1. POLYMERS AND COMPOSITE MATERIALS
Fundamentals of Polymer Technology
Thermoplastic Polymers
Thermosetting Polymers
Elastomers
Composites--Technology and Classification
Composite Materials
Guide to the Processing of Polymers and Composite Materials
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

2. Polymer
A compound consisting of long‑chain molecules, each molecule made up of repeating units connected together
There may be thousands, even millions of units in a single polymer molecule
The word polymer is derived from the Greek words poly, meaning many, and meros (reduced to mer), meaning part
Most polymers are based on carbon and are therefore considered organic chemicals
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

3. Types of Polymers Thermoplastic polymers Thermosetting polymers
Polymers can be separated into plastics and rubbers
As engineering materials, it is appropriate to divide them into the following three categories:
Thermoplastic polymers
Thermosetting polymers
Elastomers
where (1) and (2) are plastics and (3) are rubbers
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

4. Thermoplastic Polymers - Thermoplastics
Solid materials at room temperature but viscous liquids when heated to temperatures of only a few hundred degrees
This characteristic allows them to be easily and economically shaped into products
They can be subjected to heating and cooling cycles repeatedly without significant degradation
Symbolized by TP
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5. Thermosetting Polymers - Thermosets
Cannot tolerate repeated heating cycles as thermoplastics can
When initially heated, they soften and flow for molding
Elevated temperatures also produce a chemical reaction that hardens the material into an infusible solid
If reheated, thermosets degrade and char rather than soften
Symbolized by TS
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6. Elastomers (Rubbers)
Polymers that exhibit extreme elastic extensibility when subjected to relatively low mechanical stress
Some elastomers can be stretched by a factor of 10 and yet completely recover to their original shape
Although their properties are quite different from thermosets, they share a similar molecular structure that is different from the thermoplastics
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7. Market Shares
Thermoplastics are commercially the most important of the three types
About 70% of the tonnage of all synthetic polymers produced
Thermosets and elastomers share the remaining 30% about evenly, with a slight edge for the former
On a volumetric basis, current annual usage of polymers exceeds that of metals
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8. Examples of Polymers
Thermoplastics:
Polyethylene, polyvinylchloride, polypropylene, polystyrene, and nylon
Thermosets:
Phenolics, epoxies, and certain polyesters
Elastomers:
Natural rubber (vulcanized)
Synthetic rubbers, which exceed the tonnage of natural rubber
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9. Reasons Why Polymers are Important
Plastics can be molded into intricate part shapes, usually with no further processing
Very compatible with net shape processing
On a volumetric basis, polymers:
Are cost competitive with metals
Generally require less energy to produce than metals
Certain plastics are transparent, which makes them competitive with glass in some applications
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10. General Properties of Polymers
Low density relative to metals and ceramics
Good strength‑to‑weight ratios for certain (but not all) polymers
High corrosion resistance
Low electrical and thermal conductivity
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11. Limitations of Polymers
Low strength relative to metals and ceramics
Low modulus of elasticity (stiffness)
Service temperatures are limited to only a few hundred degrees
Viscoelastic properties, which can be a distinct limitation in load bearing applications
Some polymers degrade when subjected to sunlight and other forms of radiation
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12. Synthesis of Polymers They are made by chemical processing
Nearly all polymers used in engineering are synthetic
They are made by chemical processing
Polymers are synthesized by joining many small molecules together into very large molecules, called macromolecules, that possess a chain‑like structure
The small units, called monomers, are generally simple unsaturated organic molecules such as ethylene C2H4
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13. Polyethylene
Synthesis of polyethylene from ethylene monomers: (1) n ethylene monomers, (2a) polyethylene of chain length n; (2b) concise notation for depicting polymer structure of chain length n
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14. Polymerization Addition polymerization Step polymerization
As a chemical process, the synthesis of polymers can occur by either of two methods:
Addition polymerization
Step polymerization
Production of a given polymer is generally associated with one method or the other
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15. Addition Polymerization
In this process, the double bonds between carbon atoms in the ethylene monomers are induced to open up so they can join with other monomer molecules
The connections occur on both ends of the expanding macromolecule, developing long chains of repeating mers
It is initiated using a chemical catalyst to open the carbon double bond in some of the monomers
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16. Addition Polymerization
Model of addition (chain) polymerization: (1) initiation, (2) rapid addition of monomers, and (3) resulting long chain polymer molecule with n mers at termination of reaction
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17. Step Polymerization
In this form of polymerization, two reacting monomers are brought together to form a new molecule of the desired compound
As reaction continues, more reactant molecules combine with the molecules first synthesized to form polymers of length n = 2, then length n = 3, and so on
In addition, polymers of length n1 and n2 also combine to form molecules of length n = n1 + n2, so that two types of reactions are proceeding simultaneously
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18. Step Polymerization
Model of step polymerization showing the two types of reactions occurring: (left) n‑mer attaching a single monomer to form a (n+1)‑mer; and (right) n1‑mer combining with n2‑mer to form a (n1+n2)‑mer.
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19. Some Examples
Polymers produced by addition polymerization:
Polyethylene, polypropylene, polyvinylchloride, polyisoprene
Polymers produced by step polymerization:
Nylon, polycarbonate, phenol formaldehyde
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20. Degree of Polymerization
Since molecules in a given batch of polymerized material vary in length, n for the batch is an average
Its statistical distribution is normal
The mean value of n is called the degree of polymerization (DP) for the batch
DP affects properties of the polymer
Higher DP increases mechanical strength but also increases viscosity in the fluid state, which makes processing more difficult
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21. Molecular Weight
The sum of the molecular weights of the mers in the molecule
MW = n times the molecular weight of each repeating unit
Since n varies for different molecules in a batch, the molecular weight must be interpreted as an average
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22. Typical Values of DP and MW
Polymer
Polyethylene
Polyvinylchloride
Nylon
Polycarbonate
DP(n)
10,000
1,500
120
200 MW
300,000
100,000
15,000
40,000
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23. Polymer Molecular Structures
Linear structure – chain-like structure
Characteristic of thermoplastic polymers
Branched structure – chain-like but with side branches
Also found in thermoplastic polymers
Cross-linked structure
Loosely cross-linked, characteristic of elastomers
Tightly cross-linked, characteristic of thermosets
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24. Polymer Molecular Structures
Linear
Branched
Loosely cross-linked Tightly cross-linked
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25. Effect of Branching on Properties
Thermoplastic polymers always possess linear or branched structures, or a mixture of the two
Branches increase entanglement among the molecules, which makes the polymer
Stronger in the solid state
More viscous at a given temperature in the plastic or liquid state
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26. Effect of Cross-Linking on Properties
Thermosets possess a high degree of cross‑linking; elastomers possess a low degree of cross‑linking
Thermosets are hard and brittle, while elastomers are elastic and resilient
Cross‑linking causes the polymer to become chemically set
The reaction cannot be reversed
The polymer structure is permanently changed; if heated, it degrades or burns rather than melt
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27. Crystallinity in Polymers
Both amorphous and crystalline structures are possible, although the tendency to crystallize is much less than for metals or non‑glass ceramics
Not all polymers can form crystals
For those that can, the degree of crystallinity (the proportion of crystallized material in the mass) is always less than 100%
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28. Crystalline Polymer Structure
Crystallized regions in a polymer: (a) long molecules forming crystals randomly mixed in with the amorphous material; and (b) folded chain lamella, the typical form of a crystallized region
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29. Crystallinity and Properties
As crystallinity is increased in a polymer
Density increases
Stiffness, strength, and toughness increases
Heat resistance increases
If the polymer is transparent in the amorphous state, it becomes opaque when partially crystallized
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30. Low Density & High Density Polyethylene
Polyethylene type
Low density
High density
Degree of crystallinity
55%
92%
Specific gravity
0.92
0.96
Modulus of elasticity
140 MPa
(20,000 lb/in2)
700 MPa
(100,000 lb/in2)
Melting temperature
115C
(239F)
135C
(275F)
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31. Some Observations About Crystallization
Linear polymers consist of long molecules with thousands of repeated mers
Crystallization involves folding back and forth of the long chains upon themselves
The crystallized regions are called crystallites
Crystallites take the form of lamellae randomly mixed in with amorphous material
A crystallized polymer is a two‑phase system
Crystallites interspersed in an amorphous matrix
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32. Factors for Crystallization
Slower cooling promotes crystal formation and growth
Mechanical deformation, as in the stretching of a heated thermoplastic, tends to align the structure and increase crystallization
Plasticizers (chemicals added to a polymer to soften it) reduce crystallinity
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33. Thermal Behavior of Polymers
Specific volume (density)-1 as a function of temperature
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34. Additives
Properties of a polymer can often be beneficially changed by combining it with additives
Additives either alter the molecular structure or
Add a second phase, in effect transforming the polymer into a composite material
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35. Types of Additives by Function
Fillers – strengthen polymer or reduce cost
Plasticizers – soften polymer and improve flow
Colorants – pigments or dyes
Lubricants – reduce friction and improve flow
Flame retardents – reduce flammability of polymer
Cross‑linking agents – for thermosets and elastomers
Ultraviolet light absorbers – reduce degradation from sunlight
Antioxidants – reduce oxidation damage
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36. Thermoplastic Polymers (TP)
Thermoplastic polymers can be heated from solid state to viscous liquid and then cooled back down to solid
Heating and cooling can be repeated many times without degrading the polymer
Reason: TP polymers consist of linear and/or branched macromolecules that do not cross‑link upon heating
Thermosets and elastomers change chemically when heated, which cross‑links their molecules and permanently sets these polymers
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37. Mechanical Properties of Thermoplastics
Low modulus of elasticity (stiffness)
E is much lower than metals and ceramics
Low tensile strength
TS is about 10% of metal
Much lower hardness than metals or ceramics
Greater ductility on average
Tremendous range of values, from 1% elongation for polystyrene to 500% or more for polypropylene
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38. Strength vs. Temperature
Deformation resistance (strength) of polymers as a function of temperature
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39. Physical Properties of Thermoplastics
Lower densities than metals or ceramics
Typical specific gravity for polymers are 1.2 (compared to ceramics (~ 2.5) and metals (~ 7)
Much higher coefficient of thermal expansion
Roughly five times the value for metals and 10 times the value for ceramics
Much lower melting temperatures
Insulating electrical properties
Higher specific heats than metals and ceramics
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40. Commercial Thermoplastic Products and Raw Materials
Thermoplastic products include
Molded and extruded items
Fibers and filaments
Films and sheets
Packaging materials
Paints and varnishes
Starting plastic materials are normally supplied to the fabricator in the form of powders or pellets in bags, drums, or larger loads by truck or rail car
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41. Thermosetting Polymers (TS)
TS polymers are distinguished by their highly cross‑linked three‑dimensional, covalently‑bonded structure
Chemical reactions associated with cross‑linking are called curing or setting
In effect, formed part (e.g., pot handle, electrical switch cover, etc.) becomes a large macromolecule
Always amorphous and exhibits no glass transition temperature
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42. General Properties of Thermosets
Rigid - modulus of elasticity is two to three times greater than thermoplastics
Brittle, virtually no ductility
Less soluble in common solvents than thermoplastics
Capable of higher service temperatures than thermoplastics
Cannot be remelted ‑ instead they degrade or burn
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43. Cross-Linking in TS Polymers
Three categories:
Temperature‑activated systems
Catalyst‑activated systems
Mixing‑activated systems
Curing is accomplished at the fabrication plants that make the parts rather than the chemical plants that supply the starting materials to the fabricator
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44. Temperature‑Activated Systems
Curing caused by heat supplied during part shaping operation (e.g., molding)
Starting material is a linear polymer in granular form supplied by the chemical plant
As heat is added, material softens for molding, but continued heating causes cross‑linking
Most common TS systems
The term “thermoset" applies best to these polymers
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45. Catalyst‑Activated Systems
Cross‑linking occurs when small amounts of a catalyst are added to the polymer, which is in liquid form
Without the catalyst, the polymer remains stable and liquid
Once combined with the catalyst it cures and changes into solid form
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46. Mixing‑Activated Systems
Mixing of two chemicals results in a reaction that forms a cross‑linked solid polymer
Elevated temperatures are sometimes used to accelerate the reactions
Most epoxies are examples of these systems
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47. TS vs. TP Polymers
TS plastics are not as widely used as the TP
One reason is the added processing costs and complications involved in curing
Largest market share of TS = phenolic resins with  6% of the total plastics market
Compare polyethylene with  35% market share
TS Products: countertops, plywood adhesives, paints, molded parts, printed circuit boards and other fiber reinforced plastics
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48. Elastomers
Polymers capable of large elastic deformation when subjected to relatively low stresses
Some can be extended 500% or more and still return to their original shape
Two categories:
Natural rubber - derived from biological plants
Synthetic polymers - produced by polymerization processes like those used for thermoplastic and thermosetting polymers
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49. Characteristics of Elastomers
Elastomers consist of long‑chain molecules that are cross‑linked (like thermosetting polymers)
They owe their impressive elastic properties to two features:
Molecules are tightly kinked when unstretched
Degree of cross‑linking is substantially less than thermosets
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50. Elastomer Molecules
Model of long elastomer molecules, with low degree of cross‑linking: (left) unstretched, and (right) under tensile stress
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51. Elastic Behavior of Elastomer Molecule
When stretched, the molecules are forced to uncoil and straighten
Natural resistance to uncoiling provides the initial elastic modulus of the aggregate material
Under further strain, the covalent bonds of the cross‑linked molecules begin to play an increasing role in the modulus, and stiffness increases
With greater cross‑linking, the elastomer becomes stiffer and its modulus of elasticity is more linear
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52. Stiffness of Rubber
Increase in stiffness as a function of strain for three grades of rubber: natural rubber, vulcanized rubber, and hard rubber
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53. Vulcanization Considerable less than cross‑linking in thermosets
Curing to cross‑link most elastomers
Vulcanization = the term for curing in the context of natural rubber (and certain synthetic rubbers)
Typical cross‑linking in rubber is one to ten links per hundred carbon atoms in the linear polymer chain, depending on degree of stiffness desired
Considerable less than cross‑linking in thermosets
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54. Natural Rubber (NR)
NR = polyisoprene, a high molecular‑weight polymer of isoprene (C5H8)
It is derived from latex, a milky substance produced by various plants, most important of which is the rubber tree that grows in tropical climates
Latex is a water emulsion of polyisoprene (about 1/3 by weight), plus various other ingredients
Rubber is extracted from latex by various methods that remove the water
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55. Vulcanized Natural Rubber
Properties: noted among elastomers for high tensile strength, tear strength, resilience (capacity to recover shape), and resistance to wear and fatigue
Weaknesses: degrades when subjected to heat, sunlight, oxygen, ozone, and oil
Some of these limitations can be reduced by additives
Market share of NR  22% of total rubber volume (natural plus synthetic)
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56. Natural Rubber Products
Largest single market for NR is automotive tires
Other products: shoe soles, bushings, seals, and shock absorbing components
In tires, carbon black is an important additive
It reinforces the rubber, serving to increase tensile strength and resistance to tear and abrasion
Other additives: clay, kaolin, silica, talc, and calcium carbonate, as well as chemicals that accelerate and promote vulcanization
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57. Synthetic Rubbers
Development of synthetic rubbers was motivated largely by world wars when NR was difficult to obtain
Tonnage of synthetic rubbers is now more than three times that of NR
The most important synthetic rubber is styrene‑butadiene rubber (SBR), a copolymer of butadiene (C4H6) and styrene (C8H8)
As with most other polymers, the main raw material for synthetic rubbers is petroleum
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58. Thermoplastic Elastomers (TPE)
A thermoplastic that behaves like an elastomer
Elastomeric properties not from chemical cross‑links, but from physical connections between soft and hard phases in the material
Cannot match conventional elastomers in elevated temperature strength and creep resistance
Products: footwear; rubber bands; extruded tubing, wire coating; molded automotive parts, but no tires
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59. COMPOSITE MATERIALS
Technology and Classification of Composite Materials
Metal Matrix Composites
Ceramic Matrix Composites
Polymer Matrix Composites
Guide to Processing Composite Materials
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60. Composite Material Defined
A materials system composed of two or more distinct phases whose combination produces aggregate properties different 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 as distinguished from a synthesized composite)
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61. Why Composites are Important
Composites can be very strong and stiff, yet very light in weight
Strength‑to‑weight and stiffness‑to‑weight ratios are several times greater than steel or aluminum
Fatigue properties are generally better than for common engineering metals
Toughness is often greater
Possible to achieve combinations of properties not attainable with metals, ceramics, or polymers alone
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62. Disadvantages and Limitations
Properties of many important composites are anisotropic
May be an advantage or a disadvantage
Many polymer‑based composites are subject to attack by chemicals or solvents
Just as the polymers themselves are susceptible
Composite materials are generally expensive
Manufacturing methods for shaping composite materials are often slow and costly
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63. Possible Classification of Composites
Traditional composites – composite materials that occur in nature or have been produced by civilizations for many years
Examples: wood, concrete, asphalt
Synthetic composites - modern material systems normally associated with the manufacturing industries
Components are first produced separately and then combined to achieve the desired structure, properties, and part geometry
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64. Components in a Composite Material
Most composite materials consist of two phases:
Primary phase - forms the matrix within which the secondary phase is imbedded
Secondary phase - imbedded phase sometimes referred to as a reinforcing agent, because it usually strengthens the composite material
The reinforcing phase may be in the form of fibers, particles, or various other geometries
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65. Our Classification of Composite Materials
Metal Matrix Composites (MMCs) ‑ mixtures of ceramics and metals, such as cemented carbides and other cermets
Ceramic Matrix Composites (CMCs) ‑ Al2O3 and SiC imbedded with fibers to improve properties
Polymer Matrix Composites (PMCs) ‑ polymer resins imbedded with filler or reinforcing agent
Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders
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66. Functions of the Matrix Material
Primary phase provides the bulk form of the part or product made of the composite material
Holds the imbedded phase in place, usually enclosing and often concealing it
When a load is applied, the matrix shares the load with the secondary phase, in some cases deforming so that the stress is essentially born by the reinforcing agent
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67. Reinforcing Phase Function is to reinforce the primary phase
Reinforcing phase (imbedded in the matrix) is most commonly one of the following shapes: fibers, particles, or 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
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68. Physical Shapes of Imbedded Phase
Possible physical shapes of imbedded phases in composite materials: (a) fiber, (b) particle, and (c) flake
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69. Fibers
Filaments of reinforcing material, usually circular in cross section
Diameters from ~ mm to about 0.13 mm
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 material becomes oriented in the fiber axis direction and probability of defects in the structure decreases significantly
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70. Continuous Fibers vs. Discontinuous Fibers
Continuous fibers - very long; in theory, they offer a continuous path by which a load can be carried by the composite part
Discontinuous fibers (chopped sections of continuous fibers) - short lengths (L/D = roughly 100)
Whiskers = discontinuous fibers of hair-like single crystals with diameters down to about mm ( in) and very high strength
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71. Fiber Orientation – Three Cases
One‑dimensional reinforcement, in which maximum strength and stiffness are obtained in the direction of the fiber
Planar reinforcement, in some cases in the form of a two‑dimensional woven fabric
Random or three‑dimensional in which the composite material tends to possess isotropic properties
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72. Fiber Orientation
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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73. Materials for Fibers Glass – most widely used filament
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 in polymer composites
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74. Particles and Flakes
A second common shape of imbedded phase is particulate, ranging in size from microscopic to macroscopic
Flakes are basically two‑dimensional particles ‑ small flat platelets
Distribution of particles in the matrix is random
Strength and other properties of the composite material are usually isotropic
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75. Interface between Constituent Phases in Composite Material
For the composite to function, the phases must bond where they join at the interface
Direct bonding between primary and secondary phases
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76. Interphase
In some cases, a third ingredient must be added to bond primary and secondary phases
Called an interphase, it is like an adhesive
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77. Alternative Interphase Form
Formation of an interphase consisting of a solution of primary and secondary phases at their boundary
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78. Properties of Composite Materials
In selecting a composite material, an optimum combination of properties is often sought, rather than one particular property
Example: fuselage and wings of an aircraft must be lightweight, strong, stiff, and tough
Several fiber‑reinforced polymers possess these properties
Example: natural rubber alone is relatively weak
Adding carbon black increases its strength
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79. Three Factors that Determine Properties
Materials used as component phases in the composite
Geometric shapes of the constituents and resulting structure of the composite system
How the phases interact with one another
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80. Example: Fiber Reinforced Polymer
Model of fiber‑reinforced composite material showing direction in which elastic modulus is being estimated by the rule of mixtures
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81. Example: Fiber Reinforced Polymer (continued)
Stress‑strain relationships for the composite material and its constituents
The fiber is stiff but brittle, while the matrix (commonly a polymer) is soft but ductile
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82. Variations in Strength and Stiffness
Variation in elastic modulus and tensile strength as a function of direction relative to longitudinal axis of carbon fiber‑reinforced epoxy composite
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83. Importance of Geometric Shape: Fibers
Most materials have tensile strengths several times greater as fibers than as bulk materials
By imbedding the fibers in a polymer matrix, a composite material is obtained that avoids the problems of fibers but utilizes their strengths
Matrix provides the bulk shape to protect the fiber surfaces and resist buckling
When a load is applied, the low‑strength matrix deforms and distributes the stress to the high‑strength fibers
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84. Other Composite Structures
Laminar composite structure – conventional
Sandwich structure
Honeycomb sandwich structure
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85. Laminar Composite Structure
Conventional laminar structure - two or more layers bonded together in an integral piece
Example: plywood, in which layers are the same wood, but grains oriented differently to increase overall strength
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86. Sandwich Structure: Foam Core
Relatively thick core of low density foam bonded on both faces to thin sheets of a different material
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87. Sandwich Structure: Honeycomb Core
Alternative to foam core
Foam or honeycomb achieve high ratios of strength‑to‑weight and stiffness‑to‑weight
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

88. Other Laminar Composite Structures
FRPs - multi‑layered, fiber‑reinforced plastic panels for aircraft, boat hulls, other products
Printed circuit boards - layers of reinforced copper and plastic for electrical conductivity and insulation, respectively
Snow skis - layers of metals, particle board, and phenolic plastic
Windshield glass - two layers of glass on either side of a sheet of tough plastic
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

89. Metal Matrix Composites (MMCs)
Metal matrix reinforced by a second phase
Reinforcing phases:
Particles of ceramic
These MMCs are commonly called cermets
Fibers of various materials
Other metals, ceramics, carbon, and boron
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

90. Cermets Cemented carbides – most common
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 temperatures used in processing
Cermets can be subdivided into
Cemented carbides – most common
Oxide‑based cermets – less common
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

91. Cemented Carbides Tantalum carbide (TaC) and others are less common
One or more carbide compounds bonded in a metallic matrix
Common cemented carbides are based on tungsten carbide (WC), titanium carbide (TiC), and chromium carbide (Cr3C2)
Tantalum carbide (TaC) and others are less common
Metallic binders: usually cobalt (Co) or nickel (Ni)
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

92. Cemented Carbide
Photomicrograph (about 1500X) of cemented carbide with 85% WC and 15% Co (photo courtesty of Kennametal Inc.)
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

93. Cemented Carbide Properties
Typical plot of hardness and transverse rupture strength as a function of cobalt content
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

94. Applications of Cemented Carbides
Tungsten carbide cermets (Co binder)
Cutting tools, wire drawing dies, rock drilling bits, powder metal dies, indenters for hardness testers
Titanium carbide cermets (Ni binder)
Cutting tools; high temperature applications such as gas‑turbine nozzle vanes
Chromium carbide cermets (Ni binder)
Gage blocks, valve liners, spray nozzles
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

95. Ceramic Matrix Composites (CMCs)
Ceramic primary phase imbedded with a secondary 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 thermal cracking
CMCs represent an attempt to retain the desirable properties of ceramics while compensating for their weaknesses
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

96. Ceramic Matrix Composite
Photomicrograph (about 3000X) of fracture surface of SiC whisker reinforced Al2O3 (photo courtesy of Greenleaf Corp.)
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

97. Polymer Matrix Composites (PMCs)
Polymer primary phase in which a secondary phase is imbedded as fibers, particles, or flakes
Commercially, PMCs are more important than MMCs or CMCs
Examples: most plastic molding compounds, rubber reinforced with carbon black, and fiber‑reinforced polymers (FRPs)
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

98. Fiber‑Reinforced Polymers (FRPs)
PMC consisting of a polymer matrix imbedded with 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 rubber products such as tires and conveyor belts
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

99. 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, and Al2O3, and steel
Glass (in particular E‑glass) is the most common fiber material in today's FRPs
Its use to reinforce plastics dates from around 1920
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

100. Common FRP Structures
Most widely used form of FRP is a laminar structure
Made by stacking and bonding thin layers of fiber and polymer until desired thickness is obtained
By varying fiber orientation among layers, a specified level of anisotropy in properties can be achieved in the laminate
Applications: boat hulls, aircraft wing and fuselage sections, automobile and truck body panels
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

101. FRP Properties High strength‑to‑weight and modulus‑to‑weight ratios
A typical FRP weighs only about 1/5 as much as steel
Yet strength and modulus are comparable in fiber direction
Good fatigue strength
Good corrosion resistance, although polymers are soluble in various chemicals
Low thermal expansion for many FRPs
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

102. FRP Applications Example: Boeing 787
Aerospace – much of the structural weight of today’s airplanes and helicopters consist of advanced FRPs
Example: Boeing 787
Automotive – some body panels for cars and truck 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
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

103. Other Polymer Matrix Composites
Other PMCs contain particles, flakes, and short fibers
Called fillers when used in molding compounds
Two categories:
Reinforcing fillers – used to strengthen or otherwise improve mechanical properties
Extenders – used to increase bulk and reduce cost per unit weight, with little or no effect on mechanical properties
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

104. Guide to Processing Composite Materials
The two phases are typically produced separately before being combined into the composite part
Processing techniques to fabricate MMC and CMC components are similar to those used for powdered metals and ceramics
Molding processes are commonly used for PMCs with particles and chopped fibers
Specialized processes have been developed for FRPs
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version

105. Guide to the Processing of Polymers
Polymers are nearly always shaped in a heated, highly plastic state
Common operations are extrusion and molding
Molding of thermosets is more complicated because of cross‑linking
Thermoplastics are easier to mold and a greater variety of molding operations are available
Rubber processing has a longer history than plastics, and rubber industries are traditionally separated from plastics industry, even though processing is similar
©2010 John Wiley & Sons, Inc. M P Groover, Principles of Modern Manufacturing 4/e SI Version