ASTM G141-09(2013)
(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 and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G141 − 09 (Reapproved 2013)
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* D4853 Guide for Reducing Test Variability (Withdrawn
2008)
1.1 This guide covers information on sources of variability
D6631 Guide for Committee D01 for Conducting an Inter-
and strategies for its reduction in exposure testing, and for
laboratory Study for the Purpose of Determining the
taking variability into consideration in the design, execution,
Precision of a Test Method
and data analysis of both exterior and laboratory accelerated
E177 Practice for Use of the Terms Precision and Bias in
exposure tests.
ASTM Test Methods
1.2 The values stated in SI units are to be regarded sepa-
E691 Practice for Conducting an Interlaboratory Study to
rately as the standard. The inch-pound values given in paren-
Determine the Precision of a Test Method
theses are for information only.
G7 Practice for Atmospheric Environmental Exposure Test-
ing of Nonmetallic Materials
1.3 This standard does not purport to address all of the
G24 Practice for Conducting Exposures to Daylight Filtered
safety concerns, if any, associated with its use. It is the
Through Glass
responsibility of the user of this standard to establish appro-
G90 Practice for Performing Accelerated Outdoor Weather-
priate safety and health practices and determine the applica-
ing of Nonmetallic Materials Using Concentrated Natural
bility of regulatory limitations prior to use.
Sunlight
G113 Terminology Relating to Natural andArtificial Weath-
2. Referenced Documents
ering Tests of Nonmetallic Materials
2.1 ASTM Standards:
G147 Practice for Conditioning and Handling of Nonmetal-
lic Materials for Natural and Artificial Weathering Tests
G151 Practice for Exposing Nonmetallic Materials inAccel-
erated Test Devices that Use Laboratory Light Sources
G152 Practice for Operating Open Flame Carbon Arc Light
This guide is under the jurisdiction of ASTM Committee G03 on Weathering
Apparatus for Exposure of Nonmetallic Materials
and Durabilityand is the direct responsibility of Subcommittee G03.93 on Statistics.
G153 Practice for Operating Enclosed Carbon Arc Light
Current edition approved Nov. 1, 2013. Published December 2013. Originally
Apparatus for Exposure of Nonmetallic Materials
approved in 1996. Last previous edition approved in 2009 as G141 – 09. DOI:
10.1520/G0141-09R13.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. 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 (2013)
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,
differences in pollution levels, airborne particulates, mold, and
forested, (numerous classifications), open, marine, industrial,
mildew. These differences can impact material failure rates.
and so forth. Because different climates, or even different
Results from a single-exposure test cannot be used to predict
locations or orientation in the same climate, produce different
the absolute rate at which a material degrades. Several years of
rates of degradation or different degradation mechanisms, it is
repeat exposures are needed to get an “average” test result for
extremely important to know the characteristics of the expo-
any given test site.
sure sites used and to evaluate materials at sites that produce
intensification of important climate stresses. Typically, expo-
sures are conducted in “hot/wet” and “hot/dry” climates to
The boldface numbers in parentheses refer to the list of references at the end of
provide intensification of important factors such as solar this standard.
G141 − 09 (2013)
5.4 Variability Due to Test Design—Every exposure test has specimens, statistically significant performance differences
some variability inherent in its structure and design. Specimen among materials can be readily established.
placement on an exposure rack (2), and type or color of
7.1.2 Reproducibility—The G03.03 round-robin studies
adjacent specimens can also affect specimen temperature and found that between laboratory comparisons of absolute gloss
time of wetness. Sample backing or insulation as well as rack
values after a fixed exposure time is, in a practical sense,
location in an exposure site field can affect specimen tempera- impossible. Replicates specimens exposed to seemingly iden-
ture and time of wetness.
tical test conditions gave highly variable results from labora-
tory to laboratory. Other round-robin weathering studies have
5.5 Variability in Glass-filtered Daylight Exposures—Glass-
demonstrated varying degrees of variability with different
filtered daylight exposures as described by Practice G24 are
materials and property measurements (6-8) Precise control of
subject to many of the test variables previously described.
critical exposure parameters may not be feasible when devices
Recent studies conducted byASTM Subcommittee G03.02 on
are located in differing ambient laboratory conditions and
Natural Environmental Testing has demonstrated that the glass
operated by a diverse user group.
used in these exposures can be highly variable in its light
transmission characteristics between 300 and 320 nm that can
NOTE 2—Indices of precision and related statistical terms are defined in
Practice E177.
significantly impact exposure results (3). In addition, solariza-
tion processes can alter these transmission characteristics
7.2 Specific Factors Responsible for Variability in Acceler-
during the first few months of exposure. Specimen temperature
ated Laboratory Exposure Tests:
can also vary depending on location within an under glass test
7.2.1 Light sources for all test devices are subject to normal
rack (4).
manufacturing variation in peak irradiance and spectral power
distribution (SPD). In many instances, the filter glasses asso-
6. Variability in Accelerated Outdoor Exposures Using
ciated with certain devices and light sources also demonstrate
Concentrated Sunlight
significant variation in their initial UV transmission character-
istics. As the light source and filter glasses age during normal
6.1 Accelerated outdoor exposures using Fresnel concentra-
use, the irradiance and SPD can also change significantly.
tors are described in Practice G90. Test results are subject to
Instruments that monitor irradiance at 340 nm or broad-band
normal climatological and seasonal variations. Exposure peri-
radiometers (300 to 400 nm) may not detect or compensate for
ods are described by a radiant energy dose, most often in the
these changes.
UV region of sunlight. The UV content of the concentrated
sunlight is reduced during winter exposures and is also subject 7.2.2 Irradiance and specimen temperatures can vary sig-
nificantly throughout the allowed specimen exposure area,
to normal year-to-year variations.As mentioned in 5.2, current
radiant energy band passes, both total solar and broad-band especially in older test equipment.
UV, used in reporting solar dose do not adequately reflect 7.2.3 Water contaminants or impurities and poor spray
variations in the critical 290 to 310-nm range. Because of the quality, that is, clogged spray nozzles, can cause specimen
time of year differences in the amount of available ultraviolet, spotting that will give misleading durability results by impact-
timing exposures based on accumulated ultraviolet dose can ing visual observations, reducing specular gloss values, caus-
improve test-to-test variability, but may not account for the ing unnatural color shifts, or by impacting other optical
substantial specimen temperature differences that exist be- properties.
tween summer and winter.
7.2.4 Ambient temperature and humidity conditions in the
testinglaboratorycanaffecttestchamberconditionsanddevice
6.2 When test conditions specify water spray, water quality
operation. In fluorescent UV condensation devices, high am-
is extremely critical. Water contaminants or impurities can
bient tempe
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