ASTM_F_2108_-_06_2011.pdf

Designation:F210806(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 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 inducedby flight,environmental,or other factors.The transparencyattachment points 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 strips 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 inspection 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 regulatory 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 separation 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 expansion 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.Summary 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 without 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 normal 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.Apparatus5.1 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 toensure 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 inspectionarea 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 distilled water.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 Dec.1,2011.Published May 2012.Originallyapproved in 2001.Last previous edition approved in 2006 as F2108-06.DOI:10.1520/F2108-06R11.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 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 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