1、Designation: C 978 04Standard 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 C 978; the number immediately following the designa
2、tion 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the dete
3、rmination 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
4、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 pro
5、perty 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
6、 to the possibility of additional residual stressesproduced by ion exchange between glasses of different com-positions, some uncertainty may be introduced in the value ofthe stress optical coefficient in the point of interest due to a lackof accurate knowledge of chemical composition in the areas of
7、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
8、 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 give
9、n 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
10、 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 162 Terminology of Glass and Glass ProductsC 770 Test Method for Measurement of Glass Stress-Optical CoefficientE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF 218 Test Method fo
11、r Analyzing Stress in Glass3. Terminology3.1 DefinitionsFor additional definitions of terms used inthis test method, refer to Terminology C 162.3.1.1 cordan attenuated glassy inclusion possessing opti-cal and other properties differing from those of the surroundingglass. C 1623.2 Definitions of Term
12、s 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.3.2.3 polarizeran optical assembly that transmits
13、 lightvibrating in a single planar direction, typically positionedbetween a light source and the specimen being evaluated.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 ed
14、ition approved June 1, 2004. Published June 2004. Originallyapproved in 1987. Last previous edition approved in 2002 as C 978 - 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume informa
15、tion, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4 residual stresspermanent stress that is resident in aglassy matrix. Such residual stress may result either fr
16、om 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 gl
17、ass 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 remelting the exchanged glass and homog-enizing the resulting glass m
18、elt.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 analyzer.4. Summary of Test Method4.1 This test method provides for the
19、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 either rotating (11.2), bire-fringent quartz wedge (11.3), or tilting
20、 (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 the ware, butalso by additional residual stresses caused by differen
21、ces 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 maybe evaluated by performance test procedures. Such evaluationsof en
22、amel 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 ofdetermining the magnitudes and spatial distributions of re-sidual stress s
23、ystems 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 applied to a glass substrate.6. Apparatus6.1 Microscope, monocular or
24、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 microscope is used, care should be taken to ensurethat the antireflection
25、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 polarizing microscope must be equipped with arotatable analyzer elemen
26、t, 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 magnificationsranging typically from 25 to 1003.6.3 Iris Diaphragm,
27、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 retardation value centered on 565-nmwavelength.6.5 Compensator,3appropri
28、ate 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 Wedge, graduated birefringent, of continuously vary-ing thickness, t
29、ypically 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,4typically capable of allowingdetermination of five orders of retardation.6.5
30、.3 Rotating Compensator,5typically allowing a deter-mination of retardation of one order or one wavelength inmagnitude to be determined. A monochromatizing filter isusually provided by the rotating compensator manufacturer.Care should be taken to use the appropriate matching filter forthe particular
31、 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 conversion tables provided by themanufacturer, specific to the par
32、ticular 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 optical retardation to the field of view. The dishshould be of sufficient
33、 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 evaluated, generallyto within 60.01 units in refractive index as ment
34、ioned in TestMethod F 218.6.9 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 specimensection is such that the planes of stress to be examined do notinitially parallel the optical axis o
35、f the microscope.3Compensators of Senarmont, Berek, and Friedel type and graduated quartzcompensators have been found suitable for this purpose.4A compensator of the Berek type has been found satisfactory for this purpose.5Compensators of the Friedel or Senarmont type have been found satisfactoryfor
36、 this purpose.C9780426.10 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 the section is not heated duringcutting so as to affect the residual stress di
37、stribution 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 The test specimens may be sections cut from appropriatelocations containing a
38、reas of interest to be evaluated inproduction sampled articles of commerce, fired decorated orenameled ware, or laboratory specimens especially preparedfor evaluation.8. Test Specimens68.1 Ensure that the test specimen is appropriately annealed,in that retardation due to inappropriate annealing coul
39、d 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, free of ACL and other residual stress sources. Proper annealingshould result in
40、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 ware containing the POI. Thesection may then consist of a bar, a ring, or other
41、 appropriatelyshaped section.8.2.1 In the case of ring section specimens, especially thoseused for cord, vitreous enamel, or ACL stress evaluations, openthe ring section with a vertical saw cut to form a narrow kerf,relieving whatever architectural stresses may be present in thesection.8.2.2 Care sh
42、ould 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 sections being cut contain high magnitudes ofretardation at the POI, the cut
43、 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 system is properlyaligned and the objectives to be used in the examination are
44、properly centered. The objectives should be relatively lowpowered, 2.5 to 103 being used during the initial examinationprocedure. The microscope eyepiece should contain a pair ofmutually perpendicular or otherwise easily referencedcrosshairs.9.2 Orient the eyepiece such that one or both of the eyepi
45、ececrosshairs 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 orientedin the optical column at 0 or in an East-West (E-W) alignment,while the
46、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 areproperly oriented, that is, mutually perpendicular to oneanother with
47、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 alignment of the polarizer should be checkedand then the analyzer should be rota
48、ted 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 microscope accessory slot, which plateis aligned at 45 between properly cro
49、ssed 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 determine 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 b
