1、Designation: F 319 91a (Reapproved 2003)Standard Practice forPolarized Light Detection of Flaws in AerospaceTransparency Heating Elements1This standard is issued under the fixed designation F 319; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONElectrically conductive coatings used in aerospace transparencies for heating purposes may
3、containflaws 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 siz
4、e, hotspots 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 power
5、ed operationof 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 conduc
6、tive 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 as thestandard. The values in parent
7、heses are for information only.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 electricaldiscontinuity in the coating, caused generally by coatingcracks, pin holes, fine threads, scratches, and so forth.3. Summary of Practice3.1 Flaws in electrically powered
10、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 consists
11、 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. Signif
12、icance 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 for
13、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,are limited to those which produce temperature gradients when1This practice is under the jurisdiction of ASTM Committee F07 on Aero
14、spaceand Aircraft and is the direct responsibility of Subcommittee F07.08 on TransparentEnclosures and Materials.Current edition approved Oct. 1, 2003. Published October 2003. Originallyapproved in 1977. Last previous edition approved in 1997 as F 319 91a (1997)e1.1Copyright ASTM International, 100
15、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.electrically powered. Any other type of flaw, such as minorscratches parallel to the direction of electrical flow, are notdetectable.4.4 If another method (equally suitable for flaw detection) isdesignated for final opti
16、cal inspection of the laminated partunder power, the polarized light practice will not be requiredfor the final inspection.5. Apparatus5.1 The elements of the apparatus are detailed below in theirphysical relationship as shown in Fig. 1. The minimum sizeand spacing of the elements of the apparatus a
17、re 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 the testspecimen is in the light path and is uniformly back-lit. If thetest specimen is curved severely, it
18、s 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 fixed standard isnot given.5.2 The apparatus, in the order of assembly, consists of thefollowing:5.2.1 Un
19、iform 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 Screen, which converts the diffused light topolarized light.5.2.4 Transparent Dust Shield (optional).5.2.5 Su
20、pport for the specimen.5.2.6 Polarizing Viewer, hand-held or mounted so it can berotated to give maximum contrast as an analyzer.5.2.7 Electrical Power Supply, regulated.5.2.8 Timer, for controlling power application.FIG. 1 Typical Arrangement for Polarized Light MethodF 319 91a (2003)25.2.9 Meters,
21、 for measuring power input to heater element.6. Safety Precautions6.1 This practice requires application of high voltages.Exercise precautions to prevent direct or indirect exposure oftest personnel to terminals, test leads, and so forth.6.2 Wear protective glasses to prevent damage to eyes byflying
22、 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 practice, alldeliverable electrically heated transparencies test in the finallaminated condition for heater element flaws.7.2 He
23、ater 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 full-size monolithic orlaminated part as specified in drawings that detail materials anddimensions. The test specimen sh
24、all be complete and full scalewith respect to contour, conductive coating, deletion lines,bus-bars, temperature sensing elements, electrical connections,and any other permanent electrical functional parts or elementsaffecting the electrical flow direction or magnitude anywherewithin the active porti
25、on 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 incomplete fabrication does notaffect the heating pattern and maximum temperatures of theelectrically conductive coatin
26、g.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 returnedto ambient.9. Preparation of Apparatus9.1 Install the test specimen in relation to the test apparatusas shown in Fig. 1.
27、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 provisions foradjustment of the part relative to the polarizing apparatus suchthat the viewing angle does not deviate more than 20 fromnormal to t
28、he light path.10. Procedure10.1 Turn on the polarized light source.10.2 Visually survey the test specimen at a distance of 1.5 m(5 ft), using the polarizing viewer to determine defect patternsthat exist before power is applied. Mark all defect locations.The object of this step is to record defects t
29、hat are unrelated tothe energized conductive coating.10.3 Power ApplicationWith the specimen stabilized atroom temperature, apply 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
30、 gradual change in voltage.NOTE 1Care should be taken to limit application time to preventoverheating, which could occur in a few seconds.10.3.1 For electrically conductive coatings on plastic mate-rials, apply a minimum of 110 % of the nominal designvoltage.10.3.2 For electrically conductive coatin
31、gs on glass, apply aminimum of 125 % of the nominal design voltage.10.3.3 Alternative voltage levels and power-on times maybe as specified 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
32、 viewer for maximum contrast.NOTE 2The flaws are most pronounced immediately after the appli-cation of power. Flaws, depending on cause, produce star, cross, orbutterfly-shaped light patterns. The highest practical electrical power levelproduces the strongest image.NOTE 3Preliminary experimentation
33、with instrumented specimenscontaining typical flaws may be required to establish the power levels anddurations required for maximum 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
34、the primaryviewing area (as defined by the part drawing).11.2 If an eye position is not defined, view the entire heatedarea from a distance of approximately 1.5 m (5 ft). Mark allflaw locations and describe them by size, shape, and location.12. Report12.1 When required by the customer, a report shal
35、l beprepared for all specimens considered satisfactory for furtherprocessing or delivery.12.2 The report shall be a record showing the locations,sizes, and shapes of all minor heating element flaws thatappeared during power application. The dimensional recordmay be a drawing, a photo of the marked u
36、p specimen, or aphoto of the specimen under lighted conditions. The reportshall include a record of the setup, test procedures, testequipment 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.1
37、3. Precision and Bias13.1 No statement is made about either precision or bias,since the result merely establishes the detection of flawswithout specifying an acceptable criteria.14. Keywords14.1 coatings; conductive coatings; heating elements; polar-ized light; polarized light inspectionF 319 91a (2
38、003)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this 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
39、, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional st
40、andardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible 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 Co
41、mmittee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).F 319 91a (2003)4
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