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8/22/2019 Callister Ch6 Mek Oz
1/23
Chapter 6 - 1
renilecek Baz Kavramlar...
Stressand strain: Gerilme ve Genleme (Birim ekil Deiimi)
Elasticbehavior: Elastik davran
Plasticbehavior: Plastik davran
Toughnessand ductility: Tokluk ve sneklik
Chapter 6 (Blm 6):Mechanical Properties
(Mekanik zellikler)
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Chapter 6 - 2
Elastic means reversible!
Elastic Deformation
1. Initial 2. Small load 3. Unload
F
d
bonds
stretch
return to
initial
F
d
Linear-
elastic
Non-Linear-elastic
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Chapter 6 - 3
Plastic means permanent!
Plastic Deformation (Metals)
F
dlinearelastic linearelasticdplastic
1. Initial 2. Small load 3. Unload
planesstillsheared
F
delastic + plastic
bondsstretch& planesshear
dplastic
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Chapter 6 - 4
Stress-Strain Testing Typical tensile test
machine
Adapted from Fig. 6.3, Callister 7e. (Fig. 6.3 is taken from H.W.
Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of
Materials, Vol. III, Mechanical Behavior, p. 2, John Wiley and Sons,New York, 1965.)
specimenextensometer
Typical tensile
specimen
Adapted from
Fig. 6.2,
Callister 7e.
gauge
length
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Chapter 6 - 5
Linear Elastic Properties
Modulus of Elasticity, E:(also known as Young's modulus)
Hooke's Law:
s= Ee s
Linear-elastic
Ee
F
Fsimpletensiontest
8/22/2019 Callister Ch6 Mek Oz
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Chapter 6 - 6
Mechanical Properties Slope of stress strain plot (which is
proportional to the elastic modulus) dependson bond strength of metal
Adapted from Fig. 6.7,
Callister 7e.
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Chapter 6 - 7
Metals
Alloys
Graphite
Ceramics
Semicond
PolymersComposites
/fibers
E(GPa)
Based on data in Table B2,
Callister 7e.
Composite data based on
reinforced epoxy with 60 vol%
of aligned
carbon (CFRE),
aramid (AFRE), or
glass (GFRE)
fibers.
Youngs Moduli: Comparison
109Pa
0.2
8
0.6
1
Magnesium,
Aluminum
Platinum
Silver, Gold
Tantalum
Zinc, Ti
Steel, Ni
Molybdenum
Graphite
Si crystal
Glass-soda
Concrete
Si nitrideAl oxide
PC
Wood( grain)
AFRE( fibers) *
CFRE*
GFRE*
Glass fibers only
Carbon fibers only
Aramid fibers only
Epoxy only
0.4
0.8
2
46
10
2 0
4 0
6 08 0
10 0
200
600800
10 001200
400
Tin
Cu alloys
Tungsten
Si carbide
Diamond
PTFE
HDPE
LDPE
PP
Polyester
PSPET
CFRE( fibers)*
GFRE( fibers)*
GFRE(|| fibers)*
AFRE(|| fibers)*
CFRE(|| fibers)*
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Chapter 6 - 8
(at lower temperatures, i.e. T< Tmelt/3)
Plastic (Permanent) Deformation
Simple tension test:
engineering stress, s
engineering strain, e
Elastic+Plasticat larger stress
permanent (plastic)after load is removed
epplastic strain
Elasticinitially
Adapted from Fig. 6.10 (a),
Callister 7e.
8/22/2019 Callister Ch6 Mek Oz
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Chapter 6 - 9
Stress at which noticeableplastic deformation hasoccurred.
when ep = 0.002
Yield Strength, y
sy= yield strength
Note: for 2 inch sample
e= 0.002 = z/z
z= 0.004 in
Adapted from Fig. 6.10 (a),
Callister 7e.
tensile stress,s
engineering strain, e
sy
ep= 0.002
8/22/2019 Callister Ch6 Mek Oz
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Chapter 6 - 10
Room Tvalues
Based on data in Table B4,
Callister 7e.
a = annealed
hr = hot rolledag = aged
cd = cold drawn
cw = cold worked
qt = quenched & tempered
Yield Strength : ComparisonGraphite/Ceramics/Semicond
Metals/Alloys
Composites/fibers
Polymers
Yieldstr
ength,sy(MPa)
PVC
H
ardtomeasure
,
sinceintension,fra
ctureusuallyoccursbeforeyield.
Nylon 6,6
LDPE
70
20
40
6050
100
10
30
2 00
3 004 00
5 006 007 00
10 00
2 0 00
Tin (pure)
Al(6061)a
Al(6061)ag
Cu(71500)hrTa (pure)Ti (pure)aSteel (1020)hr
Steel (1020)cd
Steel (4140)a
Steel (4140)qt
Ti (5Al-2.5Sn)aW(pure)
Mo (pure)Cu(71500)cw
Hardtomeasure,
inceramicmatrixa
ndepoxymatrixcompo
sites,since
intension,frac
tureusuallyoccursbefo
reyield.
HDPEPP
humid
dry
PC
PET
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Chapter 6 - 11
Tensile Strength, TS
Metals: occurs when noticeable neckingstarts. Polymers: occurs when polymer backbonechainsare
aligned and about to break.
Adapted from Fig. 6.11,Callister 7e.
y
strain
Typical response of a metal
F= fracture or
ultimate
strength
Neckactsas stress
concentratorengineering
TS
stres
s
engineering strain
Maximum stress on engineering stress-strain curve.
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Chapter 6 - 12
Tensile Strength : Comparison
Si crystal
Graphite/Ceramics/Semicond
Metals/Alloys
Composites/fibers
Polymers
Tensile
st
rength,
TS
(MPa)
PVC
Nylon 6,6
10
100
200300
1000
Al(6061)a
Al(6061)ag
Cu(71500)hr
Ta (pure)Ti (pure)a
Steel (1020)
Steel (4140)a
Steel (4140)qt
Ti (5Al-2.5Sn)aW(pure)
Cu(71500)cw
LDPE
PP
PC PET
20
3040
2000
3000
5000
Graphite
Al oxide
Concrete
Diamond
Glass-soda
Si nitride
HDPE
wood( fiber)
wood(|| fiber)
1
GFRE(|| fiber)
GFRE( fiber)
CFRE(|| fiber)
CFRE( fiber)
AFRE(|| fiber)
AFRE( fiber)
E-glass fibCfibersAramid fib
Room Temp. valuesBased on data in Table B4,
Callister 7e.
a = annealed
hr = hot rolled
ag = aged
cd = cold drawncw = cold worked
qt = quenched & tempered
AFRE, GFRE, & CFRE =
aramid, glass, & carbon
fiber-reinforced epoxy
composites, with 60 vol%
fibers.
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Chapter 6 - 13
Plastic tensile strain at failure:
Adapted from Fig. 6.13,
Callister 7e.
Ductility
Another ductility measure: 100xA
AARA%
o
fo-
=
x 100L
LLEL%
oof -=
Engineering tensile strain, e
Engineering
tensile
stress, s
smaller %EL
larger %EL LfAo AfLo
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Chapter 6 - 14
Energy to break a unit volume of material Approximate by the area under the stress-strain
curve.
Toughness
Brittle fracture: elastic energy
Ductile fracture: elastic + plastic energy
very small toughness(unreinforced polymers)
Engineering tensile strain, e
Engineeringtensile
stress, s
small toughness (ceramics)large toughness (metals)
Adapted from Fig. 6.13,
Callister 7e.
8/22/2019 Callister Ch6 Mek Oz
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Chapter 6 - 15
Resilience, Ur
Ability of a material to store energy
Energy stored best in elastic region
If we assume a linear
stress-strain curve this
simplifies to
Adapted from Fig. 6.15,
Callister 7e.
yyr21
U es@
e
es= y dUr0
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Chapter 6 - 16
Elastic Strain Recovery
Adapted from Fig. 6.17,
Callister 7e.
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Chapter 6 - 17
Hardness Resistance to permanently indenting the surface.
Large hardness means:--resistance to plastic deformation or cracking in
compression.
--better wear properties.
e.g.,10 mm sphere
apply known force measure sizeof indent afterremoving load
dDSmaller indentsmean largerhardness.
increasing hardness
mostplastics
brassesAl alloys
easy to machinesteels file hard
cuttingtools
nitridedsteels diamond
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Chapter 6 - 18
Hardness: Measurement
Rockwell No major sample damage Each scale runs to 130 but only useful in range
20-100.
Minor load 10 kg Major load 60 (A), 100 (B) & 150 (C) kg
A = diamond, B = 1/16 in. ball, C = diamond
HB = Brinell Hardness TS(psia) = 500 x HB
TS (MPa) = 3.45 x HB
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Chapter 6 - 19
Hardness: MeasurementTable 6.5
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Chapter 6 - 20
True Stress & StrainNote: S.A. changes when sample stretched
True stress
True Strain
iT AF=s
oiT ln=e e=e
es=s
1ln
1
T
T
Adapted from Fig. 6.16,
Callister 7e.
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Chapter 6 - 21
Hardening
Curve fit to the stress-strain response:
sT =K eT ntrue stress (F/A) true strain: ln(L/Lo)
hardening exponent:n = 0.15 (some steels)to n = 0.5 (some coppers)
An increase in sydue to plastic deformation.
s
e
large hardeningsmall hardeningsy
0sy
1
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Chapter 6 - 22
Stressand strain: These are size-independentmeasures of load and displacement, respectively.
Elasticbehavior: This reversible behavior oftenshows a linear relation between stress and strain.
To minimize deformation, select a material with a
large elastic modulus (Eor G).
Toughness: The energy needed to break a unitvolume of material.
Ductility: The plastic strain at failure.
Summary
Plasticbehavior: This permanent deformationbehavior occurs when the tensile (or compressive)
uniaxial stress reaches sy.
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Chapter 6 - 23
Core Problems:
Self-help Problems:
ANNOUNCEMENTS
Reading: