StandardTestMethodfor
CompressivePropertiesofRigidPlastics1ThisstandardisissuedunderthefixeddesignationD695;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelastrevisionorreapproval.ThisstandardhasbeenapprovedforusebyagenciesoftheDepartmentofDefense.
1.Scope*
1.1Thistestmethodcoversthedeterminationoftheme-chanicalpropertiesofunreinforcedandreinforcedrigidplas-tics,includinghigh-moduluscomposites,whenloadedincompressionatrelativelylowuniformratesofstrainingorloading.Testspecimensofstandardshapeareemployed.1.2ThevaluesstatedinSIunitsaretoberegardedasthestandard.Thevaluesinparenthesesareforinformationonly.
NOTE1—Forcompressivepropertiesofresin-matrixcompositesrein-forcedwithorientedcontinuous,discontinuous,orcross-plyreinforce-ments,testsmaybemadeinaccordancewithTestMethodD3410.
E4PracticesforForceVerificationofTestingMachines6E83PracticeforVerificationandClassificationofExten-someters6E691PracticeforConductinganInterlaboratoryStudytoDeterminethePrecisionofaTestMethod73.Terminology
3.1General—ThedefinitionsofplasticsusedinthistestmethodareinaccordancewithTerminologyD883unlessotherwiseindicated.3.2Definitions:
3.2.1compressivedeformation—thedecreaseinlengthpro-ducedinthegagelengthofthetestspecimenbyacompressiveload.Itisexpressedinunitsoflength.
3.2.2compressivestrain—theratioofcompressivedefor-mationtothegagelengthofthetestspecimen,thatis,thechangeinlengthperunitoforiginallengthalongthelongitu-dinalaxis.Itisexpressedasadimensionlessratio.
3.2.3compressivestrength—themaximumcompressivestress(nominal)carriedbyatestspecimenduringacompres-siontest.Itmayormaynotbethecompressivestress(nominal)carriedbythespecimenatthemomentofrupture.3.2.4compressivestrengthatfailure(nominal)—thecom-pressivestress(nominal)sustainedatthemomentoffailureofthetestspecimenifshatteringoccurs.
3.2.5compressivestress(nominal)—thecompressiveloadperunitareaofminimumoriginalcrosssectionwithinthegageboundaries,carriedbythetestspecimenatanygivenmoment.Itisexpressedinforceperunitarea.
3.2.5.1Discussion—Theexpressionofcompressiveproper-tiesintermsoftheminimumoriginalcrosssectionisalmostuniversallyused.Undersomecircumstancesthecompressivepropertieshavebeenexpressedperunitofprevailingcrosssection.Thesepropertiesarecalled“true”compressiveprop-erties.
3.2.6compressivestress-straindiagram—adiagraminwhichvaluesofcompressivestressareplottedasordinatesagainstcorrespondingvaluesofcompressivestrainasabscis-sas.
671.3Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.Aspecificprecau-tionarystatementisgiveninNote11.
NOTE2—ThistestmethodistechnicallyequivalenttoISO604.
2.ReferencedDocuments2.1ASTMStandards:
D618PracticeforConditioningPlasticsforTesting2D638TestMethodforTensilePropertiesofPlastics2D883TerminologyRelatingtoPlastics2D3410TestMethodforCompressivePropertiesofPoly-merMatrixCompositeMaterialswithUnsupportedGageSectionbyShearLoading3D4000ClassificationSystemforSpecifyingPlasticMate-rials4D4066ClassificationSystemforNylonInjectionandEx-trusionMaterials4D5947TestMethodsforPhysicalDimensionsofSolidPlasticsSpecimens5ThistestmethodisunderthejurisdictionofASTMCommitteeD20onPlasticsandisthedirectresponsibilityofSubcommitteeD20.10onMechanicalProperties.CurrenteditionapprovedAugust10,2002.PublishedOctober2002.OriginallypublishedasD695–42T.LastpreviouseditionD695–02.2AnnualBookofASTMStandards,Vol08.01.3AnnualBookofASTMStandards,Vol15.03.4AnnualBookofASTMStandards,Vol08.02.5AnnualBookofASTMStandards,Vol08.03.
1AnnualBookofASTMStandards,Vol03.01.AnnualBookofASTMStandards,Vol14.02.
*ASummaryofChangessectionappearsattheendofthisstandard.
Copyright©ASTMInternational,100BarrHarborDrive,POBoxC700,WestConshohocken,PA19428-2959,UnitedStates.
1
3.2.7compressiveyieldpoint—thefirstpointonthestress-straindiagramatwhichanincreaseinstrainoccurswithoutanincreaseinstress.
3.2.8compressiveyieldstrength—normallythestressattheyieldpoint(seealsosection3.2.11).
3.2.9crushingload—themaximumcompressiveforceap-pliedtothespecimen,undertheconditionsoftesting,thatproducesadesignateddegreeoffailure.
3.2.10modulusofelasticity—theratioofstress(nominal)tocorrespondingstrainbelowtheproportionallimitofamaterial.Itisexpressedinforceperunitareabasedontheaverageinitialcross-sectionalarea.
3.2.11offsetcompressiveyieldstrength—thestressatwhichthestress-straincurvedepartsfromlinearitybyaspecifiedpercentofdeformation(offset).
3.2.12percentcompressivestrain—thecompressivedefor-mationofatestspecimenexpressedasapercentoftheoriginalgagelength.
3.2.13proportionallimit—thegreateststressthatamaterialiscapableofsustainingwithoutanydeviationfrompropor-tionalityofstresstostrain(Hooke’slaw).Itisexpressedinforceperunitarea.
3.2.14slendernessratio—theratioofthelengthofacol-umnofuniformcrosssectiontoitsleastradiusofgyration.Forspecimensofuniformrectangularcrosssection,theradiusofgyrationis0.289timesthesmallercross-sectionaldimension.Forspecimensofuniformcircularcrosssection,theradiusofgyrationis0.250timesthediameter.
4.SignificanceandUse
4.1Compressiontestsprovideinformationaboutthecom-pressivepropertiesofplasticswhenemployedunderconditionsapproximatingthoseunderwhichthetestsaremade.
4.2Compressivepropertiesincludemodulusofelasticity,yieldstress,deformationbeyondyieldpoint,andcompressivestrength(unlessthematerialmerelyflattensbutdoesnotfracture).Materialspossessingaloworderofductilitymaynotexhibitayieldpoint.Inthecaseofamaterialthatfailsincompressionbyashatteringfracture,thecompressivestrengthhasaverydefinitevalue.Inthecaseofamaterialthatdoesnotfailincompressionbyashatteringfracture,thecompressivestrengthisanarbitraryonedependinguponthedegreeofdistortionthatisregardedasindicatingcompletefailureofthematerial.Manyplasticmaterialswillcontinuetodeformincompressionuntilaflatdiskisproduced,thecompressivestress(nominal)risingsteadilyintheprocess,withoutanywell-definedfractureoccurring.Compressivestrengthcanhavenorealmeaninginsuchcases.
4.3Compressiontestsprovideastandardmethodofobtain-ingdataforresearchanddevelopment,qualitycontrol,accep-tanceorrejectionunderspecifications,andspecialpurposes.Thetestscannotbeconsideredsignificantforengineeringdesigninapplicationsdifferingwidelyfromtheload-timescaleofthestandardtest.Suchapplicationsrequireadditionaltestssuchasimpact,creep,andfatigue.
4.4Beforeproceedingwiththistestmethod,referenceshouldbemadetotheASTMspecificationforthematerialbeingtested.Anytestspecimenpreparation,conditioning,dimensions,andtestingparameterscoveredinthematerials
specificationshalltakeprecedenceoverthosementionedinthistestmethod.Ifthereisnomaterialspecification,thenthedefaultconditionsapply.Table1inClassificationD4000liststheASTMmaterialsstandardsthatcurrentlyexist.
5.Apparatus
5.1TestingMachine—Anysuitabletestingmachinecapableofcontrolofconstant-rate-of-crossheadmovementandcom-prisingessentiallythefollowing:
5.1.1DriveMechanism—Adrivemechanismforimpartingtothemovablecross-headmember,auniform,controlledvelocitywithrespecttothebase(fixedmember),withthisvelocitytoberegulatedasspecifiedinSection9.
5.1.2LoadIndicator—Aload-indicatingmechanismca-pableofshowingthetotalcompressiveloadcarriedbythetestspecimen.Themechanismshallbeessentiallyfreefrominertia-lagatthespecifiedrateoftestingandshallindicatetheloadwithanaccuracyof61%ofthemaximumindicatedvalueofthetest(load).TheaccuracyofthetestingmachineshallbeverifiedatleastonceayearinaccordancewithPracticesE4.
5.2Compressometer—Asuitableinstrumentfordetermin-ingthedistancebetweentwofixedpointsonthetestspecimenatanytimeduringthetest.Itisdesirablethatthisinstrumentautomaticallyrecordthisdistance(oranychangeinit)asafunctionoftheloadonthetestspecimen.Theinstrumentshallbeessentiallyfreeofinertia-lagatthespecifiedrateofloadingandshallconformtotherequirementsforaClassB-2extensometerasdefinedinPracticeE83.
NOTE3—Therequirementsforextensometerscitedhereinapplytocompressometersaswell.
5.3CompressionTool—Acompressiontoolforapplyingtheloadtothetestspecimen.Thistoolshallbesoconstructedthatloadingisaxialwithin1:1000andappliedthroughsurfacesthatareflatwithin0.025mm(0.001in.)andparalleltoeachotherinaplanenormaltotheverticalloadingaxis.ExamplesofsuitablecompressiontoolsareshowninFig.1andFig.2.5.4SupportingJig—AsupportingjigforthinspecimensisshowninFig.3andFig.4.
5.5Micrometers—Suitablemicrometers,readingto0.01mmor0.001in.formeasuringthewidth,thickness,andlengthofthespecimens.
6.TestSpecimens
6.1Unlessotherwisespecifiedinthematerialsspecifica-tions,thespecimensdescribedin6.2and6.7shallbeused.Thesespecimensmaybepreparedbymachiningoperationsfrommaterialsinsheet,plate,rod,tube,orsimilarform,ortheymaybepreparedbycompressionorinjectionmoldingofthematerialtobetested.Allmachiningoperationsshallbedonecarefullysothatsmoothsurfacesresult.Greatcareshallbetakeninmachiningtheendssothatsmooth,flatparallelsurfacesandsharp,cleanedges,towithin0.025mm(0.001in.)perpendiculartothelongaxisofthespecimen,result.
6.2Thestandardtestspecimen,exceptasindicatedin6.3-6.7,shallbeintheformofarightcylinderorprismwhoselengthistwiceitsprincipalwidthordiameter.Preferredspecimensizesare12.7by12.7by25.4mm(0.50by0.50by
NOTE1—Devicessimilartotheoneillustratedhavebeensuccessfullyusedinanumberofdifferentlaboratories.DetailsofthedevicedevelopedattheNationalInstituteforStandardsandTechnologyaregiveninthepaperbyAitchinson,C.S.,andMiller,J.A.,“ASubpressforCompressiveTests,”NationalAdvisoryCommitteeforAeronautics,TechnicalNoteNo.912,1943.
FIG.1SubpressforCompressionTests
FIG.2CompressionTool
1in.)(prism),or12.7mmindiameterby25.4mm(cylinder).Whereelasticmodulusandoffsetyield-stressdataaredesired,thetestspecimenshallbeofsuchdimensionsthattheslender-nessratioisintherangefrom11to16:1.Inthiscase,preferredspecimensizesare12.7by12.7by50.8mm(0.50by0.50by2in.)(prism),or12.7mmindiameterby50.8mm(cylinder).6.3Forrodmaterial,thetestspecimenshallhaveadiameterequaltothediameteroftherodandasufficientlengthtoallowaspecimenslendernessratiointherangefrom11to16:1.
FIG.3SupportJigforThinSpecimen
6.4Whentestingtubes,thetestspecimenshallhaveadiameterequaltothediameterofthetubeandalengthof25.4mm(1in.)(Note4).Forcrushing-loaddeterminations(atrightanglestothelongitudinalaxis),thespecimensizeshallbethesame,withthediameterbecomingtheheight.
NOTE4—Thisspecimencanbeusedfortubeswithawallthicknessof1mm(0.039in.)orover,toinsidediametersof6.4mm(0.25in.)orover,andtooutsidediametersof50.8mm(2.0in.)orless.
6.5Whereitisdesiredtotestconventionalhigh-pressurelaminatesintheformofsheets,thethicknessofwhichislessthan25.4mm(1in.),apile-upofsheets25.4mmsquare,withasufficientnumberoflayerstoproduceaheightofatleast25.4mm,maybeused.
6.6Whentestingmaterialthatmaybesuspectedofanisot-ropy,duplicatesetsoftestspecimensshallbepreparedhavingtheirlongaxisrespectivelyparallelwithandnormaltothesuspecteddirectionofanisotropy.
6.7ReinforcedPlastics,IncludingHigh-StrengthCompos-itesandHigh-StrengthCompositesandHighlyOrthotropicLaminates—Thefollowingspecimensshallbeusedforrein-forcedmaterials,orforothermaterialswhennecessarytocomplywiththeslendernessratiorequirementsortopermitattachmentofadeformation-measuringdevice.
6.7.1Formaterials3.2mm(1⁄8in.)andoverinthickness,aspecimenshallconsistofaprismhavingacrosssectionof12.7mm(1⁄2in.)bythethicknessofthematerialandalengthsuchthattheslendernessratioisintherangefrom11to16:1(Note5).
6.7.2Formaterialsunder3.2mm(1⁄8in.)thick,orwhereelasticmodulustestingisrequiredandtheslendernessratiodoesnotprovideforenoughlengthforattachmentofacompressometerorsimilardevice,aspecimenconformingtothatshowninFig.5shallbeused.ThesupportingjigshowninFig.3andFig.4shallbeusedtosupportthespecimenduringtesting(Note6).
NOTE5—Iffailureformaterialsinthethicknessrangeof3.2mm(1⁄8in.)isbydelaminationratherthanbythedesirableshearplanefracture,thematerialmaybetestedinaccordancewith6.7.2.
NOTE6—Round-robintestshaveestablishedthatrelativelysatisfactorymeasurementsofmodulusofelasticitymaybeobtainedbyapplyingacompressometertotheedgesofthejig-supportedspecimen.
NOTE1—Coldrolledsteel.
NOTE2—Furnishedfoursteelmachinescrewsandnuts,roundhead,slotted,length31.75mm(11⁄4in.).NOTE3—Grindsurfacesdenoted“Gr.”
FIG.4SupportJig,Details
FIG.5CompressionTestSpecimenforMaterialsLessthan3.2mmThick
6.8Whentestingsyntacticfoam,thestandardtestspecimenshallbeintheformofarightcylinder25.4mm(1in.)indiameterby50.8mm(2in.)inlength.
7.Conditioning
7.1Conditioning—Conditionthetestspecimensat2362°C(73.463.6°F)and5065%relativehumidityfornotlessthan40hpriortotestinaccordancewithProcedureAofPracticeD618unlessotherwisespecifiedbycontractorrelevantASTMmaterialspecification.Referencepre-testcon-ditioning,tosettledisagreements,shallapplytolerancesof61°C(1.8°F)and62%relativehumidity.
7.1.1Notethatforsomehygroscopicmaterials,suchasnylons,thematerialspecifications(forexample,ClassificationSystemD4066)callfortesting“dryas-moldedspecimens.”Suchrequirementstakeprecedenceovertheaboveroutinepreconditioningto50%RHandrequiresealingthespecimensinwatervapor-impermeablecontainersassoonasmoldedandnotremovingthemuntilreadyfortesting.
7.2TestConditions—Conductthetestsat2362°C(73.463.6°F)and5065%relativehumidityunlessotherwise
specifiedbycontractortherelevantASTMmaterialspecifica-tion.Referencetestingconditions,tosettledisagreements,shallapplytolerancesof61°C(1.8°F)and62%relativehumidity.
8.NumberofTestSpecimens
8.1Atleastfivespecimensshallbetestedforeachsampleinthecaseofisotropicmaterials.
8.2Tenspecimens,fivenormaltoandfiveparallelwiththeprincipalaxisofanisotropy,shallbetestedforeachsampleinthecaseofanisotropicmaterials.
8.3Specimensthatbreakatsomeobviousflawshallbediscardedandretestsmade,unlesssuchflawsconstituteavariable,theeffectofwhichitisdesiredtostudy.
9.SpeedofTesting
9.1Speedoftestingshallbetherelativerateofmotionofthegripsortestfixturesduringthetest.Rateofmotionofthedrivengriporfixturewhenthemachineisrunningidlemaybeusedifitcanbeshownthattheresultingspeedoftestingiswithinthelimitsofvariationallowed.
9.2Thestandardspeedoftestingshallbe1.360.3mm(0.05060.010in.)/min,exceptasnotedin10.5.4.
10.Procedure
10.1Measurethewidthandthicknessofthespecimentothenearest0.01mm(0.001in.)atseveralpointsalongitslength.Calculateandrecordtheminimumvalueofthecross-sectionalarea.Measurethelengthofthespecimenandrecordthevalue.10.2Placethetestspecimenbetweenthesurfacesofthecompressiontool,takingcaretoalignthecenterlineofitslongaxiswiththecenterlineoftheplungerandtoensurethattheendsofthespecimenareparallelwiththesurfaceofthecompressiontool.Adjustthecrossheadofthetestingmachineuntilitjustcontactsthetopofthecompressiontoolplunger.
NOTE7—Thecompressiontoolmaynotbenecessaryfortestingoflowermodulus(forexample,700MPato3500MPa(100000psito500000psi))materialiftheloadingsurfacesaremaintainedsmooth,flat,andparalleltotheextentthatbucklingisnotincurred.
10.3Placethinspecimensinthejig(Fig.3andFig.4)sothattheyareflushwiththebaseandcentered(Note8).Thenutsorscrewsonthejigshallbefingertight(Note9).Placetheassemblyinthecompressiontoolasdescribedin5.3.
NOTE8—Around-robintest,designedtoassesstheinfluenceofspecimenpositioninginthesupportingjig(thatis,flushversuscenteredmounting),showednosignificanteffectoncompressivestrengthduetothisvariable.However,flushmountingofthespecimenwiththebaseofthejigisspecifiedforconvenienceandeaseofmounting.8NOTE9—Around-robintestontheeffectoflateralpressureatthesupportingjighasestablishedthatreproducibledatacanbeobtainedwiththetightnessofthejigcontrolledasindicated.
10.4Ifonlycompressivestrengthorcompressiveyield
strength,orboth,aredesired,proceedasfollows:
10.4.1Setthespeedcontrolat1.3mm/min(0.050in./min)andstartthemachine.
10.4.2Recordthemaximumloadcarriedbythespecimenduringthetest(usuallythiswillbetheloadatthemomentofrupture).
10.5Ifstress-straindataaredesired,proceedasfollows:10.5.1Attachcompressometer.
10.5.2Setthespeedcontrolat1.3mm/min(0.050in./min)andstartthemachine.
10.5.3Recordloadsandcorrespondingcompressivestrainatappropriateintervalsofstrainor,ifthetestmachineisequippedwithanautomaticrecordingdevice,recordthecompleteload-deformationcurve.
10.5.4Aftertheyieldpointhasbeenreached,itmaybedesirabletoincreasethespeedfrom5to6mm/min(0.20to0.25in./min)andallowthemachinetorunatthisspeeduntilthespecimenbreaks.Thismaybedoneonlywithrelativelyductilematerialsandonamachinewithaweighingsystemwithresponserapidenoughtoproduceaccurateresults.11.Calculation
11.1CompressiveStrength—Calculatethecompressivestrengthbydividingthemaximumcompressiveloadcarriedby
8SupportingdataareavailablefromASTMHeadquarters.RequestRR:D20-1061.
thespecimenduringthetestbytheoriginalminimumcross-sectionalareaofthespecimen.Expresstheresultinmegapas-calsorpounds-forcepersquareinchandreporttothreesignificantfigures.
11.2CompressiveYieldStrength—Calculatethecompres-siveyieldstrengthbydividingtheloadcarriedbythespecimenattheyieldpointbytheoriginalminimumcross-sectionalareaofthespecimen.Expresstheresultinmegapascalsorpounds-forcepersquareinchandreporttothreesignificantfigures.11.3OffsetYieldStrength—Calculatetheoffsetyieldstrengthbythemethodreferredtoin3.2.11.
11.4ModulusofElasticity—Calculatethemodulusofelas-ticitybydrawingatangenttotheinitiallinearportionoftheloaddeformationcurve,selectinganypointonthisstraightlineportion,anddividingthecompressivestressrepresentedbythispointbythecorrespondingstrain,measurefromthepointwheretheextendedtangentlineintersectsthestrain-axis.Expresstheresultingigapascalsorpounds-forcepersquareinchandreporttothreesignificantfigures(seeAnnexA1).11.5Foreachseriesoftests,calculatetothreesignificantfiguresthearithmeticmeanofallvaluesobtainedandreportasthe“averagevalue”fortheparticularpropertyinquestion.11.6Calculatethestandarddeviation(estimated)asfollowsandreporttotwosignificantfigures:
s5=~(X22nX
¯2!/~n21!(1)
where:
s=estimatedstandarddeviation,X=valueofsingleobservation,nX
¯=numberofobservations,and
=arithmeticmeanofthesetofobservations.NOTE10—ThemethodfordeterminingtheoffsetcompressiveyieldstrengthissimilartothatdescribedintheAnnexofTestMethodD638.
12.Report
12.1Reportthefollowinginformation:
12.1.1Completeidentificationofthematerialtested,includ-ingtype,source,manufacturer’scodenumber,form,principaldimensions,previoushistory,etc.,
12.1.2Methodofpreparingtestspecimens,12.1.3Typeoftestspecimenanddimensions,12.1.4Conditioningprocedureused,
12.1.5Atmosphericconditionsintestroom,12.1.6Numberofspecimenstested,12.1.7Speedoftesting,
12.1.8Compressivestrength,averagevalue,andstandarddeviation,
12.1.9Compressiveyieldstrengthandoffsetyieldstrengthaveragevalue,andstandarddeviation,whenofinterest,
12.1.10Modulusofelasticityincompression(ifrequired),averagevalue,standarddeviation,12.1.11Dateoftest,and12.1.12Dateoftestmethod.
13.PrecisionandBias913.1Table1andTable2arebasedonaround-robintest
TABLE1Precision,CompressiveStrength
(ValuesinUnitsofMegapascals)
MaterialAcetal
Polystyrene
Linen-filledphenolic
Apreparedatonesource.Eachtestresultwastheaverageoffiveindividualdeterminations.Eachlaboratoryobtainedtwotestresultsforeachmaterial.
NOTE11—Caution:ThefollowingexplanationsofrandR(13.2-13.2.3)areonlyintendedtopresentameaningfulwayofconsideringtheapproximateprecisionofthistestmethod.ThedatainTable1andTable2shouldnotberigorouslyappliedtoacceptanceorrejectionofmaterial,asthesedataapplyonlytothematerialstestedintheroundrobinandareunlikelytoberigorouslyrepresentativeofotherlots,formulations,conditions,materials,orlaboratories.UsersofthistestmethodshouldapplytheprinciplesoutlinedinPracticeE691togeneratedataspecifictotheirlaboratoryandmaterialsorbetweenspecificlaboratories.Theprinciplesof13.2-13.2.3wouldthenbevalidforsuchdata.
Average100106158
SrA1.11.43.7
SRB2.13.57.5
rC3.13.910.4
RD5.99.821.0
Sristhewithin-laboratorystandarddeviationfortheindicatedmaterial.Itisobtainedbypoolingthewithin-laboratorystandarddeviationsofthetestresultsfromalloftheparticipatinglaboratories:
Sr=[[(S1)2+(S2)2+...+(Sn)2]/n]1/2.
BSRisthebetween-laboratoriesreproducibility,expressedasastandarddeviation,fortheindicatedmaterial.Cristhewithin-laboratoryrepeatabilitylimit,r=2.83Sr.DRisthebetween-laboratoryreproducibilitylimit,R=2.83SR.
TABLE2Precision,CompressiveModulus
(ValuesinUnitsofMegapascals)
MaterialAcetal
Polystyrene
Linen-filledphenolic
AAverage3.283.886.82
SrA0.140.070.23
SRB0.250.740.90
rC0.390.200.64
RD0.702.072.52
Sristhewithin-laboratorystandarddeviationfortheindicatedmaterial.Itisobtainedbypoolingthewithin-laboratorystandarddeviationsofthetestresultsfromalloftheparticipatinglaboratories:
Sr=[[(S1)2+(S2)2+...+(Sn)2]/n]1/2.
BSRisthebetween-laboratoriesreproducibility,expressedasastandarddeviation,fortheindicatedmaterial.Cristhewithin-laboratoryrepeatabilitylimit,r=2.83Sr.DRisthebetween-laboratoryreproducibilitylimit,R=2.83SR.
conductedin1987inaccordancewithPracticeE691,involv-ingthreematerialstestedbysixlaboratoriesforTestMethodD695M.Sincethetestparametersoverlapwithintolerancesandthetestvaluesarenormalized,thesamedataareusedforbothtestmethods.Foreachmaterial,allofthesampleswere
SupportingdataareavailablefromASTMHeadquarters,RequestRR:D20-1150.
913.2ConceptofrandRinTable1andTable2—IfS(r)andS(R)havebeencalculatedfromalargeenoughbodyofdata,andfortestresultsthatwereaveragesfromtestingoffivespecimensforeachtestresult,then:
13.2.1Repeatability—Twotestresultsobtainedwithinonelaboratoryshallbejudgednotequivalentiftheydifferbymorethanthe“r”forthatthematerial.“r”istheintervalrepresentingthecriticaldifferencebetweentwotestresultsforthesamematerial,obtainedbythesameoperatorusingthesameequipmentonthesamedayinthesamelaboratory.
13.2.2Reproducibility,R—Twotestresultsobtainedbydifferentlaboratoriesshallbejudgednotequivalentiftheydifferbymorethanthe“R”valueforthatmaterial.“R”istheintervalrepresentingthecriticaldifferencebetweenthetwotestresultsforthesamematerial,obtainedbydifferentoperatorsusingdifferentequipmentindifferentlaboratories.
13.2.3Anyjudgementinaccordancewith13.2.1and13.2.2wouldhaveanapproximate95%(0.95)probabilityofbeingcorrect.
13.3Therearenorecognizedstandardsbywhichtoesti-matethebiasofthistestmethod.
14.Keywords
14.1compressiveproperties;compressivestrength;modu-lusofelasticity;plastics
ANNEX
(MandatoryInformation)A1.TOECOMPENSATION
A1.1Inatypicalstress-straincurve(Fig.A1.1)thereisatoeregion,AC,thatdoesnotrepresentapropertyofthematerial.Itisanartifactcausedbyatakeupofslack,andalignmentorseatingofthespecimen.Inordertoobtaincorrectvaluesofsuchparametersasmodulus,strain,andoffsetyieldpoint,thisartifactmustbecompensatedfortogivethecorrectedzeropointonthestrainorextensionaxis.
A1.2InthecaseofamaterialexhibitingaregionofHookean(linear)behavior(Fig.A1.1),acontinuationofthelinear(CD)regionofthecurveisconstructedthroughthezero-stressaxis.Thisintersection(B)isthecorrectedzero-strainpointfromwhichallextensionsorstrainsmustbe
measured,includingtheyieldoffset(BE),ifapplicable.TheelasticmoduluscanbedeterminedbydividingthestressatanypointalongthelineCD(oritsextension)bythestrainatthesamepoint(measuredfromPointB,definedaszero-strain).A1.3Inthecaseofamaterialthatdoesnotexhibitanylinearregion(Fig.A1.2),thesamekindoftoecorrectionofthezero-strainpointcanbemadebyconstructingatangenttothemaximumslopeattheinflectionpoint(H8).ThisisextendedtointersectthestrainaxisatPointB8,thecorrectedzero-strainpoint.UsingPointB8aszerostrain,thestressatanypoint(G8)onthecurvecanbedividedbythestrainatthatpointtoobtainasecantmodulus(slopeoflineB8G8).Forthosematerialswith
NOTE1—Somechartrecordersplotthemirrorimageofthisgraph.
FIG.A1.1MaterialwithHookeanRegion
nolinearregion,anyattempttousethetangentthroughtheinflectionpointasabasisfordeterminationofanoffsetyieldpointmayresultinunacceptableerror.
NOTE1—Somechartrecordersplotthemirrorimageofthisgraph.
FIG.A1.2MaterialwithNoHookeanRegion
SUMMARYOFCHANGES
Thissectionidentifiesthelocationofselectedchangestothistestmethod.Fortheconvenienceoftheuser,CommitteeD20hashighlightedthosechangesthatmayimpacttheuseofthistestmethod.Thissectionmayalsoincludedescriptionsofthechangesorreasonsforthechanges,orboth.
D695–02a:
(1)AddedTerminologyD883.(2)AddedTestMethodsD5947.
(3)Added3.1,adjustednumberingthroughoutSection3.(4)Changedreferencein3.2.8from3.11to3.2.11.(5)Deletedlastsentenceof4.1.(6)Addedlastsentenceto4.4.
(7)Reworded5.1.1toimprovereadability(8)Changed“fortuitousflow”to“flaw”in8.3.
(9)RewordedNote11,13.2,13.2.1,and13.2.2tobeinaccordancewithGuideD4968.(10)CorrectedthetitleofFig.3.D695–02:
(1)Revised7.1and7.2.
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