1、Designation: G 90 05Standard Practice forPerforming Accelerated Outdoor Weathering of NonmetallicMaterials Using Concentrated Natural Sunlight1This standard is issued under the fixed designation G 90; the number immediately following the designation indicates the year of originaladoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) 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
3、 outdoor 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 aredescribe
4、d herein 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 o
5、f the 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 mat
6、erials 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
7、included 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, t
8、his 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 t
9、hesafety 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:2D 859 Test Method for Sili
10、ca in WaterD 1014 Practice for Conducting Exterior Exposure Tests ofPaints on SteelD 1435 Practice for Outdoor Weathering of PlasticsD 1898 Practice for Sampling of PlasticsD 4141 Practice for ConductingAccelerated Outdoor Expo-sure Tests of CoatingsD 4517 Test Method for Low-Level Total Silica in H
11、igh-Purity Water by Flameless Atomic Absorption Spectros-copyE 816 Test Method for Calibration of Pyrheliometers byComparison to Reference PyrheliometersE 824 Test Method for Transfer of Calibration from Refer-ence to Field RadiometersE 891 Tables for Terrestrial Direct Normal Solar SpectralIrradian
12、ce for Air Mass 1.5E 903 Test Method for Solar Absorptance, Reflectance, andTransmittance of Materials Using Integrated SpheresG7 Practice for Atmospheric Environmental ExposureTesting of Nonmetallic MaterialsG24 Practice for Conducting Exposures to Daylight Fil-tered through GlassG113 Terminology R
13、elating to Natural and ArtificialWeathering Tests of Nonmetallic MaterialsG 167 Test Method for Calibration of a Pyranometer Usinga PyrheliometerG 169 Guide forApplication of Basic Statistical Methods toWeathering Tests2.2 Other Standards:3SAE J576 Plastic Materials for Use in Optical Parts Such asL
14、enses and Reflectors of Motor Vehicle Lighting DevicesWMO Guide to Meteorological Instruments and Methods of1This practice is under the jurisdiction of ASTM Committee G03 on Weatheringand Durability and is the direct responsibility of Subcommittee G03.02 on Naturaland Environmental Exposure Tests.Cu
15、rrent edition approved Oct. 1, 2005. Published November 2005. Originallyapproved in 1985. Last previous edition approved in 1998 as G 90 98.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volum
16、e information, refer to the standards Document Summary page onthe ASTM website.3Available from Society of Automotive Engineers (SAE), 400 CommonwealthDr., Warrendale, PA 15096-0001.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Obse
17、rvation WMO No. 8, Fifth Edition3. Terminology3.1 DefinitionsDefinitions of terms common to G 3 dura-bility 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 te
18、st 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 comparative performance has been established forthe specific mat
19、erials 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 other factors. Therefore,even if results from a specific accele
20、rated 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.4.3 The use of a single acceleration factor relating the ra
21、teof 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 formulationmay respond differently to the increased level of irradian
22、ce 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 results from asufficient number of tests must be obtained to
23、 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 climaticfactors.4.4 Variations in results may be expect
24、ed when operatingconditions vary within the limits of this practice. For example,FIG. 1 Schematic of Fresnel-Reflecting Concentrator Accelerated Weatering Machine Single Axis TrackingG90052there can be large differences in the amount of degradation ina single material between separate, although supp
25、osedly iden-tical, exposures carried out for the same duration 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
26、and variability inirradiance, temperature and moisture levels 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 a
27、fter a specific period of exposureunless performance comparisons 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 specime
28、n be exposed with each test. The control testspecimen should meet 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 poordu
29、rability.4.6 The use of at least two replicates of each control testspecimen and each material being evaluated is recommended.Consult Guide G 169 for performing statistical analysis.5. Apparatus5.1 Test MachinesFresnel-reflector test machines used inCycles 1, 2, and 3 of Table 1 are nearly identical
30、. The onlydifference between the machines is the addition 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-suna
31、pparatus having flat mirrors so 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).F
32、IG. 2 Dual Axis TrackingG900535.1.2 The test machine is equipped 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 sur
33、face temperatures of mostspecimens to 10C above the maximum surface 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 cu
34、rrently in use have a typical specular, spectralreflectance curve 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
35、 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 amplifier to a reversible motor whichadju
36、sts 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 machines axis is oriented in the north/so
37、uthdirection, 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 the machine, the other to control the
38、 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 NozzlesThe test machine used in Cycles 1 and 3 ofTable 1 is provided with a nozzle assembly for spraying wateronto the specimens durin
39、g exposure. Fan spray nozzles whichprovide a uniform fine mist over the specimen area arerecommended.5.6 Spray OrientationThe apparatus 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
40、below the target specimen area such thatnozzles spray high purity water in an upward direction onto thespecimens.5.6.2 Specimens Face 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
41、 data has been presented indicating that exposures per-formed using different spray orientations provide equivalent results, andas 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
42、 wavelength-band specific global irradianceradiometers, each connected to an integrating device to indi-cate the energy received in 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 29
43、5 to 385 nm spectral region utilized. Cali-brations shall be performed using sunlight as the source. Thepyranometer shall be calibrated in accordance with Method E824 no less often than annually. A black-painted permanentshading disk is positioned over one radiometer as shown in Fig.6 and Figs. 7-9
44、to provide a diffuse-only measurement (exclud-ing 6 field of view).5.8 PyranometerInstrumental means of measuring full-spectrum solar 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
45、 WorldMeteorological Organization (WMO) Second Class instrumentor better as defined by the WMO Guide to MeteorologicalInstruments. The pyranometer shall be calibrated in accordancewith Test Method E 824 or G 167 at least annually.5.9 PyrheliometerInstrumental means of measuring full-spectrum solar r
46、adiant exposure ina5to6.5degree field ofview shall consist of a pyrheliometer connected to an integrat-ing device to indicate the total energy received over a givenperiod. The pyrheliometer shall be a World MeteorologicalOrganization (WMO) First Class instrument or better asdefined by the WMO Guide
47、to Meteorological Instruments.The pyrheliometer shall be calibrated in accordance with TestMethod E 816 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 par
48、ticularly silica, exposed panels will developspots or stains that do not occur in exterior exposures.6.1.2 Water used for specimen spray shall leave no objec-tional deposits or stains on the exposed specimens. It isstrongly recommended that the water contain a maximum of1-ppm solids and a maximum of
49、 0.2-ppm silica. Silica levelsshould be determined using the procedures defined in TestMethods D 859 or D 4517. Prepackaged analysis kits arecommercially available that are capable of detecting silicalevels of less than 200 parts per billion (ppb).Acombination ofdeionization and reverse osmosis treatment can effectivelyproduce water with the desired purity. If the spray water usedis above 1-ppm solids, the solids and silica levels must bereported.TABLE 1 Fresnel-Reflector Test Machine Typical Spray CyclesCycleDaytime NighttimeSprayDurationDry-TimeDurationCycles/hSpr
