1、Designation: G 156 09Standard Practice forSelecting and Characterizing Weathering ReferenceMaterials1This standard is issued under the fixed designation G 156; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard describes the criteria to be used forselection of a weathering reference material (WRM) andprocedures to be used fo
3、r determining within lab and betweenlab tolerances of changes in measured properties of a referencematerials. This standard also describes a procedure for com-paring different lots of the same type of a reference material.NOTE 1Examples of laboratory accelerated tests in which a weather-ing referenc
4、e material could be used to monitor consistency are exposuretests such as those described in Practices G 152, G 153, G 154, andG 155and other standards in which tests conducted according to thesestandards are referenced. Examples of outdoor exposures where a weath-ering reference material could be u
5、sed to monitor consistency are thoseconducted according to Practices G7, G24,orG90. A reference materialcan also be used to monitor consistency of exposure or conditioning testthat do not involve exposure to light.1.2 Weathering reference materials are most often used to(1) monitor consistency of co
6、nditions in exposure tests, (2) todetermine the time or radiant exposure at which test materialsare evaluated, (3) as a reference material for comparing to testmaterials exposed at the same time. Weathering referencematerials cannot be used to classify or characterize the relativeseverity of any exp
7、osure test because of the large variability inmaterial responses to the effects of light, heat, and water.1.3 This practice does not cover control materials which, bydefinition are selected to be of similar composition andconstruction to the test materials, and are exposed at the sametime as test ma
8、terials.1.4 This practice provides an outline of experiments re-quired to determine how the measured properties of thereference material change as a function of exposure to specifiedtest conditions. It includes establishment of reproducible mea-surement procedures, determination of the critical spec
9、tralregion in the light source causing the changes, and effects ofother critical exposure stresses such as temperature and mois-ture.2. Referenced Documents2.1 ASTM Standards:2E 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 691 Practice for Conducting an Interlaboratory S
10、tudy toDetermine the Precision of a Test MethodE 1169 Practice for Conducting Ruggedness TestsG7 Practice for Atmospheric Environmental ExposureTesting of Nonmetallic MaterialsG24 Practice for Conducting Exposures to Daylight Fil-tered Through GlassG90 Practice for Performing Accelerated Outdoor Wea
11、th-ering of Nonmetallic Materials Using Concentrated Natu-ral SunlightG113 Terminology Relating to Natural and ArtificialWeathering Tests of Nonmetallic MaterialsG 152 Practice for Operating Open Flame CarbonArc LightApparatus for Exposure of Nonmetallic MaterialsG 153 Practice for Operating Enclose
12、d Carbon Arc LightApparatus for Exposure of Nonmetallic MaterialsG 154 Practice for Operating Fluorescent Light Apparatusfor UV Exposure of Nonmetallic MaterialsG 155 Practice for Operating Xenon Arc Light Apparatusfor Exposure of Non-Metallic MaterialsG 178 Practice for Determining the Activation S
13、pectrum ofa Material (Wavelength Sensitivity to an Exposure Source)Using the Sharp Cut-On Filter or Spectrographic Tech-nique2.2 SAE Standard:SAE J1960, Accelerated Exposure of Automotive ExteriorMaterials using a Controlled Irradiance Water-CooledXenon Arc Apparatus3SAE J1885, Accelerated Exposure
14、of Automotive InteriorMaterials Using a Controlled Irradiance Water-CooledXenon Arc Apparatus31This practice is under the jurisdiction of ASTM Committee G03 on Weatheringand Durability and is the direct responsibility of Subcommittee G03.01 on JointWeathering Projects.Current edition approved June 1
15、, 2009. Published July 2009. Originally approvedin 1997. Last previous edition approved in 2002 as G 15602.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the stand
16、ards Document Summary page onthe ASTM website.3Available from Society of Automotive Engineers (SAE), 400 CommonwealthDr., Warrendale, PA 15096-0001, http:/www.sae.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. Terminology3.1
17、DefinitionsThe definitions listed in TerminologyG113are applicable to this standard.4. Significance and Use4.1 Weathering reference materials are used in laboratoryaccelerated exposure tests to verify consistency among testsrun at different times and in different laboratories, using thesame exposure
18、 conditions. Specifications defining consistencyof exposure conditions are based on the property change of areference material after a defined period of time. Someweathering reference materials are used to define periods ofexposure. Specifications calling for use of these materialsrequire the materi
19、al to be exposed until a defined change in theweathering reference material is achieved. Specifications areusually based on results for a single lot of the weatheringreference material. When a new lot of the reference material isintroduced, round-robin studies are necessary to compare thenew and old
20、 lots and to establish appropriate limits forexpected performance of the new lot.NOTE 2An example of the use of a clear polystyrene referencestandard for this purpose is given in SAE J1885 and SAE J1960.NOTE 3Some weathering reference materials (for example bluewools) are also used to define periods
21、 of exposure. Although notspecifically covered by this standard, the procedures described forcharacterizing a reference material used to monitor consistency ofexposures are also generally applicable to characterizing reference mate-rials used to define periods of exposure.4.2 It is important to test
22、 the consistency of exposure in thelaboratory accelerated device with a weathering referencematerial that responds to the test conditions similar to the waythe test materials respond. Therefore, the weathering referencematerial should be sensitive to the spectral region of the lightsource mainly res
23、ponsible for producing degradation in the testmaterials to provide the most meaningful evaluation of expo-sure test consistency. The weathering reference material shouldalso provide information on consistency of temperature andhumidity conditions if the latter are important factors indegradation of
24、the test materials.NOTE 4Material homogeneity can also be an important factor inselection of a weathering reference material, particularly if weathering isinitiated by the radiation absorbed by impurities as is the case in aliphatictype polymers exposed to radiation longer than 300 nm.4.3 The measur
25、ement of the characteristic property of aweathering reference material can be subject to error depend-ing on the instrument and the procedure used to measure theproperty. It is important to develop measurement proceduresthat are clear and which minimize chances for operatormisinterpretation. It is a
26、lso important to determine the level ofvariability caused by measurement of the characteristic prop-erty.4.4 When a reference material is used to monitor or specifythe consistency of an exposure test, it is important that anyspecification limits defined by changes in the reference mate-rial be based
27、 on a sound statistical analysis of results from aproperly designed round-robin experiment. This practice pro-vides a procedure which can be followed to set up theround-robin, analyze results, and establish reasonable limits ofchange in the characteristic property of the reference materialthat can b
28、e used in specifications.4.4.1 The results obtained according to this practice arevalid only for the exposure cycle used for the round-robin andcannot be applied to the same weathering reference materialused in a different exposure cycle.4.5 The change in characteristic property of a referencemateri
29、al may be affected by the placement of the referencematerial in the exposure device. This is often due to variationsin light intensity and temperature within the allowed exposurearea. Random placement of replicate specimens of the weath-ering reference material through-out the allowed exposure areap
30、rovides the best indication of the overall consistency of theexposure test.NOTE 5In some cases, procedures require exposure of a weatheringreference material at a specific location within the exposure device orchamber. Results for a reference material used in this way may not providean accurate repr
31、esentation of the exposure conditions in other positionswithin the device.5. Procedure5.1 Select a weathering reference material that exhibits asignificant change in a characteristic property when exposedfor an acceptable period of time, to the exposure conditionsdescribed in the applicable test pro
32、cedure.5.2 Determine the procedure used that can best measure thechange in characteristic property of the reference material.5.2.1 Conduct a series of experiments to determine theeffect of important factors in the measurement procedure. It isrecommended that this be done using a ruggedness testaccor
33、ding to Guide E 1169 to determine which factors signifi-cantly affect results. The results from this test can be used totighten the test measurement procedures.5.2.2 When the results from the ruggedness testing arecomplete, write a set of instructions for measuring the charac-teristic property that
34、is unambiguous and clearly understood byoperators who will be making the measurement. Have twooperators in one laboratory conduct the measurement on atleast three replicate specimens of the reference material.Interview the operators to determine whether the procedureprovides clear and easy to unders
35、tand directions. Modify theprocedure to remove any ambiguity in instructions.5.3 Determine the homogeneity of the weathering referencematerial by measuring the property change of randomlyselected replicate specimens that have been exposed to verytightly controlled test conditions, or by appropriate
36、chemicalanalysis techniques such as ultraviolet and/or infrared spectros-copy.5.4 For any new weathering reference material, determinethe response of the reference material to critical exposurestresses. These results are important to determining whetherthe material being considered is appropriate fo
37、r monitoring thespecific conditions of the exposure test being used. Tests todetermine the materials response to exposure stresses should bedone in a single laboratory or a series of laboratories agreedupon by all interested parties.5.4.1 Conduct experiments to determine the spectral regionof the li
38、ght source to which the characteristic property is mostG156092sensitive, i.e. the activation spectrum of the weathering refer-ence material. This can be accomplished by techniques toisolate the effects of individual narrow bands of the actinicregion of the light source. It is recommended that severa
39、ldeterminations of the activation spectrum be conducted.NOTE 6Practice G 178 describes two procedures for determination ofactivation spectra of polymers.5.4.2 Conduct experiments to determine how the rate ofchange of the characteristic property of the reference materialis affected by temperature. Th
40、is can be done by exposing aseries of reference material specimens to the light source ofchoice at a series of temperatures (with irradiance and humidityheld constant).5.4.3 Conduct a series of experiments to determine how therate of change of the characteristic property of the referencematerial is
41、affected by moisture. This can be done by conduct-ing exposure tests at constant light intensity and temperaturewhere the time of wetness or relative humidity is varied.5.4.4 A factorially designed experiment can be used todetermine the effects of moisture and humidity. Use at least twolevels of tem
42、perature and relative humidity in the designedexperiment conducted at a constant light intensity.5.5 The procedure for conducting the exposure test in whichthe weathering reference material is used should clearly specifythe levels of light intensity, filters used on light source,chamber or black pan
43、el temperature, and moisture conditions.These conditions must be specified for each different light/darkperiod used in the exposure cycle chosen.5.6 Determine the stability of the measured property of thereference material after it has been removed from the exposure.The post exposure stability of th
44、e characteristic property can bedetermined by measurements made at a series of times afterremoval from the exposure. Typically, these measurements willbe made at successively long time intervals. Some materials(for example polysulfone) show a continuing change in mea-sured property after they are re
45、moved from the exposure. If thecharacteristic property shows a change after being removedfrom the exposure, the instructions for use must clearly specifythe time after exposure when the characteristic property is to bemeasured. It is strongly recommended that the characteristicproperty of the refere
46、nce material be reasonably stable afterremoval from the exposure test.5.6.1 Property measurements must be made during theperiod when the weathering reference material is stable afterbeing exposed.NOTE 7Tests to determine wavelength sensitivity do not provideinformation about the effects of temperatu
47、re, moisture, or variation inirradiance. Variations in these other exposure stresses may alter the resultsof test used to determine wavelength sensitivity.NOTE 8In general, weathering reference materials that are stable forat least 10 days after removal from exposure will be the most useful.5.7 Afte
48、r selecting the reference material, characteristicproperty, property measurement procedure, and the desiredexposure conditions, set up a round-robin study to determinethe level of within lab repeatability and between lab reproduc-ibility for the change in property of the reference material afterspec
49、ific exposure periods.5.7.1 Conduct the round-robin according to Guide E 691.Atleast six laboratories should participate in the round robin.5.7.2 Prepare a clear set of instructions for all round-robinparticipants. The instructions should cover specimen place-ment in the exposure device, including how the referencematerial is to be mounted in specimen holder, exact exposurecycle to be used, the exact procedure for measuring character-istic property, and how data will be recorded.NOTE 9Round-robin studies can be designed to determine reproduc-ibility and repeatability limits
