1、Designation:G705Standard Practice forAtmospheric Environmental Exposure Testing ofNonmetallic Materials1This standard is issued under the fixed designation G 7; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This practice covers procedures to be followed
3、 for directexposure of nonmetallic materials to the environment. Whenoriginators of a weathering test have the actual exposureconducted by a separate agency, the specific conditions for theexposure of test and control specimens must be clearly definedand mutually agreed upon between all parties.1.2
4、For exposures behind glass, refer to Practice G24.1.3 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in parentheses are forinformation only.1.4 This practice is technically equivalent to the parts ofISO 877 that describe direct exposures of specimens to t
5、heenvironment.1.5 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 limitations prior to use.2
6、. Referenced Documents2.1 ASTM Standards:2E41 Terminology Relating to ConditioningE 824 Test Method for Transfer of Calibration from Refer-ence to Field PyranometersE 913 Test Method for Calibration of Reference Pyranom-eters with Axis Vertical by the Shading MethodE 941 Test Method for Calibration
7、of Reference Pyranom-eters with Axis Tilted by the Shading MethodG24 Practice for Conducting Exposures to Daylight Fil-tered Through GlassG113 Terminology Relating to Natural and ArtificialWeathering Tests of Nonmetallic MaterialsG 130 Test Method for Calibration of Narrow- and Broad-Band Ultraviole
8、t Radiometers Using a Spectroradiometer2.2 ASTM Adjunct:Adjunct ADJG0007 A Test Rack32.3 ISO Standards:ISO 877 PlasticsMethods of Exposure to Direct Weather-ing; to Weathering Using Glass-Filtered Daylight, and toIntensified Weathering by Daylight Using Fresnel Mir-rors4ISO 9370 PlasticsInstrumental
9、 Determination of RadiantExposure in Weathering TestsGeneral Guidance andBasic Test Method43. Terminology3.1 DefinitionsThe definitions given in Terminology E41and Terminology G113are applicable to this practice.4. Significance and Use4.1 The relative durability of materials in natural exposurescan
10、be very different depending on the location of the exposurebecause of differences in ultraviolet (UV) radiation, time ofwetness, temperature, pollutants, and other factors. Therefore,it cannot be assumed that results from one exposure in a singlelocation will be useful for determining relative durab
11、ility in adifferent location. Exposures in several locations with differentclimates which represent a broad range of anticipated serviceconditions are recommended.4.2 Because of year-to-year climatological variations, re-sults from a single exposure test cannot be used to predict theabsolute rate at
12、 which a material degrades. Several years ofrepeat exposures are needed to get an “average” test result fora given location.4.3 Solar ultraviolet radiation varies considerably as afunction of time of year. This can cause large differences in theapparent rate of degradation in many polymers. Comparin
13、g1This 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.Current edition approved Jan. 1, 2005. Published February 2005. Originallyapproved in 1969. Last previous edi
14、tion approved in 1997 as G797.2For 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.3Available from ASTM Headquarte
15、rs, 100 Barr Harbor Dr., West Consho-hocken, PA 19428.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.results for materials ex
16、posed for short periods (less than oneyear) is not recommended unless materials are exposed at thesame time in the same location.4.4 Defining exposure periods in terms of total solar orsolar-ultraviolet radiant energy can reduce variability in resultsfrom separate exposures. Solar ultraviolet measur
17、ements aretypically made using instruments which record broadband UV(for example, 295 to 385 nm) or narrow band UV, as describedin 7.2.4 and 7.2.5. An inherent limitation in solar-radiationmeasurements is that they do not reflect the effects of tempera-ture and moisture, which may also influence the
18、 rate or type ofdegradation.4.5 The design of the exposure rack, the location of thespecimen on the exposure rack, and the type or color ofadjacent specimens can affect specimen temperature and timeof wetness. In order to minimize variability caused by thesefactors, it is recommended that test speci
19、mens, control speci-mens, and any applicable weathering reference material beplaced on a single test panel or on test panels placed adjacentto each other during exposure.4.6 It is strongly recommended that at least one controlmaterial be part of any exposure evaluation. When used, thecontrol materia
20、l shall meet the requirements of TerminologyG113, and be of similar composition and construction com-pared to test specimens. It is preferable to use two controlmaterials, one with relatively good durability and one withrelatively poor durability. Unless otherwise specified, use atleast two replicat
21、e specimens of each test and control materialbeing exposed. Control materials included as part of a test shallbe used for the purpose of comparing the performance of testmaterials relative to the controls.5. Test Sites, Location of Test Fixtures, and ExposureOrientation5.1 Test SitesExposures can be
22、 conducted in any type ofclimate. However, in order to get more rapid indications ofoutdoor durability, exposures are often conducted in locationsthat receive high levels of solar radiation, temperature, andmoisture. Typically, these conditions are found in hot desertand subtropical or tropical clim
23、ates. Known attributes of theuse environment should be represented by the locations se-lected for outdoor durability evaluation. For example, if the useenvironment for the product being evaluated will includefreeze/thaw cycling, specimen exposure in a northern tempera-ture climate is recommended. In
24、 addition, exposures are oftenconducted in areas where specimens are subjected to salt air(seashore) or industrial pollutants.5.1.1 Unless otherwise specified, test fixtures or racks shallbe located in cleared areas. Unless otherwise specified, the areabeneath and in the vicinity of the test fixture
25、s shall have groundcover typical of the climatological area where the exposuresare being conducted. In desert areas, the typical ground coveris often gravel to control dust and in most temperate areas, thetypical ground cover is low-cut grass. The type of ground coverat the exposure site shall be in
26、dicated in the test report. If testfixtures are placed over ground covers not typical of theclimatological area (for example, rooftops, concrete or as-phalt), specimens may be subjected to different environmentalNOTEDetailed drawings of this test rack are available fromASTM Headquarters, 100 Barr Ha
27、rbor Dr., W. Conshohocken, PA19428. RequestAdjunctNo. 12-700070-00.FIG. 1 Typical Exposure RackG7052conditions than if using typical ground cover or exposing atground level. These differences may affect test results.5.2 The lowest row of specimens on a test fixture or rackshall be positioned at leas
28、t 0.45 m (18 in.) above the groundand shall not contact vegetation. This will also minimizedamage that might occur during area maintenance.5.3 Test fixtures shall be placed in a location so that there isno shadow on any specimen when the suns angle of elevationis greater than 20.5.4 Exposure Orienta
29、tionUnless otherwise specified, ex-posure racks shall be oriented so that specimens face theequator. Specimens can be exposed at a number of differentorientations or “exposure angles” in order to simulate end-useconditions of the material being evaluated. Typical exposureangles are as follows:5.4.1
30、Latitude AngleExposure rack is positioned so thatthe exposed surface of specimens are at an angle from thehorizontal that is equal to the geographical latitude of theexposure site.5.4.2 45Exposure rack is positioned so that the exposedspecimens are at an angle of 45 from the horizontal. This isthe m
31、ost commonly used exposure orientation.5.4.3 90Exposure rack is positioned so that the exposedspecimens are at an angle of 90 from the horizontal.5.4.4 5Exposure rack is positioned so that the exposedspecimens are at an angle of 5 from the horizontal. This angleis preferred over horizontal exposure
32、to avoid standing wateron specimens being exposed. This exposure angle typicallyreceives the highest levels of solar radiation during mid-summer and is used to test materials that would normally beused in horizontal or nearly horizontal applications.NOTE 1Exposures conducted at less than the site la
33、titude typicallyreceive more ultraviolet radiation than exposures conducted at largerangles.5.4.5 Any other angle that is mutually agreed on by allinterested parties may be used. In some instances, exposuresfacing directly away from the equator or some other specificdirection may be desired. The tes
34、t report shall contain the exactangle and specimen orientation.5.5 Specimen BackingThree types of specimen backingcan be used. Avoid comparisons between materials unless allexposures were conducted with the same specimen backing.5.5.1 Unbacked ExposuresSpecimens are exposed so thatthe portion of the
35、 test specimen being evaluated is subjected tothe effects of the weather on all sides. For materials that deformeasily during exposure, a wire mesh can be used to providesupport and prevent deformation or distortion.5.5.2 Backed ExposuresSpecimens are attached to a solidsubstrate so that only the fr
36、ont surface is exposed. Surfacetemperatures of specimens in backed exposures will be higherthan for specimens subjected to unbacked exposures. In somecases, the substrate is painted black, which produces significantdifferences in surface temperature compared to exposuresconducted on unpainted substr
37、ate. This can cause large differ-ences in degradation rates when compared to backed exposuresconducted on unpainted substrates.5.5.3 Black Box ExposureSpecimens are attached to thefront face of a black painted aluminum box (see 6.2.3). Thespecimens form the top surface of the box. If there are noten
38、ough test specimens to completely cover the top surface,open areas shall be filled with black painted sheet metal panelsso that the box is completely closed.6. Construction of Test Fixtures (Exposure Racks)6.1 Materials of ConstructionAll materials used for testfixtures shall be noncorrodible withou
39、t surface treatment.Aluminum Alloys 6061T6 or 6063T6 have been found suitablefor use in most locations. Properly primed and coated steel isFIG. 2 Backed Exposure RackG7053suitable for use in desert areas. Monel has been found suitablein highly corrosive areas. Untreated wood is acceptable indesert a
40、reas but may pose maintenance problems in other areas.(See Fig. 1.)6.1.1 For backed exposures (see 6.2.2 and Fig. 2), useexterior-grade plywood to form a solid surface to whichspecimens are directly attached. Replace the plywood whenthere is any evidence of delamination or fiber separation.FIG. 3 Bl
41、ack BoxFIG. 4 Black Box in UseG7054Medium-density overlay (MDO) or high-density overlay(HDO) plywood are satisfactory substrates and require lessfrequent replacement than plywood with no overlay. The edgesof the plywood should be sealed with a durable paint to preventdelamination.6.2 Test Fixture De
42、signTest racks shall be constructed tohold specimens or specimen holders of any convenient widthand length. Racks shall be constructed so that any contamina-tion from specimens higher on the fixture cannot directly rundown onto specimens in lower positions.56.2.1 Unbacked ExposuresTest racks shall b
43、e constructedso that most of the test specimen is exposed to the effects of theweather on all sides. Specimens are attached to the test fixtureat the top or bottom, or both, using clamping devices, properlyspaced slots, or mechanical fasteners. The method of attach-ment shall not prevent expansion a
44、nd contraction of specimenscaused by temperature or moisture. Use fastening devices forattaching specimens to the test fixture that will not corrode ordegrade and contaminate the specimens. Aluminum, properlygalvanized steel, or stainless steel fasteners are recommended.6.2.2 Backed ExposuresTest ra
45、cks shall be constructed sothat specimens are attached to a plywood substrate. Thethickness of the plywood and type of coating used shall beagreed upon by all interested parties and must be reported.NOTE 2Backed exposures as described in this standard are notinsulated exposures. For some application
46、s such as outdoor exposure testsfor roofing products, a layer of insulation material is attached behind thesolid substrate to which specimens are attached. Insulated exposures ofthis type produce higher specimen temperatures than those that would beseen on backed exposures conducted according to thi
47、s practice.6.2.3 Black Box ExposuresAn aluminum box 0.23 m (9in.) deep with the outside surface painted black. The topsurface is open and fitted with mounting strips to holdspecimens firmly in place. Two types of black boxes are incommon usage. One measures approximately 1.7 m (5.5 ft)high and 3.7 m
48、 (12 ft) wide and the other measures 1.5 m (5 ft)high and 1.8 m (6 ft) wide. Fig. 3 shows the design anddimensions for an acceptable black box. Fig. 4 shows a blackbox in use.All exposure positions on a black box shall be filledwith either test or control specimens or blank panels.7. Instrumentation
49、6,7,87.1 Unless otherwise specified, instruments for determiningclimatological data during the exposure period shall be oper-ated within 1000 m of the test racks. Data obtained shall bereported if requested as part of the results of a test.7.2 Instruments for recording the following are recom-mended:7.2.1 Ambient Temperature (Daily Maximum andMinimum)Instruments used for recording ambient tempera-ture shall be a thermocouple (Type T or J), a thermistor, or aresistance temperature device (RTD). Any instrument usedshall have a calibration traceable to the
