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