ASTM_C_978_-_04_2014.pdf

Designation:C97804(Reapproved 2014)Standard Test Method forPhotoelastic Determination of Residual Stress in aTransparent Glass Matrix Using a Polarizing Microscopeand Optical Retardation Compensation Procedures1This standard is issued under the fixed designation C978;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 the determination of residualstresses in a transparent glass matrix by means of a polarizingmicroscope using null or retardation compensation procedures.1.2 Such residual stress determinations are of importance inevaluating the nature and degree of residual stresses present inglass matrixes due to cord,or the degree of fit,or suitability ofa particular combination of glass matrix and enamel,or appliedcolor label(ACL).1.3 The retardation compensation method of optically de-termining and evaluating enamel or ACL residual stress sys-tems offers distinct advantages over methods requiring physi-cal property measurements or ware performance tests due to itssimplicity,reproducibility,and precision.1.4 LimitationsThis test method is based on the stress-optical retardation compensation principle,and is thereforeapplicable only to transparent glass substrates,and not toopaque glass systems.1.5 Due to the possibility of additional residual stressesproduced by ion exchange between glasses of differentcompositions,some uncertainty may be introduced in the valueof the stress optical coefficient in the point of interest due to alack of accurate knowledge of chemical composition in theareas of interest.1.6 This test method is quantitatively applicable to and validonly for those applications where such significant ion exchangeis not a factor,and stress optical coefficients are known ordeterminable.1.7 The extent of the ion exchange process,and hence themagnitudes of the residual stresses produced due to ionexchange will depend on the exchange process parameters.Theresidual stress determinations made on systems in which ionexchange has occurred should be interpreted with those depen-dencies in mind.1.8 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.9 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:2C162 Terminology of Glass and Glass ProductsC770 Test Method for Measurement of Glass StressOptical CoefficientE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF218 Test Method for Measuring Optical Retardation andAnalyzing Stress in Glass3.Terminology3.1 Definitions:3.1.1 For additional definitions of terms used in this testmethod,refer to Terminology C162.3.1.2 cordan attenuated glassy inclusion possessing opti-cal and other properties differing from those of the surroundingglass.3.2 Definitions of Terms Specific to This Standard:3.2.1 analyzera polarizing element,typically positionedbetween the specimen being evaluated and the viewer.3.2.2 applied color label(ACL)vitrifiable glass colordecoration or enamel applied to and fused on a glass surface.1This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and is the direct responsibility of Subcommittee C14.10 onGlass Decoration.Current edition approved May 1,2014.Published May 2014.Originallyapproved in 1987.Last previous edition approved in 2009 as C978-04(2009).DOI:10.1520/C0978-04R14.2For 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 3.2.3 polarizeran optical assembly that transmits lightvibrating in a single planar direction,typically positionedbetween a light source and the specimen being evaluated.3.2.4 residual stresspermanent stress that is resident in aglassy matrix.Such residual stress may result either from heattreatment above the strain point of the glass,or from differ-ences in thermal expansion between the glass matrix and acord,applied enamel,or ACL decoration.3.2.4.1 DiscussionThe residual stress may be modifiedeither by heat treatment above the strain point,remelting andhomogenizing the glass melt,or by removal of a fired-onceramic or glass decoration.Residual stress caused by ionexchange may only be relieved by either reexchanging theglass to its original state,removing