1、Designation: G7/G7M 11Standard Practice forAtmospheric Environmental Exposure Testing ofNonmetallic Materials1This standard is issued under the fixed designation G7/G7M; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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. Scope*1.1 This practice covers procedures to be
3、 followed 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 par
4、ties.1.2 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 speci
5、mens to theenvironment.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
6、 to use.2. Referenced Documents2.1 ASTM Standards:2E41 Terminology Relating To ConditioningE824 Test Method for Transfer of Calibration From Refer-ence to Field RadiometersE913 Method for Calibration of Reference PyranometersWith Axis Vertical by the Shading Method3E941 Test Method for Calibration o
7、f Reference Pyranom-eters With Axis Tilted by the Shading Method3G24 Practice for Conducting Exposures to Daylight FilteredThrough GlassG113 Terminology Relating to Natural andArtificial Weath-ering Tests of Nonmetallic MaterialsG130 Test Method for Calibration of Narrow- and Broad-Band Ultraviolet
8、Radiometers Using a Spectroradiometer2.2 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 Determination of RadiantExposure in Weathering
9、TestsGeneral Guidance andBasic Test Method42.3 ASTM Adjuncts:A Test Rack53. Terminology3.1 DefinitionsThe definitions given in Terminology E41and Terminology G113 are applicable to this practice.4. Significance and Use4.1 The relative durability of materials in natural exposurescan be very different
10、 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 durability in adiffere
11、nt 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 which a material
12、 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. Comparing1This practice i
13、s 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 June 1, 2011. Published July 2011. Originally approvedin 1969. Last previous edition approved in 2005
14、 as G7 05. DOI: 10.1520/G0007_G0007M-11.2For 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
15、approved version of this historical standard is referencedon www.astm.org.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.5Detailed drawings for an acceptable test rack may be obtained from ASTMInternational. Request ADJG
16、0007.1*A Summary 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.results for materials exposed for short periods (less than oneyear) is not recommended unless materials are expose
17、d 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 measurements aretypically made using instruments which record broadband UV(for example, 295 to 3
18、85 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 rate or type ofdegradation.4.5 The design of the exposure rack, the location of thespecim
19、en 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 specimens, control speci-mens, and any applicable weathering reference material beplaced on a s
20、ingle 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 material shall meet the requirements of TerminologyG113, and be of similar composition and constr
21、uction 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 replicate specimens of each test and control materialbeing exposed. Control materials included as
22、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 conducted in any type ofclimate. However, in order to get more rapid indications ofoutdoo
23、r 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 climates. Known attributes of theuse environment should be represented by the locations se-lec
24、ted 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 addition, exposures are oftenconducted in areas where specimens are subjected to salt air
25、(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 fixtures shall have groundcover typical of the climatological area where the exposuresare being c
26、onducted. 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 indicated in the test report. If testfixtures are placed over ground covers not typical of t
27、heclimatological area (for example, rooftops, concrete or as-phalt), specimens may be subjected to different environmentalNOTEDetailed drawings of this test rack are available from ASTM International, 100 Barr Harbor Dr., W. Conshohocken, PA 19428. Request AdjunctADJG0007.FIG. 1 Typical Exposure Rac
28、kG7/G7M 112conditions 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 least 0.45 m (18 in.) above the groundand shall not contact vegetation. This will also minimi
29、zedamage 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 OrientationUnless otherwise specified, ex-posure racks shall be oriented so that specimens face
30、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 Latitude AngleExposure rack is positioned so thatthe exposed surface of specimens are at
31、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 most commonly used exposure orientation.5.4.3 90Exposure rack is positioned so that the ex
32、posedspecimens 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 to avoid standing wateron specimens being exposed. This exposure angle typicallyreceives
33、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 latitude typicallyreceive more ultraviolet radiation than exposures conducted at largerangl
34、es.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 test report shall contain the exactangle and specimen orientation.5.5 Specimen BackingThree
35、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 test specimen being evaluated is subjected tothe effects of the weather on all sides. Fo
36、r 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 front surface is exposed. Surfacetemperatures of specimens in backed exposures will be high
37、erthan for specimens subjected to unbacked exposures. In somecases, the substrate is painted black, which produces significantdifferences in surface temperature compared to exposuresconducted on unpainted substrate. This can cause large differ-ences in degradation rates when compared to backed expos
38、uresconducted 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 notenough test specimens to completely cover the top surface,open areas shall be filled with b
39、lack 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 without surface treatment.AluminumAlloys 6061T6 or 6063T6 have been found suitablefor use in mo
40、st locations. Properly primed and coated steel isFIG. 2 Backed Exposure RackG7/G7M 113suitable for use in desert areas. Monel has been found suitablein highly corrosive areas. Untreated wood is acceptable indesert areas but may pose maintenance problems in other areas.(See Fig. 1.)6.1.1 For backed e
41、xposures (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 warping or distortion that changes the orientationFIG. 3 Black BoxFIG. 4 Black Box in UseG7/G7M 114of the specimens, or when there are visi
42、ble signs of delamina-tion or fiber separation. Medium-density overlay (MDO) orhigh-density overlay (HDO) plywood are satisfactory sub-strates and require less frequent replacement than plywoodwith no overlay. The edges of the plywood should be sealedwith a durable paint to prevent delamination.6.2
43、Test Fixture DesignTest 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 ExposuresTes
44、t racks shall be 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 prev
45、ent expansion and 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 E
46、xposuresTest racks shall be constructed sothat specimens are attached to a plywood substrate. Thethickness of the plywood and type of coating used, if any, shallbe agreed upon by all interested parties and must be reported.NOTE 2Backed exposures as described in this standard are notinsulated exposur
47、es. For some applications 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 co
48、nducted according to this 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
49、m (5.5 ft)high and 3.7 m (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. Instrumentation6,7,87.1 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
