1、Designation: F 2108 06Standard Practice forInspection of Transparent Parts by Prism1This standard is issued under the fixed designation F 2108; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 points are especial
3、ly 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 strips or frames
4、.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 inspection instruc-ti
5、ons 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 regulatory limitation
6、s 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 separation of a lamina
7、te 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 expansion joints a
8、nd 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. Summary of Practi
9、ce3.1 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 without brightsunligh
10、t, 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 normal viewing. For
11、 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. Apparatus5.1 PrismMater
12、ial 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 toensure the insp
13、ector 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 inspectionarea if the ins
14、pection is done in bright sunlight.1This practice is under the jurisdiction of ASTM Committee F07 on Aerospaceand Aircraft and is the direct responsibility of Subcommittee F07.08 on TransparentEnclosures and Materials.Current edition approved Nov. 1, 2006. Published December 2006. Originallyapproved
15、 in 2001. Last previous edition approved in 2001 a F 2108 - 01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Reagents6.1 Use glycerol (USP Grade) as a coupler or wetting agent.6.1.1 The wetting agent shall not harm the transpare
16、ncy (forexample, cause crazing), shall be clear, and shall have a highenough viscosity to stay in place reasonably well.6.2 Use 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 tran
17、sparency thoroughly where the prismwill 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. SeeNote 1.7.2 If using glycerol, stor
18、e 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 good viewingarea. (WarningDo not all
19、ow 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 not allow the glycerolto get on the v
20、iewing 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 coupler. The coupler material shall b
21、ecompatible 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 shape, asdescribed below) to the tr
22、ansparency. 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, the area ofinterest will be blurre
23、d. 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 night while using aflashlight.NOTE 1Any
24、 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 be moved up or down to get theviewin
25、g 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 transparency, gently rock the prism to
26、completely 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 viewdoes not contain the area of interest
27、, 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 shading the area.If the view is dark, us
28、e a flashlight. Note, the angle of view andFIG. 1 Typical Prism Angles (Side View)FIG. 2 Standard NomenclatureF2108062the 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 are
29、a of interest. Add glycerol to theprism 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
30、layer delamination, and the height of a bolthole 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 transparentportion of the transparency. Cracks, by definit
31、ion, 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 the vicinityof an uncured material, then t
32、he 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 InspectionsIn multiple-layer transpar-encie
33、s, 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 edge strip is bondedto the transparency, th
34、e 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 strip pattern. Fig. 8 shows both aresin-rich
35、 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 bubble. Also, the outline of the prism is se
36、en 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 from a bolthole to the top of the edge strips
37、 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.FIG. 3 Acceptable Air Bubbles (from Resin Curing)F21080638.6 Bondline ThicknessThough the bondline thickness ofa clear res
38、in between two 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
39、were imperative 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 t
40、ypi-cally clearer. 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.The whitening is an indication the transparency is weakened.Fig. 9 shows whitening at the top of an edge strip.
41、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 is in the prismview, the actual height of the edge b
42、lock 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 shall be used for pass/failcriteria.10. Report10.1
43、Suggested information for a report form.10.1.1 Background InformationInspectors name, inspec-tion date/time, P/N inspected, location of inspection, and areasinspected.FIG. 4 View of Bolt Holes in a Nylon/Acrylic Edge BlockFIG. 5 Cracks Stemming From a Bolt Hole (Side View)F210806410.1.2 Inspection S
44、pecificsDelamination (Y/N), cracks(Y/N), voids (Y/N), dimensional 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;ins
45、pection; prism; transparency; windscreenFIG. 6 Crack Stemming From a Bolt HoleFIG. 7 Air Bubble as Seen Through a PrismF2108065ASTM 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
46、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 reviewed every five years andif not re
47、vised, 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 theresponsible technical committee, which you
48、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.FIG. 8 Resin Rich Area and Air Bubble as Seen Through a PrismFIG. 9 Whitening of an Edge Strip as Seen Through a PrismF2108066Thi
49、s 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).F2108067
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