Handout 3 Materials Corrosion 0

8/4/2019 Handout 3 Materials Corrosion 0

1/24

CHE 3166: HANDOUT 3Stresses, Deformation and Fracture

LEARNING OBJECTIVES: Part I

Stress and Strain

Elastic Deformation

Plastic Deformation

Ductility

Toughness


2/24

Stress and Stress Types

Stress (): Force (F) / Cross-sectional Area (A)

= F / A

a es ypes o ress Tension

Compression Shear / Torsion


3/24

Common States of Stress: Ski Lift

Simple tension: Cable

Ao= cross sectionalarea (when unloaded)

FF

=F

oA

Torsion (shear): Drive Shaft

M

M Ao

2R

FsAc

o

=Fs

A


4/24

Common states of stress

Compression

Ao

Canyon Bridge, Los Alamos, NM

o

=F

ABalanced Rock, ArchesNational Park


5/24

Engineering Stress and Strain

0=Ft

Aooriginal area

before loading

Area, A

FtUnits of Stress:

N/m2 or lb/in2

Engineering stress,,,, 0000::::

Ft

=

Lo = (L-L0)

Engineering strain, : /2

L/2

Lowo


6/24

True Stress and Strain

True stress, T:

Load Fdivided by theinstantaneous cross-sectional

area Ai (after deformation) iT

A

F=

True strain,,,, ::::

0

ln

l

li

T=


7/24

Elastic Deformation

1. Initial 2. Small load 3. Unload

bonds

stretch

return toInitial

F

F

Linear-

elastic

Non-Linear-

elastic

Elastic Deformationis reversible


8/24

Plastic Deformation

1. Initial 2. Small load 3. Unload

planes

stillsheared

bondsstretch

& planesshear

Plastic Deformationis NOT reversible

F

elastic + plastic plastic

F

linearelastic

linearelastic

plastic


9/24

Linear Elastic Behaviour

When stress () is proportional to strain ()

E

F

-

elastic Fsimpletensiontest

Hooke's Law: = E

E: Slope, a Constant, also known as: Modulus of Elasticity or Youngs Modulus Stiffness of the materials

Materials resistance to elastic deformation


10/24

Youngs Modulus (E) of Different Material Types

Magnesium,

Aluminum

Platinum

Silver, Gold

Tantalum

Zinc, Ti

Steel, NiMolybdenum

Si crystal

Glass -soda

Si nitride

Al oxide

Glass fibers only

Carbon fibers only

Aramid fibers only

6080

10 0

200

600800

10 001200

400

Cu alloys

Tungsten

Si carbide

Diamond

*

A FRE(|| fibers)*

CFRE(|| fibers)*

MetalsAlloys Ceramics Polymers

Composites/fibers

E(GPa,

109 Pa)

YoungsModulus (E):

Metals:40 400 GPa

Polymers:

0.2

8

0.6

1

G raphite

Concrete

PC

Wood( grain)

AFRE( fibers) *

CFRE *

GFRE*

Epoxy only

0.4

0.8

2

4

6

10

20

PTF E

HDP E

LDPE

PP

Polyester

PS

PET

CFRE( fibers) *

G FRE( fibers)*

0.2 4GPaCeramics:

80 1200 GPa

1GPa = 103MPa = 109N/m2


11/24

Effect of Temperature on Youngs Modulus (E)

E decreases with increase in temperature


12/24

Yield Strength of Different Material Types

CeramicsMetals/Alloys Composites/fibrePolymers

y(MPa

)

,

rsbeforeyield.

300

400

500600700

1000

2000

a

Steel (1020) cdSteel (4140) a

Steel (4140) qt

Ti (5Al-2.5Sn)a

W (pure)

Mo (pure)Cu (71500) cw

,

mposites,since

beforeyield.

Room Temp. Data

Based on data in

Yields

trength,

PVC

Hardtomeasu

re

sinceintension

,fractureusuallyoc

cu

Nylon 6,6

LDPE

70

20

40

60

50

100

10

30

200

Tin (pure)

Al (6061) a

Cu (71500) hrTa (pure)Ti (pure) aSteel (1020)

hr

Hardtomeas

ur

inceramicmatrixandepoxymatrixc

intension,

fractureusuallyocc

urs

HDPEPP

humid

dry

PC

PET

Table B4,Callister 7e.a = annealedhr = hot rolledag = aged

cd = cold drawncw = cold workedqt = quenched &tempered


13/24

Tensile Strength (TS) or

Ultimate Tensile Strength (UTS)

yF= fracture or

ultimate

stren thrin

TS

s

TS / UTS: Maximum stress on an engineering stress-strain curve

strain

Typical response of a metal Neck actsas stressconcentrator

Engine

stre

Engineering strainAdapted from Fig. 6.11,

Callister 7e.

Metals: when noticeable necking starts.


14/24

Tensile Strength of Different Material Types

Room Temp. Data

Ceramics/Metals/Alloys

Composites/fibres

Polymers

(MP

a)

300

1000

Al (6061) ag

Cu (71500) hr

Ti (pure) a

Steel (1020)

Steel (4140) a

Steel (4140) qt

Ti (5Al-2.5Sn) aW (pure)

Cu (71500) cw

2000

3000

5000

Al oxide

Diamond

Si nitride

GFRE(|| fiber)CFRE(|| fiber)

AFRE(|| fiber)

E-glass fib

C fibersAramid fib

a = annealedhr = hot rolledag = aged

Si crystal

Tensile

strength,

PVC

Nylon 6,6

10

100 Al(6061) a

LDPE

PP

PC PET

20

3040

Graphite

Concrete

Glass-soda

HDPE

wood ( fiber)

wood(|| fiber)

1

GFRE( fiber)CFRE( fiber)AFRE( fiber)

cd = cold drawncw = cold workedqt = quenched & tempered

COMPOSITES:

AFRE = aramid-fiber reinforcedGFRE = glass-fiber reinforcedCFRE = carbon-fiber reinforced(each with 60 vol% fibers).


15/24

Ductility

Plastic tensile strain at failure x 100L

LLEL%

o

of

=

AoL

Engineeringtensilestress,

smaller %EL

larger %ELf

Engineering tensile strain,

Another ductility measure: 100xA

AARA%

o

fo-

=


16/24

Engineeringtensilestress,

Low toughness: ceramics

High toughness: metals

Toughness / Fracture Toughness

Energy to break a unit volume of material

Approximated by the area under the stress-strain curve

Brittle fracture: elastic energyDuctile fracture: elastic + plastic energy

Very low toughness:unreinforced polymers

Engineering tensile strain,

Why are metals/alloysand reinforced plastic

so popular as structuralmaterials?


17/24

Mechanical Properties and Testing

LEARNING OBJECTIVES: Part II

Materials response to: Excessive Loading: Tensile Test

oca ze oa ng: ar ness es Sudden Intense Loading: Impact Test

Loading at High Temperatures: Creep Test

Cyclic Loading: Fatigue Test


18/24

Excessive loading: Tensile Test


19/24

Tensile Test

Tests are performed as per the ASTM, BS, DINor Australian Standards.

A tensile test measures the resistance of amaterial to a static or slowly applied force.

A machined specimen is placed in the testing

machine and load is applied. A strain gage or extensometer is used to

measure elongation.

The stress obtained at the highest applied forceis the Tensile Strength.


20/24

Test providesdata:strength,stiffness,ductility

Tensile Test


21/24

Other Tensile Test Data

Yield Strength: The stress at which a

prescribed amount of plastic deformation(commonly, 0.2%) is produced.

specimen stretches before fracture.


22/24

Cup and Cone Fracture


23/24

Fracture: Different Types of Material

Cup and cone fracture

Brittle fracture

a) Highly ductileb) Moderately ductile

c) Brittle


24/24

Tensile Properties: Effect of Temperature

Documents

Handout 3 Materials Corrosion 0