1、Designation: C1279 09Standard 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 the yea
2、r 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 edgestress
3、es 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 gl
4、ass.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 The values stated in SI units are to be regarded asstandard. No other units of mea
5、surement are included in thisstandard.1.8 This standard does not purport to address all of thesafety concerns, if any, associated 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 li
6、mitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C162 Terminology of Glass and Glass ProductsC770 Test Method for Measurement of Glass StressOptical CoefficientC1048 Specification for Heat-Treated Flat GlassKind HS,Kind FT Coated and Uncoated GlassE691 Practice for Conducting an Int
7、erlaboratory Study toDetermine 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 element, typically positionedbetween the specimen being evaluated and the viewer.3.1.2 po
8、larizeran optical assembly that transmits lightvibrating in a single planar 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 bire
9、fringent materials: typically positioned be-tween the specimen being evaluated and the analyzer.3.2 For definition of terms used in this test method, refer toTerminology C162.4. Summary of Test Methods4.1 Two test methods are described in this standard:4.1.1 Procedure Adescribes a test method for me
10、asuringsurface stress using light propagating nearly parallel to thesurface.4.1.2 Procedure Bdescribes 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 stress
11、es, the material becomes opticallyanisotropic or birefringent. When 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 retard
12、ation is proportional to the measuredstresses, and can be accurately 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 o
13、f Subcommittee C14.08 on FlatGlass.Current edition approved Oct. 1, 2009. Published October 2009. Originallyapproved in 1994. Last previous edition approved in 2005 as C1279-05. DOI:10.1520/C1279-09.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service
14、 at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Glass Association of North America (GANA), 2925 SWWanamaker Drive, Ste A, Topeka, Kansas 666145321. http:/4Redner, A. S. and Voloshin, A. S., Proc
15、eedings of the Ninth InternationalConference on Experimental Mechanics, Denmark, 1990.1Copyright 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 glas
16、s is greatly affected by the surface and edgestress induced during the heat-treating process.5.2 The edge and surface stress levels are specified inSpecification C1048, in the Engineering Standards Manual3ofGANA Tempering Division and in foreign specifications.5.3 This test method offers a direct an
17、d convenient way tonon-destructively determine the residual state of stress on thesurface and 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 opticalapparatus that permits the injecti
18、on of polarized light rayspropagating in a thin layer adjacent to the surface (see Note 1).A prism is usually used 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 li
19、ght beam should be arriving at thecritical angle icand polarized at 45 to the entrance of the prismedge. A quartz 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
20、 the eyepiece, E, and the wedge-compensator, Wc, generates a visible set of fringes or lines ofconstant retardation 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 =
21、 stress-optical constant (see Note 2),S = surface stress in the direction perpendicular to thepath, tt = path of light 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
22、The compensator adds its own retardation. It is lin-early variable along its length y and is calculated asRc5 by (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 (lin
23、es of R = Constant) are, therefore,tilted lines. (See Fig. 2). The angle u is the tilt of these fringesrelative to 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 co
24、nstant, K MPa, determined by the manufacturer.tan u5aCSband (5)Stress 5bCa tan u5Ktan uIn the actual procedure (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 T
25、echnologies, Inc. in North Wales,Pennsylvania.NOTE 2The 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 C770.6.2 Procedure B: Measuring Edge Stress:6.2.1 Measurement of edge stress is accomplished
26、using apolarimeter equipped with a wedge-compensator, 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 vi
27、sibility of the reticle,and of photoelastic fringes near 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 wavelen
28、gth withresults of calibration expressed in nm/div.6.2.3 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
29、position with reference to the reticle.6.2.4 The uniform field does not require a reticle, and mustbe equipped with a lead screw measuring the relative motion ofits wedges.FIG. 1 Apparatus For Measuring Surface StressC1279 0927. Sampling7.1 Procedure A: Measuring Surface StressThe numberof points to
30、 be measured are determined by either the productspecification or by the following protocol described in Speci-fication C1048.7.2 Procedure B: Measuring Edge StressReadings mustbe obtained at the mid-span point of every edge.8. Conditioning8.1 In order to avoid thermal stresses, the specimen shouldb
31、e 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 oil or other chemicaldeposits.9.1.2 Place a few drops of index liquid on the tin sidesurface of the specimen at the point of i
32、nterest. The index ofFIG. 1 Apparatus For Measuring Surface Stress (continued)FIG. 2 Fringes Observed in the Plane of the CompensatorFIG. 3 Schematic of the Instrument for Measuring Edge StressC1279 093refraction of the liquid should be higher than the index of theexamined glass and lower or equal t
33、o the index of the prism.9.1.3 Perform the adjustments of the optical path in accor-dance with manufacturers specifications to obtain a clearimage of an equally-spaced set of fringes in the compensatorplane.9.1.4 Using the goniometer, measure the angle u (in de-grees) of these fringes to the plane o
34、f symmetry (see Fig. 2).9.1.5 Where surface stress at the point to be measured isknown to be uniform (within 1 in the three directions a1, a2,a3) or it is specifically prescribed to be measured at a certaindirection, take a measurement at each location(s) prescribed in7.1.9.1.5.1 In those instances
35、where uniformity at a point to bemeasured is not present or uncertain (that is, as a result ofirregular geometry, proximity of edges, or non-uniformity ofprocess), maximum and minimum surface stress can be deter-mined by orienting the instrument in three directions andmeasuring the fringe pattern an
36、gle in degrees at each directionas 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 Using a micrometer, measure the thickness of thespecimen at the location where the stress is measured.9.2
37、.2 Place the instrument in position, with a measuringreticle placed adjacent to instrument, and in close contact withthe edge of glass.9.2.3 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,
38、d (see Fig. 5),is less than 0.25 mm (0.010 in.), use visual extrapolation of theobserved fringe pattern (see 9.2.4). When the depth is equal toor greater than 0.25 mm (0.010 in.), use the extrapolationequation (see 9.2.6).9.2.4 Measurement Using Visual ExtrapolationObservethe pattern of photoelastic
39、 fringes near 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).9.2.4.1 When using a double wedge, adjust the lead-screwdriving the double
40、 wedge until the black fringe arrives to theedge (Fig. 6b) and obtain the drum reading Deof the wedgeposition.9.2.4.2 When using a single wedge compensator, adjust thewedge position until the black fringe crosses the edge a thecrosshair. (Fig. 6a) and obtain the scale reading Deon the scaleof the co
41、mpressoror on the lead screw drive drum.9.2.5 Obtain a a retardation reading (Re) using a single ordouble wedge, at the center of each edge of the glass,multipilying the scale or drum reading by the calibration factorb:Re5 De* b (6)Where:Re = is the retardation (nm)De = is the scale or drum reading
42、(number)b = is the compensator calibration, nm/division9.2.6 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 R1and R2at two points, x1and x2(Fig. 6a and Fig. 6b), of the reticle scalemust be ma
43、de. These points are to be selected per Table 1. Theretardations 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(7)9.2.7 Using a micrometer, measure the thickness of thespecimen
44、at the location where the stress is measured.FIG. 4 Orientation of the Instrument for Measuring Surface StressFIG. 5 Depth Measurement of Beveled RegionC1279 09410. Calculation and Interpretation10.1 Procedure A: Measuring Surface StressWhen themeasured angle is obtained using procedure 9.1.5, calcu
45、late thesurface stress, S, using:S 5 K tan u (8)where K is the instrument calibration constant determined bythe manufacturer, in MPa (psi).10.1.1 In those instances where the surface stress is direc-tional, assess the state of stress by comparing the reading S inthree directions a1, a2, a3. If all t
46、hree directions yield the samemeasured angles u1, u2, u3within 1, calculate the averageangle, then obtain the surface stress from Eq 9 and Eq 10.uaverage5u11u21u33(9)S 5 Ktan uaverage(10)If the measured angles u1, u2, and u3differ by more than 1,then using Eq 8, obtain the three stresses S1, S2, and
47、 S3indirections a1, a2, and a3, and then calculate the principalstresses Smax, and Smin, from Eq 11 and Eq 12.FIG. 6 a) Fringes observed on 6 mm Glass Using Single Wedge Compensator (Babinet), b) Fringes Observed Using Double WedgeCompensator (Babinet-Soleil).The readings at points X1and X2from Tabl
48、e 1 are used for the values of R1and R2in the Extrapolation Equation Procedure 9.2.6.TABLE 1 Location of Points x1and x2Thickness of Glass18 to316 inch(3 to 5 mm)14 to38 inch(6 to 10 mm)12 to1inch(12 to 24.5 mm)x1A0.6 or 0.8 mm 1.0 mm 2.0 mmx2A1.0 or 1.3 mm 1.6 mm 3.0 mmASelect X1= 0.6mm X2= 1.0mm w
49、hen the edge is not ground deeply. SelectX1=0.8mm, X2= 1.3mm when the first choice is not practical, for example, when X1falls within the area of the ground edge.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 15Stressdirectionxy xyxyxyxyxyAveragemeasured angle(degrees)23.6 29.6 53.4 54.1 55.4 55.4 61.5 64 68.4 68.4 70.6 71.9Average stress,psi2657 3454 8188 8401 8815 8815 11200 12468 15359 15359 17268 18605Aver
