Handout 3 Materials Corrosion 0
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Transcript of Handout 3 Materials Corrosion 0
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CHE 3166: HANDOUT 3Stresses, Deformation and Fracture
LEARNING OBJECTIVES: Part I
Stress and Strain
Elastic Deformation
Plastic Deformation
Ductility
Toughness
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Stress and Stress Types
Stress (): Force (F) / Cross-sectional Area (A)
= F / A
a es ypes o ress Tension
Compression Shear / Torsion
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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
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Common states of stress
Compression
Ao
Canyon Bridge, Los Alamos, NM
o
=F
ABalanced Rock, ArchesNational Park
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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
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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=
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Elastic Deformation
1. Initial 2. Small load 3. Unload
bonds
stretch
return toInitial
F
F
Linear-
elastic
Non-Linear-
elastic
Elastic Deformationis reversible
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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
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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
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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
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Effect of Temperature on Youngs Modulus (E)
E decreases with increase in temperature
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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
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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.
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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).
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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-
=
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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?
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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
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Excessive loading: Tensile Test
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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.
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Test providesdata:strength,stiffness,ductility
Tensile Test
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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.
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Cup and Cone Fracture
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Fracture: Different Types of Material
Cup and cone fracture
Brittle fracture
a) Highly ductileb) Moderately ductile
c) Brittle
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Tensile Properties: Effect of Temperature