ASTM F520-21

Standard Test Method for Environmental Resistance of Aerospace Transparencies to Artificially Induced Exposures

SIGNIFICANCE AND USE
4.1 This test method, when applied to aerospace transparencies of either monolithic glass/plastic or laminated combinations, is a measure of the ability of the transparency to withstand the effects of artificially induced environments. The test applies to configurations employing electrically conductive coatings, and also to uncoated materials.  
4.2 The resistance of the transparent enclosure to environmental effects may vary appreciably depending on the size, geometry, material of construction, coating integrity, coating density, and other factors.
SCOPE
1.1 This test method covers determination of the effects of exposure to thermal shock, condensing humidity, and simulated weather on aerospace transparent enclosures.  
1.2 This test method is not recommended for quality control, nor is it intended to provide a correlation to actual service life.  
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3.1 Exceptions—Certain inch-pound units are furnished in parentheses (not mandatory) and certain temperatures in Fahrenheit associated with other standards are also furnished.  
1.4 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.  
1.5 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

• Status: Published
• Publication Date: 30-Apr-2021
• ICS: 49.045 - Structure and structure elements
• Technical Committee: F07 - Aerospace and Aircraft
• Drafting Committee: F07.08 - Transparent Enclosures and Materials

Relations

• Refers: ASTM F319-19 - Standard Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements
• Effective Date: 01-Nov-2019
• Refers: ASTM F319-09(2014) - Standard Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements
• Effective Date: 01-Dec-2014
• Refers: ASTM G154-12 - Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials
• Effective Date: 01-Dec-2012
• Refers: ASTM D1003-11e1 - Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
• Effective Date: 15-Apr-2011
• Refers: ASTM D1003-11 - Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
• Effective Date: 15-Apr-2011
• Refers: ASTM F521-83(2010) - Standard Test Methods for Bond Integrity of Transparent Laminates
• Effective Date: 01-May-2010
• Refers: ASTM F319-09 - Standard Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements
• Effective Date: 15-May-2009
• Refers: ASTM D1003-07 - Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
• Effective Date: 01-Nov-2007
• Refers: ASTM G154-06 - Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials
• Effective Date: 05-Jun-2006
• Refers: ASTM G154-04 - Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials
• Effective Date: 01-Oct-2004
• Refers: ASTM F521-83(2004) - Standard Test Methods for Bond Integrity of Transparent Laminates
• Effective Date: 01-Oct-2004
• Refers: ASTM F319-91a(2003) - Standard Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements
• Effective Date: 01-Oct-2003
• Refers: ASTM D1003-00 - Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
• Effective Date: 10-Jun-2000
• Refers: ASTM G154-00 - Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials
• Effective Date: 10-Jun-2000
• Refers: ASTM G154-00a - Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials
• Effective Date: 10-Jun-2000

Overview

ASTM F520-21 is the standard test method developed by ASTM International for evaluating the environmental resistance of aerospace transparencies when subjected to artificially induced exposures. This test method specifically addresses how transparent aerospace enclosures, including both monolithic glass/plastic and laminated combinations, withstand the effects of thermal shock, condensing humidity, and simulated weather. The method applies to configurations with electrically conductive coatings as well as those using uncoated materials, ensuring reliable performance under challenging environmental conditions.

This standard is crucial for aerospace manufacturers, suppliers, and engineers focused on assuring the long-term durability and performance of transparency materials used in aircraft and related aerospace applications. While ASTM F520-21 is not intended for quality control or direct correlation with actual service life, it provides a unified procedure to compare material resistance under controlled, repeatable conditions using SI units as the primary measurement system.

Key Topics

• Environmental Resistance: The test evaluates a material's ability to resist degradation from temperature extremes, humidity, and simulated ultraviolet exposure.
• Specimen Types: Two main types of test specimens are defined:
  • Type A: Focuses on assessing electrical and optical properties after exposure.
  • Type B: Used for evaluating bond integrity, especially in laminated constructions.
• Test Exposures:
  • Thermal Shock: Rapid shift between extreme hot and cold temperatures to simulate real-world operational stress.
  • Condensing Humidity: Exposure to high humidity cycles to assess moisture ingress and potential damage.
  • Artificial Weathering: Simulated weather conditions using fluorescent UV lamps in accordance with recognized ASTM practices.
• Coating Assessment: Evaluates the durability and electrical properties of conductive coatings commonly used in transparency heating or anti-icing systems.
• Reporting Requirements: Comprehensive documentation of test setup, specimen details, visual inspection results, optical and electrical measurements, and procedures used.

Applications

• Aerospace Transparencies: Ensures that aerospace glazing materials such as cockpit windshields, windows, and canopies maintain structural and optical integrity in extreme environments.
• Material Selection and Design Verification: Enables engineers and designers to compare different glass, plastic, and laminate configurations for suitability in demanding operational settings.
• Component Qualification: Supports qualification of new transparency materials and coatings before service deployment.
• Safety and Compliance: Assists manufacturers in demonstrating compliance with international safety and performance standards, reducing the risk of failure during actual service.

Related Standards

ASTM F520-21 references several other important ASTM standards relevant to the evaluation of aerospace transparency materials:

• ASTM D1003: Test Method for Haze and Luminous Transmittance of Transparent Plastics.
• ASTM F319: Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements.
• ASTM F521: Test Methods for Bond Integrity of Transparent Laminates.
• ASTM G154: Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials.

These standards complement ASTM F520-21 by providing additional methods for optical evaluation, inspection of heating elements, and accelerated aging procedures.

Keywords: ASTM F520-21, environmental resistance, aerospace transparencies, humidity, thermal shock, transparency coating, artificial weathering, test method, material testing, aerospace standards.

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: F520 −21
Standard Test Method for
Environmental Resistance of Aerospace Transparencies to
Artificially Induced Exposures
ThisstandardisissuedunderthefixeddesignationF520;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope F521Test Methods for Bond Integrity of Transparent Lami-
nates
1.1 This test method covers determination of the effects of
G53Practice for Operating Light-and Water-Exposure Ap-
exposure to thermal shock, condensing humidity, and simu-
paratus (Fluorescent UV-Condensation Type) for Expo-
lated weather on aerospace transparent enclosures.
sure of Nonmetallic Materials (Withdrawn 2000)
1.2 This test method is not recommended for quality
G154Practice for Operating Fluorescent Ultraviolet (UV)
control, nor is it intended to provide a correlation to actual
Lamp Apparatus for Exposure of Nonmetallic Materials
service life.
3. Summary of Test Method
1.3 Units—The values stated in SI units are to be regarded
asstandard.Nootherunitsofmeasurementareincludedinthis 3.1 Two types of test specimens, duplicating the aerospace
standard.
transparent enclosure design, are subjected to thermal shock,
1.3.1 Exceptions—Certaininch-poundunitsarefurnishedin condensing humidity, and artificial weathering. Edge sealing
parentheses (not mandatory) and certain temperatures in Fahr-
shall be used if representative of the design.
enheit associated with other standards are also furnished. 3.1.1 TypeAspecimensshallbeusedtodeterminetheeffect
of environmental exposure on electrical and optical properties.
1.4 This standard does not purport to address all of the
3.1.2 TypeBspecimensshallbeusedtodeterminetheeffect
safety concerns, if any, associated with its use. It is the
of environmental exposure on bond integrity.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
4. Significance and Use
mine the applicability of regulatory limitations prior to use.
4.1 This test method, when applied to aerospace transpar-
1.5 This international standard was developed in accor-
encies of either monolithic glass/plastic or laminated
dance with internationally recognized principles on standard-
combinations,isameasureoftheabilityofthetransparencyto
ization established in the Decision on Principles for the
withstand the effects of artificially induced environments. The
Development of International Standards, Guides and Recom-
testappliestoconfigurationsemployingelectricallyconductive
mendations issued by the World Trade Organization Technical
coatings, and also to uncoated materials.
Barriers to Trade (TBT) Committee.
4.2 The resistance of the transparent enclosure to environ-
2. Referenced Documents
mental effects may vary appreciably depending on the size,
geometry, material of construction, coating integrity, coating
2.1 ASTM Standards:
density, and other factors.
D1003Test Method for Haze and Luminous Transmittance
of Transparent Plastics
5. Test Specimens
F319Practice for Polarized Light Detection of Flaws in
Aerospace Transparency Heating Elements 5.1 Each Type A specimen to be evaluated for external
coating durability shall be a 250 by 250mm (9.8 by 9.8in.)
cross section of the design and shall contain, as applicable,
surface coatings of operational, electrically conducting coating
This test method is under the jurisdiction of ASTM Committee F07 on
Aerospace andAircraft and is the direct responsibility of Subcommittee F07.08 on systems complete with bus bars, braids, and temperature
Transparent Enclosures and Materials.
sensors.
Current edition approved May 1, 2021. Published June 2021. Originally
5.1.1 Type A test specimens shall have a fully operational
approved in 1977. Last previous edition approved in 2016 as F520–16. DOI:
coating system, when applicable, with an average resistivity
10.1520/F0520-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. 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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F520 − 21
consistent with the average resistivity of the representative 7.2 Optical Tests—Measure each Type A specimen for
design. Reproduction of multiphase electrical circuits is not luminoustransmittanceandhazeinaccordancewithProcedure
required for these test specimens since this type of circuitry is BofTestMethodD1003.Makeatleasttwomeasurements,one
only a design technique used to accommodate limited voltage in the center and one near the edge, on each specimen. Six
resources at installation. measurements are preferred. If greater than 1% variation
5.1.2 Type A specimen testing exposure of an external exists, prepare a template from polyester film or other suitable
coating only, are independent of size but shall be of sufficient material to record these locations for indexing and correlation
size to produce representative coatings. When testing external to readings to be taken after environmental exposure.
coatings, the recommended specimen size is 250 by 250mm
NOTE 1—Paragraphs 7.3 – 7.6 are applicable to systems using electri-
(9.8 by 9.8in.). Type A specimens which are monolithic, or
cally conductive coatings.
laminated samples where only an external coating system is
7.3 Electrical Tests:
being tested, shall be tested to the same exposure intervals as
7.3.1 Bus Bar-to-Bus Bar Resistance—Measure each Type
50 by 50mm (2 by 2in.), Type B specimens (5.2).
Aspecimen for bus bar-to-bus bar resistance.Take precautions
5.1.3 Type A specimen testing for effects of exposure to
to minimize the effects of variable contact resistance. Record
components within a laminated construction, such as electrical
results and repeat the measurement after environmental expo-
components, heating films, and interlayers, taking place due to
sure prior to application of over-voltage power.
moisture ingress are dependent on size and shall receive
7.3.2 Sensing Element—Measure the resistance of the sens-
increasing exposure levels as the length of the sides of the
ing elements at a specified temperature to assure conformance
specimenincrease.250by250mmspecimensshallbeexposed
to the temperature resistance ranges certified by the element
to humidity 27 times the duration of 50 by 50mm specimens.
manufacturer.
Use of 150 by 150mm specimen shall be allowed with
7.3.3 Electrical Insulation—Test the electrical insulation by
exposure of 9 times that of corresponding 50 by 50mm
measuring leakage current on each test specimen. Apply an
specimens, or ⁄3 the duration of 250 by 250mm specimens.
alternating current potential between 1500 and 2500 V rms,
5.1.4 Type A that are both laminated and contain external
depending upon the design application and specified
coatings where both external and internal effects are to be
requirements, at 50 or 60 Hz for a period of 1 min between the
tested after exposure, must be tested independently as exter-
following:
nally coated samples, and as laminated samples, since the
(1)each sensor lead and each heater lead;
exposure durations will be different. To test effects on both
(2)each sensor lead and metal insert or spacer;
layers of a particular design, the number of samples must be
(3)each heater lead and the metal insert or spacer;
doubled, the external coating tested on one set, and internal
(4)each heater lead and metal strip placed in contact with
components tested on a second set of specimens.
the edge of the glass panel; test the entire edge of the glass
5.2 Each Type B test specimen shall be 50 by 50 mm (2 by
panel;
2 in.) and shall be of a cross section consistent with the edge
(5)each anti-ice and defog heater lead.
configuration of the representative design. Type B test speci-
Leakage current in excess of 1 mA at 1500 V rms or 4 mA at
mens are not intended to be operational electrically, but they
2500 V rms is objectionable. Monitor the current during a
shall be representative of the average resistivity of the design.
preliminarylowvoltageapplicationandterminatethetestifthe
current leakage exceeds the allowable amount prior to full
6. Preparation of Test Specimens
voltage application. Determine the resistance and decide
6.1 Prepare a minimum of three TypeAspecimens for each
whethertoproceedtofullvoltageinconformancewiththetest
design configuration. If the design contains an electrically
procedure.
activated coating, only one temperature sensor per specimen is
7.3.4 Monitor the current during gradual application of a dc
required.
voltage. Current in excess of 5 µA is objectionable. If the
6.2 Prepare a minimum of five Type B specimens for each
current exceeds 5 µA dc before 500 V dc is reached, suspend
designconfiguration.Preparethespecimeninsuchamanneras
thetestanddeterminetheresistancebeforedecidingwhetherto
to produce smooth edges and corners to prevent chipping
continue. Gradually apply and remove the potential at no
during testing. Polish at least one edge of each specimen to greater rate than 500 V rms/s.
allow inspection of the internal bonded surfaces during tensile
7.3.5 Electrically Conductive Coating Test—Test each Type
loading. Do not apply edge sealant to the specimens.
...

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 previous version. Because
it 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: F520 − 16 F520 − 21
Standard Test Method for
Environmental Resistance of Aerospace Transparencies to
Artificially Induced Exposures
This standard is issued under the fixed designation F520; 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.
1. Scope
1.1 This test method covers determination of the effects of exposure to thermal shock, condensing humidity, and simulated weather
on aerospace transparent enclosures.
1.2 This test method is not recommended for quality control, nor is it intended to provide a correlation to actual service life.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
standard.
1.3.1 Exceptions—Certain inch-pound units are furnished in parentheses (not mandatory) and certain temperatures in Fahrenheit
associated with other standards are also furnished.
1.4 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D1003 Test Method for Haze and Luminous Transmittance of Transparent Plastics
F319 Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements
F521 Test Methods for Bond Integrity of Transparent Laminates
G53 Practice for Operating Light-and Water-Exposure Apparatus (Fluorescent UV-Condensation Type) for Exposure of
Nonmetallic Materials (Withdrawn 2000)
G154 Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials
This test method is under the jurisdiction of ASTM Committee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on Transparent
Enclosures and Materials.
Current edition approved April 1, 2016May 1, 2021. Published May 2016June 2021. Originally approved in 1977. Last previous edition approved in 20102016 as
F520 – 10.F520 – 16. DOI: 10.1520/F0520-16.10.1520/F0520-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F520 − 21
3. Summary of Test Method
3.1 Two types of test specimens, duplicating the aerospace transparent enclosure design, are subjected to thermal shock,
condensing humidity, and artificial weathering. Edge sealing shall be used if representative of the design.
3.1.1 Type A specimens shall be used to determine the effect of environmental exposure on electrical and optical properties.
3.1.2 Type B specimens shall be used to determine the effect of environmental exposure on bond integrity.
4. Significance and Use
4.1 This test method, when applied to aerospace transparencies of either monolithic glass/plastic or laminated combinations, is a
measure of the ability of the transparency to withstand the effects of artificially induced environments. The test applies to on
configurations employing electrically conductive coatings, and also to uncoated materials.
4.2 The resistance of the transparent enclosure to environmental effects may vary appreciably depending on the size, geometry,
material of construction, coating integrity, coating density, and other factors.
5. Test Specimens
5.1 Each Type A specimen to be evaluated for external coating durability shall be a 250 by 250-mm250 mm (9.8 by 9.8-in.)9.8 in.)
cross section of the design and shall contain, as applicable, surface coatings of operational, electrically conducting coating systems
complete with bus bars, braids, and temperature sensors.
5.1.1 Type A test specimens shall have a fully operational coating system, when applicable, with an average resistivity consistent
with the average resistivity of the representative design. Reproduction of multiphase electrical circuits is not required for these test
specimens since this type of circuitry is only a design technique used to accommodate limited voltage resources at installation.
5.1.2 Type A specimen testing exposure of an external coating only, are independent of size but shall be of sufficient size to
produce representative coatings. When testing external coatings, the recommended specimen size is 250 by 250-mm250 mm (9.8
by 9.8-in.).9.8 in.). Type A specimens which are monolithic, or laminated samples where only an external coating system is being
tested, shall be tested to the same exposure intervals as 50 by 50-mm50 mm (2 by 2-in.),2 in.), Type B specimens (5.2).
5.1.3 Type A specimen testing for effects of exposure to components within a laminated construction, such as electrical
components, heating films, and interlayers, taking place due to moisture ingress are dependent on size and shall receive increasing
exposure levels as the length of the sides of the specimen increase. 250 by 250-mm250 mm specimens shall be exposed to humidity
27 times the duration of 50 by 50-mm50 mm specimens. Use of 150 by 150-mm150 mm specimen shall be allowed with exposure
of 9 times that of corresponding 50 by 50-mm50 mm specimens, or 1/3 ⁄3 the duration of 250 by 250-mm250 mm specimens.
5.1.4 Type A that are both laminated and contain external coatings where both external and internal effects are to be tested after
exposure, must be tested independently as externally coated samples, and as laminated samples, since the exposure durations will
be different. To test effects on both layers of a particular design, the number of samples must be doubled, the external coating tested
on one set, and internal components tested on a second set of specimens.
5.2 Each Type B test specimen shall be 50 by 50 mm (2 by 2 in.) and shall be of a cross section consistent with the edge
configuration of the representative design. Type B test specimens are not intended to be operational electrically, but they shall be
representative of the average resistivity of the design.
6. Preparation of Test Specimens
6.1 Prepare a minimum of three Type A specimens for each design configuration. If the design contains an electrically activated
coating, only one temperature sensor per specimen is required.
6.2 Prepare a minimum of five Type B specimens for each design configuration. Prepare the specimen in such a manner as to
produce smooth edges and corners to prevent chipping during testing. Polish at least one edge of each specimen to allow inspection
of the internal bonded surfaces during tensile loading. Do not apply edge sealant to the specimens.
F520 − 21
6.3 Condition all test specimens by exposing them to not less than 40 h 40 h at 23 6 2°C2 °C (73.4 6 3.6°F)3.6 °F) and 50 6
5 % relative humidity.
7. Procedure
7.1 Visual Examination—Carefully examine Type A and Type B specimens for any signs of material or manufacturing defects. A
microscope or magnifying lens, dark background, and cross lighting shall be used, as appropriate, to assist in the identification and
classification of visible defects.
7.2 Optical Tests—Measure each Type A specimen for luminous transmittance and haze in accordance with Procedure B of Test
Method D1003. Make at least two measurements, one in the center and one near the edge, on each specimen. Six measurements
are preferred. If greater than 1 % variation exists, prepare a template from polyester film or other suitable material to record these
locations for indexing and correlation to readings to be taken after environmental exposure.
NOTE 1—Paragraphs 7.3 – 7.6 are applicable to systems using electrically conductive coatings.
7.3 Electrical Tests:
7.3.1 Bus Bar-to-Bus Bar Resistance—Measure each Type A specimen for bus bar-to-bus bar resistance. Take precautions to
minimize the effects of variable contact resistance. Record results and repeat the measurement after environmental exposure prior
to application of over-voltage power.
7.3.2 Sensing Element—Measure the resistance of the sensing elements at a specified temperature to assure conformance to the
temperature resistance ranges certified by the element manufacturer.
7.3.3 Electrical Insulation—Test the electrical insulation by measuring leakage current on each test specimen. Apply an alternating
current potential between 1500 and 2500 V rms, depending upon the design application and specified requirements, at 50 or 60
Hz for a period of 1 min between the following:
(1) each sensor lead and each heater lead;
(2) each sensor lead and metal insert or spacer;
(3) each heater lead and the metal insert or spacer;
(4) each heater lead and metal strip placed in contact with the edge of the glass panel; test the entire edge of the glass panel;
(5) each anti-ice and defog heater lead.
Leakage current in excess of 1 mA at 1500 V rms or 4 mA at 2500 V rms is objectionable. Monitor the current during a preliminary
low voltage application and terminate the test if the current leakage exceeds the allowable amount prior to full voltage application.
Determ
...