1、Designation: C 1279 05Standard 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 C 1279; the number immediately following the designation indicates the y
2、ear 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of edgestr
3、esses and surface stresses in annealed, heat-strengthened,and fully tempered 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-tempered
4、 glass.1.5 Using the procedure described, surface stresses can bemeasured only on the “tin” side of float glass.1.6 Surface-stress measuring instruments are designed for aspecific range of surface index of refraction.1.7 This standard does not purport to address all of thesafety concerns, if any, as
5、sociated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:C 162 Terminology of Glass and Glass Products2C 770 Test
6、 Method for Measurements of Glass Stress-Optical Coefficient2C 1048 Specification for Heat-Treated Glass: Kind HS,Kind FT Coated and Uncoated GlassE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF 218 Test Method for Analyzing Stress in Glass2.2 Other
7、 Documents:Engineering Standards Manual3“Surface and Edge Stress in Tempered Glass”43. Terminology3.1 Definitions:3.1.1 analyzera polarizing element, typically positionedbetween the specimen being evaluated and the viewer.3.1.2 polarizeran optical assembly that transmits lightvibrating in a single p
8、lanar direction, typically positionedbetween a light source and the specimen being evaluated.3.1.3 retardation compensatoran optical device, variantsof which are used to quantify the optical retardation producedin transparent birefringent materials: typically positioned be-tween the specimen being e
9、valuated and the analyzer.3.2 For definition of terms used in this test method, refer toTerminology C 162.4. Summary of Test Methods4.1 Two test methods are described in this standard:4.1.1 Procedure A describes a test method for measuringsurface stress using light propagating nearly parallel to the
10、surface.4.1.2 Procedure B describes a test method for measuringedge-stress using light propagating in the direction perpendicu-lar to the surface.4.2 In both methods, the fundamental photoelastic conceptis used. As a result of stresses, the material becomes opticallyanisotropic or birefringent. When
11、 polarized light propagatesthrough such anisotropic materials, the differences in the speedof light rays vibrating along the maximum and minimumprincipal stress introduce a relative retardation between theserays. This relative retardation is proportional to the measuredstresses, and can be accuratel
12、y determined using compensators.For additional background see “Surface and Edge Stress inTempered Glass”4.1This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and is the direct responsibility of Subcommittee C14.08 on FlatGlass.Current edition approved April 1
13、, 2005. Published April 2005.Originally approved in 1994. Last previous edition approved in 2000 as C1279-00e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the s
14、tandards Document Summary page onthe ASTM website.3Available from Glass Association of North America (GANA), 2925 SWWanamaker Drive, Ste A, Topeka, Kansas 666145321.4Redner, A. S. and Voloshin, A. S., Proceedings of the Ninth InternationalConference on Experimental Mechanics, Denmark, 1990.1Copyrigh
15、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1 The strength and performance of heat-strengthened andfully-tempered glass is greatly affected by the surface and edgestress induced during the heat-treating process.5.
16、2 The edge and surface stress levels are specified inSpecification C 1048, in the Engineering Standards Manual3ofGTA and in foreign specifications.5.3 This test method offers a direct and convenient way tonon-destructively determine the residual state of stress on thesurface and at the edge of annea
17、led and heat-treated glass.6. Principles of Operation6.1 Procedure A: Measuring Surface Stress:6.1.1 Measurement of surface stresses requires an opticalapparatus that permits the injection of polarized light rayspropagating in a thin layer adjacent to the surface (see Note 1).A prism is usually used
18、 for this purpose. The rays emerge atcritical angle ic. The photoelastic retardation due to the surfacestresses, (see Fig. 1), is measured using a wedge-compensator.6.1.2 The incident light beam should be arriving at thecritical angle icand polarized at 45 to the entrance of the prismedge. A quartz
19、wedge-compensator, Wc, placed in the path ofemerging light adds a retardation, Rc, to the retardation Rsinduced by stresses in the surface of the specimen. Theanalyzer, A, placed between the eyepiece, E, and the wedge-compensator, Wc, generates a visible set of fringes or lines ofconstant retardatio
20、n R whereR 5 Rs1 Rc(1)Since the specimen-induced retardation is proportional to thesurface stress, S, and the path, t, we have:Rs5 CSt 5 CSax (2)where:R = is the relative retardation,C = stress-optical constant (see Note 2),S = surface stress in the direction perpendicular to thepath, tt = path of l
21、ight traveling between the entrance and exitpoints 1, 2 (Fig. 1),a = Geometrical factor, (depending upon the prism de-sign) a = t/x. This constant is determined by themanufacturer.6.1.3 The compensator adds its own retardation. It is lin-early variable along its length y and is calculated asRc5 by (
22、3)Where b is a constant, determined by the manufacturer of thecompensator. The observer sees in the compensator plane atotal retardation R.R 5 Rs1 Rc5 aCSx 1 by (4)6.1.4 The fringes (lines of R = Constant) are, therefore,tilted lines. (See Fig. 2). The angle u is the tilt of these fringesrelative to
23、 a plane containing the light path of Figs. 1 and 2.The measured stress is proportional to the tangent of the tiltangle u, measured using a goniometer, and to an instrumentcalibration constant, K MPa (psi), determined by the manufac-turer.tan u5aCSband (5)Stress 5bCa tan u5Ktan uIn the actual proced
24、ure (see 9.1 below) the operator mea-sures the tilt angle u of the observed set of fringes.NOTE 1The surface-stress measuring apparatus described in thissection is manufactured by Strainoptic Technologies, Inc. in North Wales,Pennsylvania.FIG. 1 Apparatus For Measuring Surface StressC1279052NOTE 2Th
25、e stress constant of float glass is typically 2.55 to 2.65Brewsters. Calibration can be performed using one of the test methodsdescribed in Test Methods C 770.6.2 Procedure B: Measuring Edge Stress:6.2.1 Measurement of edge stress is accomplished using apolarimeter equipped with a wedge-compensator,
26、 as shownschematically in Fig. 3.6.2.2 The angle between the polarizer and the edge of thespecimen must be 45 (see Fig. 3a), and the analyzer must beperpendicular to the polarizer. The overall magnificationshould be at least 203 to permit clear visibility of the reticle,and of photoelastic fringes n
27、ear the edge. The reticle placedadjacent to the specimen must have graduations of 0.1 mm(0.004 in.) or smaller. The resolution of the compensatorshould be at least 5 nm, and the compensator should becalibrated by the manufacturer at 565 nm wavelength withresults of calibration expressed in nm/div.6.
28、2.3 The compensator used could be of linear wedge type(Babinet) or uniform-field type (Babinet-Soleil). The linear-wedge type requires a reticle placed adjacent to the compen-sator wedge and a linear-motion scale, or lead screw, locatingthe wedge position with reference to the reticle.6.2.4 The unif
29、orm field does not require a reticle, and mustbe equipped with a lead screw measuring the relative motion ofits wedges.7. Sampling7.1 Procedure A: Measuring Surface StressThe numberof points to be measured are determined by the productspecification.7.2 Procedure B: Measuring Edge Stress Readings mus
30、tbe obtained at the mid-span point of every edge.8. Conditioning8.1 In order to avoid thermal stresses, the specimen shouldbe allowed to reach ambient temperature throughout its entiremass prior to testing.9. Procedure9.1 Procedure AMeasuring Surface Stress:9.1.1 Clean the surface of any trace of oi
31、l or other chemicaldeposits.9.1.2 Place a few drops of index liquid on the tin sidesurface of the specimen at the point of interest. The index ofrefraction of the liquid should be higher than the index of theexamined glass and lower or equal to the index of the prism.9.1.3 Perform the adjustments of
32、 the optical path in accor-dance with manufacturers specifications to obtain a clearimage of an equally-spaced set of fringes in the compensatorplane.FIG. 2 Fringes Observed in the Plane of the CompensatorFIG. 3 Schematic of the Instrument for Measuring Edge StressFIG. 4 Orientation of the Instrumen
33、t for Measuring Surface StressFIG. 5 Depth Measurement of Beveled RegionC12790539.1.4 Using the goniometer, measure the angle u (in de-grees) of these fringes to the plane of symmetry (see Fig. 2).9.1.5 In all instances where the surface stress is uniform(independent of direction), measure the angle
34、 u, orienting theinstruments plane of symmetry to measure stress parallel tothe nearest edge.9.1.5.1 In those instances where the direction of maximumand minimum stress is uncertain (as a result of irregulargeometry, proximity of edges, or non-uniformity of heat-treating process), orient the instrum
35、ent along direction a1, a2,a3, and measure the fringe pattern angle u1, u2, u3, in degrees,for each direction. Select a1, a2, a3as follows:a1parallel to the nearest edge,a245 to the nearest edge, anda3perpendicular to the nearest edge. (See Fig. 4)9.2 Procedure BMeasuring Edge Stress:9.2.1 Place the
36、 instrument in position, with a measuringreticle placed adjacent to instrument, and in close contact withthe edge of glass.9.2.2 Using the reticle graduation, measure the depth, d,inmm (in.), of the seamed or beveled region, which is non-transmitting. If the depth of the beveled region, d (see Fig.
37、5),is less than 0.25 mm (0.010 in.), use visual extrapolation of theobserved fringe pattern (see 9.2.3). When the depth is equal toor greater than 0.25 mm (0.010 in.), use the extrapolationequation (see 9.2.5).9.2.3 Measurement Using Visual ExtrapolationObservethe pattern of photoelastic fringes nea
38、r the edge of thespecimen (see Fig. 6a and Fig. 6b). Adjust the wedge (ordouble wedge) until the black fringe arrives to the edge (doublewedge, Fig. 6b), or crosses the edge at the crosshair (singlewedge, Fig. 6a).9.2.4 Obtain a reading (Re) using a single or double wedge,at the center of each edge
39、of the glass.9.2.5 Measurement Using an Extrapolation EquationIncase the seamed edge makes the reading at the edge difficult d 0.25 mm (0.01 in.), measurement of retardation R (nm) attwo points, x1and x2(Fig. 6b), of the reticle scale must bemade. These points are to be selected per Table 1. Thereta
40、rdations R1and R2(nm) are retardation values measuredusing the compensator scale at the points x1and x2. The edgeretardation Re(nm) is obtained from the equation:Re5 3.8R12 2.8R2(6)9.2.6 Using a micrometer, measure the thickness of thespecimen at the location where the stress is measured.10. Calcula
41、tion and Interpretation10.1 Procedure A: Measuring Surface StressWhen themeasured angle is obtained using procedure 9.1.5, calculate thesurface stress, S, using:S 5 K tan u (7)where K is the instrument calibration constant determined bythe manufacturer, in MPa (psi).10.1.1 In those instances where t
42、he surface stress is direc-tional, assess the state of stress by comparing the reading S inthree directions a1, a2, a3. If all three directions yield the samemeasured angles u1, u2, u3within 1, calculate the averageangle, then obtain the surface stress from Eq 8 and Eq 9.uaverage5u11u21u33(8)S 5 Kta
43、n uaverage(9)If the measured angles u1, u2, and u3differ by more than 1,then using Eq 7, obtain the three stresses S1, S2, and S3indirections a1, a2, and a3, and then calculate the principalstresses Smax, and Smin, from Eq 10 and Eq 11.Smax5S11 S321=22= S12 S2!21 S22 S3!2(10)Smin5S11 S322=22=S12 S2!
44、21 S22 S3!2(11)10.2 Procedure B: Measuring Edge Stress From themeasured retardation Recalculate the edge stress (in psi):Se5RebtCB(12)FIG. 6 a) Fringes Observed Using Wedge Compensator (Babinet), b) Fringes Observed Using Double Wedge Compensator(Babinet-Soleil)TABLE 1 Location of Points x1and x2Thi
45、ckness of Glass18 to316 inch(3 to 5 mm)14 to38 inch(6 to 10 mm)12 to1inch(12 to 24.5 mm)x10.6 or 0.8 mm 1.0 mm 2.0 mmx21.0 or 1.3 mm 1.6 mm 3.0 mmC1279054where:Re= the compensator reading (nm),t = the thickness of the glass sample (mm, in.),CB= stress-optical constant, Brewsters (1 Brwstr. = 10-12)/
46、Pa or nm/psiin.,Se= stress MPa (psi), andb = compensator constant, determined by manufacturer.11. Report11.1 At a minimum, the report must contain:11.1.1 Date of specimen manufacture11.1.2 Identification of specimen (material)11.1.3 Selected procedure11.1.4 Glass thickness11.1.5 For surface measurem
47、ent:11.1.5.1 Location(s) of measurement(s)11.1.5.2 Direction of measurement(s)11.1.5.3 Values of u1, u2, u3at each location and thecalculated stress11.1.6 For edge measurements:11.1.6.1 Location of measurement(s)11.1.6.2 Chamfer size11.1.6.3 Thickness of specimen at point of measurement11.1.6.4 Extr
48、apolation method used visual (9.2.3)orcal-culated (9.2.5)11.1.6.5 Average edge stress12. Precision and Bias5,6Procedure A12.1 An interlaboratory round robin testing was conductedin accordance with Practice E 691 to establish the precisionand bias of surface stress measurements. Table 2 summarizesthe
49、 result of this study. In this test, seven laboratories measuredsurface stress on six samples using Procedure A. Each test5Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: C14-1002.6Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: C14-1004.TABLE 2 Procedure A Result of Statistical Data Analysis(Measuring Stresses in direction X and Y at a point “A” in all samples.)Sample # 14 13 17 16 18 15Str
