lecture 7 reinforcement structures
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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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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