1、Designation: C 1377 97 (Reapproved 2003)e1Standard Test Method forCalibration of Surface/Stress Measuring Devices1This standard is issued under the fixed designation C 1377; 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 (e) indicates an editorial change since the last revision or reapproval.e1NOTEFigure 1 was editorially corrected in February 2005.1. Scope1.1 This test method covers calibration or verification ofca
3、libration, or both, of surface-stress measuring devices used tomeasure stress in annealed and heat-strengthened or temperedglass using polariscopic or refractometry based principles.1.2 This test method is nondestructive.1.3 This test method uses transmitted light, and therefore, isapplicable to lig
4、ht-transmitting glasses.1.4 This test method is not applicable to chemically tem-pered glass.1.5 Using the procedure described, surface stresses can bemeasured only on the “tin” side of float glass.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its u
5、se. 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:2C 158 Test Methods for Strength of Glass by Flexure(Determination of Modul
6、us of Rupture)C 162 Terminology of Glass and Glass ProductsC 770 Test Method for Measurements of Glass StressOptical CoefficientC 1048 Specification for Heat-Treated Flat GlassKindHS, Kind FT Coated and Uncoated GlassC 1279 Test Method for Nondestructive Photoelastic Mea-surement of Edge and Surface
7、 Stresses in Annealed,Heat-Strengthened, and Fully Tempered Flat Glass3. Terminology3.1 DefinitionsFor terminology used in this test method,refer to Terminology C 162.4. Summary of Test Method4.1 In this test method, a test bar is subjected to bendingusing deadweights or calibrated load-cells to int
8、roduce surfacestresses that can be calculated from the specimen geometry andforces applied. At a point in which the stresses are calculated,those same stresses also are measured using the instrument tobe calibrated or verified. Since both the specimen dimensionand the applied forces can be establish
9、ed accurately usingtraceable (primary) standards, the method permits a fullytraceable calibration of the stress-measuring instrument.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 t
10、he heat-treating process.5.2 The edge and surface stress levels are specified inSpecification C 1048, in the Engineering Standards Manual ofGANA3, and in foreign specifications.5.3 Surface stresses can be measured nondestructively usingmethods, such as Test Method C 1279. The calibration ofsurface m
11、easuring devices used in those procedures andperiodic verification of calibration are needed. This test methodoffers a convenient way to accomplish this task.6. Principle of Operation6.1 The instrument to be calibrated is placed on the surfaceof the calibration specimen. Stresses at a point where th
12、einstrument is placed are calculated using expressions shown inSection 9. To increase the precision of measurement, severallevels of stress are produced by applying forces incrementally.Measurement of stress using the instrument to be calibrated isrepeated for each stress level and these measurement
13、s are usedto calibrate the instrument.7. Test Specimens and Loading SchemesTwo loading geometries can be practiced: cantilever andfour-point bending.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
14、 FlatGlass.Current edition approved Oct. 1, 2003. Published October 2003. Originallyapproved in 1997. Last previous edition approved in 1997 as C 1377 97.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMS
15、tandards volume information, refer to the standards Document Summary page onthe ASTM website.3GANA, Glass Association of North America, 3310 SW Harrison St., Topeka,KS 666112279.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7.1 Can
16、tilever-Beam Specimen (Fig. 1)the dimensions ofthe specimen used for cantilever loading should be selectedwithin limits shown below:Thickness (t): 6 mm (0.22 in.) minimumWidth (w): 8t # w # 12tLength (L): 6w minimumDistance to the point of measurement (Lo): 4wClamped length: 1.5w7.1.1 A heat-strengt
17、hened or tempered specimen, with pol-ished edges is preferred, but annealed specimens can be used ifthe range of stress is less than 24.13 MPa (3500 psi).7.2 Four-Point Bending Specimen (Fig. 2)The four-pointbending specimen should be preferred since it has uniformstress in the central loading zone.
18、 The dimensions of thespecimen should be selected within the following limits:Thickness (t): minimum 2 mm (0.079 in.)Width (w): 8t # w # 12t (see Note 1)Length Lo: minimum 4wGage length Lcsection: 3wMinimum overall length L:12wEdges: Polished, no chips in the gage section, bevel less than 0.1t.NOTE
19、1When the thickness t is less than 6 mm, and width of the beamexceeds 12t, instead of the beam bending, plate bending equations shouldbe used to calculate surface stress, or suitable corrections are required inthe equations in 9.1. Barata4andAshwell5show the correction procedures.7.3 Application of
20、ForcesForces required must be calcu-lated to eliminate possible breakage. Stresses must be esti-mated first using the equations in 9.1. A tempered specimenmay be subjected to stress levels up to 10 000 psi (69 MPa).Using annealed specimens, the stress should remain at a safelevel, typically below 35
21、00 psi (24 MPa).7.3.1 Cantilever SpecimenThe specimen must beclamped securely using wood, plastic, or rubber-lined metalclamping surfaces, with rounded edges, as shown in Fig. 3. Theforces can be applied using a calibrated testing machine ordead weights, by means of knife edges, to insure exactposit
22、ioning of the line-of-loading B-B. The pad used for loadapplication can be secured from slipping using high-frictionmaterials. To eliminate possible twisting action, the knife edgeshould be narrow, or a steel ball used to center the point ofapplication of force.7.3.2 Four-Point Bending SpecimenIn th
23、e case of four-point bending, the force must be applied equally at two points,and two articulated knives or roller supports are required toascertain accurately the length L0and Lc. Particular precautionsare required to insure that the end supports do not introduce atwist in the specimen, as a result
24、 of nonparallel supportsurfaces or nonflatness of the specimen itself. Fig. 2 illustratesthe setup for application of forces to obtain tension andcompression on the upper face. Test Methods C 158 provides adescription of support design.8. Procedure8.1 When calibrating a surface polarimeter, apply fo
25、rces infive equal increments, using a testing machine or dead weight.When calibrating a critical angle measuring instrument, at leastten increments are needed, and a tempered specimen must beused.8.2 For each incremental loading, including zero, obtain theinstrument reading. Repeat the reading at le
26、ast three times, andaverage the readings. When calibrating a surface polarimeter,measure the fringe tilt u. When calibrating a differentialrefractometer, measure the differential angle using a microme-ter reticle, and read the distance between the borders ofilluminated zones at mutually perpendicula
27、r polarization inaccordance with instrument manual.8.3 Prepare a table of results, and plot these data, withapplied stress as the ordinant (x axis) and tan u (using surfacepolarimeter) or angular distance between emerging light beams(using refractometer) versus applied stress (see Fig. 4).4Barata, F
28、. I., “When Is a Beam a Plate?,” American Ceramic SocietyCommunications, May 1981.5Ashwell, D. G., “The Anticlastic Curvature of Rectangular Beams and Plates,”Journal of Aeronautics, Vol 54, 1950, pp. 708-715.FIG. 1 Cantilever Beam LoadingC 1377 97 (2003)e12FIG. 2 Calibration Using Four-Point Bendin
29、gC 1377 97 (2003)e13FIG. 3 Clamping of a Cantilever BeamFIG. 4 Graphical Plot of ResultsC 1377 97 (2003)e149. Calculation9.1 For each force increment, calculate the stress at Point Awhere measurements are obtained using the following formula:Stresspsi!5 FORCElbs!36 Loin.!win.tin.2(1)orStressMPa!5 FO
30、RCEN!36 Lomm!wmm!tmm!2(2)9.2 Construct a graph as described in 8.3 showing tan uversus stress, when using surface polarimeter, or divisionversus stress, using critical angle measurement (see Fig. 4).9.3 Trace “best fit” straight line, to establish the instrumentconstant K for the surface polarimeter
31、:K 5D StressD tan u(3)9.4 Since the relation between the measured distance andthe stress in the refractometry is nonlinear, the calibration ofthis instrument requires an annealed specimen or a specimenexhibiting known surface stress in the unloaded state. For eachincrement, add the unloaded-specimen
32、 stress to the calculatedstress and verify calibration of the critical-angle measuringinstrument provided by the manufacturer.10. Report10.1 Report the following information:10.1.1 Date of calibration,10.1.2 Type and dimension of the specimen,10.1.3 Instrument constant K established (surface polarim
33、-eter), and10.1.4 Table of data and initial specimen surface stress(critical angle measuring instrument).11. Precision and Bias11.1 The precision and bias of this test method will bedetermined by a round-robin test conducted by SubcommitteeC 14.08.612. Keywords12.1 calibration; stress measurements;
34、surface stress; tem-pered glassASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof i
35、nfringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this sta
36、ndard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your
37、views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).6Parties interested in participating in the round-robin test should contact theCommittee C-14 manager at ASTM Headquarters.C 1377 97 (2003)e15
