1、Designation: G90 10Standard Practice forPerforming Accelerated Outdoor Weathering of NonmetallicMaterials Using 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 ca
2、se of revision, 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 ou
3、tdoor exposure testing ofnonmetallic materials.1.2 This practice covers a procedure for performing accel-erated outdoor exposure testing of nonmetallic materials usinga Fresnel-reflector accelerated outdoor weathering test ma-chine. The apparatus (see Fig. 1 and Fig. 2) and guidelines aredescribed h
4、erein to minimize the variables encountered duringoutdoor accelerated 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 t
5、he exposure. Sample prepara-tion, test conditions, and evaluation of results are covered inexisting methods or specifications for specific materials.1.4 The Fresnel-reflector accelerated outdoor exposure testmachines described may be suitable for the determination ofthe relative durability of materi
6、als exposed to sunlight, heat,and moisture, provided the mechanisms of chemical or physi-cal change, or both, which control the rates of accelerationfactors for the materials do not differ significantly.1.5 This practice establishes uniform sample mounting andin-test maintenance procedures. Also inc
7、luded in the practiceare standard provisions for 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
8、 practice may notapply to specimens exceeding 13 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 thes
9、afety 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 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D859 Test Method for Silica i
10、n WaterD1014 Practice for Conducting Exterior Exposure Tests ofPaints and Coatings on Metal SubstratesD1435 Practice for Outdoor Weathering of PlasticsD1898 Practice for Sampling of Plastics3D4141 Practice for Conducting Black Box and Solar Con-centrating Exposures of CoatingsD4517 Test Method for L
11、ow-Level Total Silica in High-Purity Water by Flameless Atomic Absorption Spectros-copyE816 Test Method for Calibration of Pyrheliometers byComparison to Reference PyrheliometersE824 Test Method for Transfer of Calibration From Refer-ence to Field RadiometersE903 Test Method for Solar Absorptance, R
12、eflectance, andTransmittance of Materials Using Integrating Spheres3G7 Practice for Atmospheric Environmental Exposure Test-ing of Nonmetallic MaterialsG24 Practice for Conducting Exposures to Daylight FilteredThrough GlassG113 Terminology Relating to Natural andArtificial Weath-ering Tests of Nonme
13、tallic MaterialsG167 Test Method for Calibration of a Pyranometer Usinga PyrheliometerG169 Guide for Application of Basic Statistical Methods toWeathering TestsG173 Tables for Reference Solar Spectral Irradiances: Di-rect Normal and Hemispherical on 37 Tilted Surface1This practice is under the juris
14、diction of ASTM Committee G03 on Weatheringand Durability and is the direct responsibility of Subcommittee G03.02 on Naturaland Environmental Exposure Tests.Current edition approved June 1, 2010. Published June 2010. Originallyapproved in 1985. Last previous edition approved in 2005 as G90 05. DOI:1
15、0.1520/G0090-10.2For 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 standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this
16、 historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.2 Other Standards:SAE J576 Plastic Materials for Use in Optical Parts Such asLenses and Reflectors of Motor Vehicle Lighting Devices4
17、WMO Guide to Meteorological Instruments and Methods ofObservation WMO No. 8, Fifth Edition53. Terminology3.1 DefinitionsDefinitions 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 r
18、elative durability of materials subjected to thespecific test cycle used. No accelerated exposure test can bespecified as a total simulation of natural or field exposures.Results obtained from this practice can be considered asrepresentative of natural or field exposures only when thedegree of compa
19、rative performance has been established forthe specific materials being tested.4.2 The relative durability of materials in natural or fieldexposure can be very different depending on the location of theexposure because of differences in UV radiation, time ofwetness, temperature, pollutants, and othe
20、r factors. Therefore,even if results from a specific accelerated test condition arefound to be useful for comparing the relative durability ofmaterials exposed in a particular exterior location, it cannot beassumed that they will be useful for determining relativedurability for a different location.
21、4.3 The use of a single acceleration factor relating the rateof degradation in this accelerated exposure to the rate ofdegradation in a conventional exterior exposure is not recom-mended because the acceleration factor varies with the typeand formulation of the material. Each material and formulatio
22、nmay respond 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. Because of variability in test results under bothaccelerated and conventional exterior exposures r
23、esults from a4Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,PA 15096-0001, http:/www.sae.org.5Available from World Meteorological Organization, Geneva, Switzerland.FIG. 1 Schematic of Fresnel-Reflecting Concentrator Accelerated Weathering Machine Single Axis TrackingG90102
24、sufficient number of tests must be obtained to determine anacceleration factor for a material. Further, the accelerationfactor is applicable to only one exterior exposure locationbecause results from conventional exterior exposures can varydue to seasonal or annual differences in important climaticf
25、actors.4.4 Variations in results may be expected when operatingconditions vary within the limits of this practice. For example,there can be large differences in the amount of degradation ina single material between separate, although supposedly iden-tical, exposures carried out for the same duration
26、 or number ofexposure cycles. This practice is best used to compare therelative performance of materials tested at the same time in thesame fresnel reflector device. Because of possible variabilitybetween the same type of exposure device and variability inirradiance, temperature and moisture levels
27、at different times,comparing the amount of degradation in materials exposed forthe same duration or radiant energy at separate times is notrecommended.4.5 This practice should not be used to establish a “pass/fail” approval of materials after a specific period of exposureunless performance compariso
28、ns are made relative to a controlmaterial exposed simultaneously, or the variability in the test isdefined so that statistically significant pass/fail judgements canbe made. It is strongly recommended that at least one controltest specimen be exposed with each test. The control testspecimen should m
29、eet the requirements of Terminology G113,and be chosen so that its failure mode is the same as that of thetest specimen. It is preferable to use two control test specimens,one with relatively good durability and one with relatively poordurability.4.6 The use of at least two replicates of each contro
30、l 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 addition of a
31、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.FIG. 2 Dual Axis TrackingG901035.1.1 The Fresnel-reflector test machine is a follow-the-sunapparatus having flat mirrors so
32、positioned that the 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).5.1.2 The test machine is equippe
33、d with a blower to cool thetest specimens. The air is directed over the specimens by anadjustable deflector along one side of the target area. Forunbacked mounting, air is also directed under the specimens.This limits the increase in surface temperatures of mostspecimens to 10C above the maximum sur
34、face temperaturethat would be reached when identically mounted specimens areexposed to direct sunlight at normal incidence at the same timeand location without concentration.5.2 MirrorsThe Fresnel-reflector system mirrors of ma-chines currently in use have a typical specular, spectralreflectance cur
35、ve such as that presented in Fig. 4. Other mirrorsmay be used providing they meet the requirements of 6.2.5.3 Photoreceptor CellsTwo photoreceptor cells, such assilicon solar cells, are installed near the top of the air tunnel onthe side facing the sun. A “T” shadow maker is mounted abovethe cells t
36、o 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 amplifier to a reversible motor whichadjusts the machine to maintain focus.5.4 Tracking SystemThe test m
37、achine 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 machines axis is oriented in the north/southdirection, with the north pole being altitude-adjustable toa
38、ccount 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 the machine, the other to control the tiltelevation. The axis of the target area remains parallel to
39、 theground. The machine rotates about horizontal and vertical axesto keep the target area in focus.5.5 NozzlesThe test machine used in Cycles 1 and 3 ofTable 1 is provided with a nozzle assembly for spraying waterTABLE 1 Fresnel-Reflector Test Machine Typical Spray CyclesCycleDaytime NighttimeSprayD
40、urationDry-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 7PM to 5 AM)AThis is the cycle specif
41、ied in Procedure C of Practice D4141.FIG. 3 Schematic of Optical System for a Fresnel Reflecting Concentrator Accelerated Weathering MachineG90104onto the specimens during exposure. Fan spray nozzles whichprovide a uniform fine mist over the specimen area arerecommended.5.6 Spray OrientationThe appa
42、ratus shall be positionedso that specimens are sprayed at night either with specimensfacing up or down.5.6.1 Specimens Face DownThe apparatus is orientedwith the mirrors below the target specimen area such thatnozzles spray high purity water in an upward direction onto thespecimens.5.6.2 Specimens F
43、ace UpThe apparatus is oriented withthe mirrors above the target specimen area such that nozzlesspray high purity water in a downward direction onto thespecimens.NOTE 1No data has been presented indicating that exposures per-formed using different spray orientations provide equivalent results, andas
44、 such, may provide different test results.5.7 Ultraviolet RadiometersInstrumental means of mea-suring 295 to 385 nm ultraviolet radiant exposure shall shallconsist of two wavelength-band specific global irradianceradiometers, each connected to an integrating device to indi-cate the energy received i
45、n the specified wavelength band overa given period. The spectral response of the ultraviolet radi-ometers shall be known and shall be as flat as possiblethroughout the 295 to 385 nm spectral region utilized. Cali-brations shall be performed using sunlight as the source. Thepyranometer shall be calib
46、rated in accordance with MethodE824 no less often than annually. A black-painted permanentshading disk is positioned over one radiometer as shown in Fig.6 and Figs. 7-9 to provide a diffuse-only measurement (exclud-ing 6 field of view).5.8 PyranometerInstrumental means of measuring full-spectrum sol
47、ar radiant exposure shall consist of a pyranometerconnected to an integrating device to indicate the total energyreceived over a given period. The pyranometer shall be a WorldMeteorological Organization (WMO) Second Class instrumentor better as defined by the WMO Guide to MeteorologicalInstruments.
48、The pyranometer shall be calibrated in accordancewith Test Method E824 or G167 at least annually.5.9 PyrheliometerInstrumental means of measuring full-spectrum solar radiant exposure ina5to6.5degree field ofview shall consist of a pyrheliometer connected to an integrat-ing device to indicate the tot
49、al energy received over a givenperiod. The pyrheliometer shall be a World MeteorologicalOrganization (WMO) First Class instrument or better asdefined by the WMO Guide to Meteorological Instruments.The pyrheliometer shall be calibrated in accordance with TestMethod E816 at least annually6. Reagents and Materials6.1 Water Quality:6.1.1 The purity of water used for specimen spray is veryimportant. Without proper treatment to remove cations, anions,organics, and particularly silica, exposed panels will developspots or stains that do not occur in exterior exposures.6
