Textile Structures for Composites

Objectives

 After studying this chapter, you should be able to:  Describe major textile preform structures used in composites including their advantages and disadvantages, and how they are made.  Calculate theoretical volume fractions for selected types of preforms.  Select right type of preform for a particular end use.  Explain qualitatively the effect of fiber orientation and fiber volume fraction on composite mechanical properties.

Textile Structures for Composites

 Reading assignment:  Text book, Chapter 3;  Dow, N.F. and Tranfield, G., Preliminary investigation of feasibility of weaving triaxial fabrics (Doweave),

Textile Research Journal

, 40, 986-998 (November, 1970).

 Mohamed, M., Three dimensional textiles,

American Scientist

, 78, 530-541(November-December, 1990).

 Popper, P., Braiding, International Encyclopedia of Composites, Vol. 1, Edited by Lee, S.M., VCH Publishers, New York, 130-147 (1990).

 Jones, F.R., Handbook of Polymer-Fiber Composites, Section 1.12. Knitted reinforcements  How Nonwovens Are Made

Textile Structures for Composites

 Unidirectional  Laminae (ply)  Laminates: a stack of laminae

Textile Structures for Composites

 Two dimensional (Laminates)  Nonwoven: • • short fibers and continuous fibers, plates, particulates  Woven • • • • Biaxial Triaxial Knitted Braided

Textile Structures for Composites

 Three dimensional   Nonwoven Woven • • • • Orthogonal Multi-directional Knitted Braided  Combination

Structure property relations of composites

System Resin Bead filled Short fibers Short fibers Conti.

fibers Conti.

fibers Picture Property Strength(MPa) Modulus(GPa) Strain(%) isotropic isotropic planar isotropic planar isotropic planar isotropic planar isotropic 64 - 83 62 - 72 38 270 28 890 2.1

10.3

9.6

32 12.4

43.4

4 - 6 2 - 2.5

0.4

0.6 - 1.0

0.4

2.0

Textile Structures for Composites

 Unidirectional and 2-D preforms  Laminates  From lamina to laminate 

Lamina: unidirectional, woven

, knitted, braided

nonwoven or  Laminate  Factors effecting laminate properties      Fiber and matrix properties Interface properties Fiber volume fraction Fiber/lamina Orientation Fiber length

Orientation of short fiber composites  Fiber orientation determines the mechanical properties  Important for non-woven and sheet molding compound  Orientation characterized by normalized histograms (in plane)  Image analysis of a photograph  Directions divided into number of “bins”  The radius of each bin proportional to fraction of fibers oriented in that direction

Nonwoven preforms  Nonwoven web-forming processes:  Wet laying  Dry laying  Other Methods  Nonwoven bonding methods:  Latex bonding (2D)  Saturation bonding  Gravure printing  Screen printing  Spray bonding  Foam bonding

Nonwoven preforms

 Nonwoven bonding methods  Mechanical bonding (3D)  Needle punching  Spunlacing (water jets)  Stitch bonding  Knitting through  Thermal bonding (2D)  Through-air bonding  Calender bonding

Three dimensional textiles

 3D woven fabrics  Structure  Weaving processes  Performance  Shear strength: 300%  Interlaminar tensile strength: 200%  Flexure strength: 65% higher  Failure mode: micro-buckling of fibers

Three dimensional textiles

 Knitted and braided forms

 Weft knitting

 Warp knitting  with weft insertion  multiaxial warp knitting

 3D braiding

Braiding

 Braiding process and terminology  Braiding yarns  Axial yarns  Core yarns  Mandrel  Carrier  Horn gears  Convergence zone  Braiding angle

θ

 Pick  Width or diameter

Braiding

 Machines  Circular 144 carriers, <400 ppm  Grouped carrier <1200 ppm  Jacquard: enables connected sets of yarns to braid different patterns  Special pattern 

Solid rope: all carriers move around a horn gear in one direction

 Packing braider <230 ppm, solid square cross-section  3D: >2000 carriers circular >12000 carriers rectangular

3D-Braiding

 4-Step Braiding  Original • Step 1 • Step 2 • Step 3 • Step 4

Braiding

 Unique features:  Fabric can be formed over a complex shaped mandrel    Yarns feed on demand Yarn and elements insertion possible Possible to change the sequence of interlacing   Improved fracture toughness Decreased sensitivity to holes

Braiding

 Limitations     Move entire supply of braiding yarns Machine >> product Moderate aspect ratio only Fiber orientation angle varies arbitrarily

Comparison of textile structures for composites  Fiber orientation  Structural integrity  interlaminar connection  broken ends,  resin pocket,  formation of holes, inclusion of elements etc.

Comparison of textile structures for composites  Fiber volume fraction  Productivity  formation of the fabric,  easiness to handle,  formation of composites

Comparison among 1-D, 2-D and 3-D

 1D: Unidirectional laminates  Advantages:  Highest productivity for preforms  Highest strength and modulus in fiber oriented direction  Highest fiber volume fraction.  Disadvantages:  Poor strength and modulus in off-axis directions   Poor compression properties Delamination possible

Comparison among 1-D, 2-D and 3-D

 2D: Woven fabrics, Nonwovens, laminates with differently oriented laminas  Advantages:  High productivity.

 Better properties (tensile strength and modulus) in both X and Y directions or even diagonally.

 Disadvantages:  Poor interlaminar properties and properties in thickness directions (tensile, shear).

  Delamination possible.

Lower fiber volume fraction than 1D.

Comparison among 1-D, 2-D and 3-D

 3-D: (Woven, Nonwoven)  Advantages:  High strength and modulus in all three directions   No delamination Good structural integrity (not many broken fiber ends)  Disadvantages:   Low productivity Low fiber volume fraction

Comparison: Woven versus nonwoven

Woven Nonwoven Anisotropic Planar Isotropic High strength and modulus in fiber Low strength and modulus in all oriented directions directions Low strength in off-axis directions Strength is the same in all directions Relatively low productivity High fiber volume fraction High productivity Low fiber volume fraction

Comparison of Woven Fabrics

Properties Woven Knitted Braided Fiber orientation Orthogonal Varies Dimensional stability Structural versatility Productivity Good Poor High for 2D Low for 3D Poor Moderate High Varies Poor Good High for 2D Low for 3D

Fiber volume fraction calculation  Unidirectional composites  use the equations described earlier in the chapter for theoretical calculation  use photomicrographic method  3D composites

Fiber volume fraction calculation  2D composites

Three D woven composite

“

PERFECT” 3D ORTHOGONAL WEAVE Top view Side view

Multilayer fabrics

3D orthogonal Angle interlock Warp interlock z Warp (x) Filling (y)

2d woven fabrics

二维正交 二维三向

3D - shaped weft-knitted fabrics for preforms Altering the number of operating needles from course to course

HELMET FORM

3D Theoretical form 2D pattern Knitted fabric (Aramid fiber)

2d braiding

3d braiding