ASTM G141-09(2021)
(Guide)Standard Guide for Addressing Variability in Exposure Testing of Nonmetallic Materials
Standard Guide for Addressing Variability in Exposure Testing of Nonmetallic Materials
SIGNIFICANCE AND USE
4.1 Many standards and specifications reference exposure tests performed according to standards that are the responsibility of Committee G03 on Durability of Nonmetallic Materials. In many cases, use of the data generated in these tests fails to consider the ramifications of variability in the exposure test practices. This variability can have a profound effect on the interpretation of results from the exposure tests, and if not taken into consideration in test design and data analysis, can lead to erroneous or misleading conclusions. This guide lists some of the sources for test variability and recommends strategies for executing successful weathering studies. Not all sources of variability in weathering testing are addressed in this guide. Specific materials, sampling procedures, specimen preparation, specimen conditioning, and material property measurements can contribute significantly to variability in weathering test results. Many of these concerns are addressed in Guide G147. To reduce the contribution of an instrumental method to test variability, it is essential to follow appropriate calibration procedures and ASTM standards associated with the particular property measurement. Additional sources of variability in test results are listed in Guide D4853, along with methods for identifying probable causes.
SCOPE
1.1 This guide covers information on sources of variability and strategies for its reduction in exposure testing, and for taking variability into consideration in the design, execution, and data analysis of both exterior and laboratory accelerated exposure tests.
1.2 The values stated in SI units are to be regarded separately as the standard. The inch-pound values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G141 − 09 (Reapproved 2021)
Standard Guide for
Addressing Variability in Exposure Testing of Nonmetallic
Materials
This standard is issued under the fixed designation G141; 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 (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
No experimental procedure is exactly repeatable or reproducible. Exposure testing is susceptible to
poor test reproducibility because of many contributing factors. These include the type of material and
its homogeneity, the complexity and variability of the outdoor environment, difficulty in precisely
controllingthelaboratorytestingenvironment,andthevariabilityinthemeasurementofperformance.
It is extremely difficult to compare “absolute data,” that is, color shift, gloss, tensile, and elongation,
andsoforth,fromdifferentexposuretests.Thisistruefornaturalandacceleratedexposuresconducted
outdoors or for accelerated exposure tests conducted at different times in one laboratory or comparing
results between laboratories. The purpose of this guide is to provide the user with background
information on test variability and guidance to conduct an exposure test that will provide valid and
useful durability information.
1. Scope* 2. Referenced Documents
1.1 This guide covers information on sources of variability 2.1 ASTM Standards:
and strategies for its reduction in exposure testing, and for D4853 Guide for Reducing Test Variability (Withdrawn
taking variability into consideration in the design, execution, 2008)
and data analysis of both exterior and laboratory accelerated D6631 Guide for Committee D01 for Conducting an Inter-
exposure tests. laboratory Study for the Purpose of Determining the
Precision of a Test Method
1.2 The values stated in SI units are to be regarded sepa-
E177 Practice for Use of the Terms Precision and Bias in
rately as the standard. The inch-pound values given in paren-
ASTM Test Methods
theses are for information only.
E691 Practice for Conducting an Interlaboratory Study to
1.3 This standard does not purport to address all of the
Determine the Precision of a Test Method
safety concerns, if any, associated with its use. It is the
G7 Practice for Atmospheric Environmental Exposure Test-
responsibility of the user of this standard to establish appro-
ing of Nonmetallic Materials
priate safety, health, and environmental practices and deter-
G24 Practice for Conducting Exposures to Daylight Filtered
mine the applicability of regulatory limitations prior to use.
Through Glass
1.4 This international standard was developed in accor-
G90 Practice for Performing Accelerated Outdoor Weather-
dance with internationally recognized principles on standard-
ing of Materials Using Concentrated Natural Sunlight
ization established in the Decision on Principles for the
G113 Terminology Relating to Natural andArtificial Weath-
Development of International Standards, Guides and Recom-
ering Tests of Nonmetallic Materials
mendations issued by the World Trade Organization Technical
G147 Practice for Conditioning and Handling of Nonmetal-
Barriers to Trade (TBT) Committee.
lic Materials for Natural and Artificial Weathering Tests
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This guide is under the jurisdiction of ASTM Committee G03 on Weathering contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
andDurabilityandisthedirectresponsibilityofSubcommitteeG03.93onStatistics. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved July 1, 2021. Published July 2021. Originally approved the ASTM website.
in 1996. Last previous edition approved in 2013 as G141 – 09(2013). DOI: The last approved version of this historical standard is referenced on
10.1520/G0141-09R21. www.astm.org.
*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
G141 − 09 (2021)
G151 Practice for Exposing Nonmetallic Materials inAccel- rates of degradation or different degradation mechanisms, it is
erated Test Devices that Use Laboratory Light Sources extremely important to know the characteristics of the expo-
G152 Practice for Operating Open Flame Carbon Arc Light sure sites used and to evaluate materials at sites that produce
Apparatus for Exposure of Nonmetallic Materials intensification of important climate stresses. Typically, expo-
G153 Practice for Operating Enclosed Carbon Arc Light sures are conducted in “hot/wet” and “hot/dry” climates to
Apparatus for Exposure of Nonmetallic Materials provide intensification of important factors such as solar
G154 Practice for Operating Fluorescent Ultraviolet (UV) radiation and temperature, and to determine possible effects of
Lamp Apparatus for Exposure of Nonmetallic Materials moisture. Different exposure sites in one climate (even those in
G155 Practice for Operating XenonArc LightApparatus for close proximity) can cause significantly different results, de-
Exposure of Non-Metallic Materials pending on material.
NOTE 1—Exposures in a tropical summer rain climate (for example,
G166 Guide for Statistical Analysis of Service Life Data
Miami,Florida)andinahotdesertclimate(forexample,Phoenix,AZ)are
G169 Guide for Application of Basic Statistical Methods to
recognized as benchmarks for evaluating the durability of many different
Weathering Tests
materials.
G172 Guide for Statistical Analysis of Accelerated Service
5.2 Variability Due to Time of Year—Solar-ultraviolet
Life Data
radiation, temperature, and time of wetness vary considerably
G183 Practice for Field Use of Pyranometers, Pyrheliom-
with time of year. This can cause significant differences in the
eters and UV Radiometers
rate of degradation in many materials. Therefore, comparison
of results between short-term exposure studies (less than one
3. Terminology
full year) will be subject to greater variability. If exposures of
3.1 Definitions:
less than a full year are required, consider using times when
3.1.1 Terminology G113 is generally applicable to this
climatological stress is maximized so a worst case test result is
guide.
obtained. It may also be valuable to make several exposure
tests with varying start dates in order to provide more repre-
4. Significance and Use
sentative data. This is especially true when the material’s
4.1 Many standards and specifications reference exposure
response to the environment cannot be predetermined, or when
tests performed according to standards that are the responsi-
materials with different environmental responses are to be
bility of Committee G03 on Durability of Nonmetallic Mate-
compared. Often exposure periods are timed by total solar or
rials. In many cases, use of the data generated in these tests
solar-ultraviolet dose, or both. This approach may reduce
fails to consider the ramifications of variability in the exposure
variability in certain instances. However, an inherent limitation
testpractices.Thisvariabilitycanhaveaprofoundeffectonthe
in solar-radiation measurements is that they do not reflect the
interpretation of results from the exposure tests, and if not
effects of variation in temperature and moisture, which are
taken into consideration in test design and data analysis, can
often as important as solar radiation. Temperature and time of
lead to erroneous or misleading conclusions. This guide lists
wetness are highly dependent on time of year, especially in
some of the sources for test variability and recommends
temperate climates. With materials that are sensitive to heat or
strategies for executing successful weathering studies. Not all
moisture,orboth,thesamesolar-ultravioletradiationdosemay
sourcesofvariabilityinweatheringtestingareaddressedinthis
not give the same degree of change unless the heat and
guide. Specific materials, sampling procedures, specimen
moisture levels are also identical.
preparation, specimen conditioning, and material property
5.2.1 Another problem related to timing exposures by
measurements can contribute significantly to variability in
broad-band radiation measurements is that solar radiation in
weathering test results. Many of these concerns are addressed
the 290 to 310-nm band pass exhibits the most seasonal
in Guide G147. To reduce the contribution of an instrumental
variability. Some polymer systems are extremely sensitive to
method to test variability, it is essential to follow appropriate
radiation in this band pass. Variations in irradiance in this
calibration procedures and ASTM standards associated with
critical region (because of their relatively small magnitude) are
the particular property measurement. Additional sources of
not adequately reflected in total solar radiation or broad-band
variability in test results are listed in Guide D4853, along with
solar ultraviolet (UV) measurements.
methods for identifying probable causes.
5.2.2 The time of year (season) that an exposure test is
initiated has, in certain instances, led to different failure rates
5. Variability in Outdoor Exposure Tests
for identical materials (1).
5.1 Variability Due to Climate—Climate at the test site
5.3 Variability Due to Year-to-Year Climatological
location can significantly affect the material failure rates and
Variations—Even the comparison of test results of full-year
modes.Typicalclimatologicalcategoriesare;arctic,temperate,
exposure increments may show variability. Average
subtropical, and tropical (that are primarily functions of lati-
temperature, hours of sunshine, and precipitation can vary
tude). Subcategories may be of more importance as being
considerably from year to year at any given location. The
dictatedbygeographic,meteorological,terrain,ecological,and
microclimate for the test specimens can be affected by yearly
land-use factors, and include such categories as desert,
forested, (numerous classifications), open, marine, industrial,
and so forth. Because different climates, or even different
The boldface numbers in parentheses refer to the list of references at the end of
locations or orientation in the same climate, produce different this standard.
G141 − 09 (2021)
differences in pollution levels, airborne particulates, mold, and durability test standards that high levels of variability may be
mildew. These differences can impact material failure rates. possible with any test or material.
Results from a single-exposure test cannot be used to predict 7.1.1 Repeatability—In general, test precision within labo-
the absolute rate at which a material degrades. Several years of ratories (a single test period in a test device) will always be
repeat exposures are needed to get an “average” test result for better than precision between laboratories. By testing replicate
any given test site. specimens, statistically significant performance differences
among materials can be readily established.
5.4 Variability Due to Test Design—Every exposure test has
7.1.2 Reproducibility—The G03.03 round-robin studies
some variability inherent in its structure and design. Specimen
found that between laboratory comparisons of absolute gloss
placement on an exposure rack (2), and type or color of
values after a fixed exposure time is, in a practical sense,
adjacent specimens can also affect specimen temperature and
impossible. Replicates specimens exposed to seemingly iden-
time of wetness. Sample backing or insulation as well as rack
tical test conditions gave highly variable results from labora-
location in an exposure site field can affect specimen tempera-
tory to laboratory. Other round-robin weathering studies have
ture and time of wetness.
demonstrated varying degrees of variability with different
5.5 Variability in Glass-filtered Daylight Exposures—Glass-
materials and property measurements (6-8) Precise control of
filtered daylight exposures as described by Practice G24 are
critical exposure parameters may not be feasible when devices
subject to many of the test variables previously described.
are located in differing ambient laboratory conditions and
Recent studies conducted byASTM Subcommittee G03.02 on
operated by a diverse user group.
Natural Environmental Testing has demonstrated that the glass
NOTE 2—Indices of precision and related statistical terms are defined in
used in these exposures can be highly variable in its light
Practice E177.
transmission characteristics between 300 and 320 nm that can
7.2 Specific Factors Responsible for Variability in Acceler-
significantly impact exposure results (3). In addition, solariza-
ated Laboratory Exposure Tests:
tion processes can alter these transmission characteristics
7.2.1 Light sources for all test devices are subject to normal
during the first few months of exposure. Specimen temperature
manufacturing variation in peak irradiance and spectral power
can also vary depending on location within an under glass test
distribution (SPD). In many instances, the filter glasses asso-
rack (4).
ciated with certain devices and light sources also demonstrate
6. Variability in Accelerated Outdoor Exposures Using
significant variation in their initial UV transmission character-
Concentrated Sunlight
istics. As the light source and filter glasses age during normal
use, the irradiance and SPD can also change significantly.
6.1 Accelerated outdoor exposures using Fresnel concentra-
Instruments that monitor irradiance at 340 nm or broad-band
tors are described in Practice G90. Test results are subject to
normal climatological and seasonal variations. Exposure peri- radiometers (300 to 400 nm) may not detect or compensate for
these changes.
ods are described by a radiant energy dose, most often in the
UV region of sunlight. The UV content of the concentrated 7.2.2 Irradiance and specimen temperatures can vary sig-
nificantly throughout the allowed specimen exposure area,
sunlight is reduced during winter exposures and is also subject
especially in older test equipment.
to normal year-to-year variations.As mentioned in 5.2, current
7.2.3 Water contaminants or impurities and poor spray
radiant energy band passes, both total solar and broad-band
quality, that is, clogged spray nozzles, can cause specimen
UV, used in reporting solar dose do not adequately reflect
spotting that will give misleading durability results by impact-
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