Identifying the Problem
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Identifying the Problem
The lack of preferential anisotropic reinforcement in “mainstream” composites has provided motivation to develop materials with multidirectional strength components.
Many multidirectional systems exhibit delamination as a primary mode of failure.
Three-dimensional (3D) weaving solves both problems--but so far the composite manufacturer and weaver don’t fully communicate each other’s needs.
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Traditional 2D Weaving
filling insertion(through shed)
warp ends
harness movement
heddle eye
warp
filling
fabricformationzone
warp
fill
fabric flow
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Processing of 3D Woven Preforms
filling insertion
warp ends
shed
warp
filling insertion
weaver
fabric movement
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Typical 3D Woven Geometry
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Preform Variables fiber type (IM7, AS4) yarn size (3k, 6k, 12k) yarn distribution (%0°, %90°, %z) weave construction, particularly the placement
of the weavers (in-phase or out-of-phase)
yarn spacing (yarns per inch) fabric weight (oz/yd2) fiber volume fraction (Vf) weave angle
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Typical Constituents of 3D Woven Preforms
Most commonly used are graphite tows, with availability the limiting factor in many cases.
Density Linear densityTow cross-
sectional areaFiber type
g/ cm3 lb/ in3 tex lb/ 106 in mm2 in2 x 10-4
IM7-12k 1.77 0.064 446 25.0 0.252 3.90
AS4-3k 1.79 0.065 211 11.8 0.117 1.82
AS4-6k 1.79 0.065 425 23.8 0.237 3.67
AS4-12k 1.79 0.065 857 48.0 0.486 7.54
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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:
Vf = w
t•
%wt 11
+%wt 2
2+... +
%wt nn
⎛
⎝ ⎜ ⎞
⎠ ⎟
yarns per inch = ypii = wi
Ni
• cosα i
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Weave Angle Projection1/ ppil
tα
Np / ppil
tan α = 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
6π=
3.9×10−4 in2
6π= .00455 in
a bd
tows needed for thickness = total thickness
tow thickness=
t
2a=
0.100 inches
2 • .00455 inches=11 tows
a = AπAR
=d 14AR
AR= ba
A=πab=πa2AR
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3D Woven Preform Case Study
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:
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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 = wz
oz
yd2•106 in
11.8 lbs•
lb
16 oz•
yd
36 in
⎛ ⎝ ⎜ ⎞
⎠
2
• cos22.5( )
Vf • .064lbs
in3• .100 in•
36 in
yd
⎛
⎝ ⎜ ⎞
⎠ ⎟2
•16 oz
lb=71.26
oz
yd2
It was calculated that 74.3 oz/yd2 was needed to meet the 56% volume fraction specified
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Conclusions
The methodology has been developed for cross-disciplinary understanding of the key variables in 3D weaving
Standardization and increased use of 3D woven preforms should increase the communication between weaver and customer
The key for both sides: Understanding each other’s capabilities and limitations