1

2

San Francisco, CAMarch 19, 2010

FE/EIT Review

Materials Properties

3

This Review Session’s Agenda

� Materials Science – Quick Review

– 60 minutes

– You should already know these materials

� Practice Problems

– 20 minutes to take the practice test

– 10 minutes to go over problems

4

Materials Science

Quick Review

5

Materials Science/Properties – 7% of total

A. Properties

� mechanical

� chemical

� electrical

� physical

B. Corrosion mechanisms and control

C. Materials

� engineered materials

� ferrous metals

� nonferrous metals

6

Materials Science Review

Atomic Bonding & Crystal Structures

7

Metals form crystals; 14 basic crystalline lattice structures (unit cells) based on 7 crystal systems

2

8

How are the 7 crystal systems different?

9

90% of metals have FCC, BCC, or HCP crystal structures

3 most common unit cells

10

Some Nomenclatures

� Crystal or Space Lattice – 3D “wireframe”

– like a scaffold at a construction site

� Lattice constant

– a = 0.24nm

– b = 0.24nm

– c = 0.24nm

� 90% of metals crystallize upon solidification into 3

densely packed crystal structures:

– Body-centered cubic (BCC)

– Face-centered cubic (FCC)

– Hexagonal close-packed (HCP)

� How many unit cells in 1mm of space? (3.5 million)

ab

cLattice Constant

A Space Lattice

Examples

11

Crystalline structures of common metals

� Body-Centered Cubic (BCC):

12

Crystalline structures of common metals

� Face-Centered Cubic (FCC):

13

Crystalline structures of common metals

� Hexagonal Close-Packed (HCP):

3

14

Number of atoms in a unit cell

� Most atoms are only ‘partially’ in the unit cell!

� In a simple cubic unit cell, only 1 atom is in the unit cell

1/8 x 1 atom = 1/8 atom

There are 8 of these� Total number of atoms = 1/8 x 8 = 1

15

Coordination Number & Atomic Packing Factor

� Coordination number: number of nearest neighbors

� Atomic Packing Factor (APF)

APF = Volume of atoms in unit cell*

Volume of unit cell

*assume hard spheres

16

Miller Indices for Crystal Planes (BCC, FCC)z

x

ya b

c

4. Miller Indices (110)

example a b cz

x

ya b

c

4. Miller Indices (100)

1. Intercepts 1 1 ∞

2. Reciprocals 1/1 1/1 1/∞1 1 0

3. Reduction 1 1 0

1. Intercepts 1/2 ∞ ∞2. Reciprocals 1/½ 1/∞ 1/∞

2 0 03. Reduction 2 0 0

example a b c

17

Miller Indices for Crystal Planes (HCP)

18

Materials Science Review

2. Materials Testing

Engr Stress-Strain Curve (non-ferrous matls)

19Engineering Strain (εεεε)

En

gin

ee

rin

g S

tre

ss

(σσ σσ

)

0.002 Offset Strain

Permanent Set

4

20

Engr Stress-Strain Graph (some ferrous matls)

21

Stress-strain graphs for various metals & alloys

22

Linear Elastic Properties

• Modulus of Elasticity, E:(also known as Young's modulus)

• Hooke's Law: σ = E ε

σ

Linear-elastic

E

ε

F

Fsimple tension test

Tension

Compression

F

FSimple

compression test

23

Young’s Modulus – Stiffness of a metal

24

• Energy to break a unit volume of material• Approximated by the area under the stress-strain curve.• Unit : J/m3

• Strength ≠≠≠≠ Toughness

Toughness

Brittle fracture: elastic energy

Ductile fracture: elastic + plastic energy

very small toughness (unreinforced polymers)

Engineering tensile strain, ε

Engineering tensile stress, σ

small toughness (ceramics)

large toughness (metals)

Metals are tough – they absorb a lot of energy prior

to fracture, e.g. metal bumper, auto body

Metals are tough – they absorb a lot of energy prior

to fracture, e.g. metal bumper, auto body

25

Hardness

� Hardness: resistance of a material to plastic

deformation

� How to test hardness?

– Brinell Hardness (BHN or HB)

– Rockwell Hardness (HRB & HRC most commonly)

– Meyer, Vickers, Knoop etc.

� Hardness & Tensile Strength (TS) for steel

– TS (psi) ~ 500 BHN

– TS (MPa) ~ 3.5 BHN

e.g., 10 mm sphere

apply known force measure size of indent after removing load

dDSmaller indents mean larger hardness.

5

26increasing hardness

most plastics

brasses Al alloys

easy to machine steels file hard

cutting tools

nitrided steels diamond

27

Fracture : temperature-, environment-, loading rate- & loading history - dependent process

� Fracture is the separation of a body into 2 or more parts

in response to an externally applied stress

� Fracture involves 2 steps:

– Crack formation – presence of voids, hairline crack

– Crack propagation – crack continues to enlarge

28

• Ductile failure:--one piece

--large deformation

Figures from V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures(2nd ed.), Fig. 4.1(a) and (b), p. 66 John Wiley and Sons, Inc., 1987. Used with permission.

Example: Failure of a Pipe at different temperatures

• Brittle failure:--many pieces

--small deformation

Warm

Cold

29

• Evolution to failure (5 steps):

• Resultingfracturesurfaces(steel)

50 mm

particlesserve as void

nucleationsites.

50 mm

From V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures (2nd ed.), Fig. 11.28, p. 294, John Wiley and Sons, Inc., 1987. (Orig. source: P. Thornton, J. Mater. Sci., Vol. 6, 1971, pp. 347-56.)

100 mm

Fracture surface of tire cord wire loaded in tension. Courtesy of F. Roehrig, CC Technologies, Dublin, OH. Used with permission.

Moderately Ductile Failure (cup-n-cone fracture)

necking

σ

void

nucleation

void growth

and linkage

Crack propagation fracture

Fibrous structure (“dimples”, ½ of void)

30

Crack front is usually the “leading edge” of fracture due to “stress amplification”

σσσσ0σσσσ0

Crack Forms & Propagates

σσσσm σσσσm

σσσσm σσσσm

Crack front

Crack front

σ

Crack formation & evolution

31

Cracks amplify stress and yield materials “prematurely” ∴∴∴∴ Flaws are Stress Concentrators

where

ρt = radius of curvature

σo = applied stress

σm = stress at crack tip

Kt = stress conc factor = 2 (a/ρt)1/2

ρt

Internal Crack

Surface Crack

Sharper crack has smaller radius of curvature and larger stress

amplification

ot

/

t

om Ka

σ=

ρσ=σ

21

2

Max stress occurs at crack tip

Applied Stress

Stress conc. factor

Crack Length

(1)

Note: In this course, all cracks are treated as “elliptical cracks”.

6

32

There are 3 methods to propagate a crack and cause failure – “Failure Modes”

Mode II: Sliding ModeMode I: Opening Mode Mode III: Tearing Mode

33

We are only concerned with Mode I – it precedes majority of failures

34

Fracture Mechanics

�Stress Intensity Factor (K) :

– “severity of a crack as a function of crack size, stress, and geometry”

� In short, K = “how sensitive is the crack to crack size, stress, and geometry”

– Y is a dimensionless parameter – depends on crack &

specimen size & geometries, manner of load app.

– Usually, Y ~ 1.0 (interior crack), 1.1 (exterior crack)

– a = crack size

– σσσσ = applied stress

aYK πσ= (3)

Unit: [MPa √ √ √ √m]

Fracture – Exterior vs. Interior Crack

35

36

Fracture Mechanics

�A crack will grow and cause brittle fracture if:

�KIc is a material property

�Fracture Toughness, KIC – a measure of a material’s resistance to brittle fracture when a crack is present

�Largest, most-stressed cracks grow first!

ICI KK ≥ Critical KI value

Fracture Toughness (KIC)

37

7

38

Fracture Mechanics

39

Fatigue: mean stress, max stress, min stress, stress ratio, range of stress, stress amplitude

σσσσm = mean stress (0 in this case) σσσσm = mean stress ( ≠ ≠ ≠ ≠ 0 in this case)

σmax

σmin

σ

timeσm

σσσσa

Stress amplitude σmax

σmin time

σmS

σmax

σmin

σ

time

σmS

Mean stress ≠ 0

2

minmax σσσ

+=

m 2

minmax σσσ

−=a

minmax σσσ −=r

max

min

σ

σ=R

Mean stress =Stress amplitude =

Stress range = Stress ratio=

Mean stress = 0

40

Fatigue

� Fatigue limit = endurance limit

� It is the largest value of fluctuating stress that will not cause failure for essentially an infinite number of cycles

� For ferrous alloy,

– steels: ~ 35-60% of UTS

� For non-ferrous alloys, usually NO fatigue limit. E.g. Mg,

Cu, Al

– Fatigue Strength is used rather than fatigue limit

� Fatigue strength is the stress level at which failure will

occur for some specified # of cycles, e.g. 107 cycles

N = Cycles to failure

S = stress amplitude

Endurance limit

41

Example: σσσσa vs. N graph

42

Creep: Matl deformation occurs due to long term exposure to stress level < yield or UTS

Sample deformation at a constant stress (σσσσ) vs. time

Primary Creep: slope (creep rate)

decreases with time.

Secondary Creep: steady-state

i.e., constant slope.

Tertiary Creep: slope (creep rate)

increases with time, i.e. acceleration of rate.

σσ,ε

0 t

Mostly elastic

Creep

43

Gradient of graph

8

44

Impact Testing (Charpy Test, Izod Test) –measures impact energy (toughness)

final height initial height

�Qualitative tests, simple, economical, quick

comparison of possible materials

�Effect of Impact loading:

– Makes material more brittle (e.g. plane

hitting ocean, belly flip)

– Decreases toughness

(Charpy)

Izod Test

Charpy Test

45

Ductile-to-Brittle-Transition Temperature (DBTT)

BCC metals (e.g., iron at T < 914°C)

Impact

Energ

y

Temperature

High strength materials (σσσσ y > E/150)

polymers

More DuctileBrittle

Ductile-to-brittle transition temperature

FCC metals (e.g., Cu, Ni)

Coz BCC is not close packedEnergy is needed to push dislocation through, resulting in a sudden drop in impact energy

46

Modern steel vs. Titanic steel under impact

Results of the Charpy test for modern steel and Titanic steel [Gannon, 1995]. When a pendulum struck the modern steel, on the left, with a large

force, the sample bent without breaking into pieces; it was ductile. Under the same impact loading, the Titanic steel, on the right, was extremely

brittle; it broke in two pieces with little deformation.

Other Examples of DBTT

47

48

Materials Science Review:

Corrosion

49

Corrosion (that is due to galvanic action)

� A form of material degradation due to charge transfer,

i.e. oxidation & reduction

Fe0 ���� Fe3+ + 3e- (Oxidation)

Fe3+ + 3e- ���� Fe0 (Reduction)

� Two metals of different oxidation potentials placed in an

electrolyte (e.g. seawater, Gatorade),

���� a galvanic cell will be created

– The more electropositive electrode (anode) will corrode

– The less electropositive electrode (cathode) will be

unchanged

9

50

Galvanic Cell produces current

� Oxidation occurs at the anode (electron is released into

the external circuit)

� Reduction occurs at the cathode (electron is removed

from the external circuit)

AnodeAnode CathodeCathode

51

Oxidation Potential Table

� Standard Oxidation

potential for Corrosion

Reactions

� Key: if forward reaction

has a negative potential,

it means the reaction

won’t happen

spontaneously (i.e.,

thermodynamically unfeasible)

52

Galvanic Series in Seawater

� Tendency to corrode increases with

separation in table

53

• Uniform AttackOxidation & reductionoccur uniformly over

surface.

• Selective LeachingPreferred corrosion ofone element/constituent

(e.g., Zn from brass (Cu-Zn)).

• Stress corrosionStress & corrosionwork together

at crack tips.

• GalvanicDissimilar metals arephysically joined. The

more anodic onecorrodes.(see Table

17.2) Zn & Mgvery anodic.

• Erosion-corrosionBreak down of passivatinglayer by erosion (pipe

elbows).

Forms of Corrosion

Forms

of

corrosion

• Crevice Between two

pieces of the same metal.

Rivet holes

• IntergranularCorrosion alonggrain boundaries,

often where specialphases exist.

attacked zones

g.b. prec.

• PittingDownward propagationof small pits & holes.

54

• Self-protecting metals!

-- Metal ions combine with O

to form a thin, adhering oxide layer that slows corrosion.

• Reduce T (slows kinetics of oxidation and reduction)

• Add inhibitors

-- Slow oxidation/reduction reactions by removing reactants

(e.g., remove O2 gas by reacting it w/an inhibitor).-- Slow oxidation reaction by attaching species to

the surface (e.g., paint it!).

Controlling Corrosion

Metal (e.g., Al, stainless steel)

Metal oxide

steel pipe

Mg anode

Cu wiree-

Earth

Mg2+

e.g., Mg Anode

• Cathodic (or sacrificial) protection

-- Attach a more anodic material to the one to be protected.

Adapted from Fig. 17.23, Callister 7e. steel

zinczinc

Zn2+

2e- 2e-

e.g., zinc-coated nail

55

Materials Science Review:

Diffusion & Phase Diagrams

10

56

• In an alloy, atoms or vacancies tend to migrate from regions

of high conc. to regions of low conc.

Initially

Diffusion

After some time

Vacancy

t

57

Diffusion is important in defect movement

58

Diffusion

� Fick’s first law of diffusion:

� D, diffusion coefficient or

diffusivity, depends on the

material (D0), activation

energy (Q), and temperature

−=dx

dCDJ

−=kT

QDD O exp

59

Diffusion and Temperature

• Diffusion coefficient increases with increasing T.

= pre-exponential [m2/s]

= diffusion coefficient [m2/s]

= activation energy [J/mol or eV/atom]

= gas constant [8.314 J/mol-K]

= absolute temperature [K]

D

Do

Q

R

T

−=RT

QDD O exp

60

Binary Isomorphous Phase Diagram (complete solubility, simplest form of PD)

• Indicate phases as function of T, Co, (and P). • Generally:

-binary systems: just 2 components.

-independent variables: T and Co (P = 1 atm is almost always used).

• Phase

Diagram

for Cu-Nisystem

• 2 phases:

L (liquid)

α (FCC solid solution)

• 3 phase fields: LL + αα

wt% Ni20 40 60 80 10001000

1100

1200

1300

1400

1500

1600T(°C)

L (liquid)

α(FCC solid solution)1084°C

1455°C

61

Binary Isomorphous Phase Diagram: Cu-Ni system (complete solubility)

wt% Ni20

1200

1300

30 40 50110 0

L (liquid)

α(solid)

T(°C)

A

35Co

L: 35wt%Ni

Cu-Ni

system

4635

4332

α: 43 wt% Ni

L: 32 wt% Ni

L: 24 wt% Ni

α: 36 wt% Ni

Bα: 46 wt% NiL: 35 wt% Ni

C

D

E

24 36

11

62

Binary Eutectic Alloy System

� In some binary alloy systems, components have limited solid solubility (or partial solubility)

• Eutectic composition

freezes at lower

temperature than all other compositions.

• This lowest temperature is

called eutectic temperature.

Example : Pb-Sn alloy.

2 components has a special composition

with a min. melting T.

Tm (Pb) = 327°C, Tm (Sn) = 232°C63

Binary Eutectic Alloy: Lead-Tin (Pb-Sn)

EUTECTIC POINT

LIQUID ONLY

SOLID ONLY

Liquid α solid solution + β solid solutionEutectic temperature

Cooling

α + β

2 phases (both are

solid)

EUTECTICTEMPERATURE

Means: Pb & Sn can only dissolve in each other partially

64

Eutectic composition & temperature

� Eutectic composition:

– 61.9 wt% Sn, 38.1 wt% Pb

� Eutectic temperature: 183°C

65

Binary Eutectic Alloy: Lead-Tin (Pb-Sn)

66

Eutectic Temp =

Eutectic Composition

67

Binary Eutectic Alloy: 40 wt%Sn – 60 wt%Pb

L+αL+β

α + β

200

T(°C)

18.3

C, wt% Sn20 60 80 1000

300

100

L (liquid)

α183°C

61.9 97.8β

• For a 40 wt% Sn-60 wt% Pb alloy at 150°C, find...--the phases present: Pb-Sn

system

α + β--compositions of phases:

CO = 40 wt% Sn

--the relative amount

of each phase:150

40Co

11Cα

99Cβ

SR

Cα = 11 wt% Sn

Cβ = 99 wt% Sn

Wα=Cβ - CO

Cβ - Cα

=99 - 4099 - 11

=5988

= 67 wt%

SR+S

=

Wβ =CO - Cα

Cβ - Cα=

R

R+S

=29

88= 33 wt%=

40 - 11

99 - 11

Adapted from Fig. 9.8, Callister 7e.

12

68

L+β

α + β

200

T(°C)

C, wt% Sn20 60 80 1000

300

100

L (liquid)

α β

L+α

183°C

• For a 40 wt% Sn-60 wt% Pb alloy at 220°C, find...--the phases present: Pb-Sn

system

Adapted from Fig. 9.8, Callister 7e.

Example: Pb-Sn Eutectic System

α + L--compositions of phases:

CO = 40 wt% Sn

--the relative amount

of each phase:

Wα =CL - CO

CL - Cα=

46 - 40

46 - 17

=6

29= 21 wt%

WL =CO - Cα

CL - Cα=

23

29= 79 wt%

40Co

46CL

17Cα

220SR

Cα = 17 wt% SnCL = 46 wt% Sn

69

Fe-C Phase Diagram (partial solubility) looks complicated

70

To simplify things, you only need to focus on wt%C < 2.14%, i.e. austenite region

Hypereutectoid

0.76

Hypo-eutectoid

Eutectic Composition

Eutectoid Composition

71

Austenite can transform into diff. microstructures at different temperatures, wt% & cooling rates

Austenite (γ)

Bainite(α + Fe3C plates/needles)

Pearlite(α + Fe3C layers + a

proeutectoid phase)

Martensite(BCT phase diffusionless

transformation)

Tempered Martensite (α + very fine

Fe3C particles)

slow cool

moderatecool

rapid quench

reheat

Str

ength

Ductilit

y

Martensite T Martensite

bainite fine pearlite

coarse pearlite spheroidite

General Trends

72

Microstructures of plain carbon steel

Spheroidite Coarse Pearlite Fine Pearlite

α-ferrite (light) Cementite (dark)73

Microstructures of plain carbon steel (continued)

Bainite Martensite

13

74

Microstructures of plain carbon steel (continued)

MartensiteBCT, Single Phase

Tempered Martensiteα + Fe3C phases

Heating(250-650°C)

α-ferrite (dark)Cementite (light)

Note: Tempered martensite is similar to spheroidite in terms of microstructures, except the cementite particles in tempered martensite is much smaller. Hence tempered

martensite is much stronger than spheroidite

75

Overview of microstructures during Austenite (γγγγ) transformation at various Temperature & wt%C

Microstructures of steel at different wt% C and temperatures

Hypoeutectoid Eutectoid Hypereutectoid

Eutectoid reaction:

γ (0.76 wt%C) α (0.022wt%C) + Fe3C (6.70wt%C)heating

cooling

76

Iron-Carbon (Fe-C) Phase Diagram

• 2 important points

-Eutectoid (B):γ ⇒ α +Fe3C

-Eutectic (A):L ⇒ γ +Fe3C

Adapted from Fig. 9.24,Callister 7e.

Fe

3C

(cem

entite

)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γ (austenite)

γ+L

γ+Fe3C

α+Fe3C

L+Fe3C

δ

(Fe) Co, wt% C

1148°C

T(°C)

α 727°C = Teutectoid

A

SR

4.30

Result: Pearlite = alternating layers of α and Fe3C phases

120 µm

(Adapted from Fig. 9.27, Callister 7e.)

γ γγγ

R S

0.76

Ceute

cto

id

B

Fe3C (cementite-hard)

α (ferrite-soft)

77

Hypoeutectoid Steel

Adapted from Figs. 9.24 and 9.29,Callister 7e. (Fig. 9.24 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)

Fe

3C

(cem

entite

)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γ (austenite)

γ+L

γ + Fe3C

α+ Fe3C

L+Fe3C

δ

(Fe) Co, wt% C

1148°C

T(°C)

α727°C

(Fe-C System)

C0

0.7

6

Adapted from Fig. 9.30,Callister 7e.

proeutectoid ferritepearlite

100 µmHypoeutectoid

steel

R S

α

wα =S/(R+S)

wFe3

C

=(1-wα)

wpearlite = wγpearlite

r s

wα =s/(r+s)wγ =(1- wα)

γγ γ

γα

αα

γγγ γ

γ γγγ

78

Hypereutectoid Steel

Fe

3C

(cem

entite

)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γ (austenite)

γ+L

γ +Fe3C

α +Fe3C

L+Fe3C

δ

(Fe) Co, wt%C

1148°C

T(°C)

α

Adapted from Figs. 9.24 and 9.32,Callister 7e. (Fig. 9.24 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)

(Fe-C System)

0.7

6 Co

Adapted from Fig. 9.33,Callister 7e.

proeutectoid Fe3C

60 µmHypereutectoid steel

pearlite

R S

wα =S/(R+S)

wFe3C=(1-wα)

wpearlite = wγpearlite

sr

wFe3C=r/(r+s)

wγ =(1-w Fe3C)

Fe3C

γγγ γ

γγγ γ

γγγ γ

79

Examples: Eutectoid & Peritectic

Cu-Zn Phase diagram

Eutectoid transition δ γ + ε

Peritectic transition γ + L δ

14

80

Eutectic, peritectic, eutectoid, peritectoid

81

Classification of Steels

� Three designation schemes or “standards” by

– AISI: American Iron & Steel Institute (ferrous)

– SAE: Society of Automotive Engineers (ferrous)

– UNS: Unified Numbering System (ferrous & non-ferrous

alloys)

AISI/SAEAISI/SAE UNSUNS

1040 G10400

Examples of Alloy Code:13 – only Mn

40 – Mo only41 – Cr & Mo43 – Ni, Cr & Mo

46 – Ni & Mo (<2%Ni)48 – Ni & Mo (>3%Ni)51 – Cr only

61 – Cr & V86 – Ni, Cr, Mo92 – Si only

Type of AlloyType of Alloy wt% of Cwt% of C

“40” = 0.40 wt%C“10” = Plain carbon steel

82

AISI/SAE & UNS Designation System

83

Annealing: Heat to Tanneal, then cool slowly.

Thermal Processing of Steel (same for other metals)

Types of Annealing

• Process Anneal:

Negate effect of cold working by (recovery/ recrystallization)

• Stress Relief: Reducestress caused by:

-plastic deformation -nonuniform cooling -phase transform.

• Normalize (steels): Deform steel with largegrains, then normalizeto make grains small.

• Full Anneal (steels): Make soft steels for good forming by heating to get γ, then cool in

furnace to get coarse P.

• Spheroidize (steels): Make very soft steels for good machining. Heat just

below TE & hold for

15-25 h.

84

a) Annealing

b) Quenching

Heat Treatments

c)

c) Tempered Martensite

time (s)10 10

310

510

-1

400

600

800

T(°C)

Austenite (stable)

200

P

B

TEA

A

M + A

M + A

0%

50%

90%a)

b)

85

Thermal Processing – Time-Temperature-Transformation Diagram

15

Jominy End-Quench Test – Measure Ease of attaining hardness by quenching from austenite

� Hardenability = Ability to form martensite

� Jominy end-quench test to measure hardenability

� Hardness versus distance

from the quenched end

86

24°C water

specimen (heated to γphase field)

flat ground

Rockwell Chardness tests

Ha

rdn

ess, H

RC

Distance from quenched end 87

88

• The cooling rate varies with position.

Why Hardness Changes w/ Position

distance from quenched end (in)Hard

ness,

HR

C

20

40

60

0 1 2 3

600

400

200A → M

0.1 1 10 100 1000

T(°C)

M(start)

Time (s)

0

0%

100%

M(finish)

89

• Effect of quenching medium:

Medium

airoil

water

Severity of Quench

lowmoderate

high

Hardness

lowmoderate

high

• Effect of geometry:

When surface-to-volume ratio increases: (SA/V = 2/R)

--cooling rate increases--hardness increases

Position

centersurface

Cooling rate

lowhigh

Hardness

lowhigh

Quenching Medium & Geometry

S (Surface)

¾-R (3/4 Radius)

M-R (Mid Radius)C (Center)

1

23

Cross Section

of Bar

90

S (Surface)

¾-R (3/4 Radius)

C (Center)

M-R (Mid Radius)

91

S (Surface)

¾-R (3/4 Radius)

C (Center)

M-R (Mid Radius)

16

92

ASTM Grain Size

93

Materials Science Review:

Polymer, Composites, Concrete

Polymers

�Thermoplastics

– Can be heated to high

temp & reformed

– E.g. Polyethylene,

polycarbonate, PMMA, Polystyrene,

Polypropylene, PVC

�Thermoset Plastic

– Cannot be reformed

because of cross linkages between

polymer chains

– E.g. vulcanized rubber,

epoxy resins

94 95

Most commodity polymers are thermoplatics

Poly(ethylene terephthalate)

High density polyethylene

1

2

3 Poly(vinyl chloride)

Low density polyethylene

Polypropylene

4

5

6 Polystyrene

PET

Code Letter ID Polymer Name

HDPE

V

LDPE

PP

PS

96

Microstructures of polymers: Amorphous, Crystalline, and Semi-crystalline polymers

� Amorphous polymer

– Mixture of short and long chains

– No long-range order; “random”

– “A bowl of cooked spaghetti”

� Crystalline polymer

– Long-range order

– “A box of uncooked spaghetti”

� Semicrystalline polymer

– Consists of amorphous and

crystalline regions

– “Mixture of cooked & uncooked

spaghetti” or “half-cooked spaghetti”

Crystalline

Amorphous97

Temp greatly affects mech. properties of thermoplastic ���� Transition Temp (Tg) is key

� Thermoplastics soften (becoming more viscous) as

temperature increases.

� Strength dramatically decreases above Tg.

UTS

Temperature

17

98

Elastic modulus and TS of polymer change w/ temp: as temp ↑↑↑↑, glass ���� rubbery ���� viscous

� Large drop in Er for

T > Tg

� Sample Tg values:

Leathery

Glassy

Rubbery

Rubbery Flow

Viscous Flow (Liquid)

Polymer Tg [°C]

LDPE -110

HDPE -90

Nylon 6,6 +57

PET +69

PVC +87

PS, PMMA

+100

PC +150

Elastic modulus vs. temperature

(amorphous polystyrene)

Polymer Additives

99

Composite Materials

100

Composite Materials

101

Matrix

Fiber

Concrete

� Ingredients:

– Cement + Water + Fine aggregates (Sand) + Coarse

aggregates (Gravels)

102

Time ↑ ↑ ↑ ↑

Strength↑↑↑↑

Concrete

� Water/Cement ratio affects strength

– High W/C ���� Weak

– Optimum W/C ���� Strong

– Low W/C ���� low ‘workability’ (add superplasticizer)

103