1、Designation: C1279 09C1279 13Standard Test Method forNon-Destructive Photoelastic Measurement of Edge andSurface Stresses in Annealed, Heat-Strengthened, and FullyTempered Flat Glass1This standard is issued under the fixed designation C1279; the number immediately following the designation indicates
2、 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of ed
3、ge stresses and surface stresses in annealed, heat-strengthened, and fullytempered flat glass products.1.2 This test method is non-destructive.1.3 This test method uses transmitted light and is, therefore, applicable to light-transmitting glasses.1.4 The test method is not applicable to chemically-t
4、empered glass.1.5 Using the procedure described, surface stresses can be measured only on the “tin” side of float glass.1.6 Surface-stress measuring instruments are designed for a specific range of surface index of refraction.1.7 The values stated in SI units are to be regarded as standard. No other
5、 units of measurement are included in this standard.1.8 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 practices and determine the applicability of
6、regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C158 Test Methods for Strength of Glass by Flexure (Determination of Modulus of Rupture)C162 Terminology of Glass and Glass ProductsC770 Test Method for Measurement of Glass StressOptical CoefficientC1048 Specification for
7、 Heat-Strengthened and Fully Tempered Flat GlassE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method2.2 Other Documents:Engineering Standards Manual3“Surface and Edge Stress in Tempered Glass”43. Terminology3.1 Definitions:3.1.1 analyzera polarizing eleme
8、nt, typically positioned between the specimen being evaluated and the viewer.3.1.2 polarizeran optical assembly that transmits light vibrating in a single planar direction, typically positioned between alight source and the specimen being evaluated.3.1.3 retardation compensatoran optical device, var
9、iants of which are used to quantify the optical retardation produced intransparent birefringent materials: typically positioned between the specimen being evaluated and the analyzer.1 This test method is under the jurisdiction of ASTM Committee C14 on Glass and Glass Products and is the direct respo
10、nsibility of Subcommittee C14.08 on Flat Glass.Current edition approved Oct. 1, 2009Oct. 1, 2013. Published October 2009.October 2013 Originally approved in 1994. Last previous edition approved in 20052009 asC1279-05.-09. DOI: 10.1520/C1279-09.10.1520/C1279-13.2 For referencedASTM standards, visit t
11、heASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from Glass Association of North America (GANA), 2925800 SW Wanamaker Drive,Jackson Stree
12、t, Ste A,1500, Topeka, Kansas 666145321.666121200.http:/4 Redner, A. S. and Voloshin, A. S., Proceedings of the Ninth International Conference on Experimental Mechanics, Denmark, 1990.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of
13、what changes have been made to the previous version. Becauseit 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 versionof the standard as published by ASTM is to be considered
14、the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2 For definition of terms used in this test method, refer to Terminology C162.4. Summary of Test Methods4.1 Two test methods are described in this standard:4.1.1
15、Procedure Adescribes a test method for measuring surface stress using light propagating nearly parallel to the surface.4.1.2 Procedure Bdescribes a test method for measuring edge-stress using light propagating in the direction perpendicular tothe surface.4.2 In both methods, the fundamental photoela
16、stic concept is used. As a result of stresses, the material becomes opticallyanisotropic or birefringent. When polarized light propagates through such anisotropic materials, the differences in the speed of lightrays vibrating along the maximum and minimum principal stress introduce a relative retard
17、ation between these rays. This relativeretardation is proportional to the measured stresses, and can be accurately determined using compensators. For additionalbackground see “Surface and Edge Stress in Tempered Glass”4.5. Significance and Use5.1 The strength and performance of heat-strengthened and
18、 fully-tempered glass is greatly affected by the surface and edgestress induced during the heat-treating process.5.2 The edge and surface stress levels are specified in Specification C1048, in the Engineering Standards Manual3 of GANATempering Division and in foreign specifications.5.3 This test met
19、hod offers a direct and convenient way to non-destructively determine the residual state of stress on the surfaceand at the edge of annealed and heat-treated glass.6. Principles of Operation6.1 Procedure A: Measuring Surface Stress:6.1.1 Measurement of surface stresses requires an optical apparatus
20、that permits the injection of polarized light rays propagatingin a thin layer adjacent to the surface (see Note 1). A prism is usually used for this purpose. The rays emerge at critical angle ic.The photoelastic retardation due to the surface stresses, (see Fig. 1), is measured using a wedge-compens
21、ator.6.1.2 The incident light beam should be arriving at the critical angle ic and polarized at 45 to the entrance of the prism edge.A quartz wedge-compensator, Wc, placed in the path of emerging light adds a retardation, Rc, to the retardation Rs induced bystresses in the surface of the specimen. T
22、he analyzer, A, placed between the eyepiece, E, and the wedge-compensator, Wc, generatesa visible set of fringes or lines of constant retardation R whereR 5R s1Rc (1)Since the specimen-induced retardation is proportional to the surface stress, S, and the path, t, we have:Rs 5CSt 5CSax (2)where:R = i
23、s the relative retardation,C = stress-optical constant (see Note 2),S = surface stress in the direction perpendicular to the path, tt = path of light traveling between the entrance and exit points 1, 2 (Fig. 1),a = Geometrical factor, (depending upon the prism design) a = t/x . This constant is dete
24、rmined by the manufacturer.6.1.3 The compensator adds its own retardation. It is linearly variable along its length y and is calculated asRc 5by (3)FIG. 1 Apparatus For Measuring Surface StressC1279 132Where b is a constant, determined by the manufacturer of the compensator. The observer sees in the
25、 compensator plane a totalretardation R.R5R s1Rc 5aCSx1by (4)6.1.4 The fringes (lines of R = Constant) are, therefore, tilted lines. (See Fig. 2). The angle is the tilt of these fringes relativeto a plane containing the light path of Figs. 1 and 2. The measured stress is proportional to the tangent
26、of the tilt angle , measuredusing a goniometer, and to an instrument calibration constant, K MPa, determined by the manufacturer.tan 5aCSb and (5)Stress5 bCa tan 5K tan In the actual procedure (see 9.115.1 below) the operator measures the tilt angle of the observed set of fringes.NOTE 1The surface-s
27、tress measuring apparatus described in this section is manufactured by Strainoptic Technologies, Inc. in North Wales,Pennsylvania.NOTE 2The stress constant of float glass is typically 2.55 to 2.65 Brewsters. Calibration can be performed using one of the test methods describedin Test Methods C770.FIG
28、. 1 Apparatus For Measuring Surface Stress (continued)FIG. 2 Fringes Observed in the Plane of the CompensatorC1279 1336.2 Procedure B: Measuring Edge Stress:6.2.1 Measurement of edge stress is accomplished using a polarimeter equipped with a wedge-compensator, as shownschematically in Fig. 3.6.2.2 T
29、he angle between the polarizer and the edge of the specimen must be 45 (see Fig. 3a), and the analyzer must beperpendicular to the polarizer. The overall magnification should be at least 20 to permit clear visibility of the reticle, and ofphotoelastic fringes near the edge. The reticle placed adjace
30、nt to the specimen must have graduations of 0.1 mm (0.004 in.) orsmaller. The resolution of the compensator should be at least 5 nm, and the compensator should be calibrated by the manufacturerat 565 nm wavelength with results of calibration expressed in nm/div.6.2.3 The compensator used could be of
31、 linear wedge type (Babinet) or uniform-field type (Babinet-Soleil). The linear-wedgetype requires a reticle placed adjacent to the compensator wedge and a linear-motion scale, or lead screw, locating the wedgeposition with reference to the reticle.6.2.4 The uniform field does not require a reticle,
32、 and must be equipped with a lead screw measuring the relative motion of itswedges.7. Sampling7.1 Procedure A: Measuring Surface StressThe number of points to be measured are determined by either the productspecification or by the following protocol described in Specification C1048.7.2 Procedure B:
33、Measuring Edge StressReadings must be obtained at the mid-span point of every edge.8. Calibration and Standardization8.1 A test bar is subjected to bending using traceably certified deadweights or calibrated load-cells to introduce surface stressesthat can be calculated from the specimen geometry an
34、d forces applied. At a point in which the stresses are calculated, those samestresses also are measured using the instrument to be calibrated or verified. Since both the specimen dimension and the appliedforces can be established accurately using traceable (primary) standards, the method permits a f
35、ully traceable calibration of thestress-measuring instrument.8.2 The instrument to be calibrated is placed on the surface of the calibration specimen. Stresses at a point where the instrumentis placed are calculated using expressions shown in Section 11. To increase the precision of measurement, sev
36、eral levels of stressare produced by applying forces incrementally. Measurement of stress using the instrument to be calibrated is repeated for eachstress level and these measurements are used to calibrate the instrument.FIG. 3 Schematic of the Instrument for Measuring Edge StressC1279 1349. Test Sp
37、ecimens and Loading Schemes9.1 Two loading geometries can be practiced: cantilever and four-point bending.9.2 Cantilever-Beam Specimen (Fig. 4)the dimensions of the specimen used for cantilever loading should be selected withinlimits shown below:Thickness (t): 6 mm (0.22 in.) minimum,Width (W): 8t W
38、 12t,Length (L): 6W minimum,Distance to the point of measurement (LO): 4W, andClamped length: 1.5W9.2.1 A heat-strengthened or tempered specimen, with polished edges is preferred, but annealed specimens can be used if therange of stress is less than 24.13 MPa (3500 psi).9.3 Four-Point Bending Specim
39、en (Fig. 5)The four-point bending specimen should be preferred since it has uniform stressin the central loading zone. The dimensions of the specimen should be selected within the following limits:Thickness (t): minimum 2 mm (0.079 in.),Width (W): 8t W 12t (see Note 3),Length LO: 6W minimum,Gage len
40、gth LC sction: 3W,Minimum overall length L: 12W, andEdges: Polished, no chips in the gage section, bevel less than 0.1t.NOTE 3When the thickness t is less than 6 mm, and width of the beam exceeds 12t, instead of the beam bending, plate bending equations shouldbe used to calculate surface stress, or
41、suitable corrections are required in the equations in 11.1. Barata5 and Ashwell6 show the correction procedures.9.4 Application of ForcesForces required must be calculated to eliminate possible breakage. Stresses must be estimated firstusing the equations in 9.1. A tempered specimen may be subjected
42、 to stress levels up to 10 000 psi (69 MPa). Using annealedspecimens, the stress should remain at a safe level, typically below 3500 psi (24 MPa).9.4.1 Cantilever SpecimenThe specimen must be clamped securely using wood, plastic, or rubber-lined metal clampingsurfaces, with rounded edges, as shown i
43、n Fig. 6. The forces can be applied using a calibrated testing machine or dead weights,by means of knife edges, to insure exact positioning of the line-of-loading B-B. The pad used for load application can be securedfrom slipping using high-friction materials. To eliminate possible twisting action,
44、the knife edge should be narrow, or a steel ballused to center the point of application of force.5 Barata, F. I., “When Is a Beam a Plate?” American Ceramic Society Communications, May 1981.6 Ashwell, D. G., “The Anticlastic Curvature of Rectangular Beams and Plates,” Journal of Aeronautics, Vol 54,
45、 1950, pp. 708-715.FIG. 4 Cantilever Beam LoadingC1279 1359.4.2 Four-Point Bending SpecimenIn the case of four-point bending, the force must be applied equally at two points, and twoarticulated knives or roller supports are required to ascertain accurately the length L0 and Lc. Particular precaution
46、s are requiredto insure that the end supports do not introduce a twist in the specimen, as a result of nonparallel support surfaces or nonflatnessof the specimen itself. Fig. 5 illustrates the setup for application of forces to obtain tension and compression on the upper face.Test Methods C158 provi
47、des a description of support design.10. Calibration Procedure10.1 When calibrating a surface polarimeter, apply forces in five equal increments, using a testing machine or dead weight.When calibrating a critical angle measuring instrument, at least ten increments are needed, and a tempered specimen
48、must be used.10.2 For each incremental loading, including zero, obtain the instrument reading. Repeat the reading at least three times, andaverage the readings. When calibrating a surface polarimeter, measure the fringe tilt . When calibrating a differentialrefractometer, measure the differential an
49、gle using a micrometer reticle, and read the distance between the borders of illuminatedzones at mutually perpendicular polarization in accordance with instrument manual.FIG. 5 Calibration Using Four-Point BendingFIG. 6 Clamping of a Cantilever BeamC1279 13610.3 Prepare a table of results, and plot these data, with applied stress as the ordinant (x axis) and tan (using surfacePolarimeter or angular distance between emerging light beams (using refractometer) versus applied stress (see Fig. 7).11. Calcul
