ASTM C770-98(2008)
(Test Method)Standard Test Method for Measurement of Glass Stress—Optical Coefficient
Standard Test Method for Measurement of Glass Stress—Optical Coefficient
SIGNIFICANCE AND USE
Stress-optical coefficients are used in the determination of stress in glass. They are particularly useful in determining the magnitude of thermal residual stresses for annealing or pre-stressing (tempering) glass. As such, they can be important in specification acceptance.
SCOPE
1.1 This test method covers procedures for determining the stress-optical coefficient of glass, which is used in photoelastic analyses. In Procedure A the optical retardation is determined for a glass fiber subjected to uniaxial tension. In Procedure B the optical retardation is determined for a beam of glass of rectangular cross section when subjected to four-point bending. In Procedure C, the optical retardation is measured for a beam of glass of rectangular cross-section when subjected to uniaxial compression.
1.2 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C770 − 98(Reapproved 2008)
Standard Test Method for
Measurement of Glass Stress—Optical Coefficient
This standard is issued under the fixed designation C770; 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 pre-stressing (tempering) glass.As such, they can be important
in specification acceptance.
1.1 This test method covers procedures for determining the
stress-optical coefficient of glass, which is used in photoelastic
4. Apparatus
analyses. In Procedure A the optical retardation is determined
4.1 Stressing Equipment and Polarimeter:
for a glass fiber subjected to uniaxial tension. In Procedure B
4.1.1 Procedure A—Figs. 1 and 2 illustrate a polarimeter
the optical retardation is determined for a beam of glass of
employing a quarter-wave plate and rotatable analyzer, de-
rectangularcrosssectionwhensubjectedtofour-pointbending.
scribed in Test Method E218. The quarter-wave plate shall be
In Procedure C, the optical retardation is measured for a beam
designed for the wavelength of the light being used. The
ofglassofrectangularcross-sectionwhensubjectedtouniaxial
polarizing axes of the polarizer and analyzer shall be set at
compression.
right angles to each other with each being located at an angle
1.2 This standard does not purport to address all of the
of 45° with the horizontal and vertical.The analyzer, however,
safety concerns, if any, associated with its use. It is the
shallbemountedinarotatablemounthavingascalegraduated
responsibility of the user of this standard to establish appro-
on either side from 0 to 180°. The quarter-wave plate shall be
priate safety and health practices and determine the applica-
fixed to give maximum extinction when the polarizer and
bility of regulatory limitations prior to use.
analyzer are crossed at right angles; that is, when its polarizing
axes are set at 45° and 135° to the horizontal and vertical. In
2. Referenced Documents
place of the immersion cell E, a means of supporting and
2.1 ASTM Standards:
loading a glass specimen shall be provided, either in air (Fig.
C336Test Method for Annealing Point and Strain Point of
3(a)) or in an immersion liquid (Fig. 3(b)). In this arrangement
Glass by Fiber Elongation
the optical elements of the polarimeter between light source
C598Test Method for Annealing Point and Strain Point of
andtelescopehavebeenreversedandalargescalegraduatedin
Glass by Beam Bending
2-nm divisions is employed with the rotatable analyzer I.
E218Tentative Standard Method for Radiochemical Deter-
4.1.1.1 Fig. 3 illustrates the fiber-stressing and optical ar-
mination of Cesium-137 in Aqueous Solutions (Chlorop-
rangement used in Procedure A. Figure 3(a) shows the fiber
latinate Method) (Withdrawn 1968)
mounted vertically, positioned, and supported by two brass
collarswithswivelhandlessothatthekilogramweightmaybe
3. Significance and Use
appliedtoloadthefiber.Alightshieldhavingentranceandexit
3.1 Stress-optical coefficients are used in the determination slitssurroundsthefiberprovidingadegreeofcollimationtothe
of stress in glass. They are particularly useful in determining
light passing through the fiber and also helping to eliminate
the magnitude of thermal residual stresses for annealing or stray light.
4.1.1.2 In Fig. 3(b) the fiber is stressed while immersed in a
liquid which matches the refractive index of the fiber. This
arrangement provides more satisfactory viewing of the fiber.
This test method is under the jurisdiction of ASTM Committee C14 on Glass
and Glass Products and is the direct responsibility of Subcommittee C14.04 on
4.1.2 Procedure B:
Physical and Mechanical Properties.
4.1.2.1 The apparatus for the beam-bending procedure is
Current edition approved April 1, 2008. Published December 2008. Originally
shown in Fig. 4(a). Radiation from a white-light source passes
approved in 1973. Last previous edition approved in 2003 as C770–98(2003).
through the following components and in this sequence: a
DOI: 10.1520/C0770-98R08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
diffusingplate,anadjustableaperture,apolarizerwhoseaxisis
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 4
The last approved version of this historical standard is referenced on Goranson andAdams, “Measurement of Optical Path Differences,” Journal of
www.astm.org. Franklin Institute, Vol 216, 1933, p. 475.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C770 − 98(Reapproved 2008)
at 45° to the vertical, the glass specimen, a Babinet
compensator,apolarizerwhoseaxisisat90°tothatofthefirst
polarizer, and a telescope of modest power.
4.1.2.2 The loading scheme is shown in Fig. 4(b). Metal
fixtures shall be provided to subject the specimen to four-point
C770 − 98 (2008)
FIG. 1 Polarimeter
FIG. 2 Orientation of Polarimeter in Standard Position
bending. A support span of 115 mm and a moment arm, a, of 4.1.3.2 Force application frame, shown in Fig. 5 must
45 mm are recommended. Dimensions within 5% of these
include:
values are acceptable. Symmetrical loading is essential, and
a) Astrain-gage load cell and load cell indicator, capable of
requirescarefulcenteringoftheupperloadingblock.Theknife
measuring the force applied within 1% accuracy.
edgesshallbefinishedtoapproximately5-mmradius.Loading
b) Hydraulic or mechanical means of applying constant
canbeaccomplishedthroughayoke,whichrestsinaV-groove
force and maintaining the force during the measuring time.
in the upper loading block, and a weight pan as shown.
c) Swivel-mounted loading blocks, offering at least two
However, any convenient loading scheme at the center of the
degrees of swivel freedom, to avoid the loading on the edge.
upper block may be used.
4.1.2.3 A Babinet compensator is positioned so as to pro-
4.2 Micrometer Caliper, for measuring specimen dimen-
duce vertical fringes (Fig. 4(c)). The neutral fringe must fall
sions to 0.0025 mm (0.0001 in.).
near the center of the support span. Recommended fringe
4.3 Weights that are known to an accuracy of 61%.
spacing is 1000 6 200 nm of retardation per centimeter. In
actual practice the compensator is placed very close to the
specimen inside the loading yoke. 5. Test Specimen
4.1.2.4 Atelescope is mounted in a rotating collar equipped
5.1 Procedure A:
with an angular scale which can be read to 0.1° by a vernier.
5.1.1 Select a mass of the glass to be tested that has good
The cross hairs in the eyepiece are used to measure the tilt
optical quality with no heavy cords or striae. By conventional
angle of the neutral fringe as shown in Fig. 4(c). An 80-mm
lamp-working methods, draw 0.6 to 0.9 m (2 to 3 ft) of fiber
objective lens and 10× eyepiece are adequate components for
from the glass, sufficient to provide five specimens 76 to 102
the telescope.
mm(3to4in.)longwithtaper(variationindiameteralongthe
4.1.2.5 The adjustable aperture is set at the smallest diam-
length) less than 0.025 mm (0.001 in.) and diameters in the
eter that permits suitable viewing.As with the fiber apparatus,
range 0.635 mm (0.025 in.) to 0.760 mm (0.030 in.). The
this provides some collimation and helps to eliminate stray
light. difference in mutually perpendicular diameters at any point
along the specimen length shall be less than 0.0076 mm
4.1.3 Procedure C:
4.1.3.1 Polarimeter as described in Test Method E218. (0.0003 in.).
C770 − 98 (2008)
(a) Fiber in Air (Top View, Optical Elements)
(b) Fiber Immersed
A—Light Source J—Telescope
C—Optical cell and index liquid K—Brass collars
E—Polarizer P—Pulley system
G—Quarter-wave plate S—Shield and slits
I—Rotatable analyzer
FIG. 3 Optical and Fiber-Stressing Polarimeter Arrangement
5.1.2 Bead both ends of each specimen by holding the end 0.40 in.), and the length within the range 120 to 130 mm (4.75
in a flame with the fiber vertical until a bead of two to three to 5.10 in.). Use a fine grind for the upper and lower surfaces
fiber diameters forms. (as the beam sits on the loading fixture) and polish the viewing
5.1.3 Anneal the specimens together so as to remove most surfaces. The ends need not be finished and a simple saw cut
of the lamp-working stress (Annex A2). willsuffice.Thefourmajorsurfacesshallbeflatandparallelto
within 0.050 mm (0.002 in.).
5.2 Procedure B:
5.2.2 Before final finishing, fine anneal the glass (Annex
5.2.1 Selectamassofglasstobetestedthathasgoodoptical
A2) to such a degree that when the specimen is placed in the
qualitywithnoheavycordsorstriae.Byconventionalgrinding
fixture unloaded there is very little curvature to the portion of
methods, prepare a beam of rectangular cross section. The
the neutral fringe that appears within the specimen.
width of the beam shall be within the range 20 to 30 mm (0.8
to 1.2 in.), the thickness within the range 6 to 10 mm (0.25 to 5.3 Procedure C:
C770 − 98 (2008)
(a) Beam Stressing and Polarimeter Arrangement
(b) Beam Loading Scheme (c) View of Babinet Compensator Fringe Pattern Through Stressed Beam
a—Moment arm F—Yoke and weight pan
A—Light Source G—Babinet compensator
B—Adjustable aperature H—Polarizer
C—Polarizer I—Telescope and angular sc
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:C 770–98 (Reapproved 2003)2008)
Standard Test Method for
Measurement of Glass Stress—Optical Coefficient
This standard is issued under the fixed designation C 770; 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
1.1 This test method covers procedures for determining the stress-optical coefficient of glass, which is used in photoelastic
analyses. In Procedure A the optical retardation is determined for a glass fiber subjected to uniaxial tension. In Procedure B the
optical retardation is determined for a beam of glass of rectangular cross section when subjected to four-point bending. In
Procedure C, the optical retardation is measured for a beam of glass of rectangular cross-section when subjected to uniaxial
compression.
1.2 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C336 Test Method for Annealing Point and Strain Point of Glass by Fiber Elongation
C598 Test Method for Annealing Point and Strain Point of Glass by Beam Bending
FE218Test Method for Analyzing Stress in Glass Method for Radiochemical Determination of Cesium-137 in Aqueous
Solutions (Chloroplatinate Method)
3. Significance and Use
3.1 Stress-optical coefficients are used in the determination of stress in glass. They are particularly useful in determining the
magnitude of thermal residual stresses for annealing or pre-stressing (tempering) glass. As such, they can be important in
specification acceptance.
4. Apparatus
4.1 Stressing Equipment and Polarimeter :
4.1.1 Procedure A— Figs. 1 and 2 illustrate a polarimeter employing a quarter-wave plate and rotatable analyzer, described in
Test Method F218. The quarter-wave plate shall be designed for the wavelength of the light being used. The polarizing axes of
the polarizer and analyzer shall be set at right angles to each other with each being located at an angle of 45° with the horizontal
and vertical.The analyzer, however, shall be mounted in a rotatable mount having a scale graduated on either side from 0 to 180°.
The quarter-wave plate shall be fixed to give maximum extinction when the polarizer and analyzer are crossed at right angles; that
is, when its polarizing axes are set at 45° and 135° to the horizontal and vertical. In place of the immersion cell E, a means of
supporting and loading a glass specimen shall be provided, either in air (Fig. 3(a)) or in an immersion liquid (Fig. 3(b)). In this
arrangement the optical elements of the polarimeter between light source and telescope have been reversed and a large scale
graduated in 2-nm divisions is employed with the rotatable analyzer I.
4.1.1.1 Fig. 3 illustrates the fiber-stressing and optical arrangement used in ProcedureA. Figure 3(a) shows the fiber mounted
vertically, positioned, and supported by two brass collars with swivel handles so that the kilogram weight may be applied to load
the fiber. A light shield having entrance and exit slits surrounds the fiber providing a degree of collimation to the light passing
This test method is under the jurisdiction of ASTM Committee C14 on Glass and Glass Products and is the direct responsibility of Subcommittee C14.04 on Physical
and Mechanical Properties.
Current edition approvedApril 10, 2003.1, 2008. Published January 1999.December 2008. Originally approved in 1973. Last previous edition approved in 19952003 as
C770–958(2003).
Annual Book of ASTM Standards, Vol 15.02.
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book ofASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Goranson and Adams, “Measurement of Optical Path Differences,” Journal of Franklin Institute, Vol 216, 1933, p. 475.
Withdrawn. The last approved version of this historical standard is referenced on www.astm.org.
Working drawings of test frames are available from Strainoptic Technologies, Inc., North Wales, PA.
Goranson and Adams, “Measurement of Optical 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 States.
C 770–98 (2003)(2008)
FIG. 1 Polarimeter
FIG. 2 Orientation of Polarimeter in Standard Position
through the fiber and also helping to eliminate stray light.
4.1.1.2 In Fig. 3(b) the fiber is stressed while immersed in a liquid which matches the refractive index of the fiber. This
arrangement provides more satisfactory viewing of the fiber.
4.1.2 Procedure B:
4.1.2.1 Theapparatusforthebeam-bendingprocedureisshowninFig.4(a).Radiationfromawhite-lightsourcepassesthrough
the following components and in this sequence: a diffusing plate, an adjustable aperture, a polarizer whose axis is at 45° to the
vertical, the glass specimen, a Babinet compensator, a polarizer whose axis is at 90° to that of the first polarizer, and a telescope
of modest power.
4.1.2.2 TheloadingschemeisshowninFig.4(b).Metalfixturesshallbeprovidedtosubjectthespecimentofour-pointbending.
A support span of 115 mm and a moment arm, a, of 45 mm are recommended. Dimensions within 5% of these values are
acceptable. Symmetrical loading is essential, and requires careful centering of the upper loading block. The knife edges shall be
finished to approximately 5-mm radius. Loading can be accomplished through a yoke, which rests in a V-groove in the upper
loadingblock,andaweightpanasshown.However,anyconvenientloadingschemeatthecenteroftheupperblockmaybeused.
4.1.2.3 ABabinet compensator is positioned so as to produce vertical fringes (Fig. 4(c)). The neutral fringe must fall near the
center of the support span. Recommended fringe spacing is 1000 6 200 nm of retardation per centimeter. In actual practice the
compensator is placed very close to the specimen inside the loading yoke.
4.1.2.4 Atelescope is mounted in a rotating collar equipped with an angular scale which can be read to 0.1° by a vernier. The
cross hairs in the eyepiece are used to measure the tilt angle of the neutral fringe as shown in Fig. 4(c).An 80-mm objective lens
and 103 eyepiece are adequate components for the telescope.
4.1.2.5 The adjustable aperture is set at the smallest diameter that permits suitable viewing. As with the fiber apparatus, this
provides some collimation and helps to eliminate stray light.
4.1.3 Procedure C:
4.1.3.1 Polarimeter as described in Test Method F218.
4.1.3.2 Force application frame, shown in Fig. 5 must include:
a) A strain-gage load cell and load cell indicator, capable of measuring the force applied within 1% accuracy.
b) Hydraulic or mechanical means of applying constant force and maintaining the force during the measuring time.
c) Swivel-mounted loading blocks, offering at least two degrees of swivel freedom, to avoid the loading on the edge.
4.2 Micrometer Caliper, for measuring specimen dimensions to 0.0025 mm (0.0001 in.).
C 770–98 (2003)(2008)
(a) Fiber in Air (Top View, Optical Elements)
(b) Fiber Immersed
A—Light Source J—Telescope
C—Optical cell and index liquid K—Brass collars
E—Polarizer P—Pulley system
G—Quarter-wave plate S—Shield and slits
I—Rotatable analyzer
FIG. 3 Optical and Fiber-Stressing Polarimeter Arrangement
4.3 Weights that are known to an accuracy of 61%.
5. Test Specimen
5.1 Procedure A:
5.1.1 Select a mass of the glass to be tested that has good optical quality with no heavy cords or striae. By conventional
lamp-working methods, draw 0.6 to 0.9 m (2 to 3 ft) of fiber from the glass, sufficient to provide five specimens 76 to 102 mm
(3to4in.)longwithtaper(variationindiameteralongthelength)lessthan0.025mm(0.001in.)anddiametersintherange0.635
mm(0.025in.)to0.760mm(0.030in.).Thedifferenceinmutuallyperpendiculardiametersatanypointalongthespecimenlength
shall be less than 0.0076 mm (0.0003 in.).
5.1.2 Bead both ends of each specimen by holding the end in a flame with the fiber vertical until a bead of two to three fiber
diameters forms.
5.1.3 Anneal the specimens together so as to remove most of the lamp-working stress (Annex A2).
C 770–98 (2003)(2008)
(a) Beam Stressing and Polarimeter Arrangement
(b) Beam Loading Scheme (c) View of Babinet Compensator Fringe Pattern Through Stressed Beam
a—Moment arm F—Yoke and weight pan
A—Light Source G—Babinet compensator
B—Adjustable aperature H—Polarizer
C—Polarizer I—Telescope and angular scale
D—Beam L—Load
E—Loading fixtures u—Tile angle of neutral fringe
FIG. 4 Optical and Mechanical Details for Beam Method
(a) Load Cell
(b) Swivel
(c) Pressure Plate
(d) Specimen
(e) Spherical Washer
(f) Axial Bearing
FIG. 5 Force Application Frame
5.2 Procedure B:
5.2.1 Select a mass of glass to be tested that has good optical quality with no heavy cords or striae. By conventional grinding
methods, prepare a beam of rectangular cross section. The width of the beam shall be within the range 20 to 30 mm (0.8 to 1.2
in.), the thickness within the range 6 to 10 mm (0.25 to 0.40 in.), and the length within the range 120 to 130 mm (4.75 to 5.10
...
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