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8/20/2019 I.pengujianSifatMekanik

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Pengujian Materials

• Definition - normal load, shear load

- tension, compression

- stress, strain

• Stress and Strain Diagram• Material Characteristics

- ductility

- brittleness

- toughness - transition temperature

- endurance limit


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• Normal Load (Axial load) : Load is perpendicular to the

supporting material

! Tension Load : As the ends of material are pulled apart

to ma"e the material longer# the load is called a tension

load

! Compression Load : As the ends of material are pushed in to ma"e the material smaller# the load is called

a compression load

Tension

Compression

5.1 Classifying Load


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• Shear Load : $angential load

5.1 Classifying Load (cont)

pulling apart

Pressure

Cargo


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5.2 Stress and Strain

%n order to compare materials# &e must ha'e measures

• Stress : load per unit Area

A

Fσ =

F : load applied in pounds

A : cross sectional area in in²

: stress in psiσ

A

F F


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5.2 Stress and Strain (cont)

• Strain :! Ratio of elongation of a material to the original length

- unit deformation

oL

e

ε =

e : elongation (ft

Lo : unloaded(original length of a material (ft

: strain (ft!ft or (in!in

ε Elongation

oLLe −=

L : loaded length of a material (ft

Lo e

L


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"ald#in $ydraulic %achine for &ension ' Compression test


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5.3 Stress-Strain Diagram

• A plot of Strain 's Stress

•$he diagram gi'es us the eha'ior of the material and

material properties

• ach material produces a different stress!strain

diagram


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5.3 Stress-Strain Diagram

Strain ( ) (eLo)

)

*

+

S t r e s s

( F A )

lastic

*egion

Plastic

*egion

Strain

+ardening ,racture

ultimatetensilestrength

S l o

p e -

!

lastic region

slope./oung0s(elastic modulus

yield strength

Plastic region ultimate tensile strength

strain hardening

fracture

nec1ing

yieldstrength

2&3σ

yσ

ε!σ =

ε

σ! =

ε 12

y

ε ε

σ

!−

=


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A+4 3teel

3tress and 3train 5iagram


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5.3 Stress-Strain Diagram (cont)

• !lasti" #egion (Point . /0)

! $he material &ill return to its original shape

after the material is unloaded( li"e a ruer and)

! $he stress is linearl1 proportional to the strain in

this region

ε!σ =

: Stress(psi)

! : Elastic modulus (Young’s Modulus) (psi)

: Strain (in2in)

σ

ε

- Point 0 : 3ield Strength : a point at &hich permanent

deformation occurs ( %f it is passed# the material &ill

no longer return to its original length)

ε

σ! =or


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• $lasti" #egion (Point 0 /4)

! %f the material is loaded e1ond the 1ield strength#

the material &ill not return to its original shape

after unloading

! %t &ill ha'e some permanent deformation

! %f the material is unloaded at Point 4# the cur'e &ill

proceed from Point 4 to Point 5 $he slope &ill ethe as the slope et&een Point . and 0

! $he distance et&een Point . and 5 indicates the

amount of permanent deformation



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• Strain %ardening

! %f the material is loaded again from Point 5# the

cur'e &ill follo& ac" to Point 4 &ith the same

Elastic Modulus(slope)

! $he material no& has a higher 1ield strength of

Point 5

! *aising the 1ield strength 1 permanentl1 straining the material is called Strain Hardening.



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• &ensile Strengt' (Point 4)

! $he largest 'alue of stress on the diagram is called

Tensile Strength(TS) or Ultimate Tensile Strength

(UTS)

! %t is the maximum stress &hich the material can

support &ithout rea"ing

• Fra"tre (Point 6)

! %f the material is stretched e1ond Point 4# the stress decreases as nec"ing and non!uniform deformation

occur

! ,racture &ill finall1 occur at Point 6



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5. *aterial $ro+erties

• Strength

• +ardness

• Ductilit1

• 7rittleness

• $oughness

Characteristics of Material are descried as


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1) Strengt'

! Measure of the material propert1 to resist deformation

and to maintain its shape

! %t is 8uantified in terms of 1ield stress or ultimate tensilestrength

! +igh caron steels and metal allo1s ha'e higher strength

than pure metals

! Ceramic also exhiit high strength characteristics


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2) %ardness ! Measure of the material propert1 to resist indentation#

arasion and &ear

! %t is 8uantified 1 hardness scale such as *oc"&ell and

7rinell hardness scale

! +ardness and Strength correlate &ell ecause oth

properties are related to in!molecular onding


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3) D"tility

! Measure of the material propert1 to deform efore failure

! %t is 8uantified 1 reading the 'alue of strain at the

fracture point on the stress strain cur'e

! xample of ductile material :

lo& caron steel

aluminum

ule gum


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) ,rittleness

! Measure of the material9s inabilit to deform efore failure

! $he opposite of ductilit1

! xample of ductile material : glass# high caron steel#

ceramics

D"tile

,rittle

S t r e s

s

Strain


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5) &og'ness - Measure of the material ailit1 to asor energ

- %t is measured 1 t&o methods

a) %ntegration of stress strain cur'e

! Slo& asorption of energ1

- Asored energ1 per unit 'olume

unit : (l2in) ;(in2in) -l


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- Charp1 >!Notch $est


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• Charp1 >!Notch $est (continued)

! $he potential energ1 of the pendulum efore and after

impact can e calculated form the initial and final location

of the pendulum

! $he potential energ1 difference is the energ1 it too" to

rea" the material asored during the impact

! Charp1 test is an impact toughness measurement test

ecause the energ1 is asored 1 the specimen 'er1

rapidl1

" Purpose : to e#aluate the impact toughness as a $unction o$

temperature


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&emperature (6F C h a r p

y & o u g h n e s s (

l b 7 i n

"rittle

"eha8ior

5uctile

"eha8ior

&ransition

&emperature



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- At lo& temperature# &here the material is rittle and

not strong# little energ1 is re8uired to fracture the material

- At high temperature# &here the material is more ductileand stronger# greater energ1 is re8uired to fracture the

material

-$he transition temperature is the oundar1 et&een rittle

and ductile eha'ior

$he transition temperature is an extremel1 important

parameter in selection of construction material



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$igh Carbon 3teel

Charpy &est

3tainless 3teel


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) Fatige


• $he repeated application of stress t1picall1 produced 1

an oscillating load such as 'iration

• Sources of ship 'iration are engine % propeller and &a#es

C1cles N at ,atigue ,ailure

S t r

e s s

( p

s i

) Steel

Alminm

ndurance Limit : A certain threshold

stress &hich &ill not cause the fatigue

failure for the numer of c1cles

Aluminum has no endurance limit


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Fa"tors effe"ting *aterial $ro+erties


• $emperature :

%ncreasing temperature &ill decrease

! Modulus of lasticit1

! 3ield Strength

! $ensile Strength

Decreasing temperature &ill:

! %ncrease ductilit1

! *educe rittleness• n'ironment

! Sulfites# Chlorine# ?x1gen in &ater# *adiation

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