Properties of engineering materials

Properties of engineering materials

1. PROPERTIES OF
ENGINEERING
MATERIALS

2. INTRODUCTION
➢Thepracticalapplicationofengineeringmaterialsin
manufacturingengineeringdependsuponthroughknowledgeof
theirparticularpropertiesunderwiderangeofconditions.
➢Theterm“property”isaqualitativeorquantitativemeasureof
responseofmaterialstoexternallyimposedconditionslike
forcesandtemperature.
➢However,therangeofpropertiesfoundindifferentclassesof
materialsisverylarge.

3. CLASSIFICATION OF MATERIAL
PROPERTY:
Materialsproperties
Mechanical
thermal
opitcal
physical
magnetic
chemical
technological
electrical

4. MECHANICAL PROPERTIES:
➢Thepropertiesofmaterialsthatdeterminesitsbehaviourunderapplied
forcesarecalledmechanicalproperties.
➢Theyareusuallyrelatedtotheelasticandplasticbehaviourofthe
material.
➢Thesepropertiesareexpressedasthefunctionofstress-strain.etc
➢Asoundknowledgeofmechanicalpropertiesofmaterialsprovidesthe
basisforpredictingbehaviourofmaterialsunderdifferentload
conditionsanddesigningthecomponentsoutofthem.

5. CLASSIFICATION OF
MECHANICALPROPERTIES:
1)ELASTICITY
2)PLASTICITY
3)TOUGHNESS
4)RESILIENCE
5)TENSILESTRENGTH
6)YIELDSTRENGTH
7)IMPACTSTRENGTH
8)DUCTILITY
9)HARDNESS
10)FATIGUE
11)CREEP
12)WEARRESISTANCE

6. STRESS-STRAIN
➢Experienceshowsthatanymaterialssubjectedtoaloadmayeitherdeform,
yieldorbreak,dependingupon-
❑Themagnitudeofload
❑Natureofthematerial
❑Crosssectionaldimension
➢Theengineeringstressandstrainarebasedontheoriginalsampledimension
whichchangesduringtest.
➢Truestressandstrainonotherhandbasedonactualorinstantaneous
dimensionsandarebetterrepresentationofdeformationbehaviourofthe
material.

7. Engineeringstressandstraincurveisbasedonoriginalarea,itdescendsafter
maximumloadastheloadbearingcapacityofsampledecreaseduetoreductionin
area.
Truestress-straincurve,continuetogouptillfractureasitisbasedonactualarea
Truestress-strain
curve
Engineering stress –straincurve

8. ELASTICITY
➢Thepropertyofmaterial by virtue of which deformation caused by applied
loads disappears upon removal ofload.
➢Elasticity of the material is the power of coming back to its original position after
deformation when the stress or loadis removed.

9. ➢Thephysicalreasonsforelasticbehaviorcanbequitedifferentfor
differentmaterials.Inmetals,theatomiclatticechangessizeand
shapewhenforcesareapplied(energyisaddedtothesystem).
Whenforcesareremoved,thelatticegoesbacktotheoriginal
lowerenergystate.
➢Inengineering,theamountofelasticityofamaterialisdetermined
bytwotypesofmaterialparameter.
➢Thefirsttypeofmaterialparameteriscalledamodulus,which
measurestheamountofforceperunitarea(stress)neededto
achieveagivenamountofdeformation.Theunitsofmodulusare
pascals(Pa).
➢Ahighermodulustypicallyindicatesthatthematerialisharderto
deform.

10. ➢Thesecondtypeofparametermeasurestheelasticlimit.The
limitcanbeastressbeyondwhichthematerialnolonger
behaveselasticanddeformationofthematerialwilltakeplace.
➢Ifthestressisreleased,thematerialwillelasticallyreturntoa
permanentdeformedshapeinsteadoftheoriginalshape.

11. PLASTICITY:
➢Theplasticityofamaterialisitsabilitytoundergosomedegreeof
permanentdeformationwithoutruptureorfailure.
➢Plasticdeformationwilltakeonlyaftertheelasticlimitisexceeded.
➢It increases with increase intemperature.

12. STRESS-STRAIN CURVE FOR SHOWS
ELASTICITYAND PLASTICITY FOR
MATERIALS:

13. DUCTILITY:
➢Itistheabilityofamaterial to undergo plastic
➢deformationwithoutfracture.
➢Example:Mild steel is ductilematerial.

14. ➢Thereare twocommonmeasureofductility:-
1). Percentage elongation:
% elongation describes the extent to which specimen structure beforerepture.
% elongation=Lf-Lo/Lo*100 where,
Lf=final gaugelength
Lo = initial gaugelength

15. 2).Percentagereduction:
%reductionisameasure%changeincrosssectionalareaatpointoffracture
beforeandafterthetest.
% reduction=Af-Ao/Ao*100 where,
Af= final cross sectional area Ao= initial cross
sectionalarea

16. ➢Theamountofductilityisanimportantfactorwhenconsidering
formingoperationssuchasrollingandextrusion.Ductilityisalso
usedaqualitycontrolmeasuretoassessthelevelofimpuritiesand
properprocessingofamaterial.
➢Forductilematerial,breakingstrengthislessthanUTS,and
neckingprecedesfracture.
➢Forbrittlematerial,fractureusuallyoccurbeforeneckingand
possiblybeforetheonsetofplasticflow.

17. TOUGHNESS
➢Toughnessistheabilityofthematerialtoabsorbenergyduringplastic
deformationuptofracture.
➢.Amaterialwithhighstrengthandhighductilitywillhavemore
toughnessthanamaterialwithlowstrengthandhighductility.
➢Toughness is a good combination of strength andductility.
➢onewaytomeasuretoughnessisbycalculatingtheareaunderthestress
straincurvefromatensiletest.Thisvalueissimplycalled“material
toughness”andithasunitsofenergypervolume.
➢Materialtoughnessequatestoaslowabsorptionofenergybythe
material.

18. Several variables that have a profound influence on the toughnessof a
material:-
1).Strainrate-metalmaypossesssatisfactorytoughnessunderstatic
loadsbutmayfailunderdynamicloadsorimpact.toughnessdecreaseasthe
rateofloadingincreases.

19. 2)Temperature:-Temperatureisthesecondvariabletohaveamajor
influenceonitstoughness.Astemperatureislowered,theductilityand
toughnessalsodecrease.
3)Notcheffect:-Thethirdvariableistermednotcheffect,hastoduewith
thedistributionofstress.Amaterialmightdisplaygoodtoughnesswhen
theappliedstressisuniaxial.
➢Twoofthetoughnesspropertiesthatwillbediscussedinmoredetail
are:-
1).Impacttoughness-Theimpacttoughnessofamaterialcanbe
determinedwithaCharpytest.
➢Impacttestscontinuetobeusedasaqualitycontrolmethodtoassess
notchsensitivityandforcomparingtherelativetoughnessof
engineeringmaterials.

20. ➢Toughnessisgreatlyaffectedbytemperature,aCharpytestis
oftenrepeatednumeroustimeswitheachspecimentestedata
differenttemperature.
FIG-CHARPYTESTER

21. ➢Thisproducesagraphofimpacttoughnessforthematerialasa
function oftemperature.
➢Itcanbeseenthatatlowtemperaturesthematerialismorebrittle
andimpacttoughnessislow.Athightemperaturesthematerialis
moreductileandimpacttoughnessishigher.
➢Thetransitiontemperatureistheboundarybetweenbrittleand
ductilebehaviorandthistemperatureisoftenanextremely
importantconsiderationintheselectionofamaterial.

22. 2).Notch-Toughness:
➢Notchtoughnessistheabilitythatamaterialpossessestoabsorbenergy
inthepresenceofaflaw.
➢Notch-toughnessismeasuredwithavarietyofspecimenssuchasthe
CharpyV-notchimpactspecimenorthedynamicteartestspecimen.
➢impacttestingthetestsareoftenrepeatednumeroustimeswithspecimens
testedatadifferenttemperature.
➢Withthesespecimensandbyvaryingtheloadingspeedandthe
temperature,itispossibletogeneratecurvessuchasthoseshowninthe
graph.
➢Thematerialdevelopsplasticstrainsastheyieldstressisexceededinthe
regionnearthecracktip.

23. ➢Theamountofplasticdeformationisrestrictedbythe
surrounding material, which remains elastic.When a materialis
fromdeformingplastically,itfailsinabrittleprevented
manner.

24. It is the property of a metal, which gives it the ability to resist being
permanently deformed when a load isapplied.
The greater the hardness of the metal, the greater resistance against the
deformation.
Hardness:

25. Various hardeningprocess
❖Hall-Petch strengthening (Grainboundary)
❖Workhardening
❖Solid solutionstrengthening
❖Precipitationhardening
❖Martensitictransformation

26. MEASUREMENT
METHODS
❖Rockwell hardnesstest
❖Brinell hardnesstest
❖Vickers hardnesstest
❖Knoophardness
❖Shore
❖Mohstest
❖Barcol hardnesstest

27. HARDNESS DEPENDS ON
❖Ductility
❖Elasticstiffness
❖Plasticity
❖Strain
❖Toughness
❖Viscosity

28. FATIGUE
Metalfatigueistheprogressiveandlocalizedstructuraldamagethatoccurs
whenamaterialissubjectedtocyclicloadings.
Thehigheststressthatamaterialcanwithstandforaninfinitenumberof
cycleswithoutbreakingcalledalsoendurancelimit
Thegreatertheappliedstressrange,theshorterthelife.

29. CREEP
The tendency of a solid material to deform permanently under
the influence of mechanical stresses.
Itcanoccurasaresultoflong-termexposuretohighlevelsof
stressthatarestillbelowtheyieldstrengthofthematerial.
Creep is more severe in materials that are subjected to heat for
long periods, and generally increases as they near their melting
point.

30. INFLUENCINGFACTORS
❖Diffusion
❖Dislocation
❖Temperature
❖Stress

31. WEAR
Wear is related to interactions between surfaces and specifically the
removal and deformation of material on a surface as a result of
mechanical action of the oppositesurface.

32. CLASSIFICATIONOF WEAR
1)Adhesivewear
2) Abrasivewear
3)Surfacefatigue
4)Frettingwear
5)Erosivewear
6)Corrosive and oxidationwear