Callister Ch6 Mek Oz

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)


2/23

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


3/23

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


4/23

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


5/23

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


6/23

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.


7/23

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)*


8/23

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.


9/23

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


10/23

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


11/23

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.


12/23

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.


13/23

Chapter 6 - 13

Plastic tensile strain at failure:


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


14/23

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)


Callister 7e.


15/23

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


Callister 7e.

yyr21

U es@

e

es= y dUr0


16/23

Chapter 6 - 16

Elastic Strain Recovery


Callister 7e.


17/23

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


18/23

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


19/23

Chapter 6 - 19

Hardness: MeasurementTable 6.5


20/23

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


Callister 7e.


21/23

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


22/23

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.


23/23

Chapter 6 - 23

Core Problems:

Self-help Problems:

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