Material Properties 1

8/11/2019 Material Properties 1

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Institute of Air Safety-PAF TI-2-SJ

In the name of ALLAH,

the most gracious, the

most merciful


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Institute of Air Safety-PAF TI-2-SJ2

O my Lord! expand me my chest; Ease my task for me; and

Remove the impediment from my speech,

So they may understand what I say.


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Institute of Air Safety-PAF MF-2-IB

MATERIAL

PROPERTIES


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Classification of Materials

Metals and Alloys Ceramic, Glass, and Glass-ceramics

Polymers (plastics) and Thermoplastics

Semiconductors

Composite Materials


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Types of Loadings

Tensile Loading Compressive Loading

Shear Loading

Torsion Loading Tension Compression

Shear

Torsion


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Stress

A stress is a measure of the force in acomponent relative to the cross-sectional

area over which the force is applied.

= Force per unit area

F

A

s= F/A(units: N/m2or Pascal (Pa), psi)


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Strain

Strain is a measure of deformation (either elastic or

permanent).

= Change in length per unit original length

e= L / L0



Important Properties of Material

Strength

Elasticity

Ductility Hardness

Resilience

Toughness

Creep



Tensile Test

The most common way to assess the mechanical

property of a material (strength and ductility) is the

tensile testwhich measures the resistance of material to

a static or slowly applied force.

(b)



Sequence of Events of a Tensile-

Test Specimen

(a) Early stage of necking(b) Small voids begin to form within the necked region;

(c) Voids coalesce, producing an internal crack;(d) Rest of the cross-section begins to fail at the periphery,

by shearing(e) Final fracture surfaces, known as cup- (top fracture

surface) and cone- (bottom surface) fracture.



Tensile Test Machine



Tensile Stress-Stain Curve

STRAIN

STRESS

The resulting information is used to plot a graph which iscalled stress strain curve to assess strength and

deformability



Elastic Deformation

Associated with stretching

but not breaking the

chemical bonds between

atoms in a solid

Elastic deformation is

recovered immediately

upon unloading.

LOAD

UNLOAD



Plastic Deformation

Atoms change neighbors,returning to a stableconfiguration with new

neighbors after thedislocation has passed.

Plastic deformation is notrecoveredupon unloadingand is therefore

permanent.

LOAD

UNLOAD



Elastic Vs Plastic Deformation



Proportional Limit

PROPORTIONAL LIMIT

A

ELASTIC DEFORMATION

Beyond this stress level A:

stress & strain are no longer

proportional to each other.

The metal is no longer completely

elastic.

ELASTICRANGE

STRAIN

STRESS

Elastic Range is the:

Stress up to the proportional limit. The max stress developed which causes no

permanent deformation when the force is

removed.



Modulus of Elasticity

PROPORTIONAL LIMIT

A

ELASTI

CRANGE

ELASTIC DEORMATIOON

STRESS

STRAIN

Slope of the straight line portion

Mod of Elasticity is the ratio b/w

Proportional limit stress and the

corresponding strain.

Tan = E = a/b

MODULUS OF

ELASTICITY

E

a

b



Resilience

PROPORTIONAL LIMIT

A

ELASTI

CRANGE

ELASTIC DEORMATIOON

STRESS

STRAIN

Ability to absorb energy in elastic

range.

Area under the stress strain curve

up to the proportional limit.a

b

RESILIENCE



Yield Stress

YIELD POINT

A

ELASTIC DEORMATIOON

The stress at which rapid increase

in permanent strain occurs.

YIELD

STRESS

STR

ESS

STRAIN


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Ultimate Stress

A

MODULUS OF

ELASTICITY

RESILENCEULTIMATESTRENGTH

The highest engineering stressthat a material can with stand before

fracture.

FRACTURE POINT

PLASTIC RANGE


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Strength

Strength is the ability of a material to

resist stress without failure.


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It is the ability of a material to

return to its original size andshape after removal of a applied

force.

Elasticity


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Ductility

A measure of a materials abilityto be stretched or drawn(plastically)

Measurements: Percent

elongation or reduction inarea

The higher the %elongation,

the more ductile and formablethe material is.

x

% elongation


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Ductile Fracture Surface

ANSI 304 SS

1000x

Microvoids


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Cup-and-cone Fracture in Al


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Brittle

It is opposite to ductility.

Brittle materials don't change

shape readily under load.Normally they fail with little or

no warning.

Examples : - Glass and Concrete etc


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Brittle Fracture


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Brittle Fracture


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Brittle Fracture Surface


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Ductile vs. Brittle Failure

Adapted from Fig. 8.3, Callister 7e.

cup-and-cone fracture brittle fracture


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Comparison of Graph


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Hardness

Hardness is the ability of materialto resist indentation or abrasion.

It is most commonly measured by

the Brinell Test

BRINELL HARDNESS

TESTER


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Resilience

x

YSPL x

Resilience

Amount of energy necessaryto deform the material to the

proportional limit (PL).

The resistance of a material

to permanent deformation.

= Area under the elastic

portionof the S-S curve.


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Amount of energy necessary to cause fracture

The resistance of a material

to fracture

= Area under the elastic and

plastic portions of the S-S

curve.

Unit = N.m/m3, Joule/m3(energy per unit volume of material)

PL xx

YS

Toughness

Toughness


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Creep

Creep is that property whichcauses some material under

stress to deform slowly but

progressively over a period

of time.

It is Time-dependent

inelastic deformation.

(c)2003 Brooks/Cole, a division of Thomson Learning, Inc.

Thomson Learningis a trademark used herein under license.


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Malleability

Malleability is that property of a material that

enable it to undergo great change in shape

without rupture under compressive stress.

For example, copper, aluminum, or wrought

iron being hammered into various shapes or

steel being rolled into structural shapes orsheets


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Can you find .?

Most brittle material

Compare strength

Yield strength Ultimate strength

Fractural strength

Toughest material

Most resilience

material


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QUESTIONS ?

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Material Properties 1

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