1、Designation: F319 09 (Reapproved 2014)Standard Practice forPolarized Light Detection of Flaws in AerospaceTransparency Heating Elements1This standard is issued under the fixed designation F319; the number immediately following the designation indicates the year of originaladoption or, in the case of
2、 revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONElectrically conductive coatings used in aerospace transparencies for heating purposes may cont
3、ainflaws resulting from imperfections of materials, imperfections of manufacturing techniques, handlingdamage, or contamination. Flaws may develop before, during, or after coating and processing andusually appear as hairline cracks, scratches, or pin holes. When these flaws are of sufficient size, h
4、otspots can occur as a result of disruption and concentration of the flow of electrical current adjacent tothe flaws. These hot spots may result in reduced service life of the transparency. Hot spot flaws in thetransparency may also produce undesirable temporary distortion of vision during powered o
5、perationof the heater and permanent vision distortion after repeated cycling of the heater.Polarized light is widely used to detect electrically conductive coating flaws during aerospacetransparency processing.1. Scope1.1 This practice covers a standard procedure for detectingflaws in the conductive
6、 coating (heater element) by theobservation of polarized light patterns.1.2 This practice applies to coatings on surfaces of mono-lithic transparencies as well as to coatings imbedded inlaminated structures.1.3 The values stated in SI units are to be regarded asstandard. No other units of measuremen
7、t are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitatio
8、ns prior to use. For specificprecautionary statements see Section 6.2. Terminology2.1 Definitions:2.1.1 transparent conductive coatinga transparent thinfilm of electrically conductive material such as gold, stannousoxide, or indium oxide applied to plastic or glass which, whenbounded by connecting b
9、us-bars energized by electricity,becomes a resistance type heating element.2.1.2 electrically conductive coating flawan electrical dis-continuity in the coating, caused generally by coating cracks,pin holes, fine threads, scratches, and so forth.3. Summary of Practice3.1 Flaws in electrically powere
10、d conductive coatings pro-duce local concentrations of current, which result in tempera-ture gradients and stresses. Since glass and plastic transparen-cies are birefringent when stressed, flaws can be detected byoptical methods, and in this case by the use of polarized light.3.2 This practice consi
11、sts of directing polarized lightthrough a heated transparent test specimen and reading thetransmitted light with a polarizing screen or filter. Diffractedlight from the region of the flaw will become visible, in theform of a brighter or more intense local image, usually shapedlike a butterfly.4. Sig
12、nificance and Use4.1 This practice is useful as a screening basis for accep-tance or rejection of transparencies during manufacturing sothat units with identifiable flaws will not be carried to finalinspection for rejection at that time.4.2 This practice may also be employed as a go-no gotechnique f
13、or acceptance or rejection of the finished product.4.3 This practice is simple, inexpensive, and effective.Flaws identified by this practice, as with other optical methods,1This practice is under the jurisdiction of ASTM Committee F07 on Aerospaceand Aircraft and is the direct responsibility of Subc
14、ommittee F07.08 on TransparentEnclosures and Materials.Current edition approved Dec. 1, 2014. Published December 2014. Originallyapproved in 1977. Last previous edition approved in 2009 as F319 09. DOI:10.1520/F0319-09R14.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoh
15、ocken, PA 19428-2959. United States1are limited to those that produce temperature gradients whenelectrically powered. Any other type of flaw, such as minorscratches parallel to the direction of electrical flow, are notdetectable.5. Apparatus5.1 The elements of the apparatus are detailed below in the
16、irphysical relationship as shown in Fig. 1. The minimum sizeand spacing of the elements of the apparatus are determined bythe size and curvature of the part. The size of light source, lightdiffuser, and polarizing screen shall be large enough so thatevery portion of the electrically coated area of t
17、he testspecimen is in the light path and is uniformly back-lit. If thetest specimen is curved severely, its position may have to beadjusted during inspection so that the light path is within 20 ofnormal to the location being viewed. Since specimen size andcurvature vary considerably, a dimensionally
18、 fixed standard isnot given.5.2 The apparatus, in the order of assembly, consists of thefollowing:5.2.1 Uniform Light Source, such as a bank of fluorescentlamps.5.2.2 Translucent Light Diffusion Plate, such as milk-whiteglass located so as to provide a uniform light distribution.5.2.3 Polarizing Scr
19、een, which converts the diffused light topolarized light.5.2.4 Transparent Dust Shield (optional).5.2.5 Support for the specimen.5.2.6 Polarizing Viewer, hand-held or mounted so it can berotated to give maximum contrast as an analyzer.FIG. 1 Typical Arrangement for Polarized Light MethodF319 09 (201
20、4)25.2.7 Electrical Power Supply, regulated.5.2.8 Timer, for controlling power application.5.2.9 Meters, for measuring power input to heater element.6. Safety Precautions6.1 This practice may require application of high voltages.Exercise precautions to prevent direct or indirect exposure oftest pers
21、onnel to terminals, test leads, and so forth.6.2 Wear protective glasses to prevent damage to eyes byflying glass particles which may be generated by shatteringfrom thermal shock or handling when glass parts are tested.7. Sampling7.1 When specified for use as a final acceptance procedure,all deliver
22、able electrically heated transparencies will be testedin the final laminated condition for heater element flaws.7.2 Heater elements may be tested prior to lamination of theassembly to screen out defective or marginal electrical conduc-tive coatings.8. Test Specimen8.1 The test specimen shall be a fu
23、ll-size monolithic orlaminated part as specified in drawings that detail materials anddimensions. The test specimen shall be complete and full scalewith respect to contour, conductive coating, deletion lines,bus-bars, temperature sensing elements, electrical connections,and any other permanent elect
24、rical functional parts or elementsaffecting the electrical flow direction or magnitude anywherewithin the active portion of the conductive coating.8.2 The test specimen need not have final fabrication detailssuch as reinforcement bonding, trimming, drilling of edges,and so forth, provided that the i
25、ncomplete fabrication does notaffect the heating pattern and maximum temperatures of theelectrically conductive coating.8.3 The final inspection of a laminated part shall be con-ducted only when all elevated temperature adhesive and curecycles have been completed and the part temperature hasreturned
26、 to ambient room temperature.9. Preparation of Apparatus9.1 Install the test specimen in relation to the test apparatusas shown in Fig. 1. Position the specimen so that it is parallelto the polarizing screen.9.2 Connect the power leads to the specimen.9.3 If the part is severely curved, make provisi
27、ons foradjustment of the part relative to the polarizing apparatus suchthat the viewing angle does not deviate more than 20 fromnormal to the surface of the uniform light source diffuser plate.10. Procedure10.1 Turn on the polarized light source.10.2 Visually survey the test specimen at a distance o
28、f 1.5m, using the polarizing viewer to determine defect patterns thatexist before power is applied. Mark all defect locations. Theobject of this step is to record defects that are unrelated to theenergized conductive coating.10.3 Power ApplicationWith the specimen stabilized atroom temperature, appl
29、y the minimum voltage levels definedbelow for a period required to achieve a visually identifiablepattern of flaws. Apply voltage suddenly, by closing a switch.Do not use a gradual change in voltage.NOTE 1Care should be taken to limit application time to preventoverheating, which could occur in a fe
30、w seconds.10.3.1 For electrically conductive coatings on plasticmaterials, apply a minimum of 110 % of the nominal designvoltage.10.3.2 For electrically conductive coatings on glass, apply aminimum of 125 % of the nominal design voltage.10.3.3 Alternative voltage levels and power-on times maybe as s
31、pecified by contractual documents.10.4 Watch through the viewer for flaws, which appearduring the power cycle as intense and localized areas of lightor shadow. Rotate the viewer for maximum contrast.NOTE 2The flaws are most pronounced immediately after the appli-cation of power. Flaws, depending on
32、cause, produce star, cross, orbutterfly-shaped light patterns. The highest practical electrical power levelproduces the strongest image.NOTE 3Preliminary experimentation with instrumented specimenscontaining typical flaws may be required to establish the power levels anddurations required for maximu
33、m image strength without overheating.11. Interpretation of Results11.1 After application of power and when viewed from theeye position, record every flaw that appears in the primaryviewing area (as defined by the part drawing).11.2 If an eye position is not defined, view the entire heatedarea from a
34、 distance of approximately 1.5 m. Mark all flawlocations and describe them by size, shape, and location.12. Report12.1 When required by the customer, a report shall beprepared for all specimens considered satisfactory for furtherprocessing or delivery.12.2 The report shall be a record showing the lo
35、cations,sizes, and shapes of all minor heating element flaws thatappeared during power application. The dimensional recordmay be a drawing, a photo of the marked up specimen, or aphoto of the specimen under lighted conditions. The reportshall include a record of the setup, test procedures, testequip
36、ment used, and any other data required to confirm the useof appropriate equipment and procedures and all data requiredfor verification of the quality of the part.13. Precision and Bias13.1 No statement is made about either precision or bias,since the result merely establishes the detection of flawsw
37、ithout specifying an acceptable criteria.14. Keywords14.1 coatings; conductive coatings; heating elements; polar-ized light; polarized light inspectionF319 09 (2014)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin thi
38、s standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be
39、 reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresp
40、onsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, We
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