Ch06 Mechanical Properties

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Chapter6-

1

ISSUEST

OADDRESS...

Stressandstrain:Whataretheyandwh

yare

theyusedinsteadofloadanddeformation?

Elasticbehavior:Whenloadsaresmall,

howmuch

deformationoccurs?Whatmaterialsde

formleast?

Plasticbehavior:Atwhatpointdoespermanent

deformationoccur?Whatmaterialsare

most

resistant

topermanentd

eformation?

Toughnes

sandductility:

Whataretheyandhow

dowemeasurethem?

Chapter6:

M

echanicalProper

ties

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Chapter6-

2

What

ismechanicalproperty?

Mechan

icalPropertiesaredefinedas

deformationinthem

aterialobse

rvedwhenit

is

subjectedtotheexte

rnalforceof

stretching,

compressing,bendin

g,striking.

Factors

effectingme

chanicalpro

perties:

1.Natureoftheappliedload,

e.g.stretching,compressive,shear

2.Magnitudeoftheap

pliedforce

3.Thedur

ation(applicationtime)

e.g.maybelessthana

second,may

extendovera

perio

dofmanyye

ars.

4.Service

temperature

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Chapter6-

3

Importantmech

anicalpr

operties

Strength

Hardnes

s

Ductility

Stiffness

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Chapter6-

4

Elasticmeansreversible!

ElasticDeformatio

n

1.

Initial

2.

Smallload

3.

Unload

F

bonds

stretch

returnto

initial

F

L

inear-

e

lastic

Non-Linear-

elastic

=lfinal-linitial

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Chapter6-

5

Plasticmeanspermanent!

PlasticDeformation(M

etals)

F

linear

elastic

linear

elastic

pla

stic

1.

Initial

2.

Sma

llload

3.

Unload

planes

still

shea

red

Felastic+plastic

b

onds

stretch

&

planes

shear

plastic

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Chapter6-

7

Simpletens

ion:cable

Note:=M

/AcRhere.

CommonStatesofStress

Ao=crosssectional

area(whenunlo

aded)F

F

o

=

FA

o

=

FsA

M

M

A

o

2R

Fs

Ac

Torsion(af

ormofshear):driveshaft

Skilift(photoc

ourtesy

P.M.Anderson)

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Chapter6-

8

(photocourtesyP.M.Anderson)

Can

yonBridge,

LosAlamos,

NM

o

=

FA

Simplecom

pression:

Note:compressive

structuremember

(0

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Chapter6-

10

Tensilestra

in:

Lateralstrain:

Shearstrain

:

Str

ainisalways

dim

ensionless.

EngineeringStrain

90

90-

yx

=x/y

=tan

=

Lo

L=

Lwo

AdaptedfromFig.6.1(a)

and(c),Callister7e.

/2

L/2

Lo

wo

Ine

ngineeringpractice

itis

com

montoconvert

eng

ineeringstraininto

percentstrainorperce

nt

elon

gation

%e

ngineeringstrain=

eng

ineeringstrainx10

0%=

%e

longation

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Chapter6-

11

EN

GINEER

INGSTR

AIN

L

Engineering

stress

Engineering

(normal)strain

=

=

=

=

AF

AF

L

AF

=

=

=

22

L

LAF

=

==22

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Chapter6-

12

S

tress-StrainTesting

Typicalten

siletest

machine

AdaptedfromFig.6.3,C

allister7e.(Fig.6.3istakenfromH.W.

Hayden,W.G.Moffatt,a

ndJ.Wulff,TheStructureandPropertiesof

Materials,Vol.III,MechanicalBehavior,p.2,JohnW

ileyandSons,

NewYork,1965.)

specimen

extensometer

Ty

picaltensile

specimen

Adaptedfrom

Fig.6.2,

Callister7e.

gauge

length

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Chapter6-

13

Lin

earElasticPrope

rties

Modulusof

Elasticity,E:

(alsoknownas

Young'smodulu

s)

Hooke'sLaw:

=E

Linear-

elastic

E

F F

simple

tension

test

ModulusofElasticity

givesanideaabou

t

mate

rialsresistanceto

elasticdeformation

.

UnitsofE:[GPa]or[psi]

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Chapter6-

14

MetalAlloy

ModulusofElasticity,

E(GPa)

Alum

inum

Brass

Copper

Magnes

ium

Nickel

Steel

Titan

ium

Tungsten

69

97

110

45

207

207

107

407

YO

UNG'SM

ODULUS

(E)

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Chapter6-

15

Poisson

'sratio,

Poisson'sratio

,:

Theratiooflateralandaxialstrains.

UnitofPo

issonsratio

():dimensionless

>0.50

densityincreases