Lecture 7 Reinforcement Structures

8/8/2019 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

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to 900 g/m

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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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P.E. 406 Polymer Composites5


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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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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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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

Lecture 7 Reinforcement Structures

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