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 Picture Property Strength(MPa) Modulus(GPa) Strain(%)

Resinisotropic 64 - 83 2.1 4 - 6

Bead filledisotropic 62 - 72 10.3 2 - 2.5

Short fibers planarisotropic 38 9.6 0.4

Short fibers planarisotropic 270 32 0.6 - 1.0

Conti.fibers

planarisotropic 28 12.4 0.4

Conti.fibers

planarisotropic 890 43.4 2.0

Textile Structures for Composites

Unidirectional and 2-D preformsLaminatesFrom lamina to laminate

Lamina: unidirectional, woven, knitted, braided or nonwoven

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 photographDirections 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 fabricsStructureWeaving processesPerformance

Shear strength: 300%Interlaminar tensile strength: 200%Flexure strength: 65% higherFailure mode: micro-buckling of fibers

Three dimensional textiles

Knitted and braided formsWeft knittingWarp knitting

with weft insertion multiaxial warp knitting

3D braiding

BraidingBraiding process and

terminologyBraiding yarnsAxial yarnsCore yarnsMandrelCarrier Horn gearsConvergence zoneBraiding angle θPickWidth 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 orientationStructural integrity

interlaminar connectionbroken ends, resin pocket, formation of holes, inclusion of elements etc.

Comparison of textile structures for composites

Fiber volume fractionProductivity

formation of the fabric, easiness to handle, formation of composites

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

1D: Unidirectional laminatesAdvantages:

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 laminasAdvantages:

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

oriented directions

Low strength and modulus in all

directions

Low strength in off-axis directions Strength is the same in all

directions

Relatively low productivity High productivity

High fiber volume fraction Low fiber volume fraction

Comparison of Woven Fabrics

Properties Woven Knitted Braided

Fiber orientation Orthogonal Varies Varies

Dimensional stability

Good Poor Poor

Structural versatility

Poor Moderate Good

Productivity High for 2D

Low for 3D

High High for 2D

Low for 3D

Fiber volume fraction calculation

Unidirectional compositesuse the equations described earlier in the

chapter for theoretical calculationuse photomicrographic method

3D composites

Fiber volume fraction calculation

2D composites

Three D woven composite

“ PERFECT” 3D ORTHOGONAL WEAVE

Side view

Top view

Multilayer fabrics

3D orthogonalWarp interlock

Angle interlock

Warp (x)

Filling (y)

z

2d woven fabrics

二维正交 二维三向

3D - shaped weft-knitted fabrics for preforms

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

Altering the number of operating needles from course to course

HELMET FORM

2d braiding

3d braiding