exercises-exerciseswithworkedsolutions-ma-uoc-en

M.F.Ashby20101©M.F.Ashby,2010ForreproductionguidanceseebackpageExercisesWithWorkedSolutionsCESEduPack–ExerciseswithWorkedSolutionsM.F.Ashby20102:constraintsandobjectivesE7.DerivingandusingmaterialindicesE8.MultipleconstraintsandobjectivesE9.SelectingmaterialandshapeE10.HybridmaterialsE11.SelectingprocessesE12.MaterialsandtheenvironmentCESEduPack–ExerciseswithWorkedSolutionsM.F.Ashby20103“UsefulApproximateSolutionstoStandardProblems”(UASSP–whichcanbefoundasanopenaccessresourceontheteachingresourcewebsite.);theuseofmaterialpropertycharts;techniquesforthetranslationofdesignrequirementtoidentifyconstraintsandobjectives;thederivationofindices,screeningandranking,multi-objectiveoptimization;coupledchoiceofmaterialandshape;devisinghybrids;andthechoiceofmaterialstomeetenvironmentalcriteria.Threeimportantpoints.1.Selectionproblemsareopen-endedand,generally,under-specified;thereisseldomasingle,correctanswer.Theproperanswerisasensibletranslationofthedesignrequirementsintomaterialconstraintsandobjectives,appliedtogiveashort-listofpotentialcandidateswithcommentarysuggestingwhatsupportinginformationwouldbeneededtonarrowthechoicefurther.2.Thepositioningofselection-linesonchartsisamatterofjudgement.Thegoalistoplacethelinessuchthattheyleaveanadequatelylargeshortlistofcandidates(aimfor4orso),drawn,ifpossible,frommorethanoneclassofmaterial.3.Arequestforaselectionbasedononematerialindexalone(suchasρ/EM2/1=)iscorrectlyansweredbylistingthesubsetofmaterialsthatmaximizethisindex.Butarequestforaselectionofmaterialsforacomponent–awingspar,forinstance(whichisalight,stiffbeam,forwhichtheindexisρ/EM2/1=)–requiresmore:somematerialswithhighρ/E2/1suchassiliconcarbide,areunsuitableforobviousreasons.Itisapooranswerthatignorescommonsenseandexperienceandfailstoaddfurtherconstraintstoincorporatethem.Studentsshouldbeencouragedtodiscusstheimplicationsoftheirselectionandtosuggestfurtherselectionstages.AllthematerialsselectionproblemscanbesolvedusingtheStandarddatabasesintheCESEduPacksoftware,whichisparticularlyeffectivewhenmultiplecriteriaandunusualindicesareinvolved.ThisversionofthesolutionmanualhasbeenwrittensuchthatitcanbecompletedwithouthavingtorefertothebookMaterialsSelectioninMechanicalDesign,4thedition.TheoriginalsolutionmanualforthebookcanbefoundontheGrantaDesignwebsite.Hint:WhenusingtheCESEduPack,youcanavoidmanuallycalculatingtheaveragevaluesofmaterialproperties(theytendtospanarange)bygoingtoTools
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Numbersandcheckingthe“Displaydatarangesasaveragevalues”checkbox.CESEduPack–ExerciseswithWorkedSolutionsM.F.Ashby20104TinGlassCementTitaniumCarbonfiberPresenttheresultasashortreportofabout100-200words(roughlyhalfapage).Specimenanswer:tin.Tin(symbolSn),asilver-whitemetal,hasalonghistory.ItwastradedinthecivilisationsoftheMediterraneanasearlyas1500BC(theOldTestamentoftheChristianbiblecontainsmanyreferencestoit).Itsimportanceatthattimelayinitsabilitytohardencoppertogivebronze(coppercontainingabout10%tin),thekeymaterialforweapons,toolsandstatuaryoftheBronzeage(1500BC–500BC).Todaytinisstillusedtomakebronze,forsoldersandasacorrosionresistantcoatingonsteelsheet(“tinplate”)forfoodanddrinkcontainers–a“tinnie”,toanAustralian,isacanofbeer.Plateglassismadebyfloatingmoltenglassonabedofliquidtin(thePilkingtonprocess).Thindepositsoftincompoundsonglassgivetransparent,electricallyconductingcoatingsusedforfrost-freewindshieldsandforpanellighting.E2.2Researchtheevolutionofmaterialusein•Writingimplements(charcoal,“lead”(graphite),quillpens,steelnibpens,go