1、Designation: C770 98 (Reapproved 2013)C770 16Standard Test Method forMeasurement of Glass StressOptical Coefficient1This standard is issued under the fixed designation C770; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、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 covers procedures for determining the stress-optical coefficient of glass, which is used in photoe
3、lasticanalyses. In Procedure A the optical retardation is determined for a glass fiber subjected to uniaxial tension. In Procedure B theoptical retardation is determined for a beam of glass of rectangular cross section when subjected to four-point bending. InProcedure C, the optical retardation is m
4、easured for a beam of glass of rectangular cross-section when subjected to uniaxialcompression.1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health pr
5、actices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C336 Test Method for Annealing Point and Strain Point of Glass by Fiber ElongationC598 Test Method for Annealing Point and Strain Point of Glass by Beam BendingC1426 Practices for
6、 Verification and Calibration of PolarimetersE218F218 Tentative Standard Method for Radiochemical Determination of Cesium-137 in Aqueous Solutions (ChloroplatinateMethod)Test Method for Measuring Optical Retardation and Analyzing Stress in Glass (Withdrawn 1968)2.2NIST, Recommended Practice Guide “F
7、ractography of Ceramics and Glasses” (Section 4.6.2Flexural Strength)3. Significance and Use3.1 Stress-optical coefficients are used in the determination of stress in glass. They are particularly useful in determining themagnitude of thermal residual stresses for annealing or pre-stressing (temperin
8、g) glass. As such, they can be important inspecification acceptance.4. Apparatus4.1 Stressing Equipment and Polarimeter:4.1.1 Procedure AFigs. 1 and 2 illustrate a polarimeter employing a quarter-wave plate and rotatable analyzer,3 described inTest Method E218F218. The quarter-wave plate shall be de
9、signed for the wavelength of the light being used. The polarizing axesof the polarizer and analyzer shall be set at right angles to each other with each being located at an angle of 45 with the horizontaland vertical. The analyzer, however, shall be mounted in a rotatable mount having a scale gradua
10、ted 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; thatis, when its polarizing axes are set at 45 and 135 to the horizontal and vertical. In place of the immersion cell E, a means ofsupporting
11、 and loading a glass specimen shall be provided, either in air (Fig. 3(a) or in an immersion liquid (Fig. 3(b). In thisarrangement the optical elements of the polarimeter between light source and telescope have been reversed and a large scalegraduated in 2-nm divisions is employed with the rotatable
12、 analyzer I.1 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 Physicaland Mechanical Properties.Current edition approved Oct. 1, 2013May 1, 2016. Published October 2013June 2016. Originally approv
13、ed in 1973. Last previous edition approved in 20082013 asC770 98 (2008).(2013). DOI: 10.1520/C0770-98R13.10.1520/C0770-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refe
14、r to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.org.3 Goranson and Adams, “Measurement of Optical Path Differences,” Journal of Franklin Institute, Vol 216, 1933, p. 475.Goranson and Adams, “Measurement of
15、 OpticalPath Differences,” Journal of Franklin Institute, Vol 216, 1933, p. 475.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequa
16、tely depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
17、n, PA 19428-2959. United States14.1.1.1 Fig. 3 illustrates the fiber-stressing and optical arrangement used in Procedure A. Figure 3(a) shows the fiber mountedvertically, positioned, and supported by two brass collars with swivel handles so that the kilogram weight may be applied to loadthe fiber. A
18、 light shield having entrance and exit slits surrounds the fiber providing a degree of collimation to the light passingthrough 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. Th
19、isarrangement provides more satisfactory viewing of the fiber.4.1.2 Procedure B:4.1.2.1 The polarimetry apparatus for the beam-bending procedure is shown in Fig. 4Figs. 4 and 5(a) Radiation from awhite-light source passes through the following components and in this sequence: a diffusing plate, an a
20、djustable aperture, diffuser,a polarizer whose axis is at 45 to the vertical, the glass specimen, a Babinet compensator, a polarizer quarter-wave plate, and asecond polarizer (analyzer) whose axis is at 90 to that of the first polarizer, and a telescope of modest power. polarizer.4.1.2.2 TheAschemat
21、ic of the loading scheme is shown in Fig. 45(b) Metal fixtures shall be provided to subject the specimento four-point bending. A support span of 115 mm and a moment arm, a, of 45 mm are recommended. Dimensions within 5 %5%of these values are acceptable. Symmetrical loading is essential, and requires
22、 careful centering of the upper loading block. Theknife edges shall be finished to approximately 5-mm radius. Loading can be accomplished through a yoke, which rests in aV-grooveVgroove in the upper loading block, and a weight pan as shown. However, any convenient loading scheme at the centerof the
23、upper block may be used.4.1.2.3 A Babinet compensator is positioned so as to produce vertical fringes (Fig. 4(c). The neutral fringe must fall near thecenter of the support span. Recommended fringe spacing is 1000 6 200 nm of retardation per centimeter. In actual practice thecompensator is placed ve
24、ry close to the specimen inside the loading yoke.4.1.2.3 A telescope is mounted in a rotating collar equipped with an angular scale which can be read to 0.1polarimeter, witha rotating analyzer, calibrated to Practices C1426by a vernier. The cross hairs in the eyepiece are, and described in Test Meth
25、odC1426 and in Section 6 of this test method, is used to measure the tilt angle of the neutral fringe as shown inobserve the zeroorder(black) fringe in the mid-plane of the beam as a known Fig. 4(c). An 80-mm objective lens and 10 eyepiece are adequatecomponents for the telescope. load is applied. T
26、he readings from the analyzer scale are used in the calculation of the stress-opticalcoefficient.FIG. 1 PolarimeterFIG. 2 Orientation of Polarimeter in Standard PositionC770 1624.1.2.5 The adjustable aperture is set at the smallest diameter that permits suitable viewing. As with the fiber apparatus,
27、 thisprovides some collimation and helps to eliminate stray light.4.1.3 Procedure C:4.1.3.1 Polarimeter as described in Test Method E218F218.4.1.3.2 Force application frame, an example of which is shown in Fig. 56(a) and Fig. 6(b), must include:a) A strain-gage load cell and load cell indicator, cap
28、able 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 C
29、aliper, for measuring specimen dimensions to 0.0025 mm (0.0001 in.).4.3 Weights that are known to an accuracy of 61 %.(a) Fiber in Air (Top View, Optical Elements)(b) Fiber ImmersedALight Source JTelescopeCOptical cell and index liquid KBrass collarsEPolarizer PPulley systemGQuarter-wave plate SShie
30、ld and slitsIRotatable analyzerFIG. 3 Optical and Fiber-Stressing Polarimeter ArrangementC770 1635. Test Specimen5.1 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 conventionallamp-working methods, draw 0.6 to 0.9 m (2 to 3 f
31、t) of fiber from the glass, sufficient to provide five specimens 76 to 102 mm102 mm (3 to 4 in.) long with taper (variation in diameter along the length) less than 0.025 mm (0.001 in.) and diameters in therange 0.635 mm (0.025 in.) to 0.760 mm (0.030 in.). The difference in mutually perpendicular di
32、ameters at any point along thespecimen length 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 fiberdiameters forms.5.1.3 Anneal the specimens together so as to remove most of the lamp-w
33、orking stress (Annex A2).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 grindingmethods, prepare a beam of rectangular cross section. The width of the beam shall be within the range 20 to 30 mm (0.8 to 1.2in.), t
34、he 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 5.10in.). Use a fine grind for the upper and lower surfaces (as the beam sits on the loading fixture) and polish the viewing surfaces.The ends need not be finished and a simple saw cut
35、 will suffice. The four major surfaces shall be flat and parallel to within 0.050mm (0.002 in.).5.2.2 Before final finishing, fine anneal the glass (Annex A2) to such a degree that when the specimen is placed in the fixtureunloaded there is very little curvature to the portion of the neutral fringe
36、that appears within the specimen. (with the analyzer atzero), there is a uniformly dark field with no difference between the specimen and the background.5.3 Procedure C: C (Rectangular Beam Method):5.3.1 The thickness of the specimen (see Fig. 67) should be no less than 5 mm (316 in.).5.3.2 The widt
37、h should be no less than 10 mm (38 in.).5.3.3 The length of the specimen should be larger than 4 width, but not longer than 60 thickness, to avoid buckling failures.5.3.4 Both ends must be groundfinished flat and parallel, within 0.1 mm 0.1 mm (0.004 in.).5.4 Procedure C (Glass Disc Method):5.4.1 Th
38、e thickness of the specimen should be 5 to 10 mm (0.2 to 0.4 in.)5.4.2 The diameter should be nominally 12.7 mm (12 in.) (Accurate diameter needed for calculation.)5.4.3 The disc should be isotropic and homogenous, core drilled with both faces polished and parallel.6. Procedure6.1 Procedure A:aMomen
39、t arm FYoke and weight panALight Source GBabinet compensatorBAdjustable aperature HPolarizerCPolarizer ITelescope and angular scaleDBeam LLoadELoading fixtures Tile angle of neutral fringeFIG. 4 Optical and Mechanical Details for Beam MethodTypical Beam-Bending and Polarimeter ApparatusC770 1646.1.1
40、 Mount the fiber specimen vertically by the beaded end in the test fixture so that approximately the midlength is in thepolariscope light beam and the fiber image is clearly in focus.6.1.2 Adjust the light shield or aperture so that the slits are in the line of sight when viewing the fiber through t
41、he telescope.6.1.3 Rotate the polarimeter analyzer until a bright area or line is visible, centered in the fiber cross section and parallel to itssides (the “image” of the light source that the cylindrical fiber “lens” tends to form).6.1.4 Rotate the analyzer until the bright line becomes darkest or
42、 reaches extinction. Record the retardation indicated on thepolarimeter scale either in degrees or nanometres. Repeat five times to obtain an average “zero” scale reading, r0. Normally, thiswill be near the scale zero for a relatively unstressed fiber and may be in the direction of rotation which in
43、dicates vertical tension.Since 180 of rotation covers a retardation of one full wavelength each angular degree corresponds to 3.03 nm, if light of awavelength of 546 nm is used.6.1.5 Add a 10 N (2.25 lb) weight to the fiber loading suspension of the test fixture. Rotate the analyzer in the tension d
44、irection(Annex A1) until extinction again occurs and record the retardation indicated. Repeat this rotation about five times and obtain anaverage scale reading, r .6.1.6 Remove the fiber, measure, and record to the nearest 0.0025 mm (0.0001 in.) the average diameter,d average of diameters parallel a
45、nd perpendicular to light path! at the position where retardation was measured.6.1.7 Repeat this procedure with the other fiber specimens.6.2 Procedure B:6.2.1 With the specimen removed from the polarimeter, set the reference cross hair on and parallel to the black neutral fringe.Simultaneously set
46、the angle to zero on the rotatable reference scale. analyzer at zero degrees and observe a uniform dark field,indicating a no-stress condition.6.2.2 Place Before placing the specimen onin the metal loading support and then position the upper loading block.After carefulpositioning, engage the loading
47、 yoke and weight pan. Record the combined weight of the loading fixture, record the combinedweight (in Newtons) of the loading fixture, including the upper block, yoke, weight pan, and coupling fixtures which is fixtures,load L1. This must be known to an accuracy of 61 %. 61 %. Place the specimen on
48、 the loading support and position the upperloading block.6.2.3 With the polarized illuminator on and the light path perpendicular to the polished surfaces of the sample, slowly rotatethe analyzer until the observed light intensity of the background is at minimum (dark field). In this position, the p
49、olarizing axesof the analyzer and polarizer are mutually perpendicular (crossed) with the rotating analyzer scale at zero.6.2.4 Measure the angle of tilt (Annex A1) of the neutral fringe analyzer caused by the load L1 and record this angle as 1.Slowly rotate the analyzer in a clockwise direction until the top edge of the beam exhibits minimum light intensity. A standardwavelength (565 nm CWL) bandpass filter may be used to improve visualization of the neutral fringe under an added load.6.2.5 Add a 10 N (2.25 lb) weight. Record th
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