1-1

C H A P T E R 1

M A T E R I A L S

A N D E N G I N E E R I N G

1.1 MATERIALS AND ENGINEERING 1.1.1 Propert ies 1.1.2 Structure 1.1.3 Process ing 1.1.4 Per formance

1.2 CLASSIFICATION OF MATERIALS

1.3 MATERIALS SELECTION AND DESIGN

1-2

1.1 MATERIALS AND ENGINEERING

1.1.1 Properties

• Most material problems in engineering involve selecting or

designing materials with the appropriate properties for an

application.

There are two broad classes of properties:

• Mechanical properties (Fig. 1.1-1): hardness, strength, stiffness,

ductility, toughness, fatigue / creep / wear behaviour.

• Physical properties: electrical, magnetic, optical, thermal,

chemical behaviour, density (weight).

• Material properties may be affected by extreme

environments (e.g. very low/high temperatures (Fig. 1.1-2)

and pressures, corrosive atmospheres, radiation, etc.) or

degrade over time in normal service (corrosion and wear).

• Material properties must always be considered in the

context of the service environment.

• Properties desired in service may be different from

properties desired during manufacturing.

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Fig. 1.1-1 Some mechanical properties.

Fig. 1.1-2 Effects of temperature on properties.

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1.1.2 Structure

• It is important to realize that the structure of a material has

a profound influence on its properties.

Structure may be considered at 3 levels, depending on its

scale (Fig. 1.1-3):

• Atomic scale structure refers to the types of atoms/

elements (i.e. the composition), the arrangement of

electrons within individual atoms, interaction between

atoms (i.e. atomic bonding), and the way atoms/molecules

pack together (i.e. crystal structure in metals/ceramics)

• Microscopic scale structure, also known as

microstructure, refers to the arrangement of large groups

of atoms. Microstructure may be seen using a microscope.

By altering the microstructure, the same material may be

made to exhibit considerably different properties.

• Macroscopic scale structure, or macrostructure refers to

features that may be seen under low magnification or with

the naked eye, such as pores, voids, cracks, surface finish,

as well as shape and size.

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Fig. 1.1-3 Length scale of structures in metals and the properties which they determine. Each interval on the length scale is a factor of 1000.

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1.1.3 Processing

• Processing/synthesis methods (Fig. 1.1-4) and conditions

greatly affect material structures, and hence, properties.

• By selecting different processing routes, often involving

temperature, the microstructure of a material may be

tailored to yield diverse properties for varied applications.

Example: the same steel may be made soft and tough, or hard

and brittle, simply by cooling it very slowly or very quickly

from high temperatures (Fig. 1.1-5).

• The development of new processing techniques expand

the usefulness of traditional materials. Example: carbon has

limited application as graphite or diamond until recently,

when new processes now produce carbon fibres, carbon-

carbon composites and carbon nanotubes (Fig. 1.1-5 & Table 1.1-1).

• New synthesis methods also create new classes of materials

for new or existing applications. Example: the ability to

control the diffusion of dopant atoms into silicon gave rise to

microelectronics; or the chemical synthesis of synthetic

polymers (plastics), and composites, which have extensively

replaced metal, wood and other natural materials.

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Fig. 1.1-4 Common processes.

Fig. 1.1-5 Cooling the same steel at different rates will produce

different microstructures and hardness.

(c)

4 µm

Har

dnes

s (B

HN

)

Cooling Rate (°C/s)

100

200

300

400

500

600

(d)

30 µm

(b)

30 µm

(a)

30 µm

0.01 0.1 1 10 100 1000

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(a) Diamond

(c) Fullerene C60

(b) Graphite

(d) Carbon nanotube

Fig. 1.1-6 Different structures of carbon: (a) diamond, (b) graphite,

(c) fullerene C60, and (d) carbon nanotube.

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1.1.4 Performance

• The engineering performance of a material depends on its

properties, which is determined by the structure, which in

turn, may be controlled by the processing method (Fig. 1.1-7).

• To achieve successful and widespread adoption, the

material must also perform its given task in an economical,

environmentally and socially acceptable manner.

Fig. 1.1-7 Interrelationships between structure, properties, processing and performance.

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1.2 CLASSIFICATION OF MATERIALS

Fig. 1.2-1 Classification of materials

according to properties and structure.

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1.3 MATERIALS SELECTION AND DESIGN

• Material selection cannot be separated from the choice of

manufacturing process required to make the end product.

Fig 1.3-1 The interaction between design requirements, material, shape and process. The selection of material and process run

parallel to all stages in design.

Fig 1.3-2 The strategy for material selection: translation, screening, ranking and documentation. All

these steps may be implemented in software, alloying large populations

of materials to be investigated.

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Fig 1.3-3 Graphical tool for materials selection.

Fig 1.3-4 Strategy for selecting materials in environmentally-responsible design.

Density, ρ (Mg/m3)0.01

Str

engt

h, σ

y or

σel

(MP

a)

0.01100.1 1

0.1

1

10

100

1000

10 000

PPPE

Woods,

T

Foams

Polymers and elastomers

MetalsCeramics

Composites

Natural materials

Lead alloys

Tungsten alloys

SteelsTi alloys

Mg alloys

CFRP

GFRP

Al alloys

Rigid polymer foams

Flexible polymer foams

Ni alloys

Copper alloys

Zinc alloys

PAPEEK

PMMAPC

PET

Cork

Woods, ll

Butyl rubber

Silicone elastomers

Concrete

Tungstencarbide

Al2O3SiC

Si3N4Strength–Density

MFA, 07

Metals and polymers: yield strengthCeramics and glasses: MORElastomers: tensile tear strengthComposites: tensile failure