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.

warp ends

Traditional 2D Weaving

warp fill fabric formation zone fabric flow heddle eye warp filling insertion (through shed) harness movement filling

Processing of 3D Woven Preforms warp ends weaver filling insertion shed warp filling insertion 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/yd 2 ) fiber volume fraction (V f ) weave angle

Typical Constituents of 3D Woven Preforms  Most commonly used are graphite tows, with availability the limiting factor in many cases.

Fiber type IM7-12k AS4-3k AS4-6k AS4-12k Density g/cm 3 1.77

1.79

1.79

1.79

lb/in 3 0.064

0.065

0.065

0.065

Linear density tex 446 211 425 857 lb/10 6 in 25.0

11.8

23.8

48.0

Tow cross sectional area mm 2 0.252

0.117

0.237

0.486

in 2 x 10 -4 3.90

1.82

3.67

7.54

Preform Input Parameters

 Using fiber volume (V f ), thickness (t), ply percentages (wt%) as inputs: Vf = w t    wt%1 r  wt%2 r  ...

 wt%n r n  Here r is fiber density for each n fiber type and w is the preform areal density.

 Yarn spacings needed for each i weaver) can then be found using the tow linear density N: th system (warp, fill, yarns per inch  ypi

i

 w

i

N

i

 cos  i

Weave Angle Projection

1/ppil t  Np / ppil tan  = t  ppil N p

Determining Preform Thickness Requirements  Tows required to meet thickness can be estimated assuming a common aspect ratio (AR): d a b A   ab  a2AR a = A  AR =d 1 4AR a  A 6   3.9

 10  4 in 2 6   .00455 in tows needed for thickness  total thickness tow thickness  t 2a  0.100 inches 2  .00455 inches  11 tows

3D Woven Preform Case Study Two sample preforms were specified, each with a 45 ° weave angle requested:

Parameter

%0° fiber 0° fiber type %90° fiber 90° fiber type %z fiber z fiber type thickness (inches) Volume fraction (%)

Sample 1

47 IM7-12k 47 IM7-12k 6 AS4-3k 0.100

56

Sample 2

77 IM7-12k 17 IM7-12k 6 AS4-6k 0.100

56 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: Fiber direction % tows 0° 90° ttt Total 77 17 6 100 directional areal density (oz/yd 2 ) 57.23

12.63

4.46

74.32

0°: oz ypi = 57.23

yd 2  10 6 in 25.0 lbs  lb 16 oz  yd  36 in   2  110.4 ypi 90°: oz ypi = 12.63

yd 2  10 6 in 25.0 lbs  lb 16 oz  yd  36 in   2  24.4 ypi z: oz ypi = 4.46

yd 2  10 6 in 25.0 lbs  lb 16 oz    yd 36 in   2  cos  i = 7.9 ypi

Applying the Methodology

Parameter

Sample 1 Required

0°

Reported 34.9

34.9

Required

90°

Reported 34.9

34.9

Required

ttt

Reported 4.5

4.5

areal weight (oz/yd 2 ) yarns per inch Volume fraction 67.5

26.4

67.5

22.9

67.5

26.4

67 22.9

18.2

3.3

16 2.9

Parameter

areal weight (oz/yd 2 ) yarns per inch Volume fraction Sample 2 Required

0°

Reported 57.2

12.5

Required

90°

Reported 12.6

57.2

Required

ttt

Reported 4.5

4.5

110.4

43.2

24 7.5

24.4

9.4

110 34.6

8.3

3.3

6 2.7

Measuring the Weave Angle

Sample

1 2

Measured angle

9.0° 22.5°

Predicted angle

14.4° 22.7°

9 ° 22.5 °

Examining Volume Fraction from Input Parameters  Evaluating Sample 2: oz 6 ypi = w z yd 2  10 6 in 11.8 lbs  lb 16 oz    yd 36 in   2   w = 1.59+57.22+12.45 = 71.26 oz/yd 2 V f  .064

lbs in 3  .100 in    36 in yd  2   16 oz lb  oz 71.26

yd 2  V f = 53.7% It was calculated that 74.3 oz/yd 2 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