2. Textile Structures for Composites

3. 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.

4. Textile Structures for Composites Reading assignment: FText book, Chapter 3; FDow, N.F. and Tranfield, G., Preliminary investigation of feasibility of weaving triaxial fabrics (Doweave), Textile Research Journal, 40, 986-998 (November, 1970). FMohamed, M., Three dimensional textiles, American Scientist, 78, 530-541(November-December, 1990). FPopper, P., Braiding, International Encyclopedia of Composites, Vol. 1, Edited by Lee, S.M., VCH Publishers, New York, 130-147 (1990). FJones, F.R., Handbook of Polymer-Fiber Composites, Section 1.12. Knitted reinforcements FHow Nonwovens Are Made

5. Textile Structures for Composites Unidirectional Laminae (ply) èLaminates: a stack of laminae

6. Textile Structures for Composites Two dimensional (Laminates) Nonwoven: short fibers and continuous fibers, plates, particulates Woven Biaxial Triaxial Knitted Braided

7. Textile Structures for Composites Three dimensional Nonwoven Woven Orthogonal Multi-directional Knitted Braided Combination

8. Structure property relations of composites

9. Textile Structures for Composites Unidirectional and 2-D preforms Laminates From lamina to laminate Lamina: unidirectional, woven, knitted, braided or nonwovenwovenbraided Laminate Factors effecting laminate properties Fiber and matrix properties Interface properties Fiber volume fraction Fiber/lamina Orientation Fiber length

10. 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

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

12. Nonwoven preforms lNonwoven bonding methods l Mechanical bonding (3D) l Needle punching l Spunlacing (water jets) l Stitch bonding l Knitting through l Thermal bonding (2D) l Through-air bonding l Calender bonding

13. Three dimensional textiles 3D woven fabrics lStructure lWeaving processes lPerformance Shear strength: 300% Interlaminar tensile strength: 200% Flexure strength: 65% higher Failure mode: micro-buckling of fibers

14. Three dimensional textiles Knitted and braided forms lWeft knittingWeft knitting lWarp knitting with weft insertion multiaxial warp knitting l3D braiding3D braiding

15. Braiding Braiding process and terminology FBraiding yarns FAxial yarns FCore yarns FMandrel FCarrier FHorn gears FConvergence zone FBraiding angle θ FPick FWidth or diameter

17. Braiding Machines FCircular 144 carriers, <400 ppm FGrouped carrier <1200 ppm FJacquard: enables connected sets of yarns to braid different patterns FSpecial pattern FSolid rope: all carriers move around a horn gear in one direction FPacking braider <230 ppm, solid square cross-section F3D: >2000 carriers circular >12000 carriers rectangular

18. 3D-Braiding 4-Step Braiding Original Step 1 Step 2 Step 3 Step 4

19. 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

20. Braiding Limitations Move entire supply of braiding yarns Machine >> product Moderate aspect ratio only Fiber orientation angle varies arbitrarily

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

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

23. Comparison among 1-D, 2-D and 3-D 1D: Unidirectional laminates FAdvantages: Highest productivity for preforms Highest strength and modulus in fiber oriented direction Highest fiber volume fraction. FDisadvantages: Poor strength and modulus in off-axis directions Poor compression properties Delamination possible

24. Comparison among 1-D, 2-D and 3-D 2D: Woven fabrics, Nonwovens, laminates with differently oriented laminas FAdvantages: High productivity. Better properties (tensile strength and modulus) in both X and Y directions or even diagonally. FDisadvantages: Poor interlaminar properties and properties in thickness directions (tensile, shear). Delamination possible. Lower fiber volume fraction than 1D.

25. Comparison among 1-D, 2-D and 3-D 3-D: (Woven, Nonwoven) FAdvantages: High strength and modulus in all three directions No delamination Good structural integrity (not many broken fiber ends) FDisadvantages: Low productivity Low fiber volume fraction

26. Comparison: Woven versus nonwoven

27. Comparison of Woven Fabrics

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

29. Fiber volume fraction calculation 2D composites

30. Three D woven composite

31. PERFECT 3D ORTHOGONAL WEAVE Side view Top view

32. Multilayer fabrics 3D orthogonal Warp interlock Angle interlock Warp (x) Filling (y) z

33. 2d woven fabrics

34. 3D - shaped weft-knitted fabrics for preforms 3D Theoretical form2D pattern Knitted fabric (Aramid fiber) Altering the number of operating needles from course to course HELMET FORM

35. 2d braiding

36. 3d braiding