-,ASTMD299384R075953000284378IDesignation:D2991-844cni,AXîERICANSOCIETYFORTESTINGANb.MATERIALS1916RsceCt.,Philadelphia,Pa.19103ReprintedfromtheAnnualBookofASTMStandards,CopyrightASTMIfnetlistedinthecurrentcombinedindex,willappearinthenexteditio!.StandardPracticeforTestingSTRESS-RELAXATIONOFPLASTICS’ThisstandardisissuedunderthefixeddesignationD2991;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevkion.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelasfrevisionorreapproval.1.Scope1,IThispracticecoversthedeterminationofthetime-dependenceofstress(stressrelaxation)ofplasticsresistinglong-durationconstantstrainsatconditionsofconstanttemperatureandrela-tivehumidityandnegligiblevibration.1.2Thisstandardmayinvolvehazardoitsma-terials,operations,andequipment.Thisstandarddoesnotpurporttoaddressallofthesafityprob-lemsassociatedwithitsuse.Itistheresponsibil-ityofwhoeverusesthisstandardtoconsultandestablishappropriatesafetyandhealthpracticesanddeterminetheapplicabilityofregulatoiylimi-tationsprioriouse.2.ApplicableDocuments2.1ASTMStandards:D638TestMethodforTensilePropertiesofD695TestMethodforCompressiveProper-Plastics’tiesofRigidPlastics’3.Defdtions3.1stressrelaxation-thetime-dependentde-creaseinstressinasolidundergivenconstraintconditions.3.2initialstress-thestressintroducedintoaspecimenbyimposingthegivenconstraintcon-ditionsbeforestressrelaxationtakesplace.4.SignificanceandUse4.1Datafromstress-relaxationtestsareuseful.inpredictingthereductionofstressinmaterialssubjectedtoconstantdeformationforlongtimes,suchasthedecreaseintightnessofboltedorrivetedjoints.4.2Thistestishighlysensitivetosmallchangesinmaterialcompositionandenviron-mentalconditionsandhenceisusefulinevalu-atingtheeffectofsuchchanges.5.Grips5.1Thegripsandgrippingtechniqueshallbedesignedtominimizeeccentricloadingofthespecimen.Swiveloruniversaljointsshallbeusedbeyondeachendofthespecimen....
