ASTM F319-91a(2003)
(Practice)Standard Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements
Standard Practice for Polarized Light Detection of Flaws in Aerospace Transparency Heating Elements
SIGNIFICANCE AND USE
This practice is useful as a screening basis for acceptance or rejection of transparencies during manufacturing so that units with identifiable flaws will not be carried to final inspection for rejection at that time.
This practice may also be employed as a go-no go technique for acceptance or rejection of the finished product.
This practice is simple, inexpensive, and effective. Flaws identified by this practice, as with other optical methods, are limited to those which produce temperature gradients when electrically powered. Any other type of flaw, such as minor scratches parallel to the direction of electrical flow, are not detectable.
If another method (equally suitable for flaw detection) is designated for final optical inspection of the laminated part under power, the polarized light practice will not be required for the final inspection.
SCOPE
1.1 This practice covers a standard procedure for detecting flaws in the conductive coating (heater element) by the observation of polarized light patterns.
1.2 This practice applies to coatings on surfaces of monolithic transparencies as well as to coatings imbedded in laminated structures.
1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
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 and health practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements see Section 6.
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Designation:F319–91a (Reapproved 2003)
Standard Practice for
Polarized Light Detection of Flaws in Aerospace
Transparency Heating Elements
This standard is issued under the fixed designation F 319; 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.
INTRODUCTION
Electrically conductive coatings used in aerospace transparencies for heating purposes may contain
flaws resulting from imperfections of materials, imperfections of manufacturing techniques, handling
damage, or contamination. Flaws may develop before, during, or after coating and processing and
usually appear as hairline cracks, scratches, or pin holes. When these flaws are of sufficient size, hot
spots can occur as a result of disruption and concentration of the flow of electrical current adjacent to
the flaws. These hot spots may result in reduced service life of the transparency. Hot spot flaws in the
transparency may also produce undesirable temporary distortion of vision during powered operation
of the heater and permanent vision distortion after repeated cycling of the heater.
Polarized light is widely used to detect electrically conductive coating flaws during aerospace
transparency processing.
1. Scope 2.1.2 electrically conductive coating flaw—an electrical
discontinuity in the coating, caused generally by coating
1.1 This practice covers a standard procedure for detecting
cracks, pin holes, fine threads, scratches, and so forth.
flaws in the conductive coating (heater element) by the
observation of polarized light patterns.
3. Summary of Practice
1.2 This practice applies to coatings on surfaces of mono-
3.1 Flaws in electrically powered conductive coatings pro-
lithic transparencies as well as to coatings imbedded in
duce local concentrations of current which result in tempera-
laminated structures.
ture gradients and stresses. Since glass and plastic transparen-
1.3 The values stated in SI units are to be regarded as the
cies are birefringent when stressed, flaws can be detected by
standard. The values in parentheses are for information only.
optical methods, and in this case by the use of polarized light.
1.4 This standard does not purport to address all of the
3.2 This practice consists of directing polarized light
safety concerns, if any, associated with its use. It is the
through a heated transparent test specimen and reading the
responsibility of the user of this standard to establish appro-
transmitted light with a polarizing screen or filter. Diffracted
priate safety and health practices and determine the applica-
light from the region of the flaw will become visible, in the
bility of regulatory limitations prior to use. For specific
form of a brighter or more intense local image, usually shaped
precautionary statements see Section 6.
like a butterfly.
2. Terminology
4. Significance and Use
2.1 Definitions:
4.1 This practice is useful as a screening basis for accep-
2.1.1 transparent conductive coating—a transparent thin
tance or rejection of transparencies during manufacturing so
film of electrically conductive material such as gold, stannous
that units with identifiable flaws will not be carried to final
oxide, or indium oxide applied to plastic or glass which, when
inspection for rejection at that time.
bounded by connecting bus-bars energized by electricity,
4.2 This practice may also be employed as a go-no go
becomes a resistance type heating element.
technique for acceptance or rejection of the finished product.
4.3 This practice is simple, inexpensive, and effective.
This practice is under the jurisdiction of ASTM Committee F07 on Aerospace
Flaws identified by this practice, as with other optical methods,
andAircraft and is the direct responsibility of Subcommittee F07.08 on Transparent
are limited to those which produce temperature gradients when
Enclosures and Materials.
Current edition approved Oct. 1, 2003. Published October 2003. Originally
e1
approved in 1977. Last previous edition approved in 1997 as F 319 – 91a (1997) .
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F319–91a (2003)
electrically powered. Any other type of flaw, such as minor normal to the location being viewed. Since specimen size and
scratches parallel to the direction of electrical flow, are not curvature vary considerably, a dimensionally fixed standard is
detectable. not given.
4.4 If another method (equally suitable for flaw detection) is
5.2 The apparatus, in the order of assembly, consists of the
designated for final optical inspection of the laminated part
following:
under power, the polarized light practice will not be required
5.2.1 Uniform Light Source, such as a bank of fluorescent
for the final inspection.
lamps.
5.2.2 Translucent Light Diffusion Plate, such as milk-white
5. Apparatus
glass located so as to provide a uniform light distribution.
5.1 Theelementsoftheapparatusaredetailedbelowintheir
5.2.3 Polarizing Screen, which converts the diffused light to
physical relationship as shown in Fig. 1. The minimum size
polarized light.
and spacing of the elements of the apparatus are determined by
5.2.4 Transparent Dust Shield (optional).
the size and curvature of the part.The size of light source, light
5.2.5 Support for the specimen.
diffuser, and polarizing screen shall be large enough so that
5.2.6 Polarizing Viewer, hand-held or mounted so it can be
every portion of the electrically coated area of the test
rotated to give maximum contrast as an analyzer.
specimen is in the light path and is uniformly back-lit. If the
5.2.7 Electrical Power Supply, regulated.
test specimen is curved severely, its position may have to be
adjustedduringinspectionsothatthelightpathiswithin20°of 5.2.8 Timer, for controlling power application.
FIG. 1 Typical Arrangement for Polarized Light Method
F319–91a (2003)
5.2.9 Meters, for measuring power input to heater element. 10.3 Power Application—With the specimen stabilized at
room temperatur
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