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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