Kutz M. Handbook of materials selection

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350

Table 17 Properties of General-Purpose Elastomers

ASTM Temperature

Rubber Nomenclature Outstanding Characteristic Property Deﬁciency Use Range (⬚C)

Butadiene rubber BR Very ﬂexible; resistance to wear Sensitive to oxidation; poor

resistance to fuels and oil

⫺100 to 90

Natural rubber NR Similar to BR but less resilient Similar to BR

⫺50 to 80

Isoprene rubber IR Similar to BR but less resilient Similar to BR

⫺50 to 80

Isobutylene–isoprene rubber

(butyl rubber)

IIR High ﬂexibility; low permeability to air

⫺45 to 150

Chloroprene CR Flame resistant; fair fuel and oil resistance;

increased resistance toward oxygen,

ozone, heat, light

Poor low-temperature ﬂexibility

⫺40 to 115

Nitrile-butadiene NBR Good resistance to fuels, oils, and

solvents; improved abrasion resistance

Lower resilience; higher hysteresis;

poor electrical properties; poorer

low temperature ﬂexibility

⫺45 to 80

Styrene–butadiene rubber SBR Relatively low cost Less resilience; higher hysteresis;

limited low temperature

ﬂexibility

⫺50 to 80

Ethylene-propylene copolymer EPDM Resistance to ozone and weathering Poor hydrocarbon and oil

resistance

⫺50 to ⬍175

Polysulﬁde T Chemical resistance; resistance to ozone

and weathering

Creep; low resilience

⫺45 to 120

351

Table 18 Properties of Specialty Elastomers

ASTM Temperature

Elastomer Nomenclature Use Range (⬚C) Outstanding Characteristic Typical Applications

Silicones

(polydimethylsiloxane)

MQ ⫺100 to 300 Wide temperature range; resistance to aging,

ozone, sunlight; very high gas

permeability

Seals, molded and extruded goods; adhesives,

sealants; biomedical; personal care

products

Fluoroelastomers CFM

⫺40 to 200 Resistance to heat, oils, chemical Seals such as O-rings, corrosion resistant

coatings

Acrylic AR

⫺40 to 200 Oil, oxygen, ozone, and sunlight resistance Seals, hose

Epichlorohydrin ECO

⫺18 to 150 Resistance to oil, fuels; some ﬂame

resistance; low gas permeability

Hose, tubing, coated fabrics, vibration

isolators

Chlorosulfonated CSM

⫺40 to 150 Resistance to oil, ozone weathering,

oxidizing chemicals

Automotive hose, wire and cable, linings for

reservoirs

Chlorinated polyethylene CM

⫺40 to 150 Resistance to oils, ozone, chemicals Impact modiﬁer, automotive applications

Ethylene–acrylic

⫺40 to 175 Resistance to ozone, weathering Seals, insulation, vibration damping

Propylene oxide

⫺60 to 150 Low temperature properties Motor mounts

352 PLASTICS: THERMOPLASTICS, THERMOSETS, AND ELASTOMERS

Uses. Poly(ethylene chlorotriﬂuoroethylene) applications included wire and

cable coatings, chemical-resistant coatings and linings, molded lab ware, and

medical packing.

3.6 Poly(vinyl ﬂuoride)

Poly(vinyl ﬂuoride) ﬁlms exhibit excellent outdoor durability. It is the least

chemical-resistant ﬂuoropolymer.

Uses. Poly(vinyl ﬂuoride) uses include glazing, lighting, and coatings on

presurfaced exterior building panels.

4 THERMOSETS

Thermosetting resins are used in molded and laminated plastics.

They are ﬁrst

polymerized into a low-molecular-weight linear or slightly branched polymer or

oligomer, which is still soluble, fusible, and highly reactive during ﬁnal proc-

essing. Thermoset resins are generally highly ﬁlled with mineral ﬁllers and glass

ﬁbers. Thermosets are generally catalyzed and/or heated to ﬁnish the polymer-

ization reaction, cross-linking them to almost inﬁnite molecular weight. This

step is often referred to as cure. Such cured polymers cannot be reprocessed or

reshaped.

The high ﬁller loading and the high cross-link density of thermoset resins

results in very high densities and very low ductility, but very high rigidity and

good chemical resistance.

4.1 Phenolic Resins

Phenolic resins combine the high reactivity of phenol and formaldehyde to form

prepolymers and oligomers called resoles and novolacs. These materials are

combined with ﬁbrous ﬁllers to give a phenolic resin, which when heated pro-

vides rapid, complete cross-linking into highly cured structures. The high cross-

linked aromatic structure has high hardness, rigidity, strength, heat resistance,

chemical resistance, and good electrical properties.

Uses. Phenolic applications include automotive uses (distributor caps, ro-

tors, brake linings), appliance parts (pot handles, knobs, bases, electrical/elec-

tronic components (connectors, circuit breakers, switches), and as an adhesive

in laminated materials (e.g., plywood).

4.2 Epoxy Resins

The most common epoxy resins are prepared from the reaction of bisphenol A

and epichlorohydrin to yield low-molecular-weight resins that are liquid either

at room temperature or on warming. Each polymer chain usually contains two

or more epoxide groups. The high reactivity of the epoxide groups with amines,

anhydrides, and other curing agents provides facile conversion into highly cross-

linked materials. Cured epoxy resins exhibit hardness, strength, heat resistance,

electrical resistance, and broad chemical resistance.

Uses. Epoxy resins are used in glass reinforced, high-strength composites

in aerospace, pipes, tanks, pressure vessels; encapsulation or casting of various

electrical and electronic components (printed wiring boards, etc.); adhesives;

4 THERMOSETS 353

protective coatings in appliances, ﬂooring, and industrial equipment; and seal-

ants.

4.3 Unsaturated Polyesters

Unsaturated polyesters are prepared by the condensation polymerization of var-

ious diols and maleic anhydride to give a very viscous liquid that is dissolved

in styrene monomer. The addition of styrene lowers the viscosity to a level

suitable for impregnation and lamination of glass ﬁbers. The low-molecular-

weight polyester has numerous fumarate ester units that provide easy reactivity

with styrene monomer. Properly formulated glass-reinforced unsaturated poly-

esters are commonly referred to as sheet molding compound (SMC), or rein-

forced plastics. In combination with reinforcing materials such as glass ﬁber,

cured resins offer outstanding strength, high rigidity, impact resistance, high

strength-to-weight ratio, and chemical resistance. SMC typically is formulated

with 50% calcium carbonate ﬁller, 25% long glass ﬁber, and 25% unsaturated

polyester. The highly ﬁlled nature of SMC results in high density and brittle

easily pitted surface.

Bulk molding compound (BMC) is formulated similar to SMC except -in.

–

chopped glass is used. The shorter glass length gives easier process but lower

strength and impact.

Uses. The prime use of unsaturated polyesters is in combination with glass

ﬁbers in high-strength composites and in SMC and BMC materials. The appli-

cations include transportation markets (large body parts for automobiles, trucks,

trailers, buses, and aircraft), marine markets (small- to medium-sized boat hulls

and associated marine equipment), building panels, housing and bathroom com-

ponents (bathtub and shower stalls), appliances, and electrical/electronic com-

ponents.

4.4 Alkyd Resins

Alkyd resins are based on branched prepolymers from glycerol, phthalic anhy-

dride, and glyceryl esters of fatty acids. Alkyds have excellent heat resistance,

are dimensionally stable at high temperatures, and have excellent dielectric

strength (

⬎14 MV/m), high resistance to electrical leakage, and excellent arc

resistance.

Uses. Alkyd resin applications include drying oils in enamel paints, lacquers

for automobiles and appliances; and molding compounds when formulated with

reinforcing ﬁllers for electrical applications (circuit breaker insulation, encap-

sulation of capacitors and resistors, and coil forms).

4.5 Diallyl Phthalate

Diallyl phthalate (DAP) is the most widely used compound in the allylic family.

The neat resin is a medium-viscosity liquid. These low-molecular-weight pre-

polymers can be reinforced and compression molded into highly cross-linked,

completely cured products.

The most outstanding properties of DAP are excellent dimensional stability

and high insulation resistance. In addition, DAP has high dielectric strength,

excellent arc resistance, and chemical resistance.

354 PLASTICS: THERMOPLASTICS, THERMOSETS, AND ELASTOMERS

Uses. DAP applications include electronic parts, electrical connectors, bases

and housings. DAP is also used as a coating and impregnating material.

4.6 Amino Resins

The two main members of the amino family of thermosets are the melamine

and urea resins. They are prepared from the reaction of melamine and urea with

formaldehyde. In general, these materials exhibit extreme hardness, scratch re-

sistance, electrical resistance, and chemical resistance.

Uses. Melamine resins ﬁnd use in colorful, rugged dinnerware, decorative

laminates (countertops, tabletops, and furniture surfacing), electrical applications

(switchboard panels, circuit breaker parts, arc barriers, and armature and slot

wedges), and adhesives and coatings.

Urea resins are used in particleboard binders, decorative housings, closures,

elecrical parts, coatings, and paper and textile treatment.

5 GENERAL-PURPOSE ELASTOMERS

Elastomers are polymers that can be stretched substantially beyond their original

length and can retract rapidly and forcibly to essentially their original dimensions

(on release of the force).

39,40

The optimum properties and/or economics of many rubbers are obtained

through formulating with reinforcing agents, ﬁllers, extending oils, vulcanizing

agents, antioxidants, pigments, etc. End-use markets for formulated rubbers in-

clude automotive tire products (including tubes, retread applications, valve

stems, and inner liners), adhesives, cements, caulks, sealants, latex foam prod-

ucts, hose (automotive, industrial, and consumer applications), belting (V-

conveyor and trimming), footwear (heels, soles, slab stock, boots, and canvas),

molded, extruded, and calendered products (athletic goods, ﬂooring, gaskets,

household products, O-rings, blown sponge, thread, and rubber sundries). A list

of general-purpose elastomers and properties is summarized in Table 17.

6 SPECIALTY ELASTOMERS

Specialty rubbers offer higher performance over general-purpose rubbers and

ﬁnd use in more demanding applications.

They are more costly and hence are

produced in smaller volumes. Properties and uses are summarized in Table 18.

REFERENCES

1. S. H. Goodman (ed.), Handbook of Thermoset Plastics, 2nd ed., Plastics Design Library, Brook-

ﬁeld, CT, 1999.

2. E. N. Peters, Desk Reference of Polymer Characterization and Analysis, R. F. Brady, Jr. (ed.),

American Chemical Society, Washington, DC, 2002.

3. O. Olabisi (ed.), Handbook of Thermoplastics, Marcel Dekker, New York, 1998.

4. D. A. Smith (ed.), Addition Polymers: Formation and Characterization, Plenum Press, New York,

1968.

5. G. M. Benedikt and B. L. Goodall (eds.), Metallocene-Catalyzed Polymers—Materials, Proper-

ties, Processing and Markets, Plastics Design Library, Brookﬁeld, CT, 1998.

6. V. Shah (ed.), Handbook of Polyoleﬁns, 2nd ed. revised and expanded, Wiley, New York, 1998.

7. A. J. Peacock, Handbook of Polyethylene: Structures, Properties, and Applications, Marcel Dek-

ker, New York, 2000.

8. H. G. Karian (ed.), Handbook of Polypropylene and Polypropylene Composites, Marcel Dekker,

New York, 1999.

REFERENCES 355

9. Polypropylene—The Deﬁnitive User’s Guide, Plastics Design Library, Brookﬁeld, CT, 1998.

10. H. Vernaleken, Interfacial Synthesis, Vol. II, F. Millich and C. Carraher (eds.), Marcel Dekker,

New York, 1977, Chapter 13.

11. E. J. Wickson (ed.), Handbook of PVC Formulating, Wiley, New York, 1993.

12. D. W. Fox and E. N. Peters, Applied Polymer Science, 2nd ed., R. W. Tess and G. W. Poehlein

(eds.), American Chemical Society, Washington, DC, 1985.

13. E. N. Peters and R. K. Arisman, Applied Polymer Science—21st Century, C. D. Craver and C. E.

Carraher (eds.), Elsevier, New York, 2000.

14. D. B. G. Jaquiss, W. F. H. Borman, and R. W. Campbell, Kirk-Othmer Encyclopedia of Chemical

Technology, 3rd ed., Vol. 18, Interscience, New York, 1982.

15. L. Bottenbruch (ed.), Engineering Thermoplastics: Polycarbonates–Polyacetals–Polyesters–

Cellulose Esters, Hanser Gardner, Cincinnati, OH, 1996.

16. M. I. Kohan (ed.), Nylon Plastics Handbook SPE Monograph, Hanser Gardner, Cincinnati, OH,

1995.

17. S. M. Ahorani, n-Nylons: Their Synthesis, Structure and Properties, Wiley, New York, 1997.

18. R. R. Gallucci, Conference Proceedings for the Society of Plastics Engineers, Inc., 44th Annual

Technical Conference, Society of Plastics Engineers, Washington, DC, 1986.

19. E. N. Peters, Conference Proceedings for the Society of Plastics Engineers, Inc., 55th Annual

Technical Conference, Society of Plastics Engineers, Washington, DC, 1997.

20. B. Majumdar and D. R. Paul, Polymer Blends, Vol. 2, D. R. Paul and C. P. Bucknall (eds.),

Wiley, New York, 1999.

21. J. M. Short and H. W. Hill, Chemtech 2, 481 (1972).

22. Polycarbonates: Science and Technology, D. G. LeGrand and J. T. Bendler (eds.), Marcel Dekker,

New York, 1999.

23. D. W. Fox, Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 18, 3rd ed., Interscience,

New York, 1982.

24. H. Schnell, Chemistry and Physics of Polycarbonates, Wiley-Interscience, New York, 1964.

25. J. E. Harris, Handbook of Plastic Materials and Technology. I. I. Rubin (ed.), Wiley-Interscience,

New York, 1990.

26. R. N. Johnson, A. G. Farnham, R. A. Clendinning, W. F. Hale, and C. N. Merriam, J. Polym.

Sci., Part A-1 5, 2375 (1967).

27. L. M. Robeson, Handbook of Plastic Materials and Technology, I. I. Rubin (ed.), Wiley-

Interscience, New York, 1990.

28. T. W. Haas, Handbook of Plastic Materials and Technology, I. I. Rubin (ed.), Wiley-Interscience,

New York, 1990.

29. A. S. Hay, J. Polym. Sci. 58, 581 (1962).

30. D. M. White and G. D. Cooper, Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 18,

3rd ed., Interscience, New York, 1982.

31. E. P. Cizek, U. S. Patent 3.338,435, 1968.

32. C. E. Sroog, J. Polym. Sci. Macromol. Rev. 11, 161 (1976).

33. D. E. Floryan and I. W. Serfaty, Mod. Plastics, 59, 146 (1982).

34. I. W. Serfaty Handbook of Plastic Materials and Technology, I. I. Rubin (ed.), Wiley-Interscience,

New York, 1990.

35. J. L. Thorne, Handbook of Plastic Materials and Technology, I. I. Rubin (ed.), Wiley-Interscience,

New York, 1990.

36. S. Ebnesajjad, Fluoroplastics, Volume I: Non-melt Processible Fluoroplastics, Plastics Design

Library, Brookﬁeld, CT, 2000.

37. C. A. Sperati, Handbook of Plastic Materials and Technology, I. I. Rubin (ed.), Wiley-

Interscience, New York, 1990.

38. S. H. Goodman (ed.), Handbook of Thermoset Plastics, 2nd ed., Plastics Design Library, Brook-

ﬁeld, CT, 1999.

39. P. A. Ciullo and N. Hewitt, The Rubber Formulary, Plastics Design Library, Brookﬁeld, CT,

1999.

40. M. Morton (ed.), Rubber Technology, Van Norstrand Reinhold, New York, 1973.

41. J. M. Zeigler and F. W. G. Fearon (eds.), Silicone-Based Polymer Science: A Comprehensive

Resource, American Chemical Society, Washington, DC, 1990.

357

CHAPTER 12

COMPOSITE MATERIALS

Carl Zweben

Devon, Pennsylvania

1 INTRODUCTION 357

1.1 Classes and Characteristics

of Composite Materials 358

1.2 Comparative Properties of

Composite Materials 359

1.3 Manufacturing Considerations 363

2 REINFORCEMENTS AND

MATRIX MATERIALS 364

2.1 Reinforcements 364

2.2 Matrix Materials 368

3 PROPERTIES OF COMPOSITE

MATERIALS 372

3.1 Mechanical Properties of

Composite Materials 375

3.2 Physical Properties of

Composite Materials 386

REFERENCES 397

BIBLIOGRAPHY 397

1 INTRODUCTION

The development of composite materials and related design and manufacturing

technologies is one of the most important advances in the history of materials.

Composites are multifunctional materials having unprecedented mechanical and

physical properties that can be tailored to meet the requirements of a particular

application. Many composites also exhibit great resistance to high-temperature

corrosion and oxidation and wear. These unique characteristics provide the me-

chanical engineer with design opportunities not possible with conventional

monolithic (unreinforced) materials. Composites technology also makes possible

the use of an entire class of solid materials, ceramics, in applications for which

monolithic versions are unsuited because of their great strength scatter and poor

resistance to mechanical and thermal shock. Further, many manufacturing pro-

cesses for composites are well adapted to the fabrication of large, complex struc-

tures, which allows consolidation of parts, reducing manufacturing costs.

Composites are important materials that are now used widely, not only in the

aerospace industry, but also in a large and increasing number of commercial

mechanical engineering applications, such as internal combustion engines; ma-

chine components; thermal control and electronic packaging; automobile, train,

and aircraft structures and mechanical components, such as brakes, drive shafts,

ﬂywheels, tanks, and pressure vessels; dimensionally stable components; process

industries equipment requiring resistance to high-temperature corrosion, oxida-

Reprinted in part from Mechanical Engineers’ Handbook, 2nd ed., Wiley, New York, 1998, by per-

mission of the publisher.

HandbookofMaterialsSelection.EditedbyMyerKutz

358 COMPOSITE MATERIALS

Table 1 Types of Composite Materials

Reinforcement

Matrix

Polymer Metal Ceramic Carbon

Polymer X X X X

Metal X X X X

Ceramic X X X X

Carbon X X X X

tion, and wear; offshore and onshore oil exploration and production; marine

structures; sports and leisure equipment; and biomedical devices.

It should be noted that biological structural materials occurring in nature are

typically some type of composite. Common examples are wood, bamboo, bone,

teeth, and shell. Further, use of artiﬁcial composite materials is not new. Straw-

reinforced mud bricks were employed in biblical times. Using modern termi-

nology, discussed later, this material would be classiﬁed as an organic

ﬁber-reinforced ceramic matrix composite.

In this chapter, we consider the properties of reinforcements and matrix ma-

terials (Section 2) and the properties of composites (Section 3).

1.1 Classes and Characteristics of Composite Materials

There is no universally accepted deﬁnition of a composite material. For the

purpose of this work, we consider a composite to be a material consisting of

two or more distinct phases, bonded together.

Solid materials can be divided into four categories: polymers, metals, ceram-

ics, and carbon, which we consider as a separate class because of its unique

characteristics. We ﬁnd both reinforcements and matrix materials in all four

categories. This gives us the ability to create a limitless number of new material

systems with unique properties that cannot be obtained with any single mono-

lithic material. Table 1 shows the types of material combinations now in use.

Composites are usually classiﬁed by the type of material used for the matrix.

The four primary categories of composites are polymer matrix composites

(PMCs), metal matrix composites (MMCs), ceramic matrix composites (CMCs),

and carbon/carbon composites (CCCs). At this time, PMCs are the most widely

used class of composites. However, there are important applications of the other

types, which are indicative of their great potential in mechanical engineering

applications.

Figure 1 shows the main types of reinforcements used in composite materials:

aligned continuous ﬁbers, discontinuous ﬁbers, whiskers (elongated single crys-

tals), particles, and numerous forms of ﬁbrous architectures produced by textile

technology, such as fabrics and braids. Increasingly, designers are using hybrid

composites that combine different types of reinforcements to achieve more ef-

ﬁciency and to reduce cost.

A common way to represent ﬁber-reinforced composites is to show the ﬁber

and matrix separated by a slash. For example, carbon ﬁber-reinforced epoxy is

typically written ‘‘carbon/epoxy,’’ or, ‘‘C/Ep.’’ We represent particle reinforce-

ments by enclosing them in parentheses followed by ‘‘p’’; thus, silicon carbide

(SiC) particle-reinforced aluminum appears as ‘‘(SiC)p/Al.’’

1 INTRODUCTION 359

Fig. 1 Reinforcement forms.

Composites are strongly heterogeneous materials; that is, the properties of a

composite vary considerably from point to point in the material, depending on

which material phase the point is located in. Monolithic ceramics and metallic

alloys are usually considered to be homogeneous materials, to a ﬁrst approxi-

mation.

Many artiﬁcial composites, especially those reinforced with ﬁbers, are an-

isotropic, which means their properties vary with direction (the properties of

isotropic materials are the same in every direction). This is a characteristic they

share with a widely used natural ﬁbrous composite, wood. As for wood, when

structures made from artiﬁcial ﬁbrous composites are required to carry load in

more than one direction, they are used in laminated form.

Many ﬁber-reinforced composites, especially PMCs, MMCs, and CCCs, do

not display plastic behavior as metals do, which makes them more sensitive to

stress concentrations. However, the absence of plastic deformation does not

mean that composites are brittle materials like monolithic ceramics. The hetero-

geneous nature of composites results in complex failure mechanisms that impart

toughness. Fiber-reinforced materials have been found to produce durable, reli-

able structural components in countless applications. The unique characteristics

of composite materials, especially anisotropy, require the use of special design

methods.

1.2 Comparative Properties of Composite Materials

There are a large and increasing number of materials that fall in each of the

four types of composites, making generalization difﬁcult. However, as a class

of materials, composites tend to have the following characteristics: high strength;

high modulus; low density; excellent resistance to fatigue, creep, creep rupture,

corrosion, and wear; and low coefﬁcient of thermal expansion (CTE). As for

monolithic materials, each of the four classes of composites has its own partic-

360 COMPOSITE MATERIALS

Fig. 2 Speciﬁc tensile strength (tensile strength divided by density) as a function of

speciﬁc modulus (modulus divided by density) of composite materials and

monolithic metals and ceramics.

ular attributes. For example, CMCs tend to have particularly good resistance to

corrosion, oxidation, and wear, along with high-temperature capability.

For applications in which both mechanical properties and low weight are

important, useful ﬁgures of merit are speciﬁc strength (strength divided by spe-

ciﬁc gravity or density) and speciﬁc stiffness (stiffness divided by speciﬁc grav-

ity or density). Figure 2 presents speciﬁc stiffness and speciﬁc tensile strength

of conventional structural metals (steel, titanium, aluminum, magnesium, and

beryllium), two engineering ceramics (silicon nitride and alumina), and selected

composite materials. The composites are PMCs reinforced with selected contin-