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COMPOSTES
Groover
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Composite Material Defined
A materials system composed of two or moredistinct phases whose combinationproduces aggregate properties that aredifferent from those of its constituents
Examples: Cemented carbides (WC with Co binder)
Plastic molding compounds with fillers
Rubber mixed with carbon black
Wood (a natural composite asdistinguished from a synthesizedcomposite)
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The Reinforcing Phase Function is to reinforce the primary phase
Imbedded phase is most commonly one of thefollowing shapes:
Fibers
Particles
Flakes
Also, secondary phase can take the form of an
infiltrated phase in a skeletal or porous matrix Example: a powder metallurgy part
infiltrated with polymer
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Physical Shapes of Imbedded Phase
Figure 9.1 Possible physical shapes of imbedded phases incomposite materials: (a) fiber, (b) particle, and (c) flake.
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FibersFilaments of reinforcing material, usually circular
in cross-section Diameters from less than 0.0025 mm to about
0.13 mm, depending on material Filaments provide greatest opportunity for
strength enhancement of composites Filament form of most materials is
significantly stronger than the bulk form
As diameter is reduced, the materialbecomes oriented in the fiber axis directionand probability of defects in the structuredecreases significantly
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Continuous vs. Discontinuous Fibers
Continuous fibers - very long; in theory, theyoffer a continuous path by which a load can becarried by the composite part
Discontinuous fibers (chopped sections of
continuous fibers) - short lengths (L/D =roughly 100)
Whiskers = discontinuous fibers of hair-likesingle crystals with diameters down to about0.001 mm (0.00004 in.) and very highstrength
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Fiber Orientation Three Cases One-dimensional reinforcement, in which
maximum strength and stiffness are obtained inthe direction of the fiber
Planar reinforcement, in some cases in theform of a two-dimensional woven fabric
Random or three-dimensional in which thecomposite material tends to possess isotropicproperties
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Fiber Orientation
Figure 9.3 Fiber orientation in composite materials: (a)one-dimensional, continuous fibers; (b) planar,continuous fibers in the form of a woven fabric; and (c)random, discontinuous fibers.
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Materials for Fibers Fiber materials in fiber-reinforced composites
Glass most widely used filament
Carbon high elastic modulus
Boron very high elastic modulus
Polymers - Kevlar
Ceramics SiC and Al2O3 Metals - steel
Most important commercial use of fibers is inpolymer composites
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Particles and Flakes
A second common shape of imbedded phaseisparticulate, ranging in size from microscopicto macroscopic
Flakes are basically two-dimensional
particles - small flat platelets Distribution of particles in the composite matrix
is random
Strength and other properties of thecomposite material are usually isotropic
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The Interface There is always an interface between
constituent phases in a composite material
For the composite to function, the phases mustbond where they join at the interface
Figure 9.4 Interfaces between phases in a composite material: (a)direct bonding between primary and secondary phases.
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Other Composite Structures
Laminar composite structure conventional
Sandwich structure
Honeycomb sandwich structure
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Two or more layers bonded together in anintegral piece
Example: plywood, in which layers are thesame wood, but grains are orienteddifferently to increase overall strength
Figure 9.7 Laminar composite
structures: (a) conventionallaminar structure.
Laminar Composite Structure
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Relatively thick core of low density foambonded on both faces to thin sheets of adifferent material
Figure 9.7 Laminarcomposite structures:(b) sandwich structureusing foam core.
Sandwich Structure: Foam Core
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Alternative to foam core
Foam or honeycomb achieve high ratios ofstrength-to-weight and stiffness-to-weight
Figure 9.7 Laminarcomposite structures:(c) sandwich structure
using honeycomb core.
Sandwich Structure: Honeycomb Core
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Other Laminar Composite Structures
Automotive tires - multiple layers of rubberbonded together with reinforcing agent
FRPs - multi-layered, fiber-reinforced plasticpanels for aircraft, boat hulls, other products
Printed circuit boards - layers of reinforcedcopper and plastic for electrical conductivityand insulation, respectively
Snow skis - layers of metals, particle board,and phenolic plastic
Windshield glass - two layers of glass oneither side of a sheet of tough plastic
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Metal Matrix Composites (MMCs)Metal matrix reinforced by a second phase
Reinforcing phases:
1. Particles of ceramic
These MMCs are commonly calledcermets
2. Fibers of various materials
Other metals, ceramics, carbon, and
boron
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Cermets
MMC with ceramic contained in a metallic matrix
The ceramic often dominates the mixture,sometimes up to 96% by volume
Bonding can be enhanced by slight solubility
between phases at elevated temperaturesused in processing
Cermets can be subdivided into
1. Cemented carbides most common
2. Oxide-based cermets less common
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Figure 9.8 Photomicrograph (about 1500X) of cementedcarbide with 85% WC and 15% Co (photo courtesty ofKennametal Inc.).
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Ceramic Matrix Composites (CMCs)
Ceramic primary phase imbedded with asecondary phase, usually consisting of fibers
Attractive properties of ceramics: high stiffness,hardness, hot hardness, and compressive
strength; and relatively low density Weaknesses of ceramics: low toughness and
bulk tensile strength, susceptibility to thermalcracking
CMCs represent an attempt to retain thedesirable properties of ceramics whilecompensating for their weaknesses
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Polymer Matrix Composites (PMCs)Polymer primary phase in which a secondary
phase is imbedded as fibers, particles, orflakes
Commercially, PMCs are more important thanMMCs or CMCs
Examples: most plastic moldingcompounds, rubber reinforced with carbonblack, and fiber-reinforced polymers (FRPs)
FRPs are most closely identified with the termcomposite
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Fiber-Reinforced Polymers (FRPs)
PMC consisting of a polymer matrix imbeddedwith high-strength fibers
Polymer matrix materials:
Usually a thermosetting plastic such as
unsaturated polyester or epoxy Can also be thermoplastic, such as nylons
(polyamides), polycarbonate, polystyrene,and polyvinylchloride
Fiber reinforcement is widely used in rubberproducts such as tires and conveyor belts
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Fibers in PMCs Various forms: discontinuous (chopped),
continuous, or woven as a fabric
Principal fiber materials in FRPs are glass,carbon, and Kevlar 49
Less common fibers include boron, SiC, andAl2O3, and steel
Glass (in particular E-glass) is the mostcommon fiber material in today's FRPs
Its use to reinforce plastics dates fromaround 1920
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Common FRP Structure
Most widely used form of FRP is a laminarstructure
Made by stacking and bonding thin layers offiber and polymer until desired thickness is
obtained By varying fiber orientation among layers, a
specified level of anisotropy in propertiescan be achieved in the laminate
Applications: boat hulls, aircraft wing andfuselage sections, automobile and truck bodypanels
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FRP Applications Aerospace much of the structural weight of
todays airplanes and helicopters consist ofadvanced FRPs Example: Boeing 787
Automotive some body panels for cars andtruck cabs Low-carbon sheet steel still widely used due
to its low cost and ease of processing Sports and recreation
FRPs used for boat hulls since 1940s Fishing rods, tennis rackets, golf club shafts,
helmets, skis, bows and arrows
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Figure 9.11 Composite materials in the Boeing 757 (photo courtesyof Boeing Commercial Airplane Co.).
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Guide to Processing Composite Materials The two phases are typically produced
separately before being combined into thecomposite part
Processing techniques to fabricate MMCand CMC components are similar to thoseused for powdered metals and ceramics
Molding processes are commonly used forPMCs with particles and chopped fibers
Specialized processes have beendeveloped for FRPs
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
SHAPING PROCESSES FORPOLYMER MATRIX COMPOSITES
Apolymer matrix composite (PMC) is a compositematerial consisting of a polymer imbedded with areinforcing phase such as fibers or powders
1. Starting Materials for PMCs2. Open Mold Processes
3. Closed Mold Processes
4. Filament Winding
5. Pultrusion Processes
6. Other PMC Shaping Processes
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PMC Shape Processing Many PMC shaping processes are slow and
labor intensive In general, techniques for shaping composites
are less efficient than for other materials -Why? Composites are more complex than other
materials, consisting of two or more phases For FRPs, there is the need to orient the
reinforcing phase Composite processing technologies have
not been the object of refinement over asmany years as processes for other materials
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Categories of FRP Shape Processes
Open mold processes - some of the originalFRP manual procedures for laying resins andfibers onto forms
Closed mold processes - much the same asthose used in plastic molding
Filament winding - continuous filaments aredipped in liquid resin and wrapped around arotating mandrel, producing a rigid, hollow,cylindrical shape
Pultrusion - similar to extrusion only adapted toinclude continuous fiber reinforcement
Other - operations not in previous categories
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Starting Materials for PMCs In a PMC, the starting materials are:
A polymer
A reinforcing phase
They are processed separately beforebecoming phases in the composite
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Polymer Matrix
Thermosetting (TS) polymers are the mostcommon matrix materials
Principal TS polymers are:
Phenolics used with particulate
reinforcing phases Polyesters and epoxies - most closely
associated with FRPs
Thermoplastic molding compounds includefillers or reinforcing agents
Nearly all rubbers are reinforced with carbonblack
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Reinforcing Agent Possible geometries - fibers, particles, and
flakes
Possible materials - ceramics, metals, otherpolymers, or elements such as carbon or boron
Particles and flakes are used in many plasticmolding compounds
Of most engineering interest is the use of fibersas the reinforcing phase in FRPs
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Combining Matrix and Reinforcement
1. The starting materials arrive at the fabricationoperation as separate entities and arecombined into the composite during shaping
Filament winding and pultrusion, in which
reinforcing phase = continuous fibers2. The two component materials are combinedinto some starting form that is convenient foruse in the shaping process
Molding compounds
Prepregs
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Molding CompoundsFRP composite molding compounds consist of
the resin matrix with short randomly dispersedfibers, similar to those used in plastic molding
Most molding compounds for compositeprocessing are thermosetting polymers
Since they are designed for molding, they mustbe capable of flowing
Accordingly, they have not been cured prior
to shape processing Curing is done during and/or after final
shaping
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Prepregs
Fibers impregnated with partially cured TS resinsto facilitate shape processing
Available as tapes or cross-plied sheets orfabrics
Curing is completed during and/or aftershaping
Advantage: prepregs are fabricated withcontinuous filaments rather than choppedrandom fibers, thus increasing strength andmodulus
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Open Mold ProcessesFamily of FRP shaping processes that use a
single positive or negative mold surface toproduce laminated FRP structures
The starting materials (resins, fibers, mats, andwoven rovings) are applied to the mold inlayers, building up to the desired thickness
This is followed by curing and part removal
Common resins are unsaturated polyesters
and epoxies, using fiberglass as thereinforcement
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Open Mold FRP Processes
1. Hand lay-up
2. Spray-up
3. Automated tape-laying machines
The differences are in the methods of applying
the laminations to the mold, alternative curingtechniques, and other differences
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Hand Lay-Up MethodOpen mold shaping method in which successive
layers of resin and reinforcement are manuallyapplied to an open mold to build the laminatedFRP composite structure
Labor-intensive
Finished molding must usually be trimmed witha power saw to size outside edges
Oldest open mold method for FRP laminates,
dating to the 1940s when it was first used forboat hulls
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Figure 15.4 Hand lay-up : (1) mold is treated with mold release agent; (2) thin gelcoat (resin) is applied, to the outside surface of molding; (3) when gel coat haspartially set, layers of resin and fiber are applied, the fiber is in the form of mator cloth; each layer is rolled to impregnate the fiber with resin and remove air;(4) part is cured; (5) fully hardened part is removed from mold.
Hand Lay-Up Method
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Products Made by Hand Lay-Up Generally large in size but low in production
quantity - not economical for high production
Applications:
Boat hulls
Swimming pools
Large container tanks
Movie and stage props
Other formed sheets The largest molding ever made was ship hulls
for the British Royal Navy: 85 m (280 ft) long
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Spray-Up Method
Liquid resin and chopped fibers are sprayed ontoan open mold to build successive FRPlaminations
Attempt to mechanize application of resin-fiber
layers and reduce lay-up time Alternative for step (3) in the hand lay-up
procedure
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Figure 15.5 Spray-up method
Spray-Up Method
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Products Made by Spray-Up
Boat hulls, bathtubs, shower stalls, automobileand truck body parts, recreational vehiclecomponents, furniture, large structural panels,and containers
Movie and stage props are sometimes madeby this method
Since products made by spray-up haverandomly oriented short fibers, they are not asstrong as those made by lay-up, in which thefibers are continuous and directed
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Automated Tape-Laying MachinesAutomated tape-laying machines operate by
dispensing a prepreg tape onto an open moldfollowing a programmed path
Typical machine consists of overhead gantry towhich the dispensing head is attached
The gantry permits x-y-z travel of the head, forpositioning and following a defined continuouspath
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Figure 15.6 Automated tape-laying machine (photocourtesy of Cincinnati Milacron).
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Curing in Open Mold Processes Curing is required of all thermosetting resins
used in FRP laminated composites
Curing cross-links the polymer, transforming itfrom its liquid or highly plastic condition into ahardened product
Three principal process parameters in curing:
1. Time
2. Temperature
3. Pressure
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Closed Mold Processes
Performed in molds consisting of two sectionsthat open and close each molding cycle
Tooling cost is more than twice the cost of acomparable open mold due to the more
complex equipment required in theseprocesses
Advantages of a closed mold are: (1) goodfinish on all part surfaces, (2) higher productionrates, (3) closer control over tolerances, and(4) more complex three-dimensional shapesare possible
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Classification of Closed Mold Processes Three classes based on their counterparts in
conventional plastic molding:
1. Compression molding
2. Transfer molding
3. Injection molding
The terminology is often different whenpolymer matrix composites are molded
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Compression Molding PMC Processes
A charge is placed in lower mold section, and thesections are brought together under pressure,causing charge to take the shape of the cavity
Mold halves are heated to cure TS polymer
When molding is sufficiently cured, the moldis opened and part is removed
Several shaping processes for PMCs based oncompression molding
The differences are mostly in the form of thestarting materials
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Transfer Molding PMC ProcessesA charge of thermosetting resin with short fibers is
placed in a pot or chamber, heated, andsqueezed by ram action into one or more moldcavities
The mold is heated to cure the resin
Name of the process derives from the fact thatthe fluid polymer is transferred from a pot into amold
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Injection Molding PMC Processes
Injection molding is noted for low costproduction of plastic parts in large quantities
Although most closely associated withthermoplastics, the process can also be
adapted to thermosets Processes of interest in the context of PMCs:
Conventional injection molding
Reinforced reaction injection molding
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Filament WindingResin-impregnated continuous fibers are wrapped
around a rotating mandrel that has the internalshape of the desired FRP product; the resin isthen cured and the mandrel removed
The fiber rovings are pulled through a resin bathimmediately before being wound in a helicalpattern onto the mandrel
The operation is repeated to form additional
layers, each having a criss-cross pattern with theprevious, until the desired part thickness hasbeen obtained
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Figure 15.8 Filament winding.
Filament Winding
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Figure 15.10 Filament winding machine (photo courtesyof Cincinnati Milacron).
Filament Winding Machine
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Pultrusion Processes
Similar to extrusion (hence the name similarity)but workpiece is pulled through die (so prefix"pul-" in place of "ex-")
Like extrusion, pultrusion produces continuous
straight sections of constant cross section Developed around 1950 for making fishing
rods of glass fiber reinforced polymer (GFRP)
A related process, calledpulforming, is used tomake parts that are curved and which mayhave variations in cross section throughouttheir lengths
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PultrusionContinuous fiber rovings are dipped into a resin
bath and pulled through a shaping die wherethe impregnated resin cures
The sections produced are reinforcedthroughout their length by continuous fibers
Like extrusion, the pieces have a constantcross section, whose profile is determined bythe shape of the die opening
The cured product is cut into long straightsections
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Figure 15.11 Pultrusion process
Pultrusion Process
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PulformingPultrusion with additional steps to form the length
into a semicircular contour and alter the crosssection at one or more locations along thelength
Pultrusion is limited to straight sections ofconstant cross section
There is also a need for long parts withcontinuous fiber reinforcement that are curvedrather than straight and whose cross sections
may vary throughout length Pulforming is suited to these less regular
shapes
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing3/e
Figure 15.12 Pulforming process (not shown in thesketch is the cut-off of the pulformed part).
Pulforming Process
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Other PMC Shaping Processes Centrifugal casting
Tube rolling
Continuous laminating
Cutting of FRPs
In addition, many traditional thermoplasticshaping processes are applicable to FRPs withshort fibers based on TP polymers
Blow molding Thermoforming
Extrusion