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Page|1 TeacherNotes-MaterialsTesting:Plastics–ReMSTEP(DeakinUniversity)
T E A C H E R N O T E S
MaterialsTesting:Plastics:TeacherNotes
Overview/IntroductionMaterialsscientistsendeavourtofindorimprovematerialstoreplacecurrentlyusedmaterialsornewmaterialsfornoveluses.Theyalsoresearchimproved,moreefficientandmoreeconomicprocessesformanufacturingthesematerials.Systematictestingformsanintegralpartofthedevelopmentprocess.
Thisactivityengagesstudentsintestingthepropertiesofplasticfromdifferentsupermarketbags.Thisisdonewithinthecontextofestablishingthestandardsneededtobemetbyabiodegradablereplacementforcurrentlyusedplastic.
InPart1,studentssimulatethetensilestrengthtestingmethodemployedbymaterialsscientists.
InPart2,theresistancetodamagefrompuncturebyasharpobjectismeasured.
ThisLLAaddressesarangeofoutcomesdescribedintheAustralianandVictorianCurriculum.BoththeAustralianandVictoriancurriculumaccentuatesstudentlearningaboutdynamicforces:theforcesinvolvedinthemotionofobjects.Ofequalimportanceinscienceandengineering,though,andofrelevancetoeverydayexperience,arestaticforces:thoseforcesthatactonstationaryobjects.Staticforcesareimportantwhenunderstandingthestrengthandotherphysicalpropertiesofstructuresandmaterials.AlsoaddressedinthisLLAarescienceinquirywithspecificfocusonanalysingandevaluatingdataandtheapplicationofscienceunderstandinginsolvingproblems.
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CurriculumOutcomes:AustralianCurriculumF-10Years5and6
Scienceasahumanendeavour• Scientificknowledgeisusedtosolveproblemsandinform
personalandcommunitydecisions(ACSHE083)(ACSHE100)
Years7and8
Scienceasahumanendeavour• Peopleusescienceunderstandingandskillsintheiroccupations
andthesehaveinfluencedthedevelopmentofpracticesinareasofhumanactivity(ACSHE121)(ACSHE136)
ScienceUnderstanding:Chemicalsciences• Propertiesofthedifferentstatesofmattercanbeexplainedin
termsofthemotionandarrangementofparticles(ACSSU151)
CurriculumOutcomes:AustralianCurriculumTechnologiesF-10Years5and6
DesignTechnologies• Explorethecharacteristicsandpropertiesofmaterialsand
componentsthatareusedtoproducedesignedsolutions(ACTDEK004)
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CurriculumOutcomes:VictorianCurriculumF-10Levels5and6
Scienceasahumanendeavour• Scientificunderstandings,discoveriesandinventionsareusedto
informpersonalandcommunitydecisionsandtosolveproblemsthatdirectlyaffectpeople’slives(VCSSU073)
ScienceUnderstanding:Chemicalsciences• Solids,liquidsandgasesbehaveindifferentwaysandhave
observablepropertiesthathelptoclassifythem(VCSSU076)
Levels7and8
Scienceasahumanendeavour• Scientificknowledgeandunderstandingoftheworldchangesas
newevidencebecomesavailable;scienceknowledgecandevelopthroughcollaborationandconnectingideasacrossthedisciplinesandpracticeofscience(VCSSU089)
• Scienceandtechnologycontributetofindingsolutionstoarangeofcontemporaryissues;thesesolutionsmayimpactonotherareasofsocietyandinvolveethicalconsiderations(VCSSU090)
ScienceUnderstanding:Chemicalsciences• Thepropertiesofthedifferentstatesofmattercanbeexplained
intermsofthemotionandarrangementofparticles(VCSSU096)o modellingthearrangementofparticlesinsolids,liquids
andgases
ScienceUnderstanding:Physicalsciences• Changetoanobject’smotioniscausedbyunbalancedforces
actingontheobject;Earth’sgravitypullsobjectstowardsthecentreofEarth(VCSSU103)
o investigatingtheeffectsofapplyingdifferentforcestofamiliarobjects.
Page|4 TeacherNotes-MaterialsTesting:Plastics–ReMSTEP(DeakinUniversity)
CurriculumOutcomes:VictorianCurriculumTechnologiesF-10
DesignandTechnologies:TechnologiesContexts• Engineeringprinciplesandsystems.Analysehowmotion,force
andenergyareusedtomanipulateandcontrolelectromechanicalsystemswhendesigningsimple,engineeredsolutions(VCDSTC045)
• Materialsandtechnologiesspecialisation.Analysewaystoproducedesignedsolutionsthroughselectingandcombiningcharacteristicsandpropertiesofmaterials,systems,components,toolsandequipment(VCDSTC048)
KeyKnowledgeandSkillsIncompletingthisactivity,studentsexploreandapplyarangeofconceptsandterms.Someofthesetermsandconceptsaredescribed,definedandexplainedbelow.
Controlledvariables-Variablesthatarekeptconstant.
Dependentvariable-Variablethatchangesinresponsetochangesintheindependentvariableandthatisobservedormeasured.
Elasticity–Thepropertytostretchwhenpulledorpushedandthenreturntoitsoriginalshapewhenthepullorpushisstopped.
Failure–Thetermusedwhenamaterialbreaksduetheforcebeingappliedtoit.
Fairtest-Whentestingdifferentmaterialsallthevariablesexcepttheonebeingtestedneedtobekeptthesame.
Flexibility–Thedegreetowhichanobjectcanbebentwithoutbreaking.
Force-apushorapull.
Independentvariable-Variablethatisdeliberatelychanged.
Kilogramweight–Theforceofgravityonaone-kilogrammass.
Load–Adownwardsforcethatisbeingappliedtoanobject.
Newton–Aunitofforce.
Page|5 TeacherNotes-MaterialsTesting:Plastics–ReMSTEP(DeakinUniversity)
Plasticity–Thepropertyofmaterialreferringtoitbeingabletopermanentlychangeshape.
Punctureforceistheforcerequiredtopushanobjectintoorthroughamaterial.
StaticForce–Thepullorpushonorwithinastationaryobject.
Stiffness–Theresistancetochangingshapewhenforcesareapplied.Astiffmaterialdoesn’tbendortwisteasily.
Strength–Theabilityofamaterialtoresistbreakingwhenaforceisapplied.
TensileStrength–Theresistanceofamaterialtobreakingundertension.
Tension–Thepullingforcewhenanobjectisstretched.
Variable-Somethingthatcanchange.
Weight–Theforceofgravityintheobject.
KeyScienceInquirySkillsInconductingthisactivity,studentsneedto:
• identifyvariablesrelevantinthetest• determinetheindependent,dependentandcontrolvariables• takestepstoensureaccuracyinmeasurement• recorddatasystematically• analysedata• drawconclusionsbasedonevidence
Backgroundinformation
PlasticsPlasticsarethequintessentialmodernmaterial,replacingtraditionalmaterialsforavastrangeofuses.Theycanbemouldedorextrudedintoalmostanydesiredshapeandcanbeproducedwithpropertiesdesignedtomatchspecificuses.Plasticscanbetransparent,translucentoropaque,colouredorcolourless,flexibleorrigid,hardorsoft,stickyornon-stick,chemicallyinertorbiodegradable.
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Chemically,plasticsareorganicpolymerssynthesisedfromarangeofpetrochemicalornaturalmaterials.Polymersareformedfromchemicalunitscalledmonomersthatarereactedtoformlongchainmoleculesandnetworks.Differencesinthelengthofthechainsandthedegreeofcross-linkingbetweenchainscausesdifferencesinhardness,strength,flexibilityandthermalproperties.Plasticswithdesiredcharacteristicscanbeproducedbyselectingappropriatemonomers,controllingtheconditionsofthepolymerizationreaction,andadjustingadditivessuchasplasticisers.
ScienceandengineeringconceptsInmaterialsscience,thestrengthofamaterialmayrefertoitsabilitytoresisttensionforces,compressionforces,shearforces,torsion(twisting)orimpactforces.Inthisactivity,however,wewillbefocusingontensilestrength.Tensilestrengthisthematerial’sabilitytowithstandpullingforce.
*Ifoneendofthepieceofmaterialisfixed,theforcemarkedwiththeasteriskwillbeanupwardreactionforce(reactiontothedownwardloadforce).
Whenoneendofasampleofmaterialisfixed,andaprogressivelyincreasingload,orpullingforceisapplied,thematerialwillbegintostretchandtypicallygoesthroughanumberofphases:
1. anelasticphasewherethematerialwillreturntoitsoriginallengthwhentheforceisremoved
2. aplasticphaseinwhichchangeinlengthand/orshapeismoreorlesspermanentanditdoesnotreturntoitsoriginallengthafterremovaloftheforce.
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3. ‘failure’wherethematerialbreaks.
SomeexcellentanimatedgraphicalrepresentationsofthesephasescanbefoundattheMichiganTechnologicalUniversity(2017)website<http://www.mtu.edu/materials/k12/experiments/tensile/>.
Pedagogy
InquirySkillsThisisaninquiryactivitythatcanbeadjustedbytheteachertobeasguidedorasopen-endedasdesired.Thestudentnotesbeginwithspecificdirectionsbutlaterquestionsallowstudentstoconductmoreindependentinvestigations.Theteachermay,however,decidetoprovidecloseguidanceanddirectionthroughouttheactivity.
Teachersmayusetheinquiryscaffoldingtool1toassistdecisionmakingaboutthedegreeofsupporttoprovidestudentsforeachphaseoftheinquiryprocess.
1 Inquiryscaffoldingtool.NationalResearchCouncil(2000);Bruck,L.B.,Bretz,S.L.,&Towns,M.H.,2008.AdaptedfortheVictorianCurriculumbyLim,K.F.(2016),unpublished.)
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Theactivitypresentedinthestudentnotesisdesignedtomovethestudentfromadirectedinquirythroughtomoreindependentinquiry.Thestudentmeasuresthestrengthofasinglepieceofplasticbyfollowingdirections,repeatsthiswithotherpiecesofplastic.The
Page|9 TeacherNotes-MaterialsTesting:Plastics–ReMSTEP(DeakinUniversity)
reasonforstartingwithmoredirectionissothatthestudentshavesomeknowledgeandexperiencetoapplytomoreopen-endedinvestigationslateron.
InPart1:theyusescientificknowledgeandfindingsfrominvestigationstoidentifyrelationships,evaluateclaimsanddrawconclusions.Theyreflectonthemethodusedtoinvestigateaquestionorsolveaproblem,includingevaluatingthequalityofthedatacollected,andidentifyimprovementstothemethod.
ConceptualdevelopmentInadditiontothedevelopmentofinquiryskillsanintendedlearningoutcomeoftheseactivitiesistohavestudentsrefinetheirunderstandingoftheparticlemodelofmatter.
RepresentationconstructionapproachUsingarepresentationconstructionapproach(Tytler,Prain,HubberandWaldrip2013)canhelp.Theteachercanencouragethestudentstorepresentwhatishappeningasaloadisaddedtotheteststripofplastic.Therepresentationcouldbeatamacrolevelshowingtheforcesinvolved,shapechangesandfailure.However,thestudentscanbechallengedtorepresentwhatishappeningtotheparticlesintheplasticasloadisadded.Thestudentscanbechallengedtorepresentthewaytheparticlesofplasticmightbehaveduringtheelasticandplasticphases.
Therepresentationswillmostlikelytobedrawings(annotateddiagrams),buttheycouldalsobemodelsorroleplays.Suchrepresentationsprovideinsightintostudents’conceptions.Whateverformtherepresentationstaketheyaffordanopportunitytoengagewiththestudentsindialogueabouttheirconceptionswiththepurposeofdevelopingandrefiningtheirrepresentationsandhencetheirconceptualisationoftheparticlemodelofmatter.
Teachingnotes
Calculatingpercentagechangeinlength
Percentage change in length = Final length( )- Initial length( )
Initial length × 100%
Example:
Page|10 TeacherNotes-MaterialsTesting:Plastics–ReMSTEP(DeakinUniversity)
Percentage change in length = 21 cm( )- 20 cm( )
20 cm × 100%
= 5%
AssessmentTheteacherscancomparethestudent’sperformancewiththecurriculumdescriptorsandmakejudgementsaboutwhethertheoutcomeshavebeenachieved.
Extensionwithsomeadvancedideasandmathematics
Teachersmaychoosetoextendablestudentsbyexploringdifferentmaterialsorbyencouragingthemtomakemorevalidmeasurementssothattheengineeringstressandstrainarecalculatedandplotted.(Stressisforceperunitarea-strainisthedeformationofasolidduetostress.)Todothisthestudentswillneedtomeasure/estimatethethicknessofeachsampleofplastic.Thiscouldbedonebymeasuringmanylayersofplastic.Themultiplelayerscanbegeneratedbyfoldingasheetinhalfandtheninhalfagainandagain.Thethicknessafter7foldsisequivalentto128sheetsandafter8folds256sheets.Thethicknessofthefoldedplasticcanbemeasuredwitharulerorbetter,withamicrometrecalliper.Thelayersneedtobesqueezedtogethersothelayersofplasticaretouchingoneanother,butcareneedstobetakenthatthecallipersdonotbiteintotheplasticcuttingthroughlayers.Todeviseamethodforaccuratelyestimatingthethicknessoftheplasticisanextensionactivityinitself.
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Thestudentcancreateatableinwhichtheycanrecordeachofthemeasurementsandcalculationsneededtogenerateastressvsstrain.Theywillthenbeabletocomparethecharacteristicsofeachplastictested.Alternatively,thedatacouldberecordedinMicrosoftExcelandtheappropriateformulaeusedtocalculatestressandstrainforarangeofloads.
Atypicalengineeringstressvsstraingraphisshowninthefigurebelow:
Atypicalstressvsstraincurveforamaterialthatdemonstrateselastic
andplasticpropertiesunderload
Whyaretheaxesturnedaround?• Thestudentexperimenthasthestress(force)asthe
independentvariableandthestretchingresponse(dependentvariable)ismeasured.
• However,engineerstypicallyuseequipmentthatwillstretchthematerialtoaparticularlength,thusputtingthestrain(deformationorextension)astheindependentvariableandthestressontheverticalaxis.
ReferencesAustralianAcademyofScience(2016).Thefutureofplastics,<http://www.nova.org.au/earth-environment/future-plastics>.
Bruck,L.B.,Bretz,S.L.,&Towns,M.H.(2008)Characterizingthelevelofinquiryintheundergraduatelaboratory.JournalofCollegeScience,38(1),52-58.
MichiganTechnologicalUniversity(2017).TensileTestExperiment,<http://www.mtu.edu/materials/k12/experiments/tensile/>
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TheEngineeringToolbox(nodate).Stress,StrainandYoung'sModulus,<http://www.engineeringtoolbox.com/stress-strain-d_950.html>.
NationalResearchCouncil(2000).Inquiryandthenationalscienceeducationstandards:Aguideforteachingandlearning.WashingtonDC:NationalAcademicPress.
Shah,K.P.(nodate).TheHandBookonMechanicalMaintenance,<http://practicalmaintenance.net/?p=1135>.
Tytler,R.,Prain,V.,Hubber,P.,&Waldrip,B.(Eds.).(2013).Constructingrepresentationstolearninscience.SpringerScience&BusinessMedia.
Suggestions:SuggestionsforimprovementsoftheseactivitiesshouldbesenttotheProjectOfficer,ASELLforSchools(Victoria),[email protected].
CopyrightandCreativeCommonsThemoralrightsoftheauthors,StuartPalmer,IanBentley,PetaWhite,RussellTytler,KieranLim,JohnLong,andMaryVamvakashavebeenassertedundertheAustralianCopyrightAct1968(Cth).Exceptinglogos,trademarksorotherthird-partycontentasindicated,thisresourceisdistributedunderaCreativeCommons‘Attribution-NonCommercial-ShareAlike’4.0InternationalLicense.