identifying the problem the lack of preferential anisotropic reinforcement in “mainstream”...
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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.
Traditional 2D Weaving
filling insertion(through shed)
warp ends
harness movement
heddle eye
warp
filling
fabricformationzone
warp
fill
fabric flow
Processing of 3D Woven Preforms
filling insertion
warp ends
shed
warp
filling insertion
weaver
fabric movement
Typical 3D Woven Geometry
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
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
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
Weave Angle Projection1/ ppil
tα
Np / ppil
tan α = t• ppil
Np
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
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.
Example Calculations
Example Calculations for Sample 2, using IM7-12k graphite tows for all inputs:
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
Measuring the Weave Angle
9 °
22.5 °
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
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
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