Lecture 7 Reinforcement Structures

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    P.E. 406 Polymer Composites

    Different forms

    Following are the major forms of glass fiber

    that are mostly used in RP industry;

    1. Continuous Filament Roving2. Chopped Strand Mat (CSM)

    3. Continuous Filament Mat

    4. Woven Fabrics5. Non-woven (noncrimp) Fabrics

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    1. Continuous Filament Roving

    They consist of one or more strands of fibers

    parallel wound, without twist, into a spool or

    cheese

    The number of strands and spool size depend

    upon the end use

    Major use is in Filament winding and

    Pultrusion for continuous length products, like

    pipes, tanks, pillars and rods

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    2. Chopped Strand Mat (CSM)

    In CSM rovings are chopped and dispersed

    uniformly on a mat forming stage. The fibers

    are firmly bound in the mat but have excellent

    wet-out characteristics

    The binders are usually of the two forms

    Emulsion (which is based on polyvinyl acetate

    emulsion

    Powder (which is based on bisphenol polyester

    powder)

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    CSM is supplied in a range of weights from

    225 g/m

    2

    to 900 g/m

    2

    containing 3-6 % binderby weight, and usually made to be polyester

    compatible

    Hence, their use with epoxy resins is limited,

    but some types of mat are better than others

    in this respect, e.g. powder bonded mat

    In addition to normal CSMs, products are

    available with combined CSM with glass fibertissue, woven rovings and unidirectional

    rovings to form combination mats

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    3. Continuous Filament Mat

    Continuous Filament Mat (CFM) consists of

    multiple layers of continuous glass fibers

    deposited in a swirl like pattern

    CFM is finding increasing use in matched-die

    molding, where it can fill deep mould cavities,

    and in resin transfer molding (RTM).

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    4. Woven Fabrics

    Woven fabrics are used in trailers, containers,

    water tower blades, and in other marine wet

    lay-up applications

    The amount of fiber in different directions is

    controlled by the weave pattern.

    Common weave styles are shown in next slide

    Woven fabrics have the advantage of being

    inexpensive

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    Hybrid fabrics in various combinations, such as

    glass/carbon and Aramid/carbon, are alsoavailable.

    For lightning strike purposes, conductive wires

    are woven into fabric forms to distribute theenergy imparted by lightning, thus minimizing

    damage to the structure.

    Woven fabrics are also used to make prepregs,

    as well as in RTM and SRIM processes as

    feedstock

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    5. Non-woven (noncrimp) Fabrics

    In noncrimp fabrics, yarns are placed parallel

    to each other as shown in Figure and then

    stitched together using polyester thread

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    Warp unidirectional fabric

    Warp unidirectional fabric is used when fibers

    are needed in one direction only, for example,

    in stiffness-critical applications such as water

    ski applications where the fabric is laid along

    the length of the ski to improve resistance to

    bending

    In warp fabrics, reinforcements are laid at 0(or warp direction) only as shown in Figure

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    Weft unidirectional fabric

    Weft fabrics are typically used in filament

    wound tubes and pipes and also pultruded

    components where reinforcement in the weft

    direction is necessary

    In weft unidirectional fabrics, reinforcements

    are laid at 90 (or weft direction) only as

    shown in Figure on next slide

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    Non-woven (noncrimp) Fabrics

    Noncrimp fabrics offer greater flexibility

    compared to woven fabrics. For example,

    fibers can be laid at almost any angle from 0

    to 90, including 45, 90, 30, 60, and 22,

    and then stitched to make multi-axial stitched

    plies, whereas woven fabrics are made from

    rovings mostly on the 0 and 90 axes.

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    Non-woven (noncrimp) Fabrics

    Noncrimp fabrics offer greater strength

    because fibers remain straight; whereas in

    woven fabrics, fibers bend over each other.

    Noncrimp fabrics are available in a thick layer

    and thus an entire laminate could be achieved

    in a single-layer fabric. This is useful in making

    thicker laminates such as boat hulls andreduces the number of fabrication steps

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    To make noncrimp glass fabrics, input rovings

    are selected by yield numbers in combinations

    of 113, 218, 450, 675, 1200, and 1800 yd/lb. A

    larger yield number denotes a finer roving

    and, therefore, more yards are required to

    achieve a given weight. The selection of yield number is determined

    by the physical, mechanical, and aesthetic

    requirements of the laminate. The finerfilaments mean higher fiber content and less

    resin.

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    Non-woven (noncrimp) Fabrics

    To meet the market need for heavier fabrics,

    stitched fabrics with various combinations of

    plies are produced.

    On the next slide Figure shows a bi-ply fabric

    in which woven fabrics and a chopped strand

    mat are stitched together to form the fabric.

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    Illustration of bi-ply fabric