1、Designation: G90 17Standard Practice forPerforming Accelerated Outdoor Weathering of MaterialsUsing Concentrated Natural Sunlight1This standard is issued under the fixed designation G90; the number immediately following the designation indicates the year of originaladoption or, in the case of revisi
2、on, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 Fresnel-reflecting concentrators using the sun as sourceare utilized in the accelerated outdoor exposu
3、re testing ofmaterials.1.2 This practice covers a procedure for performing accel-erated outdoor exposure testing of materials using a Fresnel-reflector accelerated outdoor weathering test machine. Theapparatus (see Fig. 1 and Fig. 2) and guidelines are describedherein to minimize the variables encou
4、ntered during outdooraccelerated exposure testing.1.3 This practice does not specify the exposure conditionsbest suited for the materials to be tested but is limited to themethod of obtaining, measuring, and controlling the proce-dures and certain conditions of the exposure. Samplepreparation, test
5、conditions, and evaluation of results arecovered in existing methods or specifications for specificmaterials.1.4 The Fresnel-reflector accelerated outdoor exposure testmachines described may be suitable for the determination ofthe relative durability of materials exposed to sunlight, heat,and moistu
6、re, provided the mechanisms of chemical or physi-cal change, or both, which control the acceleration factors forthe materials do not differ significantly.1.5 This practice establishes uniform sample mounting andin-test maintenance procedures. Also included in the practiceare standard provisions for
7、maintenance of the machine andFresnel-reflector mirrors to ensure cleanliness and durability.1.6 This practice shall apply to specimens whose size meetsthe dimensions of the target board as described in 8.2.1.7 For test machines currently in use, this practice may notapply to specimens exceeding 13
8、mm (12 in.) in thicknessbecause cooling may be questionable.1.8 Values stated in SI units are to be regarded as thestandard. The inch-pound units in parentheses are provided forinformation only.1.9 This standard does not purport to address all of thesafety concerns, if any, associated with its use.
9、It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.10 This international standard was developed in accor-dance with internationally recognized principles
10、on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D859 Test Method for Silica in WaterD1
11、014 Practice for Conducting Exterior Exposure Tests ofPaints and Coatings on Metal SubstratesD1435 Practice for Outdoor Weathering of PlasticsD1898 Practice for Sampling of Plastics (Withdrawn 1998)3D4141 Practice for Conducting Black Box and Solar Con-centrating Exposures of CoatingsD4364 Practice
12、for Performing Outdoor Accelerated Weath-ering Tests of Plastics Using Concentrated SunlightD4517 Test Method for Low-Level Total Silica in High-Purity Water by Flameless Atomic Absorption Spectros-copyD5722 Practice for Performing Accelerated Outdoor Weath-ering of Factory-Coated Embossed Hardboard
13、 Using Con-centrated Natural Sunlight and a Soak-Freeze-Thaw Pro-cedureE816 Test Method for Calibration of Pyrheliometers byComparison to Reference Pyrheliometers1This practice is under the jurisdiction of ASTM Committee G03 on Weatheringand Durabilityand is the direct responsibility of Subcommittee
14、 G03.02 on Naturaland Environmental Exposure Tests.Current edition approved Dec. 1, 2017. Published December 2017. Originallyapproved in 1985. Last previous edition approved in 2010 as G90 10. DOI:10.1520/G0090-17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM C
15、ustomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C70
16、0, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the Wo
17、rld Trade Organization Technical Barriers to Trade (TBT) Committee.1E824 Test Method for Transfer of Calibration From Refer-ence to Field RadiometersE903 Test Method for Solar Absorptance, Reflectance, andTransmittance of Materials Using Integrating SpheresG7 Practice for Atmospheric Environmental E
18、xposure Test-ing of Nonmetallic MaterialsG24 Practice for Conducting Exposures to Daylight FilteredThrough GlassG113 Terminology Relating to Natural and Artificial Weath-ering Tests of Nonmetallic MaterialsG167 Test Method for Calibration of a Pyranometer Using aPyrheliometerG169 Guide for Applicati
19、on of Basic Statistical Methods toWeathering TestsG173 Tables for Reference Solar Spectral Irradiances: DirectNormal and Hemispherical on 37 Tilted SurfaceG179 Specification for Metal Black Panel and White PanelTemperature Devices for Natural Weathering Tests2.2 Other Standards:SAE J576 Plastic Mate
20、rials for Use in Optical Parts Such asLenses and Reflectors of Motor Vehicle Lighting Devices4SAE J1961 Accelerated Exposure of Automotive ExteriorMaterials Using A Solar Fresnel Reflector ApparatusWMO Guide to Meteorological Instruments and Methods ofObservation WMO No. 8, Fifth Edition52.3 ISO Sta
21、ndards:6ISO 48921 Plastics Methods of Exposure to LaboratoryLight SourcesPart 1: General Guidance4Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,PA 15096-0001, http:/www.sae.org.5Available from World Meteorological Organization, Geneva, Switzerland.6Available from Internati
22、onal Organization for Standardization (ISO), ISOCentral Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,Geneva, Switzerland, http:/www.iso.org.FIG. 1 Schematic of Fresnel-Reflecting Concentrator Accelerated Weathering Machine Single Axis TrackingG901723. Terminology3.1 Definitions
23、Definitions of terms common to G03 du-rability standards can be found in Terminology G113.4. Significance and Use4.1 Results obtained from this practice can be used tocompare the relative durability of materials subjected to thespecific test cycle used. Results obtained from this practice canbe cons
24、idered as representative of natural weathering onlywhen the degree of comparative performance has been estab-lished for the specific materials being tested.4.2 The acceleration factor relating the rate of degradationin this accelerated exposure to the rate of degradation in anatural weathering expos
25、ure varies with the type and formula-tion of the material. Each material and formulation mayrespond differently to the increased level of irradiance anddifferences in temperature and humidity. Thus an accelerationfactor determined for one material may not be applicable toother materials. For this re
26、ason, the use of a single accelerationfactor is not recommended.Also, a different acceleration factormay be obtained by using different mirror types and configu-rations. Because of variability in test results for both acceler-ated and natural weathering exposures, results from a sufficientnumber of
27、tests must be obtained to determine an accelerationfactor for a material. Further, the acceleration factor is appli-cable to only one exposure location because results fromnatural weathering will vary due to seasonal or annual differ-ences in climatic factors.4.3 The relative durability of materials
28、 determined by thispractice can be used to determine the relative durability of thematerials exposed under natural weathering conditions pro-vided the materials have similar acceleration factors. However,even if results from a specific accelerated test condition arefound to be useful for comparing t
29、he durability of materialsexposed in a particular exterior location, it cannot be assumedthat they will be useful for determining the relative durabilityfor a different location. The relative durability of materials innatural weathering exposure can be very different dependingFIG. 2 Dual Axis Tracki
30、ngG90173on the location of the exposure because of differences inimportant climatic factors, such as sunlight, time of wetness,temperature, pollutants, etc.4.4 Variations in results may be expected when operatingconditions vary within the limits of this practice. For example,there can be large diffe
31、rences in the amount of degradation ina single material between separate, although supposedlyidentical, exposures carried out for the same duration ornumber of exposure cycles. This practice is best used tocompare the relative performance of materials tested at thesame time in the same fresnel refle
32、ctor device. Because ofpossible variability between the same type of exposure deviceand variability in irradiance, temperature and moisture levels atdifferent times, comparing the amount of degradation inmaterials exposed for the same duration or radiant energy atseparate times is not recommended.4.
33、5 This practice should not be used to establish a “pass/fail” approval of materials after a specific period of exposureunless performance comparisons are made relative to a controlmaterial exposed simultaneously. It is strongly recommendedthat at least one control test specimen be exposed with eacht
34、est. It is preferable to use two control test specimens, one withrelatively good durability and one with relatively poor dura-bility. Alternatively, the variability in the test can be defined sothat statistically significant pass/fail judgements can be made.4.6 The use of at least three replicates o
35、f each control testspecimen and each material being evaluated is recommended.Consult Guide G169 for performing statistical analysis.5. Apparatus5.1 Test MachinesFresnel-reflector test machines used inCycles 1, 2, and 3 of Table 1 are nearly identical. The onlydifference between the machines is the a
36、ddition of a waterdelivery system to the device used in Cycles 1 and 3. Use of thespecific cycle should relate to end use of the material andshould be agreed upon by all interested parties.5.1.1 The Fresnel-reflector test machine is a follow-the-sunapparatus having flat mirrors so positioned that th
37、e suns raysstrike them at near-normal incident angles while in operation.The mirrors are arranged to simulate tangents to a parabolictrough in order to reflect sunlight uniformly onto the specimensin the target area (see Fig. 1, Fig. 2, and Fig. 3).TABLE 1 Fresnel-Reflector Test Machine Typical Spra
38、y CyclesCycleDaytime NighttimeSprayDurationDry-TimeDurationCycles/hSprayDurationDry-TimeDurationCycles/h1 8 min 52 min 1 8 min water is sprayed on thetest specimens at:9:00 p.m.12:00 midnight3:00 a.m.2 no water spray used no water spray used3Ano water spray used 3 min 12 min 4 cycles per hour(from 7
39、PM to 5 AM)AThis is the cycle specified in Procedure C of Practice D4141.G901745.2 MirrorsThe Fresnel-reflector system mirrors of typi-cal machines currently in use have a typical specular, spectralreflectance curve such as that presented in Fig. 4. Other mirrortypes and configurations may be used p
40、roviding they meet therequirements of 6.2.FIG. 3 Schematic of Optical System for a Fresnel Reflecting Concentrator Accelerated Weathering MachineFIG. 4 Typical Specular Reflectance of Mirror MaterialG901755.3 Photoreceptor CellsTwo photoreceptor cells, such assilicon solar cells, are installed near
41、the top of the air tunnel onthe side facing the sun. A “T” shadow maker is mounted abovethe cells to illuminate equally one-half of each cell when thetest machine is in proper focus. As one cell receives moreradiation than the other, the balance is disturbed and a signal isfurnished through an ampli
42、fier to a reversible motor whichadjusts the machine to maintain focus.5.4 Tracking SystemThe test machine shall be equippedwith a system to keep the target area in focus throughout theday. Several options are possible.5.4.1 Single-axis tracking with manual altitude adjustment(Fig. 1). The test machi
43、nes axis is oriented in the north/southdirection, with the north pole being altitude-adjustable toaccount for seasonable variations in solar altitude at zenith.5.4.2 Dual axis tracking (Fig. 2). The test machine isequipped with two sets of photoreceptor cells, one to controlthe azimuth rotation of t
44、he machine, the other to control the tiltelevation. The axis of the target area remains parallel to theground. The machine rotates about horizontal and vertical axesto keep the target area in focus.5.5 TemperatureThe test machine is equipped with ablower to cool the test specimens. The air is direct
45、ed over thespecimens by an adjustable deflector along one side of thetarget area. For unbacked mounting, air is also directed underthe specimens. This limits the increase in surface temperaturesof most specimens to 10C above the maximum surfacetemperature that would be reached when identically mount
46、edspecimens are exposed to direct sunlight at normal incidence atthe same time and location without concentration.5.5.1 Temperature ControlUnless otherwise specified, ifmeasurement of uninsulated black- or white-panel temperatureis required, the panels shall be constructed, calibrated, andmaintained
47、 according to Specification G179 except that thesize shall be a minimum width of 50 mm by 125 mm. Unlessotherwise specified, if measurement of insulated black- orwhite-panel temperature is required, the panels shall be con-structed and maintained according to ISO 4892-1.NOTE 1If an insulated black-p
48、anel temperature is used, the tempera-ture indicated will be higher than that indicated by an uninsulatedblack-panel thermometer under typical exposure conditions.5.5.2 Typically, temperature of specimens is not controlledon solar concentrating test devices. Typical specimen tempera-tures obtained a
49、re likely to be greater than the temperature thatwould be experienced if the specimen were exposed to directsolar radiation at normal incidence (without concentration) atthe same time. Temperature differences between exposureswith and without concentration depend on the specimenabsorptance and total coefficient of heat transfer, thickness,backing, and composition. During daytime exposures in solarconcentrating test devices, variation in cloud cover may causespecimen temperatures to vary.5.5.3 If control of specimen temperature is required, thetemperature of an un
