Presentation on theme: "Textile Structures for Composites Objectives After studying this chapter, you should be able to: Describe major textile preform structures used in composites."— Presentation transcript:
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: 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
Textile Structures for Composites Unidirectional Laminae (ply) èLaminates: 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
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
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 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
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
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
Three dimensional textiles Knitted and braided forms lWeft knittingWeft knitting lWarp knitting with weft insertion multiaxial warp knitting l3D braiding3D braiding
Braiding Braiding process and terminology FBraiding yarns FAxial yarns FCore yarns FMandrel FCarrier FHorn gears FConvergence zone FBraiding angle θ FPick FWidth or diameter
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 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
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.
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
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