1、Designation: F2108 06 (Reapproved 2011)F2108 17Standard 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 las
2、t revision. 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 induced by flight, environmental, or other factors. The transparencyattach
3、ment points are especially subject to fatigue. These areas of fatigue are often obstructed or hidden from normal inspection.An inspector, following the techniques described in this practice, shall use a prism to view damage located near transparency boltholes, voids, and delamination that are hidden
4、 by edge strips or frames.1.2 The purpose of this practice is to provide acceptable methods for performing prism inspections of transparent materials withspecific emphasis on aircraft windscreens and canopies. Caveats and lessons learned from experience are included to assist authorsin writing tailo
5、red inspection instructions for specific applications.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability o
6、f regulatorylimitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade
7、Organization Technical Barriers to Trade (TBT) Committee.2. Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 coupler, na liquid refractive index-matching agent or wetting agent (for example, glycerol) used to create optical contact(coupling) between the prism and transparency.2.1.
8、2 delamination, nthe separation of a laminate into its constituent parts. An edge delamination is open to the laminatesfree edge. An internal delamination is contained within the laminate.2.1.3 edge attachment, nthe means of fastening the side edges of a transparency to the aircraft structure. Edge
9、attachmentsalso include expansion joints and any other connection between the transparency and the aircraft structure.2.1.4 prism, na transparent optical element with polished plane faces for the entrance and exit sides. Prisms use refraction orinternal reflection or both to change the direction of
10、the propagation of light.3. Summary of Practice3.1 Prism inspections shall be performed with the aid of a prism and a wetting agent. The wetting agent is between the prismand transparency to ensure good visibility. The examiner looks through the prism to see the area of the transparency below thepri
11、sm. The exam is best done without bright sunlight, which causes glare. The examiner changes his angle of view and inspectsthe area seen in the prism. A trained eye can detect anomalies such as cracks, delaminations, and voids.4. Significance and Use4.1 Prisms are useful tools for viewing areas other
12、wise obstructed or hidden from normal viewing. For example, transparencybolt holes, voids, and delaminations that are covered by edge strips or frames can be seen through a prism. The prism, once putagainst the transparency, with a coupling agent to wet the surfaces, allows viewing of the area below
13、 where the prism is placed.5. Apparatus5.1 PrismMaterial shall be of the same hardness as or softer than the transparency to avoid scratches. The angles of the prismshouldshall be set so as to maximize the viewing area. In the case of a complex shape, the position of the inspectors head and1 This pr
14、actice is under the jurisdiction of ASTM Committee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on TransparentEnclosures and Materials.Current edition approved Dec. 1, 2011June 1, 2017. Published May 2012June 2017. Originally approved in 2001. Last previous e
15、dition approved in 2006 as F2108 - 06.DOI: 10.1520/F2108-06R11.10.1520/F2108-17.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequa
16、tely depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
17、n, PA 19428-2959. United States1potential interference problems shall be considered to ensure the inspector can look through the prism at the proper angles. Atypical prism is a 306090 triangle, although the prism does not need to be triangular; it could be a simple rectagon shape.shapeis also suitab
18、le.5.2 FlashlightA high output, halogen bulb works best.5.3 CoverTo allow the inspector to shade the inspection 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 (for example
19、, 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 agency or parts manufacturer. One example is to use a water rinse to cleanthe area of the transparency thoro
20、ughly where the prism will be placed. Assure the prism is also clean. Any debris will causescratches to the delicate optical surfaces.7.1.1 Clean the prism with standard optical cleaning solutions appropriate for the material from which it is made. See Note 1.7.2 If using glycerol, store it in a coo
21、l dry place, such as a refrigerator designated for chemicals, so it will be thicker. Applyseveral drops of coupler to the side of the prism that goes against the transparency. Ensure there is enough coupling between theprism and transparency to allow a good viewing area. (WarningDo not allow the pri
22、sm to slide along the transparency with nowetting agent between them or scratches will occur.)7.3 The prism is placed on the transparency and the viewing area location as shown in Fig. 1. When moving the prism alongthe transparency use light pressure. Do not allow the glycerol to get on the viewing
23、surface of the prism, as it will smear theviewing area.7.4 A coupler is required to provide an optical path between the 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 be com
24、patiblewith the transparency material, the clearer and the more viscous the better. Gentle pressure between the prism and canopy keepsair out of the coupler and allows the coupler to spread farther. See Note 2.7.5 Gently press the prism (of appropriate size and shape, as described below) to the tran
25、sparency. Alter the pressure on theprism corners to remove any trapped air. To keep the prism clean, the least amount of glycerol shall be used. Hold only the edgesof the prism and use gentle pressure. (WarningIf the coupler gets onto the viewing face of the prism, the area of interest willbe blurre
26、d. Keep the prisms viewing face clean.)FIG. 1 Typical Prism Angles (Side View)F2108 1727.6 A light source, such as a flashlight aids in optical clarification. This inspection technique does not work well in brightsunlight. Bright sunlight causes glare that clouds the viewing area. The inspection wor
27、ks best at night while using a flashlight.NOTE 1Any debris will cause scratches to the delicate optical surfaces.NOTE 2Using too much coupler will make cleanup more difficult and make it difficult to keep the prism viewing area clean.7.7 Look through the top of the prism to view the area of interest
28、. The prism shall be moved up or down to get the viewingarea to the proper depth. When looking through the prism, change the angle of view (left to right). Begin to move the prism alongthe area of interest. Continue looking through the prism, altering angle of view. If an air bubble gets trapped bet
29、ween the prismand transparency, gently rock the prism to completely wet out the surface of the prism and transparency. If more glycerol is needed,lift the prism and add glycerol or add glycerol just in front of the prism so the prism will slide over the glycerol.7.8 Look through the viewing area of
30、the prism. If the view does not contain the area of interest, the prism shall be lifted slightlyor moved side to side. If the area of interest cannot be brought into sight, alter the prism dimensions may need to be altered.dimensions. Fig. 1 illustrates how the inspectors eye is able to see into the
31、 transparency. If the view is hazy, try shading the area.If the view is dark, use a flashlight. Note, the angle of view and the 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 as required to view the ent
32、ire area of interest. Add glycerol to the prismor transparency or both as needed.7.9.1 Photographs shall be taken through the prism view to aid in documentation of findings.8. Guidelines for Interpreting Findings in the Prism View8.1 Bolt Hole InspectionsBolt holes shall be inspected for radial crac
33、ks, inner layer delamination, and the height of a bolt holerelative to any edge strips. Figs. 3 and 4 show examples of how areas over bolt holes can look.8.2 Crack InspectionsCracks can originate from bolt holes or where edge strips/edge blocks meet the transparent portion ofthe transparency. Cracks
34、, by definition, have a physical gap between the two halves. If a crack occurs while wet installing afastener, then sealant can fill the crack. Sealant in a crack will show up as the sealant color or a brownish color. If the crack occursafter the sealant is dry or not in the vicinity of an uncured m
35、aterial, then the air in the gap will make the crack look opaque.Occasionally, the striations and crack direction can be seen while looking through the prism. Fig. 5 shows a side view of cracksstemming from a bolt hole. Fig. 6 shows a prism view of a crack.8.3 Delamination InspectionsIn multiple-lay
36、er transparencies, delamination resulting from drilling operations can bedetected. Inner layer delamination can occur in monolithic materials. Because of the air gap between inner layers, the delaminationappears cloudy in the prism view.8.4 Void/Resin-Rich InspectionsIf an edge strip is bonded to th
37、e transparency, the potential for voids and or resin-rich areasexists at the bondline. Voids and air bubbles appear clear or cloudy while resin-rich areas are dark as shown in Fig. 7. Voids, airbubbles, and resin-rich areas block the view behind it and thus break up the edge strip pattern. Fig. 8 sh
38、ows both a resin-rich area(on the edge strip) and an air bubble (at the edge block bondline). Note that in Fig. 8 the resin-rich area is darker than the air bubbleFIG. 2 Standard NomenclatureF2108 173and that the edge strip pattern is slightly visible behind the resin-rich area but not at all visibl
39、e below the air bubble. Also, theoutline of the prism is seen at the edges of the figure.8.5 Dimensional TolerancesIf inspecting a new transparency, a prism can assist in determining if the correct dimensions weremet. For example, if the canopy is drilled and fastened to its frame in one operation,
40、the distance from a bolt hole to the top ofthe edge strips on both the inside and outside can be measured. Or, if a butt block is used, the prism inspection can assure the buttblocks alignment relative to the transparency and edge strips.8.6 Bondline ThicknessThough the bondline thickness of a clear
41、 resin between two clear laminates cannot be easilydistinguished (if at all), the bondline thickness between reinforced members of the transparency can be distinguished. For example,if both edge strips and an edge block are used, the bondline between them (appearing clear) can be determined. Also, i
42、f it wereimperative for the bondline thickness to be known for a hidden area (optically noncritical), it may be is possible to add a dye tothe resin to give a distinction between it and the laminate.FIG. 3 Acceptable Air Bubbles (from Resin Curing)FIG. 4 View of Bolt Holes in a Nylon/Acrylic Edge Bl
43、ockF2108 174FIG. 5 Cracks Stemming From a Bolt Hole (Side View)FIG. 6 Crack Stemming From a Bolt HoleF2108 1758.7 Other AnomaliesWhen comparing new transparencies versus in-service transparencies, new transparencies are typicallyclearer. As the transparency ages, certain areas tend to get a whitenin
44、g effect. The whitening can be a result of environmentalconditions such as UV exposure and thermal cycling. The whitening is an indication the transparency is weakened. Fig. 9 showswhitening at the top of an edge strip.9. Finding Interpretations9.1 Flaw SizeThe length of flaws is true as viewed in t
45、he prism. The prism skews the height of flaws. To determine the flawheight, the flaw size shall be compared to something of known height. For instance, if an edge block is in the prism view, the actualheight of the edge block to the apparent height gives the ratio required for determining the flaw h
46、eight. Also, if the edge strip hasa weave pattern of known height it may also be used. height, this known height is also of use for flaw size computation. For bolthole flaws, the flaw size relative to a bolt hole size within the prism view shall be used for pass/fail criteria.FIG. 7 Air Bubble as Se
47、en Through a PrismFIG. 8 Resin Rich Area and Air Bubble as Seen Through a PrismF2108 17610. Report10.1 Suggested information for a report form.10.1.1 Background InformationInspectors name, inspection date/time, P/N inspected, location of inspection, and areasinspected.10.1.2 Inspection SpecificsDela
48、mination (Y/N), cracks (Y/N), voids (Y/N), dimensional tolerances (Y/N), bondline thickness(Y/N), bolt hole flaws (Y/N), and other anomalies (list).10.1.3 Individual comments including any recommendations and actions.11. Keywords11.1 bolt-hole inspection; canopy; cracks; delaminations; inspection; p
49、rism; transparency; windscreenASTM 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, 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 comme
