1、Designation: G7/G7M 11G7/G7M 13Standard 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
2、year of last 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*Scope1.1 This practice covers pr
3、ocedures to be followed for direct exposure of nonmetallic materials to the environment. Whenoriginators of a weathering test have the actual exposure conducted by a separate agency, the specific conditions for the exposureof test and control specimens must be clearly defined and mutually agreed upo
4、n between all parties.1.2 For exposures behind glass, refer to Practice G24.1.3 The values stated in either SI units or inch-pound units are to be regarded separately as the standard. The inch-pound unitsgiven in parentheses are for information only.values stated in each system may not be exact equi
5、valents; therefore, each systemshall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.4 This practice is technically equivalent to the parts of ISO 877 that describe direct exposures of specimens to theenvironment.1.5 This st
6、andard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 A
7、STM Standards:2E41 Terminology Relating To ConditioningE824 Test Method for Transfer of Calibration From Reference to Field RadiometersE913 Method for Calibration of Reference Pyranometers With Axis Vertical by the Shading Method (Withdrawn 2005)3E941 Test Method for Calibration of Reference Pyranom
8、eters With Axis Tilted by the Shading Method (Withdrawn 2005)3G24 Practice for Conducting Exposures to Daylight Filtered Through GlassG113 Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic MaterialsG130 Test Method for Calibration of Narrow- and Broad-Band Ultraviolet Ra
9、diometers Using a Spectroradiometer2.2 ISO Standards:ISO 877 PlasticsMethods of Exposure to Direct Weathering; to Weathering Using Glass-Filtered Daylight, and to IntensifiedWeathering by Daylight Using Fresnel Mirrors4ISO 9370 PlasticsInstrumental Determination of Radiant Exposure in Weathering Tes
10、tsGeneral Guidance and Basic TestMethod42.3 ASTM Adjuncts:A Test Rack51 This practice is under the jurisdiction of ASTM Committee G03 on Weathering and Durabilityand is the direct responsibility of Subcommittee G03.02 on Natural andEnvironmental Exposure Tests.Current edition approved June 1, 2011Ju
11、ne 1, 2013. Published July 2011June 2013. Originally approved in 1969. Last previous edition approved in 20052011 asG7 05.G7/G7M 11. DOI: 10.1520/G0007_G0007M-11.10.1520/G0007_G0007M-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceast
12、m.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.org.4 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor,
13、 New York, NY 10036, http:/www.ansi.org.5 Detailed drawings for an acceptable test rack may be obtained from ASTM International. Request ADJG0007.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the pre
14、vious version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Ch
15、anges section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 DefinitionsThe definitions given in Terminology E41 and Terminology G113 are applicable to this practice.4. Significanc
16、e and Use4.1 The relative durability of materials in natural exposures can be very different depending on the location of the exposurebecause of differences in ultraviolet (UV) radiation, time of wetness, temperature, pollutants, and other factors. Therefore, it cannotbe assumed that results from on
17、e exposure in a single location will be useful for determining relative durability in a differentlocation. Exposures in several locations with different climates which represent a broad range of anticipated service conditions arerecommended.4.2 Because of year-to-year climatological variations, resu
18、lts from a single exposure test cannot be used to predict the absoluterate at which a material degrades. Several years of repeat exposures are needed to get an “average” test result for a given location.4.3 Solar ultraviolet radiation varies considerably as a function of time of year. This can cause
19、 large differences in the apparentrate of degradation in many polymers. Comparing results for materials exposed for short periods (less than one year) is notrecommended unless materials are exposed at the same time in the same location.4.4 Defining exposure periods in terms of total solar or solar-u
20、ltraviolet radiant energy can reduce variability in results fromseparate exposures. Solar ultraviolet measurements are typically made using instruments which record broadband UV (forexample, 295 to 385 nm) or narrow band UV, as described in 7.2.4 and 7.2.5. An inherent limitation in solar-radiationm
21、easurements is that they do not reflect the effects of temperature and moisture, which may also influence the rate or type ofdegradation.4.5 The design of the exposure rack, the location of the specimen on the exposure rack, and the type or color of adjacentspecimens can affect specimen temperature
22、and time of wetness. In order to minimize variability caused by these factors, it isrecommended that test specimens, control specimens, and any applicable weathering reference material be placed on a single testpanel or on test panels placed adjacent to each other during exposure.4.6 It is strongly
23、recommended that at least one control material be part of any exposure evaluation. When used, the controlmaterial shall meet the requirements of Terminology G113, and be of similar composition and construction compared to testspecimens. It is preferable to use two control materials, one with relativ
24、ely good durability and one with relatively poor durability.Unless otherwise specified, use at least two replicate specimens of each test and control material being exposed. Control materialsincluded as part of a test shall be used for the purpose of comparing the performance of test materials relat
25、ive to the controls.NOTE 1Detailed drawings of this test rack are available from ASTM International, 100 Barr Harbor Dr., W. Conshohocken, PA 19428. RequestAdjunct ADJG0007.FIG. 1 Typical Exposure RackG7/G7M 1325. Test Sites, Location of Test Fixtures, and Exposure Orientation5.1 Test SitesExposures
26、 can be conducted in any type of climate. However, in order to get more rapid indications of outdoordurability, exposures are often conducted in locations that receive high levels of solar radiation, temperature, and moisture.Typically, these conditions are found in hot desert and subtropical or tro
27、pical climates. Known attributes of the use environmentshould be represented by the locations selected for outdoor durability evaluation. For example, if the use environment for theproduct being evaluated will include freeze/thaw cycling, specimen exposure in a northern temperature climate is recomm
28、ended.In addition, exposures are often conducted in areas where specimens are subjected to salt air (seashore) or industrial pollutants.5.1.1 Unless otherwise specified, test fixtures or racks shall be located in cleared areas. Unless otherwise specified, the areabeneath and in the vicinity of the t
29、est fixtures shall have ground cover typical of the climatological area where the exposures arebeing conducted. In desert areas, the typical ground cover is often gravel to control dust and in most temperate areas, the typicalground cover is low-cut grass. The type of ground cover at the exposure si
30、te shall be indicated in the test report. If test fixturesare placed over ground covers not typical of the climatological area (for example, rooftops, concrete or asphalt), specimens maybe subjected to different environmental conditions than if using typical ground cover or exposing at ground level.
31、 These differencesmay affect test results.5.2 The lowest row of specimens on a test fixture or rack shall be positioned at least 0.45 m (18 in.)18 in. above the groundand shall not contact vegetation. This will also minimize damage that might occur during area maintenance.5.3 Test fixtures shall be
32、placed in a location so that there is no shadow on any specimen when the suns angle of elevation isgreater than 20.5.4 Exposure OrientationUnless otherwise specified, exposure racks shall be oriented so that specimens face the equator.Specimens can be exposed at a number of different orientations or
33、 “exposure angles” in order to simulate end-use conditions ofthe material being evaluated. Typical exposure angles are as follows:5.4.1 Latitude AngleExposure rack is positioned so that the exposed surface of specimens are at an angle from the horizontalthat is equal to the geographical latitude of
34、the exposure site.5.4.2 45Exposure rack is positioned so that the exposed specimens are at an angle of 45 from the horizontal.This is the mostcommonly used exposure orientation.5.4.3 90Exposure rack is positioned so that the exposed specimens are at an angle of 90 from the horizontal.5.4.4 5Exposure
35、 rack is positioned so that the exposed specimens are at an angle of 5 from the horizontal. This angle ispreferred over horizontal exposure to avoid standing water on specimens being exposed. This exposure angle typically receivesthe highest levels of solar radiation during mid-summer and is used to
36、 test materials that would normally be used in horizontal ornearly horizontal applications.NOTE 1Exposures conducted at less than the site latitude typically receive more ultraviolet radiation than exposures conducted at larger angles.FIG. 2 Backed Exposure RackG7/G7M 1335.4.5 Any other angle that i
37、s mutually agreed on by all interested parties may be used. In some instances, exposures facingdirectly away from the equator or some other specific direction may be desired. The test report shall contain the exact angle andspecimen orientation.5.5 Specimen BackingThree types of specimen backing can
38、 be used. Avoid comparisons between materials unless allexposures were conducted with the same specimen backing.5.5.1 Unbacked ExposuresSpecimens are exposed so that the portion of the test specimen being evaluated is subjected to theeffects of the weather on all sides. For materials that deform eas
39、ily during exposure, a wire mesh can be used to provide supportand prevent deformation or distortion.5.5.2 Backed ExposuresSpecimens are attached to a solid substrate so that only the front surface is exposed. Surfacetemperatures of specimens in backed exposures will be higher than for specimens sub
40、jected to unbacked exposures. In some cases,the substrate is painted black, which produces significant differences in surface temperature compared to exposures conducted onunpainted substrate. This can cause large differences in degradation rates when compared to backed exposures conducted onunpaint
41、ed substrates.5.5.3 Black Box ExposureSpecimens are attached to the front face of a black painted aluminum box (see 6.2.3).The specimensform the top surface of the box. If there are not enough test specimens to completely cover the top surface, open areas shall befilled with black painted sheet meta
42、l panels so that the box is completely closed.6. Construction of Test Fixtures (Exposure Racks)6.1 Materials of ConstructionAll materials used for test fixtures shall be noncorrodible without surface treatment. AluminumAlloys 6061T6 or 6063T6 have been found suitable for use in most locations. Prope
43、rly primed and coated steel is suitable for usein desert areas. Monel has been found suitable in highly corrosive areas. Untreated wood is acceptable in desert areas but may posemaintenance problems in other areas. (See Fig. 1.)6.1.1 For backed exposures (see 6.2.2 and Fig. 2), use exterior-grade pl
44、ywood to form a solid surface to which specimens aredirectly attached. Replace the plywood when there is any warping or distortion that changes the orientation of the specimens, orwhen there are visible signs of delamination or fiber separation. Medium-density overlay (MDO) or high-density overlay (
45、HDO)plywood are satisfactory substrates and require less frequent replacement than plywood with no overlay. The edges of the plywoodshould be sealed with a durable paint to prevent delamination.FIG. 3 Black BoxG7/G7M 1346.2 Test Fixture DesignTest racks shall be constructed to hold specimens or spec
46、imen holders of any convenient width andlength. Racks shall be constructed so that any contamination from specimens higher on the fixture cannot directly run down ontospecimens in lower positions.56.2.1 Unbacked ExposuresTest racks shall be constructed so that most of the test specimen is exposed to
47、 the effects of theweather on all sides. Specimens are attached to the test fixture at the top or bottom, or both, using clamping devices, properlyspaced slots, or mechanical fasteners. The method of attachment shall not prevent expansion and contraction of specimens causedby temperature or moisture
48、. Use fastening devices for attaching specimens to the test fixture that will not corrode or degrade andcontaminate the specimens. Aluminum, properly galvanized steel, or stainless steel fasteners are recommended.6.2.2 Backed ExposuresTest racks shall be constructed so that specimens are attached to
49、 a plywood substrate. The thicknessof the plywood and type of coating used, if any, shall be agreed upon by all interested parties and must be reported.NOTE 2Backed exposures as described in this standard are not insulated exposures. For some applications such as outdoor exposure tests for roofingproducts, a layer of insulation material is attached behind the solid substrate to which specimens are attached. Insulated exposures of this type producehigher specimen temperatures than those that would be seen on backed exposures conducted according
