ASTM_C_770_-_16.pdf

Designation:C77016Standard Test Method forMeasurement of Glass StressOptical Coefficient1This standard is issued under the fixed designation C770;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 This test method covers procedures for determining thestress-optical coefficient of glass,which is used in photoelasticanalyses.In Procedure A the optical retardation is determinedfor a glass fiber subjected to uniaxial tension.In Procedure Bthe optical retardation is determined for a beam of glass ofrectangular cross section when subjected to four-point bending.In Procedure C,the optical retardation is measured for a beamof glass of rectangular cross-section when subjected to uniaxialcompression.1.2 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:2C336 Test Method for Annealing Point and Strain Point ofGlass by Fiber ElongationC598 Test Method for Annealing Point and Strain Point ofGlass by Beam BendingC1426 Practices for Verification and Calibration of Polarim-etersF218 Test Method for Measuring Optical Retardation andAnalyzing Stress in Glass2.2NIST,Recommended Practice Guide“Fractography of Ce-ramics and Glasses”(Section 4.6.2Flexural Strength)3.Significance and Use3.1 Stress-optical coefficients are used in the determinationof stress in glass.They are particularly useful in determiningthe magnitude of thermal residual stresses for annealing orpre-stressing(tempering)glass.As such,they can be importantin specification acceptance.4.Apparatus4.1 Stressing Equipment and Polarimeter:4.1.1 Procedure AFigs.1 and 2 illustrate a polarimeteremploying a quarter-wave plate and rotatable analyzer,3de-scribed in Test Method F218.The quarter-wave plate shall bedesigned for the wavelength of the light being used.Thepolarizing axes of the polarizer and analyzer shall be set atright angles to each other with each being located at an angleof 45 with the horizontal and vertical.The analyzer,however,shall be mounted in a rotatable mount having a scale graduatedon either side from 0 to 180.The quarter-wave plate shall befixed to give maximum extinction when the polarizer andanalyzer are crossed at right angles;that is,when its polarizingaxes are set at 45 and 135 to the horizontal and vertical.Inplace of the immersion cell E,a means of supporting andloading a glass specimen shall be provided,either in air(Fig.3(a)or in an immersion liquid(Fig.3(b).In this arrangementthe optical elements of the polarimeter between light sourceand telescope have been reversed and a large scale graduated in2-nm divisions is employed with the rotatable analyzer I.4.1.1.1 Fig.3 illustrates the fiber-stressing and optical ar-rangement used in Procedure A.Figure 3(a)shows the fibermounted vertically,positioned,and supported by two brasscollars with swivel handles so that the kilogram weight may beapplied to load the fiber.Alight shield having entrance and exitslits surrounds the fiber providing a degree of collimation to thelight passing through the fiber and also helping to eliminatestray light.4.1.1.2 In Fig.3(b)the fiber is stressed while immersed in aliquid which matches the refractive index of the fiber.Thisarrangement provides more satisfactory viewing of the fiber.4.1.2 Procedure B:4.1.2.1 The polarimetry apparatus for the beam-bendingprocedure is shown in Figs.4 and 5.Radiation from awhite-light source passes through the following componentsand in this sequence:a diffuser,a polarizer whose axis is at 451This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and is the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved May 1,2016.Published June 2016.Originallyapproved in 1973.Last previous edition approved in 2013 as C770 98(2013).DOI:10.1520/C0770-16.2For 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.3Goranson and Adams,“Measurement of Optical Path Differences,”Journal ofFranklin Institute,Vol 216,1933,p.475.Goranson and Adams,“Measurement ofOptical Path Differences,”Journal of Franklin Institute,Vol 216,1933,p.475.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 to the vertical,the glass specimen,a quarter-wave plate,and asecond polarizer(analyzer)whose axis is at 90 to that of thefirst polarizer.4.1.