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PhysicalPropertiesofMaterials QUALITATIVEPROBLEMS
3.13 WhatisthefundamentaldifferencebetweenmechanicalpropertiesofmaterialsdiscussedinChapter2,andphysicalpropertiesofmaterials,described inthischapter?
Mechanicalpropertiesarestrengthandelasticmodulus;physicalpropertiesincludedensity,magneticproperties,meltingpointandspecificheat.Abasicdifferenceisthat,given thechemistryofamaterial,thephysicalpropertiesareessentiallyconstant,whilethe mechanicalpropertiescanbechangedduetothemanufacturingstrategyused.
3.14 Describethesignificanceofstructuresandmachinecomponentsmadeoftwo materialswithdifferentcoefficientsofthermalexpansion.
Thestructuralfitofthemachinecomponentswilldependonthethermalexpansion coefficient.Forinstance,iftwomaterialswithdifferentthermalexpansioncoefficientsare assembledtogetherbysomemeansandthenheated,thestructurewilldevelopinternal stressesduetounevenexpansion.Ifthesestressesarehighenough,thestructurewill warp,bend,orbuckleinordertobalanceorrelievethestresses;itwillpossiblyretain someinternal(residual)stressesaswell.Ifpreventedfromwarping,thestructurewill develophighinternalstresseswhichcanleadtocracks.Thisisnotalwaysdetrimental; shrinkfitsaredesignedrecognizingthatmaterialsmayhavedifferentcoefficientsof thermalexpansion,andsomemachineelementssuchasthermocouplesandtemperature probesarebasedonamismatchofthermalexpansioncoefficients.
3.15 Whichofthepropertiesdescribedinthischapterareimportantfor(a)pots andpans,(b)cookiesheetsforbaking,(c)rulers,(d)paperclips,(e)music wire,and(f)beveragecans?Explainyouranswers.
i.Potsandpans:Theserequireahighmeltingpointsothattheydon’tchangephase duringuse;theyshouldbecorrosionresistant,cleanableinwatersolutions,and haveahighthermalconductivity.Therequirementsaresimilartoacookiesheet describednext.
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ii.Cookiesheet:Requirescorrosionresistanceathightemperatures,thespecificheat shouldallowforrapidheatingofthesheet,andahighthermalconductivityshould allowforevendistributionofheatacrossthesheet.Themeltingtemperatureshould behighenoughthatthesheetcansafelywithstandbakingtemperatures.
iii.Ruler:Shouldhavelowthermalexpansiontomaintainthemeasurementsaccurately andalowdensitytomakeiteasytocarry.
iv.Paperclip:Shouldbecorrosionresistant,withastiffnessthatholdspaperstogether withoutrequiringexcessiveforce.
v.Musicwire:Musicwire,asusedforguitars,ispreloadedtoaveryhightensionin ordertoachievedesiredresonance.Assuch,itshouldhaveaveryhighstrengthand thepropercombinationofstiffnessanddensitytoachievetheproperacoustics.
vi.Beveragecan:Shouldhaveahighthermalconductivity,lowdensity,andgood corrosionresistance.
3.16 NoteinTable3.1thatthepropertiesofthealloysofmetalshaveawide rangecomparedwiththepropertiesofthepuremetals.Explainwhy.
Alloyingelementstendtodisturbthecrystallatticeofthebasemetal,andtheydosoby distortingthelatticebyoccupyinglatticesites(substitutionalatoms),spacesbetween latticesites(interstitials),orformingasecondphase(anintermetalliccompoundofthe twoelements).Latticedistortionwillreducepropertiesthatdependonarepeating lattice,suchasthermalconductivityandmeltingpoints.Propertiessuchasdensity andspecificheatgenerallydependonthepropertiesofthealloyingelements,andrange aroundthevalueforthealloybasemetal.Also,‘alloys’isagenericterm,andcaninclude averywiderangeofconcentrationandtypesofalloyingelement,whereaspuremetals have,bydefinition,onlyonechemistry.
3.17
Rankthefollowinginorderofincreasingthermalconductivity:aluminum, copper,silicon,titanium,ceramics,andplastics.Commentonhowthisrankinginfluencesapplicationsofthesematerials.
ThermalconductivitydataiscontainedinTable3.1onp.89.Thesematerials,inorderof increasingthermalconductivity,arerankedplastics(0.1-0.4W/mK),ceramics(10-17), titanium(17),aluminum(222),copper(393).Thisrankingshowswhymaterialssuch asaluminumandcopperareusedasheatsinkmaterials,andwhypolymersareusedas ainsulator.Titaniumandceramicmaterials,havinganintermediatevalueofthermal conductivity,aresuitableforneitherinsulationorheatdissipation,andthereforedonot havemanythermalapplications.
3.18 Doescorrosionhaveanybeneficialeffects?Explain.
Corrosionisthoughtofmainlyasadetrimentalphenomenon.However,suchmanufacturingprocessesaschemicalmachiningandchemicalmechanicalpolishingrelyon corrosioneffects.Also,tosomeextent,cleaningofsurfacesreliesoncorrosion.
3.19 Explainhowthermalconductivitycanplayaroleinthedevelopmentof residualstressesinmetals.
Thermalconductivityisoneofthemostimportantmaterialpropertiesaffectingthermal stress(alongwiththermalexpansion).Intermsofresidualstresses,itismuchless importantthantheprocessinghistory.However,unevencoolingofcastings(PartII)or welds(PartVI),forexample,cancausewarpageandresidualstresses.
PhysicalPropertiesofMaterials 40
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3.20 Whatmaterialpropertiesaredesirableforheatshieldssuchasthoseplaced onthespaceshuttle?
Materialpropertiesrequiredforheatshieldsaresufficientstrengthsothattheydonot failupontakeoff,reentry,andlanding;theymusthaveahighmeltingpointsothatthey donotchangephaseordegradeatthehightemperaturesdevelopedduringreentry,and theymustbeexceptionallyhighthermalinsulatorssothattheshuttlecabindoesnot heatsignificantlyduringreentry.
3.21 Listexamplesofproductswherematerialsthataretransparentaredesired. Listapplicationsforopaquematerials.
Thisisanopen-endedproblem,andstudentsshouldbeencouragedtodeveloptheirown examplesbasedontheirinsightsandexperiences.Thefollowingareexamplesofproductswheretransparencyisdesired:windowsandwindshields,bottles,fluidcontainers (toallowdirectobservationofcontentvolumes),wrappingandpackaging,andglasses (eyewear).Thefollowingareexamplesofproductswhereopacityisdesired:windows inrestrooms(ifpresent),glassinlightbulbstoproduceadiffuselight,foodpackaging toprotectthecontentsfromlightradiationandassociateddegradation,andproduct housingsforaestheticreasons.
3.22 RefertoFig.3.2andexplainwhythetrendsseenaretobeexpected. Thisisanopen-endedproblemandstudentsshouldbeencouragedtodeveloptheir ownobstervations.Thetrendsarenottoosurprisingqualitatively,butthequantitative natureofthetrendsisatfirstverysurprising.Forexample,itisnotsurprisingthat high-modulusgraphiteoutperformssteel,aspeopleareexposedtosportingequipment suchastennisracquetsthataremadeoftheformerbutneverthelatter.However,people don’texpectgraphitetobe14timesbetterthansteel.Anothersurpriseinthetrendsis thepoorperformanceofglassfibersinanepoxymatrix.However,glassisprettydense, soweightsavingsarenotgenerallythereasonsforusingglassreinforcement.
3.23 Twophysicalpropertiesthathaveamajorinfluenceonthecrackingofworkpieces,tools,ordiesduringthermalcyclingarethermalconductivityand thermalexpansion.Explainwhy.
Crackingresultsfromthermalstressesthatdevelopinthepartduringthermalcycling. Thermalstressesmaybecausedbothbytemperaturegradientsandbyanisotropyof thermalexpansion.Highthermalconductivityallowstheheattobedissipatedfaster andmoreevenlythroughoutthepart,thusreducingthetemperaturegradient.Ifthe thermalexpansionislow,thestresseswillbelowerforagiventemperaturegradient. Whenthermalstressesreachacertainlevelinthepart,crackingwilloccur.Ifamaterial hashigherductility,itwillbeabletoundergomorebyplasticdeformationbeforepossible fracture,andthetendencyforcrackingwillthusdecrease.
3.24
Whichofthematerialsdescribedinthischapterhasthehighest(a)density, (b)electricalconductivity,(c)thermalconductivity,(d)specificheat,(e) meltingpoint,and(f)cost.
AscanbeseenfromTable3.1onp.89,thehighestdensityisfortungsten,andthe highestelectricalconductivityandthermalconductivityinsilver.Thehighestspecific heatisforMonelK-500at1050MPa,andthehighestcost(whichvariesfromtimeto time)isusuallyisassociatedwithsuperalloys.
PhysicalPropertiesofMaterials 41
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3.25
Whichpropertiesdescribedinthischaptercanbeaffectedbyapplyinga coating?
Acoatingcanaffectthedensityifthecoatingisverylarge,itcanaffecttheelectrical, magneticandopticalpropertiesasdiscussedinSection3.7,anditcanaffectthethermal conductivity(Section3.6)and,especially,corrosionresistance(Section3.8).
QUANTITATIVEPROBLEMS
3.26
Ifweassumethatalltheworkdoneinplasticdeformationisconvertedinto heat,thetemperatureriseinaworkpieceis(1)directlyproportionaltothe workdoneperunitvolumeand(2)inverselyproportionaltotheproductof thespecificheatandthedensityoftheworkpiece.UsingFig.2.5,andletting theareasunderthecurvesbetheunitworkdone,calculatethetemperature risefor(a)8650steel,(b)304stainlesssteel,and(c)1100-H14aluminum. WeusethefollowinginformationgiveninChapters2and3:Theareaunderthetrue stress-truestraincurveandthephysicalpropertiesforeachofthethreemetals.We thenfollowtheprocedurediscussedonp.62anduseEq.(2.16)onp.81.Thus,for(a) 8650steel,theareaunderthecurveinFig.2.5onp.62isabout u =72, 000in-lb/in3 Assumeadensityof ρ =0 3lb/in3 andaspecificheat c =0 12BTU/lb ◦F.Therefore,
∆T = 72, 000 (0 3)(0 12)(778)(12) =214◦F
For(b)304stainlesssteel,wehave u =175, 000, ρ =0 3and c =0 12,hence∆T = 520◦F.For(c)1100-H14aluminum,wehave u =25, 000in.-lb/in3 , ρ =0 0975and c =0 215;hence∆T =128◦F.
3.27 Thenaturalfrequency, f ,ofacantileverbeamisgivenby
f =0.56 EIg wL4 , where E isthemodulusofelasticity, I isthemomentofinertia, g isthe gravitationalconstant, w istheweightofthebeamperunitlength,and L is thelengthofthebeam.Howdoesthenaturalfrequencyofthebeamchange, ifatall,asitstemperatureisincreased?Assumethatthematerialissteel. Let’sassumethatthebeamhasasquarecrosssectionwithasideoflength h.Note, however,thatanycrosssectionwillresultinthesametrends,sostudentsshouldn’t bediscouragedfromconsidering,forexample,circularcrosssections.Themomentof inertiaforasquarecrosssectionis
I = h4 12
Themomentofinertiawillincreaseastemperatureincreases,becausethecrosssection willbecomelargerduetothermalexpansion.Theweightperlength, w,isgivenby
PhysicalPropertiesofMaterials 42
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w = W L
where W istheweightofthebeam.Since L increaseswithincreasingtemperature, theweightperlengthwilldecreasewithincreasingtemperature.Alsonotethatthe modulusofelasticitywilldecreasewithincreasingtemperature(seeFig.2.6onp.63). Considertheratioofinitialfrequency(subscript1)tofrequencyatelevatedtemperature
Simplifyingfurther,
Tocomparetheseeffects,considerthecaseofcarbonsteel.Figure2.6onp.63shows adropinelasticmodulusfrom190to130GPaoveratemperatureincreaseof1000◦C. FromTable3.1onp.89,thecoefficientofthermalexpansionforsteelis14.5 µm/m◦C (averageoftheextremevaluesgiveninthetable),sothatthechangeinfrequencyis:
Thus,thenaturalfrequencyofthebeamdecreaseswhenheated.Thisisageneraltrend (andnotjustforcarbonsteel),namelythatthethermalchangesinelasticmodulusplays alargerrolethanthethermalexpansionofthebeam.
3.28 Plotthefollowingforthematerialsdescribedinthischapter:elasticmodulusversusdensity,yieldstressversusdensity,thermalconductivityversus density.Commentontheimplicationsoftheseplots.
Theplotsareshownbelow,basedonthedatagiveninTables2.2onp.58,and3.1on p.89.Averagevalueshavebeenusedtoobtaintheseplots.
PhysicalPropertiesofMaterials 43
(subscript2): f1 f2 = 0 56 E1I1g w1L4 1 0.56 E2I2g w2L4 2 = E1I1 (W/L1)L4 1 E2I2 (W/L2)L4 2 = E1I1 L3 1 E2I2 L3 2
f1 f2 = E1I1L3 2 E2I2L3 1 = E1h4 1L3 2 E2h4 2L3 a Letting α bethecoefficientofthermalexpansion,wecanwrite h2 = h1 (1+ α∆T ) L2 = L1 (1+ α∆T ) Therefore,thefrequencyratiois f1 f2 = E1h4 1L3 2 E2h4 2L3 1 = E1h4 1L3 1 (1+ α∆T )3 E2h4 1 (1+ α∆T )4 L3 1 = E1 E2 (1+ α∆T )
f1 f2 = E1 E2 (1+ α∆T ) = 190 130[1+(14 5 × 10 6)(1000)] =1.20
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3.29 Itcanbeshownthatthermaldistortioninprecisiondevicesislowforhigh valuesofthermalconductivitydividedbythethermalexpansioncoefficient. RankthematerialsinTable3.1accordingtotheirabilitytoresistthermal distortion.
ThecalculationsusingthedatainTable3.1onp.89areasfollows.Whenarangeof valuesisgivenforanalloy,theaveragevaluehasbeenused.Thesematerialshavebeen rankedaccordingtotheratioofthermalconductivitytothermalexpansioncoefficient.
PhysicalPropertiesofMaterials 44 0 200 400 600 800 1000 1200 0500010,00015,00020,000 Yield stress (MPa) Density (kg/m3) Lead Magnesium Aluminum Copper Stainless steel Nickel Tungsten Titanium Molybdenum Steel 0 50 100 150 200 250 300 350 400 0500010,00015,00020,000 Elastic modulus (GPa) Tungsten Molybdenum Copper Nickel Steel Titanium Density (kg/m3) Aluminum Magnesium Lead 0 50 100 150 200 250 300 350 400 0.11101001000 Elastic modulus (GPa) Molybdenum Copper Nickel Steel Titanium Relative Cost Aluminum Magnesium
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3.30
AddacolumntoTable3.1thatliststhevolumetricheatcapacityofthematerialslisted,expressedinunitsofJ/cm3 -K.Comparetheresultstothevalue forliquidwater(4.184J/cm3 -K).Notethatthevolumetricheatcapacityof amaterialistheproductofitsdensityandspecificheat. Theadditionalcolumniscalculatedasfollows.Notethatoneneedstobecarefulabout keepingconsistentunits.
PhysicalPropertiesofMaterials 45 MaterialThermalThermal k/α conductivity,expansion k coefficient, α Tungsten1664.536.9 Molybdenumalloys1425.127.8 Copper39316.523.8 Silver42919.322.2 Silicon1487.6319.4 Beryllium1468.517.2 Gold31719.316.4 Copperalloys 2341813.0 Aluminum 22223.69.41 Tantalumalloys 54 6.58.31 Aluminumalloys 180237.72 Columbium(niobium)52 7.17.32 Nickel 9213.36.92 Iron 7411.56.43 Magnesium 154265.92 Magnesiumalloys 106264.10 Nickelalloys 3715.52.42 Steels 3314.52.28 Titanium 178.352.04 Leadalloys 3529.11.20 Lead 3529.41.19 Titaniumalloys 10 8.81.14
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SYNTHESIS,DESIGNANDPROJECTS
3.31 ConductaliteraturesearchandaddthefollowingmaterialstoTable3.1: cork,cement,ice,sugar,lithium,graphene,andchromium. Theadditionsareasbelow.Notethatspecificvaluesmaychangedependingonsource cited.
i.Cork:density=193kg/m3,meltingpointisunavailable(corkdoesn’tmelt),specific heat=2000J/kgK,thermalconductivity=0.05W/mK,coefficientofthermal expansion=30-50 µm/m ◦C,electricalresistivityupto1010 Ωcm.
PhysicalPropertiesofMaterials 46 SpecificVolumetricheatRelative Densityheatcapacityvolumetric Material(kg/m3)(J/kgK)(J/cm3 K)heatcapacity Aluminum2700900 2.43 0.58 Aluminumalloys2630-2820880-9202.31-2.590.55-0.62 Beryllium 185418843.49 0.83 Columbium(niobium)8580272 2.33 0.56 Copper 8970385 3.45 0.82 Copperalloys 7470-8940377-4352.81-3.890.67-0.93 Gold 19,300129 2.49 0.59 Iron 7860460 3.61 0.86 Steels 6920-9130448-5023.10-4.580.74-1.09 Lead 11,350130 1.47 0.35 Leadalloys 8850-11,350126-1881.12-2.130.27-0.51 Magnesium 174510251.79 0.43 Magnesiumalloys1770-178010461.85 0.44 Molybdenumalloys10,210276 2.83 0.68 Nickel 8910440 3.92 0.94 Nickelalloys 7750-8850381-5442.95-4.810.70-1.15 Silicon 2330712 1.66 0.40 Silver 10,500235 2.47 0.59 Tantalumalloys 16,600142 2.36 0.56 Titanium 4510519 2.34 0.56 Titaniumalloys4430-4700502-5442.22-2.560.53-0.61 Tungsten 19,290138 2.66 0.64 Zinc 7140385 2.75 0.66 Zincalloys 6640-72004022.67-2.890.64-0.69 Ceramics 2300-5500750-9501.72-5.220.41-1.25 Glasses 2400-2700500-8501.2-2.30.29-0.55 Graphite 1900-22008401.60-1.850.38-0.44 Plastics 900-20001000-20000.9-4.00.21-0.96 Wood 400-7002400-28000.96-1.960.23-0.47
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ii.Cement:density=3120kg/m3,meltingpointisunavailable(cementdoesn’tmelt), specificheat=3300J/kgK,thermalconductivity=0.1W/mK,coefficientof thermalexpansion=7.4-13 µm/m ◦C.
iii.Ice:density=920kg/m3,meltingpointis0C,specificheat=2100J/kgK,thermal conductivity=2W/mK,coefficientofthermalexpansion=50 µm/m ◦C,electrical resistivity=182kΩ-m.
iv.Sugar:density=1587kg/m3,meltingpoint=185◦C,specificheat=1250J/kgK,
v.Lithium:density=535kg/m3,meltingpoint=180◦,specificheat=3582J/kgK, thermalconductivity=84.8W/mK,electricalresistivity=92 8 × 10 9 Ω-m.
3.32 Fromyourownexperience,makealistofparts,components,orproducts thathavecorrodedandhavehadtobereplacedordiscarded.
Bythestudent.Thisisanopen-endedproblemthathavemanypossibleanswers,and thesewillvarydependingonthebackgroundofthestudent.Therearemanyparts, usuallyassociatedwithrustedsteel,e.g.,automobileframesandbodies,bolts,bicycle pedals,etc.Otherpartsthatarecommonlycorrodedincludeautomotivebatterycableterminals,marinepartsofallkinds(especiallyifoceangoing),nameplatesonold machinery,etc.Ifoneextendsthediscussiontocorrosion-assistedfailure,onecanincludejustaboutallpartswhichfailbyfatigue,includingshafts,andairplanefuselages asshownbelow.Thisphotographisadramaticexampleofcorrosion-assistedfatigue ofanaircraftfuselagethatoccurredmid-flight.(
Source: FromHamrock,B.J.,etal., FundamentalsofMachineElements,2nded.,NewYork,McGraw-Hill,2005,p.265.).
3.33 Listapplicationswherethefollowingpropertieswouldbedesirable:(a)high density,(b)lowdensity,(c)highmeltingpoint,(d)lowmeltingpoint,(e) highthermalconductivity,and(f)lowthermalconductivity.
Bythestudent.Thisisanopen-endedproblem,andmanypossibleanswersexist.Some examplesare:
i.Highdensity:Addingweighttoapart(likeananchor,barbellsoraboat),asan inertialelementinaself-windingwatch,andweightsforverticallyslidingwindows. Also,projectilessuchasbulletsandshotgunparticlesareapplicationswherehigh densityisadvantageous.
PhysicalPropertiesofMaterials 47
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ii.Lowdensity:Airplanecomponents,aluminumtubingfortents,ladders,andhighspeedmachineryelements.Mostsportinggoodsgivebetterperformanceifdensity andhenceweightislow,suchastennisrackets,skis,etc.
iii.Highmeltingpoint:Creep-resistantmaterialssuchasforgas-turbinebladesoroven insulation.Moldmaterialsfordiecastingneedtohavehighmeltingpoints,asdo filamentsforlightbulbs.
iv.Lowmeltingpoint:Solderingwire,fuseelements,waxforinvestmentcasting,and lubricantsthatdependonaphasechangeareexamplesofsuchapplications.
v.Highthermalconductivity:Rapidextractionofheatinradiatorsandheatexchangers,andcoolingfinsforelectricalcircuitsandtransformers.Cuttingtoolswithhigh thermalconductivitycanhelpkeeptemperatureslowinmachining.Diesininjectionmoldingwithhighthermalconductivitycanextractheatmorequicklyallowing higherproductionrates.
vi.Lowthermalconductivity:Coffeecups,winterclothing,andoveninsulationrequire lowthermalconductivity.Inaddition,handlesoncookware,lubricantsforhot forging,andthermosmaterials(unlessevacuated)needlowthermalconductivities.
Bythestudent.Thisproblemisopen-endedandthestudentsshouldbeencouragedto developanswersbasedontheirexperienceandtraining.Twoexamplesare:(a)Tent tubing:requireslightweightmaterialforeaseofcarrying,whilepossessingsufficiently highstrengthandstiffnesstosupporttheweightofthetenttarpwithoutexcessive bendingorbowing.(b)Racquetballortennisracquet:requireslightweightmaterial forcontrolovertheracquet’sdirection;also,highstrengthandstiffnessarerequiredto efficientlytransfertheenergyoftheracquettotheball.
3.35 Designseveralmechanismsorinstrumentsbasedonutilizingthedifferences inthermalexpansionofmaterials,suchasbimetallicstripsthatdevelopa curvaturewhenheated.
Bythestudent.Instrumentswillhaveacommonprincipleofmeasuringorregulating temperaturessuchasthermometersorbutterflyvalveswhichregulatefluidflowwhen temperaturesvary.
3.36 ForthematerialslistedinTable3.1,determinethespecificstrengthand specificstiffness.Describeyourobservations.
Selectedresultsareasfollows(thevalueswhichgivehighestpossiblequantitieshave beenused,e.g.,highstiffnessandlowdensity).DataistakenfromTable2.2onp.58.
PhysicalPropertiesofMaterials 48
3.34 Describeseveralapplicationsinwhichbothspecificstrengthandspecific stiffnessareimportant.
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3.37
Themaximumcompressiveforcethatalightweightcolumncanwithstand beforebucklingdependsontheratioofthesquarerootofthestiffnesstothe densityforthematerial.ForthematerialslistedinTable2.2,determine(a) theratiooftensilestrengthtodensityand(b)theratioofelasticmodulusto density.Commentonthesuitabilityofeachforbeingmadeintolightweight columns.
ThisproblemusestheresultsfromProblem3.36.Tomakealightweightcolumn,one hastomaximizethespecificstrengthandthespecificstiffness.Reviewingthevalues obtained,onecanobservethat:(a)Puremetalsarenotusefulwhereasalloysaremuch morepreferable;(b)Titaniumalloyshavethehighestspecificstrength(31,700m);(c) Aluminumalloyshavethehighestspecificstiffness(3.1);and(d)Amongthelestdesirable materialsareleadandcopper.Notethattheseresultsareconsistentwiththematerials ofchoiceformodernaircraft.
3.38 DescribepossibleapplicationsanddesignsusingalloysexhibitingtheInvar effectoflowthermalexpansion.
Bythestudent.Ifthereisessentiallynothermalexpansion,thematerialisexceptional forsituationswherethermalfatigueisaconsideration,orforprecisioninstrumentswhere nothermalexpansionwouldbehighlydesirable.Examplesoftheformerincludefurnace sensorsandelectricalcomponents,andexamplesofthelatterincludemicromanipulators andmicro-electromechanicalsystems(MEMS);seeCh.29.
3.39 Collectsomepiecesofdifferentmetallicandnonmetallicmaterialslistedin Table3.2.Usingsimpletestsand/orinstruments,determinethevalidityof thedescendingorderofthephysicalpropertiesshowninthetable.
Bythestudent.Thisisagoodprojectforstudents,andsomedifferencesinthetrends canbeobserveddependingonthealloy,itssource,andamountofcoldwork,heat treatingorannealingithasundergone.
PhysicalPropertiesofMaterials 49 Material YE DensitySpec.strengthSpec.stiffness (MPa)(GPa)(kg/m3)(m ×103)(m ×106) Aluminum356927001.3 2.6 Alalloys55079263021.3 3.1 Copper7610589700.86 1.2 Cualloys1100150747015.0 2.05 Iron20519078602.66 2.5 Steels1725200692025.4 2.9 Lead141411,3500.13 0.126 Pballoys141488500.161 0.16 Magnesium1304117457.6 2.4 Mgalloys30545177017.6 2.6 Moalloys207036010,21020.7 3.6 Nickel10518089101.2 2.06 Nialloys1200214775015.8 2.8 Titanium3448045107.8 1.8 Tialloys1380130443031.7 3.0 Tungsten55035019,2902.9 1.8
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3.40 Designanactuatortoturnonaswitchwhenthetemperaturedropsbelowacertainlevel.Usetwomaterialswithdifferentcoefficientsofthermal expansioninyourdesign.
Thisisanopen-endedproblemwithalargenumberofacceptableanswers.Thethermal expansioneffectcanbeusedtodeformacantilever,forexample,toactuateaswitch. Alternatively,twomaterialsthatarelongandthincanbeweldedattheirends.They canthenbewrappedaroundamandrel,sothatafterelasticrecoverytheytakeonthe shapeofaspiral.Theangulardisplacementoftheendsvarieswithtemperature;apeg attachedtooneendwhilefixingtheotherwillturnonaswitchassoonasthepeg translatestoanotherpeginaretainingfixture.Thisprincipalwasusedtogreatsuccess incarburatorsinautomobilesbeforethe1980sinordertoachieveproperair/fuelratios asfunctionsoftemperature.
3.41 ConductanInternetandtechnicalliteraturereviewandwriteaone-page paperhighlightingapplicationsofpiezoelectricmaterials.
Bythestudent.Piezoelectricmaterialsarewidelyusedasactuatorsandresonators, especiallyatsmallscale,andforsensorssuchaspressuremeasuringsensors.Piezoelectric materialscanbeappliedascoatingsandindesiredshapesformemosdevicesaswell.
3.42 Ithasbeenwidelyreportedthatmechanicalpropertiessuchasstrengthand ductilitycanbeverydifferentformicro-scaledevicesthanaremeasuredat normallengthscales.Explainwhetherornotyouwouldexpectthephysical propertiesdescribedinthischaptertobescaledependent.
Sincenanomaterialshavefinestructure,theyhaveveryhighstrength,hardness,and strength-to-weightratioscomparedtotraditionalmaterials.However,physicalpropertiesarenotasscaledependent.Thatis,amaterial’sdensityisthesameatlargeand smalllengthscales.Thereisalimittothis,ofcourse-avolumeoftenatomswithone vacancyhasalowerdensitythanalargevolumewherethevacanciesarenotingeneral 10%ofthevolume.Studentsshouldbeencouragedtoobtainestimatesofmicroand nanoscalevaluesandcomparethemtovaluessuchasinTable3.1.
3.43 Ifyouweregivenametal(notanalloy)andaskedtoidentifyit,list(in order)theexperimentsormeasurementsyouwouldperform.Explainwhat influencetheshapeofthemetalwouldhaveonyourprioritization.
Bythestudent.Thisisanoutstandingproblemforagroupassignment.Studentsshould beencouragedtodevelopasmanytestsaspossible.Somestudentswillimmediatelyturn tothemostadvancedmethodspossible-chromatography,forexample.However,they shouldbeencouragedtothinofsimplertests-measuringdensity,forexample.Simple, inexpensivetestscanbepreferredoverelaboratetestswithexpensiveequipment.For example,atensiontestcanproducealotofdatathatcanbeusedtoestimateamaterial class.StudentsshouldconsidermechanicalpropertiesfromChapter2andphysical propertiesfromthischapterascharacteristicsthatcandifferentiatematerials.
PhysicalPropertiesofMaterials 50
© 2014 Pearson Education, Inc. Upper Saddle River, NJ. All rights reserved. This publication is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited reproduction ,storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to : Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458. Manufacturing Engineering and Technology 7th Edition Kalpakjian Solutions Manual Visit TestBankDeal.com to get complete for all chapters