1、Designation: G141 09Standard Guide forAddressing Variability in Exposure Testing of NonmetallicMaterials1This standard is issued under the fixed designation G141; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONNo experimental procedure is exactly repeatable or reproducible. Exposure testing is susceptible topoor test reproducibility b
3、ecause 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 difficul
4、t 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 be
5、tween 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. Scope*1.1 This guide covers information on sources of variabilityand strategies for
6、 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 paren
7、-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 limitat
8、ions prior to use.2. Referenced Documents2.1 ASTM Standards:2D4853 Guide for Reducing Test Variability3D6631 Guide for Committee D01 for Conducting an Inter-laboratory Study for the Purpose of Determining thePrecision of a Test MethodE177 Practice for Use of the Terms Precision and Bias inASTM Test
9、MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG7 Practice for Atmospheric Environmental Exposure Test-ing of Nonmetallic MaterialsG24 Practice for Conducting Exposures to Daylight FilteredThrough GlassG90 Practice for Performing Accelerated Ou
10、tdoor Weather-ing of Nonmetallic Materials Using Concentrated NaturalSunlightG113 Terminology Relating to Natural andArtificial Weath-ering Tests of Nonmetallic MaterialsG147 Practice for Conditioning and Handling of Nonmetal-lic Materials for Natural and Artificial Weathering TestsG151 Practice for
11、 Exposing Nonmetallic Materials in Ac-celerated Test Devices that Use Laboratory Light SourcesG152 Practice for Operating Open Flame Carbon Arc LightApparatus for Exposure of Nonmetallic MaterialsG153 Practice for Operating Enclosed Carbon Arc LightApparatus for Exposure of Nonmetallic MaterialsG154
12、 Practice for Operating Fluorescent Light Apparatusfor UV Exposure of Nonmetallic MaterialsG155 Practice for Operating XenonArc LightApparatus forExposure of Non-Metallic MaterialsG166 Guide for Statistical Analysis of Service Life Data1This guide is under the jurisdiction of ASTM Committee G03 on W
13、eatheringand Durability and is the direct responsibility of Subcommittee G03.93 on Statistics.Current edition approved Dec. 1, 2009. Published February 2010. Originallyapproved in 1996. Last previous edition approved in 2003 as G141 03. DOI:10.1520/G0141-09.2For referenced ASTM standards, visit the
14、ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1*A Summ
15、ary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.G169 Guide for Application of Basic Statistical Methods toWeathering TestsG172 Guide for Statistical Analysis of Accelerated Se
16、rviceLife DataG183 Practice for Field Use of Pyranometers, Pyrheliom-eters and UV Radiometers3. Terminology3.1 Definitions:3.1.1 Terminology G113 is generally applicable to thisguide.4. Significance and Use4.1 Many standards and specifications reference exposuretests performed according to standards
17、 that are the responsi-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
18、 from the exposure 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
19、in weathering testing 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 G147. To reduce
20、 the contribution 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 D4853, along withmethods for identif
21、ying probable causes.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 o
22、f lati-tude). Subcategories 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 dif
23、ferent locationsor 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
24、. Typically, expo-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. Different exposure sites in one climate (even those inclose proximity) can cause significantl
25、y different results, de-pending on 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 YearSol
26、ar-ultraviolet radia-tion, temperature, and time of wetness vary considerably withtime of year. This can cause significant differences in the rateof degradation in many materials. Therefore, comparison ofresults between short-term exposure studies (less than one fullyear) will be subject to greater
27、variability. If exposures of 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 es
28、pecially true when the materialsresponse 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.
29、 However, an inherent limitationin 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
30、materials that are sensitive 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 radiatio
31、n inthe 290 to 310-nm band pass exhibits the most seasonalvariability. Some 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 bro
32、ad-bandsolar ultraviolet (UV) 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).45.3 Variability Due to Year-to-Year ClimatologicalVariationsEven the comparison of test results of full-y
33、earexposure increments may 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 mild
34、ew.These differences can impact material failure rates. Resultsfrom a single-exposure test cannot be used to predict theabsolute rate at which a material degrades. Several years ofrepeat exposures are needed to get an “average” test result forany given test site.5.4 Variability Due to Test DesignEve
35、ry exposure test hassome variability 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 rack4The boldface numbers in parentheses refer
36、 to the list of references at the end ofthis standard.G141 092location in an exposure site field can affect specimen tempera-ture and time of wetness.5.5 Variability in Glass-filtered Daylight ExposuresGlass-filtered daylight exposures as described by Practice G24 aresubject to many of the test vari
37、ables previously described.Recent 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 320 nm that cansignificantly impact exposure results
38、(3). In addition, solariza-tion 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 Acce
39、lerated outdoor exposures using Fresnel concentra-tors are described in Practice G90. 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
40、 is reduced during winter exposures and is also subjectto normal year-to-year variations. As mentioned in 5.2, currentradiant energy band passes, both total solar and broad-bandUV, used in reporting solar dose do not adequately reflectvariations in the critical 290 to 310-nm range. Because of thetim
41、e of year differences in the amount of available ultraviolet,timing exposures based on accumulated ultraviolet dose canimprove test-to-test variability, but may not account for thesubstantial specimen temperature differences that exist be-tween summer and winter.6.2 When test conditions specify wate
42、r spray, water qualityis extremely critical. Water contaminants or impurities cancause specimen spotting that will give misleading durabilityresults.7. Variability in Laboratory Exposure Tests7.1 Practices G151, G152, G153, G154, and G155 describelaboratory accelerated weathering tests and are refer
43、enced inmany ASTM standards describing tests for particular products.A round-robin evaluation of filtered open flame carbon-arc,fluorescent UV, and xenon-arc exposures was performed be-tween 1985 and 1992 comparing the gloss retention of variousvinyl tapes (5). Although the variability reported is s
44、pecific tothe materials tested and the participating laboratories, thesereferenced round-robin studies serve as a warning to users ofdurability test standards that high levels of variability may bepossible with any test or material.7.1.1 RepeatabilityIn general, test precision within labo-ratories (
45、a single test period in a test device) will always bebetter than precision between laboratories. By testing replicatespecimens, statistically significant performance differencesamong materials can be readily established.7.1.2 ReproducibilityThe G03.03 round-robin studiesfound that between laboratory
46、 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 studies havedemonstrated varying degree
47、s of variability with differentmaterials and property measurements (6-8) 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 precision and related statistical terms
48、are defined inPractice E177.7.2 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). In many instances, the filter glasses
49、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 Water contaminants or impurities and p
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