1、Designation: F2108 06 (Reapproved 2011)Standard Practice forInspection of Transparent Parts by Prism1This standard is issued under the fixed designation F2108; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 Aerospace transparencies undergo high stresses inducedby flight, environmental, or other factors. The transparencyattachment poin
3、ts are especially subject to fatigue. These areasof fatigue are often obstructed or hidden from normal inspec-tion. An inspector, following the techniques described in thispractice, shall use a prism to view damage located neartransparency bolt holes, voids, and delamination that arehidden by edge s
4、trips or frames.1.2 The purpose of this practice is to provide acceptablemethods for performing prism inspections of transparent ma-terials with specific emphasis on aircraft windscreens andcanopies. Caveats and lessons learned from experience areincluded to assist authors in writing tailored inspec
5、tion instruc-tions for specific applications.1.3 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 regula
6、tory limitations prior to use.2. Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 coupler, na liquid refractive index-matching agentor wetting agent (for example, glycerol) used to create opticalcontact (coupling) between the prism and transparency.2.1.2 delamination, nthe separat
7、ion of a laminate into itsconstituent parts. An edge delamination is open to the lami-nates free edge. An internal delamination is contained withinthe laminate.2.1.3 edge attachment, nthe means of fastening the sideedges of a transparency to the aircraft structure. Edge attach-ments also include exp
8、ansion joints and any other connectionbetween the transparency and the aircraft structure.2.1.4 prism, na transparent optical element with polishedplane faces for the entrance and exit sides. Prisms userefraction or internal reflection or both to change the directionof the propagation of light.3. Su
9、mmary of Practice3.1 Prism inspections shall be performed with the aid of aprism and a wetting agent. The wetting agent is between theprism and transparency to ensure good visibility. The examinerlooks through the prism to see the area of the transparencybelow the prism. The exam is best done withou
10、t brightsunlight, which causes glare. The examiner changes his angleof view and inspects the area seen in the prism. A trained eyecan detect anomalies such as cracks, delaminations, and voids.4. Significance and Use4.1 Prisms are useful tools for viewing areas otherwiseobstructed or hidden from norm
11、al viewing. For example,transparency bolt holes, voids, and delaminations that arecovered by edge strips or frames can be seen through a prism.The prism, once put against the transparency, with a couplingagent to wet the surfaces, allows viewing of the area belowwhere the prism is placed.5. Apparatu
12、s5.1 PrismMaterial shall be of the same hardness as orsofter than the transparency to avoid scratches. The angles ofthe prism should be set so as to maximize the viewing area. Inthe case of a complex shape, the position of the inspectorshead and potential interference problems shall be considered to
13、ensure the inspector can look through the prism at the properangles. A typical prism is a 306090 triangle, although theprism does not need to be triangular; it could be a simplerectagon shape.5.2 FlashlightA high output, halogen bulb works best.5.3 CoverTo allow the inspector to shade the inspection
14、area if the inspection is done in bright sunlight.6. Reagents6.1 Use glycerol (USP Grade) as a coupler or wetting agent.6.1.1 The wetting agent shall not harm the transparency (forexample, cause crazing), shall be clear, and shall have a highenough viscosity to stay in place reasonably well.6.2 Use
15、distilled water.7. Procedure7.1 Use methods shall be approved by the procuring agencyor parts manufacturer. One example is to use a water rinse toclean the area of the transparency thoroughly where the prism1This practice is under the jurisdiction of ASTM Committee F07 on Aerospaceand Aircraft and i
16、s the direct responsibility of Subcommittee F07.08 on TransparentEnclosures and Materials.Current edition approved Dec. 1, 2011. Published May 2012. Originallyapproved in 2001. Last previous edition approved in 2006 as F2108 - 06. DOI:10.1520/F2108-06R11.1Copyright ASTM International, 100 Barr Harbo
17、r Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.will be placed. Assure the prism is also clean. Any debris willcause scratches to the delicate optical surfaces.7.1.1 Clean the prism with standard optical cleaning solu-tions appropriate for the material from which it is made. Se
18、eNote 1.7.2 If using glycerol, store it in a cool dry place, such as arefrigerator designated for chemicals, so it will be thicker.Apply several drops of coupler to the side of the prism thatgoes against the transparency. Ensure there is enough couplingbetween the prism and transparency to allow a g
19、ood viewingarea. (WarningDo not allow the prism to slide along thetransparency with no wetting agent between them or scratcheswill occur.)7.3 The prism is placed on the transparency and the viewingarea location as shown in Fig. 1. When moving the prism alongthe transparency use light pressure. Do no
20、t allow the glycerolto get on the viewing surface of the prism, as it will smear theviewing area.7.4 A coupler is required to provide an optical path betweenthe prism and canopy. Placing small amounts (several drops) ofcoupler on both the canopy and the prism tends to work best.Glycerol is a good co
21、upler. The coupler material shall becompatible with the transparency material, the clearer and themore viscous the better. Gentle pressure between the prism andcanopy keeps air out of the coupler and allows the coupler tospread farther. See Note 2.7.5 Gently press the prism (of appropriate size and
22、shape, asdescribed below) to the transparency. Alter the pressure on theprism corners to remove any trapped air. To keep the prismclean, the least amount of glycerol shall be used. Hold only theedges of the prism and use gentle pressure. (WarningIf thecoupler gets onto the viewing face of the prism,
23、 the area ofinterest will be blurred. Keep the prisms viewing face clean.)7.6 A light source, such as a flashlight aids in opticalclarification. This inspection technique does not work well inbright sunlight. Bright sunlight causes glare that clouds theviewing area. The inspection works best at nigh
24、t while using aflashlight.NOTE 1Any debris will cause scratches to the delicate opticalsurfaces.NOTE 2Using too much coupler will make cleanup more difficult andmake it difficult to keep the prism viewing area clean.7.7 Look through the top of the prism to view the area ofinterest. The prism shall b
25、e moved up or down to get theviewing area to the proper depth. When looking through theprism, change the angle of view (left to right). Begin to movethe prism along the area of interest. Continue looking throughthe prism, altering angle of view. If an air bubble gets trappedbetween the prism and tra
26、nsparency, gently rock the prism tocompletely wet out the surface of the prism and transparency.If more glycerol is needed, lift the prism and add glycerol oradd glycerol just in front of the prism so the prism will slideover the glycerol.7.8 Look through the viewing area of the prism. If the viewdo
27、es not contain the area of interest, the prism shall be liftedslightly or moved side to side. If the area of interest cannot bebrought into sight, the prism dimensions may need to bealtered. Fig. 1 illustrates how the inspectors eye is able to seeinto the transparency. If the view is hazy, try shadi
28、ng the area.If the view is dark, use a flashlight. Note, the angle of view andthe angle of the flashlight shall be varied to obtain the bestcombination for each inspection.7.9 After inspecting the area in sight, move the prism asrequired to view the entire area of interest. Add glycerol to theprism
29、or transparency or both as needed.7.9.1 Photographs shall be taken through the prism view toaid in documentation of findings.8. Guidelines for Interpreting Findings in the PrismView8.1 Bolt Hole InspectionsBolt holes shall be inspected forradial cracks, inner layer delamination, and the height of a
30、boltFIG. 1 Typical Prism Angles (Side View)FIG. 2 Standard NomenclatureF2108 06 (2011)2hole relative to any edge strips. Figs. 3 and 4 show examplesof how areas over bolt holes can look.8.2 Crack InspectionsCracks can originate from boltholes or where edge strips/edge blocks meet the transparentport
31、ion of the transparency. Cracks, by definition, have aphysical gap between the two halves. If a crack occurs whilewet installing a fastener, then sealant can fill the crack. Sealantin a crack will show up as the sealant color or a brownish color.If the crack occurs after the sealant is dry or not in
32、 the vicinityof an uncured material, then the air in the gap will make thecrack look opaque. Occasionally, the striations and crackdirection can be seen while looking through the prism. Fig. 5shows a side view of cracks stemming from a bolt hole. Fig. 6shows a prism view of a crack.8.3 Delamination
33、InspectionsIn multiple-layer transpar-encies, delamination resulting from drilling operations can bedetected. Inner layer delamination can occur in monolithicmaterials. Because of the air gap between inner layers, thedelamination appears cloudy in the prism view.8.4 Void/Resin-Rich InspectionsIf an
34、edge strip is bondedto the transparency, the potential for voids and or resin-richareas exists at the bondline. Voids and air bubbles appear clearor cloudy while resin-rich areas are dark as shown in Fig. 7.Voids, air bubbles, and resin-rich areas block the view behindit and thus break up the edge s
35、trip pattern. Fig. 8 shows both aresin-rich area (on the edge strip) and an air bubble (at the edgeblock bondline). Note that in Fig. 8 the resin-rich area is darkerthan the air bubble and that the edge strip pattern is slightlyvisible behind the resin-rich area but not at all visible below theair b
36、ubble. Also, the outline of the prism is seen at the edges ofthe figure.8.5 Dimensional TolerancesIf inspecting a new transpar-ency, a prism can assist in determining if the correct dimen-sions were met. For example, if the canopy is drilled andfastened to its frame in one operation, the distance fr
37、om a bolthole to the top of the edge strips on both the inside and outsidecan be measured. Or, if a butt block is used, the prisminspection can assure the butt blocks alignment relative to thetransparency and edge strips.8.6 Bondline ThicknessThough the bondline thickness ofa clear resin between two
38、 clear laminates cannot be easilydistinguished (if at all), the bondline thickness between rein-forced members of the transparency can be distinguished. Forexample, if both edge strips and an edge block are used, thebondline between them (appearing clear) can be determined.Also, if it were imperativ
39、e for the bondline thickness to beknown for a hidden area (optically noncritical), it may bepossible to add a dye to the resin to give a distinction betweenit and the laminate.8.7 Other AnomaliesWhen comparing new transparenciesversus in-service transparencies, new transparencies are typi-cally clea
40、rer. As the transparency ages, certain areas tend to geta whitening effect. The whitening can be a result of environ-mental conditions such as UV exposure and thermal cycling.FIG. 3 Acceptable Air Bubbles (from Resin Curing)F2108 06 (2011)3The whitening is an indication the transparency is weakened.
41、Fig. 9 shows whitening at the top of an edge strip.9. Finding Interpretations9.1 Flaw SizeThe length of flaws is true as viewed in theprism. The prism skews the height of flaws. To determine theflaw height, the flaw size shall be compared to something ofknown height. For instance, if an edge block i
42、s in the prismview, the actual height of the edge block to the apparent heightgives the ratio required for determining the flaw height. Also,if the edge strip has a weave pattern of known height it mayalso be used. For bolt hole flaws, the flaw size relative to a bolthole size within the prism view
43、shall be used for pass/failcriteria.10. Report10.1 Suggested information for a report form.10.1.1 Background InformationInspectors name, inspec-tion date/time, P/N inspected, location of inspection, and areasinspected.10.1.2 Inspection SpecificsDelamination (Y/N), cracks(Y/N), voids (Y/N), dimension
44、al tolerances (Y/N), bondlinethickness (Y/N), bolt hole flaws (Y/N), and other anomalies(list).10.1.3 Individual comments including any recommenda-tions and actions.11. Keywords11.1 bolt-hole inspection; canopy; cracks; delaminations;inspection; prism; transparency; windscreenFIG. 4 View of Bolt Hol
45、es in a Nylon/Acrylic Edge BlockFIG. 5 Cracks Stemming From a Bolt Hole (Side View)F2108 06 (2011)4FIG. 6 Crack Stemming From a Bolt HoleFIG. 7 Air Bubble as Seen Through a PrismF2108 06 (2011)5FIG. 8 Resin Rich Area and Air Bubble as Seen Through a PrismFIG. 9 Whitening of an Edge Strip as Seen Thr
46、ough a PrismF2108 06 (2011)6ASTM 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 infr
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