ASTM C978-04(2019)
(Test Method)Standard Test Method for Photoelastic Determination of Residual Stress in a Transparent Glass Matrix Using a Polarizing Microscope and Optical Retardation Compensation Procedures
Standard Test Method for Photoelastic Determination of Residual Stress in a Transparent Glass Matrix Using a Polarizing Microscope and Optical Retardation Compensation Procedures
SIGNIFICANCE AND USE
5.1 The quality and performance of an article of glassware may be affected not only by the presence of residual stresses due to heat treatment above the strain point in the ware, but also by additional residual stresses caused by differences in thermal 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, or ACL stresses and the resulting performance of such items may be evaluated by performance test procedures. Such evaluations of enamel or ACL stresses may also be accomplished through the determination of appropriate physical properties of the decoration and matrix glass, or by analytical methods.
5.3 This test method offers a direct and convenient means of determining the magnitudes and spatial distributions of residual stress systems in glass substrates. The test method is simple, convenient, and quantitatively accurate.
5.4 This test method is useful in evaluating the degree of compatibility between the coefficient of thermal expansion of an enamel or ACL applied to a glass substrate.
SCOPE
1.1 This test method covers the determination of residual stresses in a transparent glass matrix by means of a polarizing microscope using null or retardation compensation procedures.
1.2 Such residual stress determinations are of importance in evaluating the nature and degree of residual stresses present in glass matrixes due to cord, or the degree of fit, or suitability of a particular combination of glass matrix and enamel, or applied color label (ACL).
1.3 The retardation compensation method of optically determining and evaluating enamel or ACL residual stress systems offers distinct advantages over methods requiring physical property measurements or ware performance tests due to its simplicity, reproducibility, and precision.
1.4 Limitations—This test method is based on the stress-optical retardation compensation principle, and is therefore applicable only to transparent glass substrates, and not to opaque glass systems.
1.5 Due to the possibility of additional residual stresses produced by ion exchange between glasses of different compositions, some uncertainty may be introduced in the value of the stress optical coefficient in the point of interest due to a lack of accurate knowledge of chemical composition in the areas of interest.
1.6 This test method is quantitatively applicable to and valid only for those applications where such significant ion exchange is not a factor, and stress optical coefficients are known or determinable.
1.7 The extent of the ion exchange process, and hence the magnitudes of the residual stresses produced due to ion exchange will depend on the exchange process parameters. The residual stress determinations made on systems in which ion exchange has occurred should be interpreted with those dependencies in mind.
1.8 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C978 − 04 (Reapproved 2019)
Standard Test Method for
Photoelastic Determination of Residual Stress in a
Transparent Glass Matrix Using a Polarizing Microscope
and Optical Retardation Compensation Procedures
This standard is issued under the fixed designation C978; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope residual stress determinations made on systems in which ion
exchangehasoccurredshouldbeinterpretedwiththosedepen-
1.1 This test method covers the determination of residual
dencies in mind.
stresses in a transparent glass matrix by means of a polarizing
1.8 The values stated in SI units are to be regarded as the
microscopeusingnullorretardationcompensationprocedures.
standard. The values given in parentheses are for information
1.2 Such residual stress determinations are of importance in
only.
evaluating the nature and degree of residual stresses present in
1.9 This standard does not purport to address all of the
glass matrixes due to cord, or the degree of fit, or suitability of
safety concerns, if any, associated with its use. It is the
aparticularcombinationofglassmatrixandenamel,orapplied
responsibility of the user of this standard to establish appro-
color label (ACL).
priate safety, health, and environmental practices and deter-
1.3 The retardation compensation method of optically de-
mine the applicability of regulatory limitations prior to use.
termining and evaluating enamel or ACL residual stress sys-
1.10 This international standard was developed in accor-
tems offers distinct advantages over methods requiring physi-
dance with internationally recognized principles on standard-
calpropertymeasurementsorwareperformancetestsduetoits
ization established in the Decision on Principles for the
simplicity, reproducibility, and precision.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.4 Limitations—This test method is based on the stress-
Barriers to Trade (TBT) Committee.
optical retardation compensation principle, and is therefore
applicable only to transparent glass substrates, and not to
2. Referenced Documents
opaque glass systems.
2.1 ASTM Standards:
1.5 Due to the possibility of additional residual stresses
C162Terminology of Glass and Glass Products
produced by ion exchange between glasses of different
E691Practice for Conducting an Interlaboratory Study to
compositions,someuncertaintymaybeintroducedinthevalue
Determine the Precision of a Test Method
of the stress optical coefficient in the point of interest due to a
F218Test Method for Measuring Optical Retardation and
lack of accurate knowledge of chemical composition in the
Analyzing Stress in Glass
areas of interest.
3. Terminology
1.6 Thistestmethodisquantitativelyapplicabletoandvalid
3.1 Definitions:
onlyforthoseapplicationswheresuchsignificantionexchange
3.1.1 For additional definitions of terms used in this test
is not a factor, and stress optical coefficients are known or
method, refer to Terminology C162.
determinable.
3.1.2 cord—an attenuated glassy inclusion possessing opti-
1.7 The extent of the ion exchange process, and hence the
calandotherpropertiesdifferingfromthoseofthesurrounding
magnitudes of the residual stresses produced due to ion
glass.
exchangewilldependontheexchangeprocessparameters.The
3.2 Definitions of Terms Specific to This Standard:
3.2.1 analyzer—a polarizing element, typically positioned
between the specimen being evaluated and the viewer.
This test method is under the jurisdiction of ASTM Committee C14 on Glass
and Glass Products and is the direct responsibility of Subcommittee C14.10 on
Glass Decoration. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Feb. 1, 2019. Published February 2019. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1987. Last previous edition approved in 2014 as C978-04 (2014). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C0978-04R19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C978 − 04 (2019)
3.2.2 applied color label (ACL)—vitrifiable glass color microscope heads frequently contain a second, separate polar-
decoration or enamel applied to and fused on a glass surface. izingelementintendedtominimizeinternalreflections.Ifsuch
a binocular microscope is used, care should be taken to ensure
3.2.3 polarizer—an optical assembly that transmits light
that the antireflection polarizing element is removed from the
vibrating in a single planar direction, typically positioned
field of view. An eyepiece containing mutually perpendicular
between a light source and the specimen being evaluated.
or otherwise easily referenced crosshairs should be provided.
3.2.4 residual stress—permanent stress that is resident in a
For retardation determinations using rotating compensation
glassy matrix. Such residual stress may result either from heat
methods, the polarizing microscope must be equipped with a
treatment above the strain point of the glass, or from differ-
rotatableanalyzerelement,havingascalegraduatedindegrees
ences in thermal expansion between the glass matrix and a
of rotation, capable of being read to at least 1°, and a
cord, applied enamel, or ACL decoration.
quarter-wave plate, properly indexed.
3.2.4.1 Discussion—The residual stress may be modified
6.2 White Light Source should be provided, together with
either by heat treatment above the strain point, remelting and
homogenizing the glass melt, or by removal of a fired-on strain-free objective lenses yielding overall magnifications
ceramic or glass decoration. Residual stress caused by ion ranging typically from 25 to 100×.
exchange may only be relieved by either reexchanging the
6.3 Iris Diaphragm, enabling collimation of the light beam
glass to its original state, removing the exchanged glass from
transmitted through the specimen being evaluated.
the matrix, or by remelting the exchanged glass and homog-
enizing the resulting glass melt. 6.4 Compensator, fixed full-wave retardation, commonly
referred to as a sensitive tint plate, full-wave plate, or gypsum
3.2.5 retardation compensator—an optical device, variants
plate, having a fixed retardation value centered on 565-nm
of which are used to quantify the optical retardation produced
wavelength.
in transparent birefringent materials, typically positioned be-
tween the specimen being evaluated and the analyzer.
6.5 Compensator, appropriate variable retardation, used to
null or compensate, and thereby determine, the magnitude of
4. Summary of Test Method
the stress-optical retardation effect produced by the residual
stress induced in the glass substrate. Variable compensators
4.1 This test method provides for the quantitative determi-
may be used.
nation of residual stresses in transparent glass matrixes by
6.5.1 Wedge, graduated birefringent, of continuously vary-
means of photoelastic retardation compensation procedures.
Compensation is achieved by producing a retardation null or ingthickness,typicallymadeofcrystallinequartz,calibratedto
extinction in the specimen using either rotating (11.2), bire- yieldretardationvaluesdirectlyandcoveringarangeoffourto
fringent quartz wedge (11.3), or tilting (11.4) optical retarda- six orders of retardation, or approximately from 2200 to
tion compensators. 3300-nm total retardation.
6.5.2 Tilting Compensator, typically capable of allowing
5. Significance and Use
determination of five orders of retardation.
6.5.3 Rotating Compensator, typically allowing a determi-
5.1 The quality and performance of an article of glassware
nation of retardation of one order or one wavelength in
may be affected not only by the presence of residual stresses
magnitude to be determined. A monochromatizing filter is
due to heat treatment above the strain point in the ware, but
usually provided by the rotating compensator manufacturer.
also by additional residual stresses caused by differences in
Care should be taken to use the appropriate matching filter for
thermalexpansionbetweentheglasssubstrate,andeithercord,
the particular rotating compensator being used.
fired-on vitreous enamel, or ACL decoration.
5.2 The effects of those additional residual cord, enamel, or 6.6 Data Conversion Tables—The latter two tilting and
ACLstresses and the resulting performance of such items may
rotating variable compensator types provide raw data in the
beevaluatedbyperformancetestprocedures.Suchevaluations form of angles of rotation, from which retardation data may be
of enamel orACL stresses may also be accomplished through
obtained through the use of conversion tables provided by the
the determination of appropriate physical properties of the
manufacturer, specific to the particular rotating compensator
decoration and matrix glass, or by analytical methods.
being used.
5.3 Thistestmethodoffersadirectandconvenientmeansof
6.7 Glass Immersion Dish, strain-free, flat bottomed, of
determining the magnitudes and spatial distributions of re-
sufficient diameter to conveniently fit on the microscope stage.
sidual stress systems in glass substrates. The test method is
The immersion dish should not, in and of itself, add any
simple, convenient, and quantitatively accurate.
significant optical retardation to the field of view. The dish
should be of sufficient depth to enable the specimen section
5.4 This test method is useful in evaluating the degree of
being evaluated to be completely immersed in an index of
compatibility between the coefficient of thermal expansion of
refraction matching immersion fluid.
an enamel or ACL applied to a glass substrate.
6.8 Suitable Immersion Fluid, having an index of refraction
6. Apparatus
matching that of the glass substrate being evaluated, generally
6.1 Microscope, monocular or binocular polarizing, having to within 60.01 units in refractive index as mentioned in Test
a rotating, and preferably graduated, sample stage. Binocular Method F218.
C978 − 04 (2019)
6.9 Sample Holder, to orient and maintain the planes of properly centered. The objectives should be relatively low
stress at the point of interest (POI), parallel to the optical powered, 2.5 to 10× being used during the initial examination
column of the microscope, if the geometry of the specimen procedure. The microscope eyepiece should contain a pair of
section is such that the planes of stress to be examined do not mutually perpendicular or otherwise easily referenced
initially parallel the optical axis of the microscope. crosshairs.
6.10 Means of Preparing the Section Containing the POI to
9.2 Orienttheeyepiecesuchthatoneorbothoftheeyepiece
be Analyzed, such as an abrasive or diamond-impregnated
crosshairs parallel the 45° diagonal positions in the field of
cutoff wheel, or a hot wire bottle-cutting apparatus. Care
view. The crosshairs will be used to orient the sections for
should be taken to ensure that the section is not heated during
which retardation determinations are to be made.
cutting so as to affect the residual stress distribution in the
9.3 The microscope polarizing element should be oriented
specimen section.
intheopticalcolumnat0°orinanEast-West(E-W)alignment,
6.11 Means of Physically Measuring the Optical Path
while the analyzer should be set in the field of view at 90° or
Length, paralleling the stress planes through the thickness of
a North-South (N-S) alignment, perpendicular to the polarizer.
the section containing the POI to within 0.03 mm (0.001 in.).
The microscope field of view should be at maximum darkness
or extinction at this point if the polarizing elements are
7. Sampling
properly oriented, that is, mutually perpendicular to one
7.1 Thetestspecimensmaybesectionscutfromappropriate
another with no compensator installed.
locations containing areas of interest to be evaluated in
9.4 If the field of view should not be at maximum darkness
production sampled articles of commerce, fired decorated or
or extinction, the less-than-dark or brightened field indicates
enameled ware, or laboratory specimens especially prepared
that the polarizing elements are not mutually perpendicular.
for evaluation.
The East-West alignment of the polarizer should be checked
8. Test Specimens
and then the analyzer should be rotated to a mutually perpen-
dicular alignment with the polarizer, a position where the field
8.1 Ensure that the test specimen is appropriately annealed,
of view is at its darkest, extinction position.
in that retardation due to inappropriate annealing could affect
the retardation due to the stress systems being evaluated at the
9.5 Oninsertionofafixed,sensitivetintplateorafull-wave
POI.
retardation plate in the microscope accessory slot, which plate
isalignedat45°betweenproperlycrossedpolarizingelements,
NOTE 1—To ensure proper annealing, determine the stress-optical
retardationinacomparablereferenceareaofthetestspecimenawayfrom
the darkened extinction field of view should then become
the POI, free of ACL and other residual stress sources. Proper annealing
reddish-purple or magenta in color.
shouldresultinminimalretardationduetoannealingstressintheselected
reference area.
10. Calibration and Standardization
8.2 Cut a section, of generally not less than 2.0 mm (0.08
10.1 For microscopes and compensators that are not
in.) and not more than 30.0 mm (1.18 in.) in optical path
factory-standardized to determine the optical sign of stresses,
length, from the portion of the ware containing the POI. The
thesenseofthestressesbeingevaluated,thatis,theirtensileor
sectionmaythenconsistofabar,aring,orotherappropriately
compressive nature, must be established for the particular
shaped section.
microscope being used with either a sensitive tint plate or
8.2.1 In the case of ring section specimens, especially those
full-wave fixed retardation compensator installed in the micro-
usedforcord,vitreousenamel,orACLstressevaluations,open
scope column accessory slot between crossed polarizers. This
the ring section with a vertical saw cut to form a narrow kerf,
may be accomplished, for instance, by positioning a well-
relieving whatever architectural stresses may be present in the
annealed split ring section, containing a saw cut or kerf,
...
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