components of 3-D Woven Fabrics Longitudinal yarns
Parallel to warp direction Weaving yarns (web yarns)
Lie in warp-thickness plane Surface weavers
Lie in warp-thickness planeLocated at t=0, t=max
Filling yarnsLie in fill-thickness planeGenerally aligned with the fill direction
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Components of 3-D Woven Fabrics
warp
Fills
Longitudinals
Weaver
SurfaceWeaver
1/hp
t
θ
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Physical Relationships of 3-D Woven Fabrics Vf = ∑ i / c
c = (1/hp) (1/hw) t
i = mi Ai lill = (1/hp)
lw = (1/hp)/cos(θw)
ls = (1/hp)/cos(θs)
lp = (1/hw)
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Process Variables
Yarn sizes (all independent) Reed size (limited by yarn size) Picks per inch (limited by yarn size) Weave angle Number of filled warp positions
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Preform Input Parameters Using fiber volume (Vf), thickness (t), ply percentages (wt
%) as inputs:
Here is fiber density for each n fiber type and w is the preform areal density.
Yarn spacings needed for each ith system (warp, fill, weaver) can then be found using the tow linear density N:
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Weave Angle Projection1/ ppil
t
Np / ppil
tan = t ppil
Np
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Determining Preform Thickness Requirements Tows required to meet thickness can be estimated
assuming a common aspect ratio (AR):
a A
6 3.9 10
4in
2
6 .00455 in
a bd
tows needed for thickness total thickness
tow thickness t
2a 0.100 inches
2 .00455 inches11 tows
a = AAR
=d 14AR
AR=ba
Aaba2AR
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3D Woven Preform Case Study
Parameter Sample 1 Sample 2
%0° fiber 47 77
0° fiber type IM7-12k IM7-12k
%90° fiber 47 17
90° fiber type IM7-12k IM7-12k
%z fiber 6 6
z fiber type AS4-3k AS4-6k
thickness (inches) 0.100 0.100
Volume fraction (%) 56 56
Two sample preforms were specified, each with a 45°weave angle requested:
The preforms were procured from a weaver, then evaluated based on the design methodology.
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Example Calculations Example Calculations for Sample 2, using IM7-12k
graphite tows for all inputs:
Fiber direction % tows directional arealdensity(oz/yd2)
0° 77 57.23
90° 17 12.63
ttt 6 4.46
Total 100 74.32
0°: ypi = 57.23oz
yd2
106
in
25.0 lbs
lb
16 oz yd
36 in
2
110.4 ypi
90°: ypi = 12.63oz
yd2 10
6in
25.0 lbs lb
16 oz yd
36 in
2
24.4 ypi
z: ypi = 4.46oz
yd2 10
6in
25.0 lbs lb
16 oz yd
36 in
2
cosi = 7.9 ypi
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Applying the Methodology
Parameter 0° 90° ttt
Required Reported Required Reported Required Reported
areal weight(oz/yd2)
34.9 34.9 34.9 34.9 4.5 4.5
yarns per inch 67.5 67.5 67.5 67 18.2 16
Volume fraction 26.4 22.9 26.4 22.9 3.3 2.9
Parameter 0° 90° ttt
Required Reported Required Reported Required Reported
areal weight(oz/yd2)
57.2 12.5 12.6 57.2 4.5 4.5
yarns per inch 110.4 24 24.4 110 8.3 6
Volume fraction 43.2 7.5 9.4 34.6 3.3 2.7
Sample 1
Sample 2
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Measuring the Weave Angle
9 °
22.5 °
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Examining Volume Fraction from Input Parameters Evaluating Sample 2:
6 ypi = wzoz
yd2 10
6in
11.8 lbs lb
16 oz yd
36 in
2cos 22.5
w = 1.59+57.22+12.45 = 71.26 oz/yd2
Vf .064
lbs
in3 .100 in
36 in
yd
2
16 oz
lb71.26
oz
yd2
Vf = 53.7%
It was calculated that 74.3 oz/yd2 was needed to meet the 56% volume fraction specified
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Example
6 ends per inch, 6 picks per inch, 4 picks thick
12K AS-4 yarns long. & fill, 6K weavers, no surface weavers
Weaver yarn ratio - rise/run =tan(θw) ar
Thickness = 0.25 inch All warp slots filled aspect ratio = (np mp)/t
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Effect of Weave yarn ratio on Fiber Volume Fraction
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0 2 4 6 8 10 12 14
Weave Angle Ratio
Fib
er
Volu
me F
racti
on 4 epi
6 epi
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Effect of Weave Yarn Ratio on Weave Angle
10
20
30
40
50
60
70
0 2 4 6 8 10 12 14
Weave Angle Ratio
Weave A
ng
le (
deg
)
4 ppi6 ppi
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Effect of Weave Angle on Distribution Based on varying weave yarn ratio only
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 5 10 15 20 25 30 35 40 45
Weave Angle (deg)
Dis
trib
uti
on
Rati
o
Percent longitudinal
Percent weaver
Percent fill
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Effect of picks per inch on Fiber Volume Fraction
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 2 4 6 8 10 12 14 16
Picks per inch
Fib
er
Volu
me F
racti
on
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Effect of picks per inch on Weave angle
0
5
10
15
20
25
30
35
40
45
0 2 4 6 8 10 12 14 16
Picks per inch
Weave A
ng
le (
deg
)
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Effect of Weave Angle on Distribution Based on varying ppi only
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 5 10 15 20 25 30 35 40 45
Weave Angle (deg)
Dis
trib
uti
on
Rati
o
Percent longitudinal
Percent weaver
Percent fill
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Production of Complex Shaped Weaves Complex shape - complex, but uniform
section Very complex shape - complex,
nonuniform section
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Production of Complex Shaped Weaves Consider section as consisting of
rectangular pieces Develop weave parameters for each
piece Develop interconnection paths
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Production of Very Complex Shaped Weaves Decompose part into rectangular and
shell sections Consider impact of cutting yarns Consider "folding" type operations
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Ideal vs. Actual Geometry
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Bad Control Parameters
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Bad Control Parameters
Bad scan of image Mistake in keying of "dots and spots" Slipped card/chain at pick insertion
failure
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Compression Induced Errors
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RTM & Handling Induced Errors