1、Designation: C978 04 (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 follo
2、wing 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
3、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 d
4、ue 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 requirin
5、g 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
6、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
7、 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 resi
8、dual 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
9、 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 o
10、f 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 Me
11、thod 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
12、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 tes
13、t 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 (20
14、09).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, 10
15、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.3 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 r
16、esident 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 hea
17、t 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 the exchanged glass fromthe matrix, or by r
18、emelting the exchanged glass and homog-enizing the resulting glass melt.3.2.5 retardation compensatoran optical device, variantsof which are used to quantify the optical retardation producedin transparent birefringent materials, typically positioned be-tween the specimen being evaluated and the anal
19、yzer.4. Summary of Test Method4.1 This test method provides for the quantitative determi-nation of residual stresses in transparent glass matrixes bymeans of photoelastic retardation compensation procedures.Compensation is achieved by producing a retardation null orextinction in the specimen using e
20、ither rotating (11.2), bire-fringent quartz wedge (11.3), or tilting (11.4) optical retarda-tion compensators.5. Significance and Use5.1 The quality and performance of an article of glasswaremay be affected not only by the presence of residual stressesdue to heat treatment above the strain point in
21、the ware, butalso by additional residual stresses caused by differences inthermal expansion between the glass substrate, and either cord,fired-on vitreous enamel, or ACL decoration.5.2 The effects of those additional residual cord, enamel, orACL stresses and the resulting performance of such items m
22、aybe evaluated by performance test procedures. Such evaluationsof enamel or ACL stresses may also be accomplished throughthe determination of appropriate physical properties of thedecoration and matrix glass, or by analytical methods.5.3 This test method offers a direct and convenient means ofdeterm
23、ining the magnitudes and spatial distributions of re-sidual stress systems in glass substrates. The test method issimple, convenient, and quantitatively accurate.5.4 This test method is useful in evaluating the degree ofcompatibility between the coefficient of thermal expansion ofan enamel or ACL ap
24、plied to a glass substrate.6. Apparatus6.1 Microscope, monocular or binocular polarizing, havinga rotating, and preferably graduated, sample stage. Binocularmicroscope heads frequently contain a second, separate polar-izing element intended to minimize internal reflections. If sucha binocular micros
25、cope is used, care should be taken to ensurethat the antireflection polarizing element is removed from thefield of view. An eyepiece containing mutually perpendicularor otherwise easily referenced crosshairs should be provided.For retardation determinations using rotating compensationmethods, the po
26、larizing microscope must be equipped with arotatable analyzer element, having a scale graduated in degreesof rotation, capable of being read to at least 1, and aquarter-wave plate, properly indexed.6.2 White Light Source should be provided, together withstrain-free objective lenses yielding overall
27、magnificationsranging typically from 25 to 100.6.3 Iris Diaphragm, enabling collimation of the light beamtransmitted through the specimen being evaluated.6.4 Compensator, fixed full-wave retardation, commonlyreferred to as a sensitive tint plate, full-wave plate, or gypsumplate, having a fixed retar
28、dation value centered on 565-nmwavelength.6.5 Compensator, appropriate variable retardation, used tonull or compensate, and thereby determine, the magnitude ofthe stress-optical retardation effect produced by the residualstress induced in the glass substrate. Variable compensatorsmay be used.6.5.1 W
29、edge, graduated birefringent, of continuously vary-ing thickness, typically made of crystalline quartz, calibrated toyield retardation values directly and covering a range of four tosix orders of retardation, or approximately from 2200 to3300-nm total retardation.6.5.2 Tilting Compensator, typically
30、 capable of allowingdetermination of five orders of retardation.6.5.3 Rotating Compensator, typically allowing a determi-nation of retardation of one order or one wavelength inmagnitude to be determined. A monochromatizing filter isusually provided by the rotating compensator manufacturer.Care shoul
31、d be taken to use the appropriate matching filter forthe particular rotating compensator being used.6.6 Data Conversion TablesThe latter two tilting androtating variable compensator types provide raw data in theform of angles of rotation, from which retardation data may beobtained through the use of
32、 conversion tables provided by themanufacturer, specific to the particular rotating compensatorbeing used.6.7 Glass Immersion Dish, strain-free, flat bottomed, ofsufficient diameter to conveniently fit on the microscope stage.The immersion dish should not, in and of itself, add anysignificant optica
33、l retardation to the field of view. The dishshould be of sufficient depth to enable the specimen sectionbeing evaluated to be completely immersed in an index ofrefraction matching immersion fluid.6.8 Suitable Immersion Fluid, having an index of refractionmatching that of the glass substrate being ev
34、aluated, generallyto within 60.01 units in refractive index as mentioned in TestMethod F218.6.9 Sample Holder, to orient and maintain the planes ofstress at the point of interest (POI), parallel to the opticalcolumn of the microscope, if the geometry of the specimenC978 04 (2014)2section is such tha
35、t the planes of stress to be examined do notinitially parallel the optical axis of the microscope.6.10 Means of Preparing the Section Containing the POI tobe Analyzed, such as an abrasive or diamond-impregnatedcutoff wheel, or a hot wire bottle-cutting apparatus. Careshould be taken to ensure that t
36、he section is not heated duringcutting so as to affect the residual stress distribution in thespecimen section.6.11 Means of Physically Measuring the Optical PathLength, paralleling the stress planes through the thickness ofthe section containing the POI to within 0.03 mm (0.001 in.).7. Sampling7.1
37、The test specimens may be sections cut from appropriatelocations containing areas of interest to be evaluated inproduction sampled articles of commerce, fired decorated orenameled ware, or laboratory specimens especially preparedfor evaluation.8. Test Specimens38.1 Ensure that the test specimen is a
38、ppropriately annealed,in that retardation due to inappropriate annealing could affectthe retardation due to the stress systems being evaluated at thePOI.NOTE 1To ensure proper annealing, determine the stress-opticalretardation in a comparable reference area of the test specimen away fromthe POI, fre
39、e of ACL and other residual stress sources. Proper annealingshould result in minimal retardation due to annealing stress in the selectedreference area.8.2 Cut a section, of generally not less than 2.0 mm (0.08in.) and not more than 30.0 mm (1.18 in.) in optical pathlength, from the portion of the wa
40、re containing the POI. Thesection may then consist of a bar, a ring, or other appropriatelyshaped section.8.2.1 In the case of ring section specimens, especially thoseused for cord, vitreous enamel, orACLstress evaluations, openthe ring section with a vertical saw cut to form a narrow kerf,relieving
41、 whatever architectural stresses may be present in thesection.8.2.2 Care should be taken to ensure that both cut sectionsurfaces are parallel to each other, and are perpendicular to theoptical path length of the section paralleling the planes ofresidual stress in the POI being evaluated.8.3 If the s
42、ections being cut contain high magnitudes ofretardation at the POI, the cut section thickness may bedecreased proportionately from the thickness values listed in8.2 to decrease the magnitude of retardation to be measured atthe POI.9. Preparation of Apparatus9.1 Ensure that the microscope optical sys
43、tem is properlyaligned and the objectives to be used in the examination areproperly centered. The objectives should be relatively lowpowered, 2.5 to 10 being used during the initial examinationprocedure. The microscope eyepiece should contain a pair ofmutually perpendicular or otherwise easily refer
44、encedcrosshairs.9.2 Orient the eyepiece such that one or both of the eyepiececrosshairs parallel the 45 diagonal positions in the field ofview. The crosshairs will be used to orient the sections forwhich retardation determinations are to be made.9.3 The microscope polarizing element should be orient
45、edin the optical column at 0 or in an East-West (E-W) alignment,while the analyzer should be set in the field of view at 90 ora North-South (N-S) alignment, perpendicular to the polarizer.The microscope field of view should be at maximum darknessor extinction at this point if the polarizing elements
46、 areproperly oriented, that is, mutually perpendicular to oneanother with no compensator installed.9.4 If the field of view should not be at maximum darknessor extinction, the less-than-dark or brightened field indicatesthat the polarizing elements are not mutually perpendicular.The East-West alignm
47、ent of the polarizer should be checkedand then the analyzer should be rotated to a mutually perpen-dicular alignment with the polarizer, a position where the fieldof view is at its darkest, extinction position.9.5 On insertion of a fixed, sensitive tint plate or a full-waveretardation plate in the m
48、icroscope accessory slot, which plateis aligned at 45 between properly crossed polarizing elements,the darkened extinction field of view should then becomereddish-purple or magenta in color.10. Calibration and Standardization10.1 For microscopes and compensators that are notfactory-standardized to d
49、etermine the optical sign of stresses,the sense of the stresses being evaluated, that is, their tensile orcompressive nature, must be established for the particularmicroscope being used with either a sensitive tint plate orfull-wave fixed retardation compensator installed in the micro-scope column accessory slot between crossed polarizers. Thismay be accomplished, for instance, by positioning a well-annealed split ring section, containing a saw cut or kerf, in thefield of view as shown in Fig. 1. A bar section, or othercalibration section, may be similarly bent produ
