Fundamentals of Materials Science and Engineering - An Integrated Approach

Fundamentals of Materials Science and Engineering - An Integrated Approach

(Parte 3 de 7)

STRUCTURAL COMPOSITES 650

15.14 Laminar Composites 651

15.15 Sandwich Panels 651

Summary 654 Important Terms and Concepts 656 References 656 Questions and Problems 656

16 Corrosion and Degradation of Materials 660

Learning Objectives 661 16.1 Introduction 661

CORROSION OF METALS 661

16.2 Electrochemical

Considerations 662 16.3 Corrosion Rates 670 16.4 Prediction of Corrosion

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Contents • xxi

CORROSION OF CERAMIC MATERIALS 694

16.1 Swelling and Dissolution 695 16.12 Bond Rupture 697

Summary 699 Important Terms and Concepts 701 References 701 Questions and Problems 701

17 Thermal Properties 705

Summary 718 Important Terms and Concepts 719 References 719 Questions and Problems 719

18 Magnetic Properties 722

Learning Objectives 723 18.1 Introduction 723 18.2 Basic Concepts 723 18.3 Diamagnetism and

Ferrimagnetism 731 18.6 The Influence of Temperature on Magnetic Behavior 735 18.7 Domains and Hysteresis 736 18.8 Magnetic Anisotropy 740 18.9 Soft Magnetic Materials 741 18.10 Hard Magnetic Materials 744 18.1 Magnetic Storage 747

Summary 753 Important Terms and

Concepts 755

References 755 Questions and Problems 755

19 Optical Properties 759

Learning Objectives 760 19.1 Introduction 760

BASIC CONCEPTS 760

19.2 Electromagnetic Radiation 760 19.3 Light Interactions With

Solids 762 19.4 Atomic and Electronic Interactions 763

OPTICAL PROPERTIES OF METALS 764

OPTICAL PROPERTIES OF NONMETALS 765

APPLICATIONS OF OPTICAL PHENOMENA 775

Communications 781 Summary 785 Important Terms and Concepts 787 References 787 Questions and Problems 787

20 Economic, Environmental, and Societal Issues in Materials Science and Engineering 789

Learning Objectives 790 20.1 Introduction 790

ECONOMIC CONSIDERATIONS 790

ENVIRONMENTAL AND SOCIETAL CONSIDERATIONS 792

20.5 Recycling Issues in Materials

Science and Engineering 794 Summary 797 References 798 Design Questions 798

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Appendix A The International System of Units (SI) 799

Appendix B Properties of Selected Engineering Materials 801

B.6 Linear Coefficient of Thermal

Expansion 815

Appendix C Costs and Relative Costs for Selected Engineering Materials 829

Appendix D Repeat Unit Structures for Common Polymers 834

Appendix E Glass Transition and Melting Temperatures for Common Polymeric Materials 838

Answers to Selected Problems 855

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List of Symbols

The number of the section in which a symbol is introduced or explained is given in parentheses.

A = area A = angstrom unit

Ai = atomic weight of element i (2.2) APF = atomic packing factor (3.4) a = lattice parameter: unit cell x-axial length (3.4) a = crack length of a surface crack (9.5) at% = atom percent (5.6) B = magnetic flux density (induction) (18.2)

Br = magnetic remanence (18.7) BCC = body-centered cubic crystal structure

Ci = concentration (composition) of component i in wt% (5.6)

C′i = concentration (composition) of component i in at% (5.6)

Cv,Cp = heat capacity at constant volume, pressure (17.2)

CPR = corrosion penetration rate (16.3) CVN = Charpy V-notch (9.8) %CW = percent cold work (8.1) c = lattice parameter: unit cell z-axial length (3.1)

cv,cp = specific heat at constant volume, pressure (17.2)

DP = degree of polymerization (4.5) d = diameter d = average grain diameter (8.9) dhkl = interplanar spacing for planes of Miller indices h, k, and l (3.20)

E = energy (2.5) E = modulus of elasticity or Young’s modulus (7.3) e = electric field intensity (12.3)

Ef = Fermi energy (12.5) Eg = band gap energy (12.6) e = electric charge per electron (12.7) e– = electron (16.2) erf = Gaussian error function (6.4) exp = e, the base for natural logarithms

FCC = face-centered cubic crystal structure (3.4)

HCP = hexagonal close-packed crystal structure (3.4)

HK = Knoop hardness (7.16)

HRB, HRF = Rockwell hardness: B and F scales (7.16)

• xi

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HR15N, HR45W = superficial Rockwell hardness: 15N and 45W scales (7.16) iC = corrosion current density (16.4)

KIc = plane strain fracture toughness for mode I crack lc = critical fiber length (15.4) ln = natural logarithm log = logarithm taken to base 10 M = magnetization (18.2)

Mn = polymer number-average molecular weight (4.5)

Mw = polymer weight-average molecular weight (4.5) mol% = mole percent

N = number of fatigue cycles (9.10)

NA = Avogadro’s number (3.5)

Nf = fatigue life (9.10) n = principal quantum number

(2.3) n = number of atoms per unit cell (3.5) n = strain-hardening exponent (7.7) n = number of electrons in an electrochemical reaction (16.2) n = number of conducting electrons per cubic meter (12.7) n = index of refraction (19.5) n′ = for ceramics, the number of formula units per unit cell (3.7) ni = intrinsic carrier (electron and hole) concentration (12.10)

P–B ratio = Pilling–Bedworth ratio (16.10) p = number of holes per cubic meter (12.10)

Q = activation energy Q = magnitude of charge stored (12.18)

%RA = ductility, in percent reduction in area (7.6) r = interatomic distance (2.5) r = reaction rate (16.3) rA, rC = anion and cation ionic radii (3.6)

S = fatigue stress amplitude (9.10)

SEM = scanning electron microscopy or microscope T = temperature

TC = superconducting critical temperature (18.12)

Tg = glass transition temperature (1.15)

Tm = melting temperature TEM = transmission electron microscopy or microscope

TS = tensile strength (7.6) t = time direction (3.13)

V = electrical potential difference (voltage) (12.2)

Vi = volume fraction of phase i (10.8) v = velocity vol% = volume percent

Wi = mass fraction of phase i (10.8) wt% = weight percent (5.6) x = length x = space coordinate Y = dimensionless parameter or function in fracture toughness expression (9.5)

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List of Symbols • xxv y = space coordinate z = space coordinate α = lattice parameter: unit cell y–z interaxial angle (3.1) α, β, γ = phase designations αl = linear coefficient of thermal expansion (17.3) β = lattice parameter: unit cell x–z interaxial angle (3.1) γ = lattice parameter: unit cell x–y interaxial angle (3.1) γ = shear strain (7.2) = precedes the symbol of a parameter to denote finite change = engineering strain (7.2)

= dielectric permittivity (12.18) r = dielectric constant or relative permittivity (12.18) s = steady-state creep rate (9.16) θD = Debye temperature (17.2) λ = wavelength of electromagnetic

μr = relative magnetic permeability (18.2)

ρt = radius of curvature at the tip of a crack (9.5) σc = critical stress for crack propagation (9.5) σ′m = stress in matrix at composite failure (15.5) σT = true stress (7.7) σw = safe or working stress (7.20) τc = fiber–matrix bond strength/matrix shear yield strength (15.4) τcrss = critical resolved shear stress (8.6) χm = magnetic susceptibility (18.2) c = composite cd = discontinuous fibrous composite cl = longitudinal direction (aligned fibrous composite) ct = transverse direction (aligned fibrous composite) f = final f = at fracture f = fiber i = instantaneous m = matrix m, max = maximum min = minimum 0 = original 0 = at equilibrium 0 = in a vacuum

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Chap ter 1 Introduction

A familiar item that is fabricated from three different material types is the beverage container. Beverages are marketed in aluminum (metal) cans (top), glass (ceramic) bottles (center), and plastic (polymer) bottles (bottom). (Permission to use these photographs was granted by the Coca-Cola Company. Coca-Cola, Coca-Cola Classic, the Contour Bottle design and the Dynamic Ribbon are registered trademarks of The Coca-Cola Company and used with its express permission.)

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Learning Objectives

After careful study of this chapter you should be able to do the following:

1. List six different property classifications of materials that determine their applicability.

2. Cite the four components that are involved in the design, production, and utilization of materials, and briefly describe the interrelationships among these components.

3. Cite three criteria that are important in the materials selection process.

4. (a) List the three primary classifications of solid materials, and then cite the distinctive chemical feature of each.

(b) Note the two types of advanced materials and, for each, its distinctive feature(s).

5. (a) Briefly define “smart material/system.”

(b) Briefly explain the concept of “nanotechnology” as it applies to materials.

1.1 HISTORICAL PERSPECTIVE

Materialsareprobablymoredeep-seatedinourculturethanmostofusrealize.Transportation, housing, clothing, communication, recreation, and food production— virtually every segment of our everyday lives is influenced to one degree or another by materials. Historically, the development and advancement of societies have been intimately tied to the members’ ability to produce and manipulate materials to fill their needs. In fact, early civilizations have been designated by the level of their materials development (Stone Age, Bronze Age, Iron Age).1

The earliest humans had access to only a very limited number of materials, those that occur naturally: stone, wood, clay, skins, and so on. With time they discovered techniques for producing materials that had properties superior to those of the natural ones; these new materials included pottery and various metals. Furthermore, it was discovered that the properties of a material could be altered by heat treatments and by the addition of other substances. At this point, materials utilization was totally a selection process that involved choosing from a given, rather limited set of materials the one best suited for an application by virtue of its characteristics. It was not until relatively recent times that scientists came to understand the relationships between the structural elements of materials and their properties. This knowledge, acquired over approximately the past 100 years, has empowered them to fashion, to a large degree, the characteristics of materials. Thus, tens of thousands of different materials have evolved with rather specialized characteristics that meet the needs of our modern and complex society; these include metals, plastics, glasses, and fibers.

The development of many technologies that make our existence so comfortable has been intimately associated with the accessibility of suitable materials. An advancement in the understanding of a material type is often the forerunner to the stepwiseprogressionofatechnology.Forexample,automobileswouldnothavebeen possible without the availability of inexpensive steel or some other comparable substitute.Inourcontemporaryera,sophisticatedelectronicdevicesrelyoncomponents that are made from what are called semiconducting materials.

1 The approximate dates for the beginnings of Stone, Bronze, and Iron Ages were 2.5 million bc, 3500 bc and 1000 bc, respectively.

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1.2 Materials Science and Engineering • 3

1.2 MATERIALS SCIENCE AND ENGINEERING

Sometimes it is useful to subdivide the discipline of materials science and engineering into materials science and materials engineering subdisciplines. Strictly speaking, “materials science” involves investigating the relationships that exist between the structures and properties of materials. In contrast, “materials engineering” is, on the basis of these structure–property correlations, designing or engineering the structure of a material to produce a predetermined set of properties.2 From a functional perspective, the role of a materials scientist is to develop or synthesize new materials, whereas a materials engineer is called upon to create new products or systems using existing materials, and/or to develop techniques for processing materials. Most graduates in materials programs are trained to be both materials scientists and materials engineers.

“Structure” is at this point a nebulous term that deserves some explanation. In brief, the structure of a material usually relates to the arrangement of its internal components. Subatomic structure involves electrons within the individual atoms and interactions with their nuclei. On an atomic level, structure encompasses the organization of atoms or molecules relative to one another. The next larger structural realm,whichcontainslargegroupsofatomsthatarenormallyagglomeratedtogether, is termed “microscopic,” meaning that which is subject to direct observation using some type of microscope. Finally, structural elements that may be viewed with the naked eye are termed “macroscopic.”

Thenotionof“property”deserveselaboration.Whileinserviceuse,allmaterials are exposed to external stimuli that evoke some type of response. For example, a specimensubjectedtoforceswillexperiencedeformation,orapolishedmetalsurface will reflect light. A property is a material trait in terms of the kind and magnitude of response to a specific imposed stimulus. Generally, definitions of properties are made independent of material shape and size.

Virtually all important properties of solid materials may be grouped into six different categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative. For each there is a characteristic type of stimulus capable of provoking different responses. Mechanical properties relate deformation to an applied load or force; examples include elastic modulus and strength. For electrical properties, such as electrical conductivity and dielectric constant, the stimulus is an electric field. The thermal behavior of solids can be represented in terms of heat capacity and thermal conductivity. Magnetic properties demonstrate the response of a material to the application of a magnetic field. For optical properties, the stimulus is electromagnetic or light radiation; index of refraction and reflectivity are representative optical properties. Finally, deteriorative characteristics relate to the chemical reactivity of materials. The chapters that follow discuss properties that fall within each of these six classifications.

In addition to structure and properties, two other important components are involved in the science and engineering of materials—namely, “processing” and “performance.”Withregardtotherelationshipsofthesefourcomponents,thestructureof amaterialwilldependonhowitisprocessed.Furthermore,amaterial’sperformance will be a function of its properties. Thus, the interrelationship between processing, structure, properties, and performance is as depicted in the schematic illustration shown in Figure 1.1. Throughout this text we draw attention to the relationships

(Parte 3 de 7)

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