ASTM_F_2156_-_11.pdf

Designation:F215611Standard Test Method forMeasuring Optical Distortion in Transparent Parts UsingGrid Line Slope1This standard is issued under the fixed designation F2156;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 When an observer looks through an aerospacetransparency,relative optical distortion results,specifically inthick,highly angled,multilayered plastic parts.Distortionoccurs in all transparencies but is especially critical to aero-space applications such as combat and commercial aircraftwindscreens,canopies,or cabin windows.This is especiallytrue during operations such as takeoff,landing,and aerialrefueling.It is critical to be able to quantify optical distortionfor procurement activities.1.2 This test method covers the apparatus and proceduresthat are suitable for measuring the grid line slope(GLS)oftransparent parts,including those that are small or large,thin orthick,flat or curved,or already installed.This test method isnot recommended for raw material.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3.1 ExceptionThe values given in parentheses are forinformation 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 limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF733 Practice for Optical Distortion and Deviation of Trans-parent Parts Using the Double-Exposure MethodF801 Test Method for Measuring Optical Angular Deviationof Transparent Parts3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 design eye,nthe reference point in aircraft designfrom which all anthropometrical design considerations aretaken.3.1.2 distortion,nthe rate of change of deviation resultingfrom an irregularity in a transparent part.3.1.2.1 DiscussionDistortion shall be expressed as theslope of the angle of localized grid line bending,for example,1 in 5(see Fig.1).3.1.3 grid board,nan optical evaluation tool used todetect the presence of distortion in transparent parts.3.1.3.1 DiscussionThe grid board is usually,but notalways,a vertical rectangular backboard with horizontal andvertical intersecting lines with maximum contrast between thewhite lines and the black background.3.1.4 grid line slope,nan optical distortion evaluationparameter that compares the slope of a deviated grid line to thatof a nondeviated grid line.3.1.4.1 DiscussionThe degree of deviation shall be indi-cated by a ratio,for example,1 in 2,1 in 8,or 1 in 20(thevisual optical quality improves as the second number getslarger.)3.1.5 installed angle,nthe transparency orientation asinstalled in the aircraft,defined by the angle between ahorizontal line(line of sight)and a plane tangent to the surfaceof the transparency(see Fig.2).3.1.6 repeatability limit(rL),nfrom Practice E177,27.3.2,“approximately 95%of individual test results from laborato-ries similar to those in an Inter-laboratory Study(ILS)can beexpected to differ in absolute value from their average value byless than 1.96s(about 2s).”3.1.6.1 Discussionin terms of this test method,approxi-mately 95%of all pairs of replications from the sameevaluator and the same photo differ in absolute value by lessthan the rL.1This test method is under the jurisdiction of ASTM Committee F07 onAerospace and Aircraft,and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved Dec.1,2011.Published January 2012.Originallyapproved in 2001.Last previous edition approved in 2006 as F2156-06.DOI:10.1520/F2156-11.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.7 reproducibility limit(RL),nfrom Practice E177,27.3.3,“approximately 95%of all pairs of test results fromlaboratories similar to those in the study can be expected todiffer in absolute value by less than 1.9602s(about 2.02s)=2.77s(or about 2.8s).This index is also known as the 95%limit on the difference between two test results.”FIG.1 Optical Distortion Represented By TangentFIG.2 Schematic Diagrams of GLS Photographic Recording DistancesF2156 112 3.1.7.1 Discussionin terms of this