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MATERIAL PROPERTY CHARTS

4 . 1 I N T R O D U C T I O N A N D S Y N O P S I S 4 . 2 E X P L O R I N G M A T E R I A L P R O P E R T I E S

4 . 3 T H E M A T E R I A L P R O P E R T Y C H A R T S

T H E M O D U L U S - D E N S I T Y C H A R T

T H E M O D U L U S S T R E N G T H C H A R T

T H E M O D U L U S - S T R E N G T H C H A R T

T H E S P E C I F I C S T I F F N E S S - S P E C I F I C S T R E N G T H C H A R T

T H E F R A C T U R E T O U G H N E S S - M O D U L U S C H A R T

T H E F R A C T U R E T O U G H N E S S - S T R E N G T H C H A R T

T H E L O S S C O E F F I C I E N T - M O D U L U S C H A R T

T H E T H E R M A L E X P A N S I O N - T H E R M A L C O N D U C T I V I T Y C H A R T

T H E T H E R M A L E X P A N S I O N - M O D U L U S C H A R T

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4.1 : INTRODCUTION AND SYNOPSIS

Values that design-limiting properties can have.

One property can be displayed as a ranked list or bar chart, but

it seldom that the performance of a component depends on just

one property.

More often it is a combination of properties that matter;

1. the need for stiffness at low weight,2. for thermal conduction coupled with corrosion resistance

3. Strength combined with toughness

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4.2 : EXPLORING MATERIAL PROPERTIES

Each property of engineering material has a characteristic range

of values.

The materials are segregated by class.

Each class shows a characteristic range :

1) Metals and ceramics have high moduli

2) Polymers have low

3) Hybrids have a wide range ( low to high)

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4.3: THE MATERIAL PROPERTY CHART

4.3.1 MODULUS-DENSITY CHART

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THE DENSITY

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The density of a solid depends on

1. the atomic weight of its atoms or ions

2. their size

3. the way they are packed. Size of atoms does not vary much: most have a

volume within a factor of two of 2x10-29 m3

Packing fractions do not vary much either- a

factor of two more or less. Close packing gives a

packing fraction of 0.74. Open network is 0.34 (

diamond cubic structure)

The spread of density comes mainly from the

spread of atomic weight, ranging from 1 for H to

238 for uranium.

Metals are dense because they are made of

heavy atoms, packed closely together.

Ceramics-have lower densities than metals

because they contain light O,N or C atoms. Polymers -have low densities because they are

largely made of carbon and hydrogen in more

open amorphous or crystalline packings.

Foams- materials made up of cells containing a

large fraction of pore space.

METALS

CERAMICS

POLYMERS & ELASTOMERS

FOAMS

DENSITY

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THE MODULI The moduli of most materials depend on 2 factors

1) Bond stiffness

2) Number of bonds per-unit volume

A bond is like a spring, it has a spring constant, S ( N/m).

Young modulus, E, is roughly where E = S/r

The wide range of moduli is largely caused by the range of values of S

a) The covalent bond is stiff ( S= 20-200N/m)b) The metallic and the ionic a little less ( S= 15-100N/m)

Metals have high moduli because close gives a high bond density and the bond is

strong.

Polymers- contain both strong diamond-like covalent bonds and weak hydrogen or

van der waals bonds (S= 0.5-2 N/m)

Elastomers- have a low E because their weak secondary bonds have melted as their

glass temperature, Tg is below room temperature- leaving only the very weak

entropic restoring force associated with tangled, long-chain molecules.

Foams- have low moduli because the cell walls bend easily when material is loaded.

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4.3.2 THE STRENGTH-DENSITY CHART

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Strength definitions

1) Metal and polymers- yield strength

2) Brittle ceramic- Flexural strength or modulus of rupture

3) Elastomers- The tensile tear strength

4) Composite- tensile failure strength ( the compressive strength can be less by up to 30% because

of fiber buckling)

Range of strength for engineering materials : 0.01MPa (foams) to 10,000 MPa (diamond)

The single most important concept this wide range is the lattice resistance

Plastic shear in a crystal involves the motion of dislocations.

Pure metal is soft because the nonlocalized metallic bond does little to hinder dislocation

motion.

Ceramic are hard because their more localized covalent and ionic bonds lock the dislocation

places. Lattice resistance is low- the material can be strengthened by introducing obstacles to slip.

In metals-this achieved by adding alloying elements particles

In polymers- by cross-linking

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4.3.3 MODULUS-STRENGTH CHART

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0.01-0.1-

polymer

Composit

e = 0.01

Metal=

factor of10 smaller

Elastomer Low moduli= 1-

10

f/E = fracture strain(The strain at which the material ceases

to be linearly elastic)

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4.3.4 THE SPECIFIC STIFFNESS-SPECIFIC STRENGTH CHART

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Application in selecting materials for light

springs and energy storage devices

These are

measures of

mechanical

efficiency

CFRP-The

most attractive

specific

properties.

Ceramic-

exceptionally

high stiffness

per-unit weightand their strength

per-unit weight is

good but it

brittleness

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4.4.5 THE FRACTURE TOUGHNESS-MODULUS CHART

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S E L E C T I O N

Increasing the

strength of a

material is useful

only as long as

the material

remains plastics

and does not

become brittle.

The resistance to the

propagation of a crack

is measured by the

fracture toughness, K1c

Super tough

material (metal

group)-show

substantial

plasticity before

they break.

At the lower

end, range

brittle materials.

When loaded

remain elastic

until theyfracture

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4.3.6 THE FRACTURE TOUGHNESS-STRENGTH CHART

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Application in selecting

materials for the safe design of

load-bearing structures.

Stress concentration at

the tip of a crack

generates a process

zone

Metal- plasticzone in ductile

solids

Micro-cracking

in ceramic

Composite-

Zone ofdelamination,

debonding or

fiber pull out.

Material towards the

bottom right have high

strength and lowtoughness.

Toward the top left-

opposite.

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4.3.8 THE THERMAL CONDUCTIVITY-ELECTRICAL RESISTIVITY CHART

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Flow heat through a

material at steadystate is the thermalconductivity,

(unit:W/m.k)

Valence electron in

metals are freemoving like a gas

within a lattice of

metal.

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4.3.10 THE THERMAL EXPANSION-THERMAL CONDUCTIVITY CHART

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THE CHARTS SHOWS CONTOURS OF/,

A QUANTITY IMPORTANT IN DESIGNING

AGAINST THERMAL DISTORTION.

Almost all solids

expand on heating.

The bond between a

pair of atoms

behave like a linear

elastic spring when

relative

displacement of

atoms is small but

when it is large, the

spring is nonlinear.Most bond stiffer when

atoms are pushed

together and less stiff

when they are pulled

apart.Such bond are

anharmonic

T is , the

anharmonicity of thebond pushes the atoms

apart, increasing their

mean spacing. The

effect is measured by

the linear expansion

coefficient.

Polymer have large values of

,roughly 10 x greater than metaland almost 100x than ceramics.

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4.3.11 THE THERMAL EXPANSION-MODULUS CHART

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THERMAL STRESS IS THE STRESS THAT

APPEARS IN A BODY WHEN IT IS HEATED

OR COOLED BUT PREVENTED FROM

EXPANDING OR CONTRACTING.DEPENDS ON THE and E