Designation:G156−17StandardPracticeforSelectingandCharacterizingWeatheringReferenceMaterials1ThisstandardisissuedunderthefixeddesignationG156;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thisstandarddescribesthecriteriatobeusedforselectionofaweatheringreferencematerial(WRM)andprocedurestobeusedfordeterminingwithinlabandbetweenlabtolerancesofchangesinmeasuredpropertiesofweatheringreferencematerials.Thisstandardalsodescribesaprocedureforcomparingdifferentlotsofthesametypeofaweatheringreferencematerial.NOTE1—Examplesoflaboratoryacceleratedtestsinwhichaweather-ingreferencematerialcouldbeusedtomonitorconsistencyareexposuretestssuchasthosedescribedinPracticesG152,G153,G154,andG155andotherstandardsinwhichtestsconductedaccordingtothesestandardsarereferenced.Examplesofoutdoorexposureswhereaweath-eringreferencematerialcouldbeusedtomonitorconsistencyarethoseconductedaccordingtoPracticesG7,G24,orG90.Areferencematerialcanalsobeusedtomonitorconsistencyofexposureorconditioningtestthatdonotinvolveexposuretolight.1.2Weatheringreferencematerialsaremostoftenusedto(1)monitorconsistency(thatis,repeatability,reproducibility,orboth)ofexposuretests,(2)todeterminethetimeorradiantexposureatwhichtestmaterialsareevaluated,(3)asareferencematerialforcomparingtotestmaterialsexposedatthesametime.Weatheringreferencematerialscannotbeusedtoclassifyorcharacterizetherelativeseverityofanyexposuretestbecauseofthelargevariabilityinmaterialresponsestotheeffectsoflight,heat,andwater.1.3Thispracticedoesnotcovercontrolmaterialswhich,bydefinitionareselectedtobeofsimilarcompositionandconstructiontothetestmaterials,andareexposedatthesametimeastestmaterials.1.4Thispracticeprovidesanoutlineofexperimentsre-quiredtodeterminehowthemeasuredpropertiesofthereferencematerialchangeasafunctionofexpos...
