1、Designation: G 141 03Standard Guide forAddressing Variability in Exposure Testing of NonmetallicMaterials1This standard is issued under the fixed designation G 141; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONNo experimental procedure is exactly repeatable or reproducible. Exposure testing is susceptible topoor test reproducibilit
3、y because of many contributing factors. These include the type of material andits homogeneity, the complexity and variability of the outdoor environment, difficulty in preciselycontrolling the laboratory testing environment, and the variability in the measurement of performance.It is extremely diffi
4、cult to compare “absolute data,” that is, color shift, gloss, tensile, and elongation,and so forth, from different exposure tests. This is true for natural and accelerated exposures conductedoutdoors or for accelerated exposure tests conducted at different times in one laboratory or comparingresults
5、 between laboratories. The purpose of this guide is to provide the user with backgroundinformation on test variability and guidance to conduct an exposure test that will provide valid anduseful durability information.1. Scope1.1 This guide covers information on sources of variabilityand strategies f
6、or its reduction in exposure testing, and fortaking variability into consideration in the design, execution,and data analysis of both exterior and laboratory acceleratedexposure tests.1.2 The values stated in SI units are to be regarded sepa-rately as the standard. The inch-pound values given in par
7、en-theses are for information only.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limit
8、ations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 4853 Guide for Reducing Test VariabilityD 6631 Guide for Committee D01 for Conducting andInterlaboratory Study, and Determining the Precision of aTest MethodE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 69
9、1 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG 7 Practice for Atmospheric Environmental ExposureTesting of Nonmetallic MaterialsG 24 Practice for Conducting Exposures to Daylight Fil-tered Through GlassG 90 Practice for Performing Accelerated Outdoor W
10、eath-ering of Nonmetallic Materials Using Concentrated Natu-ral SunlightG 113 Terminology Relating to Natural and ArtificialWeathering Tests for Nonmetallic MaterialsG 147 Practice for Conditioning and Handling of Nonme-tallic Materials for Natural and Artificial Weathering TestsG 151 Practice for E
11、xposing Nonmetallic Materials in Ac-celerated Test Devices That Use Laboratory Light SourcesG 152 Practice for Operating Open Flame Carbon-ArcLight Apparatus for Exposure of Nonmetallic MaterialsG 153 Practice for Operating Enclosed Carbon-Arc LightApparatus for Exposure of Nonmetallic MaterialsG 15
12、4 Practice for Operating Fluorescent Light Apparatusfor Exposure of Nonmetallic MaterialsG 155 Practice for Operating Xenon-Arc Light Apparatusfor Exposure of Nonmetallic Materials1This guide is under the jurisdiction of ASTM Committee G03 on Durability ofNonmetallic Materials and is the direct resp
13、onsibility of Subcommittee G03.93 onStatistics.Current edition approved Dec. 1, 2003. Published January 2004. Originallyapproved in 1996. Last previous edition approved in 1996 as G 141 96.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servic
14、eastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.G 166 Guide for Statistical Analysis of Service Life Data
15、G 169 Guide for Application of Basic Statistical Methods toWeathering Tests3. Terminology3.1 Definitions:3.1.1 Terminology G 113 is generally applicable to thisguide.4. Significance and Use4.1 Many standards and specifications reference exposuretests performed according to standards that are the res
16、ponsi-bility of Committee G03 on Durability of Nonmetallic Mate-rials. In many cases, use of the data generated in these testsfails to consider the ramifications of variability in the exposuretest practices. This variability can have a profound effect on theinterpretation of results from the exposur
17、e tests, and if nottaken into consideration in test design and data analysis, canlead to erroneous or misleading conclusions. This guide listssome of the sources for test variability and recommendsstrategies for executing successful weathering studies. Not allsources of variability in weathering tes
18、ting are addressed in thisguide. Specific materials, sampling procedures, specimenpreparation, specimen conditioning, and material propertymeasurements can contribute significantly to variability inweathering test results. Many of these concerns are addressedin Guide G 147. To reduce the contributio
19、n of an instrumentalmethod to test variability, it is essential to follow appropriatecalibration procedures and ASTM standards associated withthe particular property measurement. Additional sources ofvariability in test results are listed in Guide D 4853, along withmethods for identifying probable c
20、auses.5. Variability in Outdoor Exposure Tests5.1 Variability Due to ClimateClimate at the test sitelocation can significantly affect the material failure rates andmodes. Typical climatological categories are; arctic, temperate,subtropical, and tropical (that are primarily functions of lati-tude). S
21、ubcategories may be of more importance as beingdictated by geographic, meteorological, terrain, ecological, andland-use factors, and include such categories as desert, for-ested, (numerous classifications), open, marine, industrial, andso forth. Because different climates, or even different location
22、sor orientation in the same climate, produce different rates ofdegradation or different degradation mechanisms, it is ex-tremely important to know the characteristics of the exposuresites used and to evaluate materials at sites that produceintensification of important climate stresses. Typically, ex
23、po-sures are conducted in “hot/wet” and “hot/dry” climates toprovide intensification of important factors such as solarradiation and temperature, and to determine possible effects ofmoisture. Exposure sites in one climate (even those in closeproximity) can cause significantly different results, depe
24、ndingon material.NOTE 1Exposures in a tropical summer rain climate (for example,Miami, Florida) and in a hot desert climate (for example, Phoenix, AZ) arerecognized as benchmarks for evaluating the durability of many differentmaterials.5.2 Variability Due to Time of YearSolar-ultraviolet radia-tion,
25、 temperature, and time of wetness vary considerably withtime of year. This can cause significant differences in the rateof degradation in many polymers. Therefore, comparison ofresults between short-term exposure studies (less than one fullyear) will be subject to greater variability. If exposures o
26、f lessthan a full year are required, consider using times whenclimatological stress is maximized so a worst case test result isobtained. It may also be valuable to make several exposuretests with varying start dates in order to provide more repre-sentative data. This is especially true when the mate
27、rialsresponse to the environment cannot be predetermined, or whenmaterials with different environmental responses are to becompared. Often exposure periods are timed by total solar orsolar-ultraviolet dose, or both. This approach may reducevariability in certain instances. However, an inherent limit
28、ationin solar-radiation measurements is that they do not reflect theeffects of variation in temperature and moisture, which areoften as important as solar radiation. Temperature and time ofwetness are highly dependent on time of year, especially intemperate climates. With materials that are sensitiv
29、e to heat ormoisture, or both, the same solar-ultraviolet radiation dose maynot give the same degree of change unless the heat andmoisture levels are also identical.5.2.1 Another problem related to timing exposures bybroad-band radiation measurements is that solar radiation inthe 290 to 310-nm band
30、pass exhibits the most seasonalvariability. Many polymer systems are extremely sensitive toradiation in this band pass. Variations in irradiance in thiscritical region (because of their relatively small magnitude) arenot adequately reflected in total solar radiation or broad-bandsolar ultraviolet (U
31、V) measurements.5.2.2 The time of year (season) that an exposure test isinitiated has, in certain instances, led to different failure ratesfor identical materials (1).35.3 Variability Due to Year-to-Year ClimatologicalVariationsEven the comparison of test results of full-yearexposure increments may
32、show variability. Average tempera-ture, hours of sunshine, and precipitation can vary considerablyfrom year to year at any given location. The microclimate forthe test specimens can be affected by yearly differences inpollution levels, airborne particulates, mold, and mildew.These differences can im
33、pact material failure rates. Resultsfrom a single-exposure test cannot be used to predict theabsolute rate at which a polymer degrades. Several years ofrepeat exposures are needed to get an “average” test result forany given test site.5.4 Variability Due to Test DesignEvery exposure test hassome var
34、iability inherent in its structure and design. Specimenplacement on an exposure rack (2), and type or color ofadjacent specimens can also affect specimen temperature andtime of wetness. Sample backing or insulation as well as racklocation in an exposure site field can affect specimen tempera-ture an
35、d time of wetness.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.G1410325.5 Variability in Glass-filtered Daylight ExposuresGlass-filtered daylight exposures as described by Practice G 24 aresubject to many of the test variables previously described.R
36、ecent studies conducted by ASTM Subcommittee G03.02 onNatural Environmental Testing has demonstrated that the glassused in these exposures can be highly variable in its lighttransmission characteristics between 300 and 400 nm that cansignificantly impact exposure results (3). In addition, solariza-t
37、ion processes can alter these transmission characteristicsduring the first few months of exposure. Specimen temperaturecan also vary depending on location within an under glass testrack (4).6. Variability in Accelerated Outdoor Exposures UsingConcentrated Sunlight6.1 Accelerated outdoor exposures us
38、ing Fresnel concentra-tors are described in Practice G 90. Test results are subject tonormal climatological and seasonal variations. Exposure peri-ods are described by a radiant energy dose, most often in theUV region of sunlight. The UV content of the concentratedsunlight is significantly reduced d
39、uring winter exposures and isalso subject to normal year-to-year variations. As mentioned in5.2, current radiant energy band passes, both total solar andbroad-band UV, used in reporting solar dose do not adequatelyreflect variations in the critical 290 to 310-nm range. Becauseof the time of year dif
40、ferences in the amount of availableultraviolet, timing exposures based on accumulated ultravioletdose can improve test-to-test variability, but may not accountfor the substantial specimen temperature differences that existbetween summer and winter.6.2 Significant variability in test results can occu
41、r betweenlaboratories conducting accelerated outdoor exposures usingconcentrated sunlight (4). Identical materials exposed for thesame time period, but at different sites within close proximityto each other, had significantly different failure rates.6.3 When test conditions specify water spray, wate
42、r qualityis extremely critical. Water contaminants or impurities cancause specimen spotting that will give misleading durabilityresults.7. Variability in Laboratory Exposure Tests7.1 Practices G 151, G 152, G 153, G 154, and G 155 de-scribe laboratory accelerated weathering tests and are refer-enced
43、 in many ASTM standards describing tests for particularproducts. A round-robin evaluation of carbon-arc, fluorescentUV, and xenon-arc exposures was performed between 1985and 1992 comparing the gloss retention of various vinyl tapes(6). Although the variability reported is specific to the materialste
44、sted and the participating laboratories, these referencedround-robin studies serve as a warning to users of durabilitytest standards that high levels of variability may be possiblewith any test or material.7.1.1 RepeatabilityIn general, test precision within labo-ratories (a single test period in a
45、test device) will always bebetter than precision between laboratories. By testing replicatespecimens, statistically significant performance differencesamong materials can be readily established during a specificexposure period in an individual test device.7.1.2 ReproducibilityThe G03.03 round-robin
46、studiesfound that between laboratory comparisons of absolute glossvalues after a fixed exposure time is, in a practical sense,impossible. Replicates specimens exposed to seemingly iden-tical test conditions gave highly variable results from labora-tory to laboratory. Other round-robin weathering stu
47、dies havedemonstrated varying degrees of variability with differentmaterials and property measurements (7-9) Precise control ofcritical exposure parameters may not be feasible when devicesare located in differing ambient laboratory conditions andoperated by a diverse user group.NOTE 2Indices of prec
48、ision and related statistical terms are defined inPractice E 177.7.2 Specific Factors Responsible for Variability in Acceler-ated Laboratory Exposure Tests:7.2.1 Light sources for all test devices are subject to normalmanufacturing variation in peak irradiance and spectral powerdistribution (SPD). I
49、n many instances, the filter glasses asso-ciated with certain devices and light sources also demonstratesignificant variation in their initial UV transmission character-istics. As the light source and filter glasses age during normaluse, the irradiance and SPD can also change significantly.Instruments that monitor irradiance at 340 nm or broad-bandradiometers (300 to 400 nm) may not detect or compensate forthese changes.7.2.2 Irradiance and specimen temperatures can vary sig-nificantly throughout the allowed specimen exposure area,especially in older test equipment.7.2.3 Wat
