ASTM C770-98(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:C 770–98 (Reapproved 2003)
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope scribed in Test Method F218. The quarter-wave plate shall be
designed for the wavelength of the light being used. The
1.1 This test method covers procedures for determining the
polarizing axes of the polarizer and analyzer shall be set at
stress-optical coefficient of glass, which is used in photoelastic
right angles to each other with each being located at an angle
analyses. In Procedure A the optical retardation is determined
of 45° with the horizontal and vertical.The analyzer, however,
for a glass fiber subjected to uniaxial tension. In Procedure B
shallbemountedinarotatablemounthavingascalegraduated
the optical retardation is determined for a beam of glass of
on either side from 0 to 180°. The quarter-wave plate shall be
rectangularcrosssectionwhensubjectedtofour-pointbending.
fixed to give maximum extinction when the polarizer and
In Procedure C, the optical retardation is measured for a beam
analyzer are crossed at right angles; that is, when its polarizing
ofglassofrectangularcross-sectionwhensubjectedtouniaxial
axes are set at 45° and 135° to the horizontal and vertical. In
compression.
place of the immersion cell E, a means of supporting and
1.2 This standard does not purport to address all of the
loading a glass specimen shall be provided, either in air (Fig.
safety concerns, if any, associated with its use. It is the
3(a)) or in an immersion liquid (Fig. 3(b)). In this arrangement
responsibility of the user of this standard to establish appro-
the optical elements of the polarimeter between light source
priate safety and health practices and determine the applica-
andtelescopehavebeenreversedandalargescalegraduatedin
bility of regulatory limitations prior to use.
2-nm divisions is employed with the rotatable analyzer I.
2. Referenced Documents
4.1.1.1 Fig. 3 illustrates the fiber-stressing and optical
arrangement used in Procedure A. Figure 3(a) shows the fiber
2.1 ASTM Standards:
mounted vertically, positioned, and supported by two brass
C336 Test Method forAnnealing Point and Strain Point of
collarswithswivelhandlessothatthekilogramweightmaybe
Glass by Fiber Elongation
appliedtoloadthefiber.Alightshieldhavingentranceandexit
C598 Test Method forAnnealing Point and Strain Point of
slitssurroundsthefiberprovidingadegreeofcollimationtothe
Glass by Beam Bending
light passing through the fiber and also helping to eliminate
F218 Test Method for Analyzing Stress in Glass
stray light.
3. Significance and Use
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
3.1 Stress-optical coefficients are used in the determination
arrangement provides more satisfactory viewing of the fiber.
of stress in glass. They are particularly useful in determining
4.1.2 Procedure B:
the magnitude of thermal residual stresses for annealing or
4.1.2.1 The apparatus for the beam-bending procedure is
pre-stressing (tempering) glass.As such, they can be important
shown in Fig. 4(a). Radiation from a white-light source passes
in specification acceptance.
through the following components and in this sequence: a
4. Apparatus
diffusingplate,anadjustableaperture,apolarizerwhoseaxisis
at 45° to the vertical, the glass specimen, a Babinet compen-
4.1 Stressing Equipment and Polarimeter:
sator, a polarizer whose axis is at 90° to that of the first
4.1.1 Procedure A— Figs. 1 and 2 illustrate a polarimeter
polarizer, and a telescope of modest power.
employing a quarter-wave plate and rotatable analyzer, de-
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
This test method is under the jurisdiction of ASTM Committee C14 on Glass
bending. A support span of 115 mm and a moment arm, a, of
and Glass Products and is the direct responsibility of Subcommittee C14.04 on
45 mm are recommended. Dimensions within 5% of these
Physical and Mechanical Properties.
Current edition approved April 10, 2003. Published January 1999. Originally values are acceptable. Symmetrical loading is essential, and
approved in 1973. Last previous edition approved in 1995 as C770–95.
requirescarefulcenteringoftheupperloadingblock.Theknife
Annual Book of ASTM Standards, Vol 15.02.
edgesshallbefinishedtoapproximately5-mmradius.Loading
Goranson andAdams, “Measurement of Optical Path Differences,” Journal of
canbeaccomplishedthroughayoke,whichrestsinaV-groove
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)
FIG. 1 Polarimeter
FIG. 2 Orientation of Polarimeter in Standard Position
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. 4.2 Micrometer Caliper, for measuring specimen dimen-
4.1.2.3 A Babinet compensator is positioned so as to pro- sions to 0.0025 mm (0.0001 in.).
duce vertical fringes (Fig. 4(c)). The neutral fringe must fall 4.3 Weights that are known to an accuracy of 61%.
near the center of the support span. Recommended fringe
5. Test Specimen
spacing is 1000 6 200 nm of retardation per centimeter. In
actual practice the compensator is placed very close to the 5.1 Procedure A:
specimen inside the loading yoke. 5.1.1 Select a mass of the glass to be tested that has good
4.1.2.4 Atelescope is mounted in a rotating collar equipped optical quality with no heavy cords or striae. By conventional
with an angular scale which can be read to 0.1° by a vernier. lamp-working methods, draw 0.6 to 0.9 m (2 to 3 ft) of fiber
The cross hairs in the eyepiece are used to measure the tilt from the glass, sufficient to provide five specimens 76 to 102
angle of the neutral fringe as shown in Fig. 4(c). An 80-mm mm(3to4in.)longwithtaper(variationindiameteralongthe
objective lens and 103 eyepiece are adequate components for length) less than 0.025 mm (0.001 in.) and diameters in the
the telescope. range 0.635 mm (0.025 in.) to 0.760 mm (0.030 in.). The
4.1.2.5 The adjustable aperture is set at the smallest diam- difference in mutually perpendicular diameters at any point
eter that permits suitable viewing.As with the fiber apparatus, along the specimen length shall be less than 0.0076 mm
this provides some collimation and helps to eliminate stray (0.0003 in.).
light. 5.1.2 Bead both ends of each specimen by holding the end
4.1.3 Procedure C: in a flame with the fiber vertical until a bead of two to three
4.1.3.1 Polarimeter as described in Test Method F218. fiber diameters forms.
4.1.3.2 Force application frame, shown in Fig. 5 must 5.1.3 Anneal the specimens together so as to remove most
include: of the lamp-working stress (Annex A2).
a) Astrain-gage load cell and load cell indicator, capable of 5.2 Procedure B:
measuring the force applied within 1% accuracy. 5.2.1 Selectamassofglasstobetestedthathasgoodoptical
b) Hydraulic or mechanical means of applying constant qualitywithnoheavycordsorstriae.Byconventionalgrinding
force and maintaining the force during the measuring time. methods, prepare a beam of rectangular cross section. The
C 770–98 (2003)
(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
width of the beam shall be within the range 20 to 30 mm (0.8 5.3 Procedure C:
to 1.2 in.), the thickness within the range 6 to 10 mm (0.25 to 5.3.1 The thickness of the specimen (see Fig. 6) should be
0.40 in.), and the length within the range 120 to 130 mm (4.75 no less than 5 mm ( ⁄16 in.).
to 5.10 in.). Use a fine grind for the upper and lower surfaces 5.3.2 The width should be no less than 10 mm ( ⁄8 in.).
(as the beam sits on the loading fixture) and polish the viewing 5.3.3 The length of the specimen should be larger than 43
surfaces. The ends need not be finished and a simple saw cut width, but not longer than 603 thickness, to avoid buckling
willsuffice.Thefourmajorsurfacesshallbeflatandparallelto failures.
within 0.050 mm (0.002 in.). 5.3.4 Both ends must be ground flat and parallel, within 0.1
5.2.2 Before final finishing, fine anneal the glass (Annex mm (0.004 in.).
A2) to such a degree that when the specimen is placed in the
6. Procedure
fixture unloaded there is very little curvature to the portion of
the neutral fringe that appears within the specimen. 6.1 Procedure A:
C 770–98 (2003)
(a) Beam Stressing and Polarimeter Arrangement
(b) Beam Loading Scheme (c) V
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