ASTM G156-97
(Practice)Standard Practice for Selecting and Characterizing Weathering Reference Materials Used to Monitor Consistency of Conditions in an Exposure Test
Standard Practice for Selecting and Characterizing Weathering Reference Materials Used to Monitor Consistency of Conditions in an Exposure Test
SCOPE
1.1 This standard describes the criterion to be used for selection of a WRM and procedures to be used for determining within lab and between lab tolerances of changes in measured properties of a reference material intended for use in monitoring operating conditions to establish the consistency of exposure tests.
Note 1—Examples of laboratory accelerated tests in which a weathering reference material could be used to monitor consistency are light and water exposure tests such as those described in Practices G 152, G 153, and G 154 G 155and other standards in which tests conducted according to these standards are referenced. Examples of outdoor exposures where a weathering reference material could be used to monitor consistency are those conducted according to Practices G 7, G 24, or G 90. A reference material can also be used to monitor consistency of exposure or conditioning test that do not involve exposure to light.
1.2 This practice does not cover (1) control materials used for comparison of stability with test materials, or (2) standard materials used to time exposures.
1.3 This practice provides an outline of experiments required to determine how the measured properties of the reference material change as a function of exposure to specified test conditions. It includes establishment of reproducible measurement procedures, determination of the critical region in the light source causing the changes, and effects of other critical exposure stresses such as temperature and moisture.
1.4 This practice describes procedures for conducting round-robin tests with the weathering reference material to determine reproducibility of the reference material property change in exposures conducted in different laboratories, and the repeatability when replicate reference material specimens are exposed in a single device and tested in one laboratory.
1.5 This practice describes procedures for using the results from analysis of variance on results from round-robin tests to determine the contribution of the exposure, the measurement device, reference material variability, and operator error to total variability.
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Designation: G 156 – 97
Standard Practice for
Selecting and Characterizing Weathering Reference
Materials Used to Monitor Consistency of Conditions in an
Exposure Test
This standard is issued under the fixed designation G 156; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope device, reference material variability, and operator error to total
variability.
1.1 This standard describes the criterion to be used for
selection of a WRM and procedures to be used for determining
2. Referenced Documents
within lab and between lab tolerances of changes in measured
2.1 ASTM Standards:
properties of a reference material intended for use in monitor-
D 3045 Practice for Heat Aging of Plastics Without Load
ing operating conditions to establish the consistency of expo-
D 3980 Practice for conducting an Interlaboratory Study for
sure tests.
Tess of Paints and Related Coatings
NOTE 1—Examples of laboratory accelerated tests in which a weather-
E 177 Practice for Use of the Terms Precision and Bias in
ing reference material could be used to monitor consistency are light and
ASTM Test Methods
water exposure tests such as those described in Practices G 23, G 26, and
E 691 Practice for Conducting an Interlaboratory Study to
G 53 and other standards in which tests conducted according to these
Determine Precision of a Test Method
standards are referenced. Examples of outdoor exposures where a weath-
E 1169 Guide for Conducting Ruggedness Tests
ering reference material could be used to monitor consistency are those
conducted according to Practices G 7, G 24, or G 90. A reference material G 7 Practice for Atmospheric Environmental Exposure
can also be used to monitor consistency of oven aging exposures such as
Testing of Nonmetallic Materials
those described in Practice D 3045.
G 23 Practice for Operating Light-Exposure Apparatus
1.2 This practice does not cover (1) control materials used (Carbon-Arc Type) With and Without Water for Exposure
for comparison of stability with test materials, or (2) standard of Nonmetallic Materials
materials used to time exposures. G 24 Practice for Conducting Exposures to Daylight Fil-
1.3 This practice provides an outline of experiments re- tered Through Glass
quired to determine how the measured properties of the G 26 Practice for Operating Light-Exposure Apparatus
reference material change as a function of exposure to specified (Xenon-Arc Type) With and Without Water for Exposure
test conditions. It includes establishment of reproducible mea- of Nonmetallic Material s
surement procedures, determination of the critical region in the G 53 Practice for Operating Light-Exposure Apparatus
light source causing the changes, and effects of other critical (Fluorescent UV-Condensation Type) for Exposure of
exposure stresses such as temperature and moisture. Nonmetallic Materials
1.4 This practice describes procedures for conducting G 90 Practice for Performing Accelerated Outdoor Weath-
round-robin tests with the weathering reference material to ering of Nonmetallic Materials Using Concentrated Natu-
determine reproducibility of the reference material property ral Sunlight
change in exposures conducted in different laboratories, and G 113 Terminology Relating to Natural and Artificial
the repeatability when replicate reference material specimens Weathering Tests of Nonmetallic Materials
are exposed in a single device and tested in one laboratory. 2.2 SAE Standard:
1.5 This practice describes procedures for using the results SAE J1960, Accelerated Exposure of Automotive Exterior
from analysis of variance on results from round-robin tests to Materials using a Controlled Irradiance Water-Cooled
determine the contribution of the exposure, the measurement Xenon Arc Apparatus
Annual Book of ASTM Standards, Vol 08.02.
1 3
This practice is under the jurisdiction of ASTM Committee G-3 on Weathering Discontinued—See Annual Book of ASTM Standards, Vol 06.02.
and Durability and is the direct responsibility of Subcommittee G03.01 on Joint Annual Book of ASTM Standards, Vol 14.02.
Weathering Projects. Available from Society of Automotive Engineers, 400 Commonwealth Drive,
Current edition approved Dec. 10, 1997. Published March 1998. Warrendale, PA 15096.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
G 156
SAE J1885, Accelerated Exposure of Automotive Interior 4.4.1 The results obtained according to this practice are
Materials Using a Controlled Irradiance Water-Cooled valid only for the exposure cycle used for the round-robin and
Xenon Arc Apparatus cannot be applied to the same weathering reference material
used in a different exposure cycle.
3. Terminology
4.5 The change in characteristic property of a reference
3.1 Definitions—The definitions listed in Terminology
material may be affected by the placement of the reference
G 113 are applicable to this standard.
material in the exposure device. This is often due to variations
in light intensity and temperature within the allowed exposure
4. Significance and Use
area. Random placement of replicate specimens of the weath-
4.1 Weathering reference materials are used in laboratory
ering reference material through-out the allowed exposure area
accelerated exposure tests to establish consistency among tests
provides the best indication of the overall consistency of the
run at different times and in different laboratories in the same
exposure test.
type of device. Specifications defining consistency of exposure
NOTE 5—In some cases, procedures require exposure of a weathering
conditions based on the property change of a reference material
reference material at a specific location within the exposure device or
are usually based on results for a single lot of the reference
chamber. Results for a reference material used in this way may not provide
material. When a new lot of the reference material is intro-
an accurate representation of the exposure conditions in other positions
duced, round-robin studies are necessary to compare the new
within the device.
and old lots and to establish appropriate limits for expected
5. Procedure
performance of the new lot.
5.1 Select a reference material which exhibits a measurable
NOTE 2—An example of the use of a clear polystyrene reference
change in a characteristic property when exposed in the
standard for this purpose is given in SAE J1885 and SAE J1960.
NOTE 3—Some weathering reference materials (for example blue specific type of device and exposure cycle to be monitored.
wools) are also used to define periods of exposure. Although not
5.2 Determine the procedure used that can best measure the
specifically covered by this standard, the procedures described for
change in characteristic property of the reference material.
characterizing a reference material used to monitor consistency of
5.2.1 Conduct a series of experiments to determine the
exposures are also generally applicable to characterizing reference mate-
effect of important factors in the measurement procedure. It is
rials used to define periods of exposure.
recommended that this be done using a ruggedness test
4.2 It is important to test the consistency of exposure in the
according to Guide E 1169 to determine which factors signifi-
laboratory accelerated device with a weathering reference
cantly affect results. The results from this test can be used to
material that responds to the test conditions similar to the way
tighten the test measurement procedures.
the test materials respond. Therefore, the weathering reference
5.2.2 When the results from the ruggedness testing are
material should be sensitive to the spectral region of the light
complete, write a set of instructions for running the test used to
source mainly responsible for producing degradation in the test
determine the level of the characteristic property that is
materials to provide the most meaningful evaluation of expo-
unambiguous and clearly understood by operators who will be
sure test consistency. The weathering reference material should
making the measurement. Have two operators in one labora-
also provide information on consistency of temperature and
tory conduct the measurement on at least three replicate
humidity conditions if the latter are important factors in
specimens of the reference material. Interview the operators to
degradation of the test materials.
determine whether the procedure provides clear and easy to
understand directions. Modify the procedure to remove any
NOTE 4—Material homogeneity can also be an important factor in
selection of a weathering reference material, particularly if weathering is
ambiguity in instructions.
initiated by the radiation absorbed by impurities as is the case in aliphatic
5.3 Determine the homogeneity of the weathering reference
type polymers exposed to radiation longer than 300 nm.
material by measuring the property change of randomly
4.3 The measurement of the characteristic property of a selected replicate specimens that have been exposed to very
weathering reference material can be subject to error depend- tightly controlled test conditions, or by appropriate chemical
ing on the instrument and the procedure used to measure the analysis techniques such as ultraviolet and/or infrared spectro-
property. It is important to develop measurement procedures scopic analysis.
that are clear and which minimize chances for operator 5.4 For any new weathering reference material, determine
the response of the reference material to critical exposure
misinterpretation. It is also important to determine the level of
variability caused by measurement of the characteristic prop- stresses. These results are important to determining whether
the material being considered is appropriate for monitoring the
erty.
4.4 When a reference material is used to monitor or specify specific conditions of the exposure test being used. Tests to
the consistency of an exposure test, it is important that any determine the materials response to exposure stresses should be
specification li
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