1、Designation:F21805 Designation: F218 12Standard Test Method forMeasuring Optical Retardation and Analyzing Stress inGlass1This standard is issued under the fixed designation F218; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the
2、 year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the analysis of stress in glass by means of a polarimeter based on the principles dev
3、eloped by Jessopand Friedel (1, 2).2Stress is evaluated as a function of optical retardation, that is expressed as the angle of rotation of an analyzingpolarizer that causes extinction in the glass.1.2 There is no known ISO equivalent to this standard.1.3 This standard does not purport to address al
4、l 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 regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C162 Terminology of Gl
5、ass and Glass ProductsC770 Test Method for Measurement of Glass StressOptical CoefficientC978 Test Method for Photoelastic Determination of Residual Stress in a Transparent Glass Matrix Using a PolarizingMicroscope and Optical Retardation Compensation ProceduresC1426 Practices for Verification and C
6、alibration of Polarimeters3. Terminology3.1 For definitions of terms used in this standard, refer to Terminology C162.4. Significance and Use4.1 The performance of glass products may be affected by presence of residual stresses due to process, differential thermalexpansion between fused components,
7、and by inclusions. This test method provides means of quantitative evaluation of stresses.5. Calibration and Standardization5.1 Whenever calibration of the polarimeter is required by product specification, Practices C1426 for verification and calibrationshould be used.6. Polarimeter6.1 The polarimet
8、er shall consist of an arrangement similar to that shown in Fig. 1. A description of each component follows:6.1.1 Source of LightEither a white light or a monochromatic source such as sodium light (l 589 nm) or a white light coveredwith a narrow-band interferential filter B, (see Fig. 1,) transmitti
9、ng the desired monochromatic wavelength.NOTE 1The white light should provide a source of illumination with solar temperature of at least that of Illuminant A.6.1.2 FilterThe filter should be placed between the light source and the polarizer, or between the analyzer and the viewer (seeFig. 1).1This t
10、est 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 Sept. 15, 2005. Published November 2005. Originally approved in 1950. Last previous edition app
11、roved in 2000 as F21895(2000). DOI:10.1520/F0218-05.Current edition approved March 1, 2012. Published March 2012. Originally approved in 1950. Last previous edition approved in 2005 as F218 05. DOI:10.1520/F0218-12.2The boldface numbers in parentheses refer to the reports and papers appearing in the
12、 list of references at the end of this test method.3For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.1This do
13、cument 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 adequately depict all changes accurately, ASTM recommends that users consult prior editions a
14、s 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 Conshohocken, PA 19428-2959, United States.6.1.3 DiffuserA piece of opal glass or a ground glass o
15、f photographic quality.6.1.4 PolarizerA polarizing element housed in a rotatable mount capable of being locked in a fixed position shown inFig. 2 and Fig. 4.6.1.5 Immersion CellRectangular glass jar with strain-free, retardation-free viewing sides filled with a liquid having the sameindex of refract
16、ion as the glass specimen to be measured. It may be surmounted with a suitable device for holding and rotatingthe specimen, such that it does not stress the specimen.NOTE 2Suitable index liquids may be purchased or mixed as required. Dibutyl phthalate (refractive index 1.489), and tricresyl phosphat
17、e (index1.555) may be mixed to produce any desired refractive index between the two limits, the refractive index being a linear function of the proportion of oneliquid to the other. Other liquids that may be used are:Liquid Refractive IndexCinnamic aldehyde 1.62Oil of cassia 1.61Monochlorobenzene 1.
18、525Carbon tetrachloride 1.463Dipentene (Eastman) 1.473NOTE 3Cases may arise where the refraction liquid may contaminate the specimen. When the sample is viewed through faces that are essentiallyparallel, elimination of the liquid will cause only a minor error. However, when viewing through faces of
19、the sample that are not parallel, the use of liquidof same refraction index is essential.6.1.6 Full-Wave (Sensitive Tint) Plate, having a retardation of 565 6 5 nm, which produces, with white light, a violet-red color.It should be housed in a rotatable mount capable of being locked in a fixed positi
20、on shown in Fig. 2.6.1.7 Quarter-Wave Plate, having a retardation equivalent to one quarter of the wavelength of monochromatic light being used,or 141 6 5 nm when white light is used. It should be housed in a rotatable mount capable of being locked in a fixed position shownin Fig. 2.ALight source (w
21、hite, sodium vapor, or mercury vapor arc)BFilter (used only with mercury arc light) (used with white light)CDiffuserDPolarizerEImmersion cellFFull-wave plate (used only with white light)GQuarter-wave plateHAnalyzerITelescopeFIG. 1 PolarimeterThe direction of vibration of the polarizer and analyzer m
22、ay be oriented 90 from indicated positions.FIG. 2 Orientation of Polarimeter in Standard PositionF218 1226.1.8 AnalyzerIdentical to the polarizer. It should be housed in a rotatable mount capable of being rotated 360, and agraduated dial indicating the angular rotation a of the analyzer from its sta
23、ndard position. The polarizer must be lockable inposition shown in Fig. 2.6.1.9 Telescope, short-focus, having a suitable magnifying power over the usable focusing range.7. Setup of Polarimeter7.1 The standard setup of the polarimeter is illustrated in Fig. 2. Two reference directions must be identi
24、fied:NOTE 1When the legs are squeezed together, Sides A and C becometensile and Sides B and D become compressive.NOTE 2MaterialCane glass of approximately 7 mm diameter,annealed after forming.NOTE 3When viewed in the polarimeter, immerse in a liquid havingthe same refractive index as the glass.FIG.
25、3 Reference SpecimenNOTEStress Sxin Vertical (NS) Position.FIG. 4 Orientation of the Polarizer, Analyzer, Quarter-Wave Plate, Full-Wave Plate, and of Stresses Sxand Syin the Region of InterestF218 1237.1.1 Vertical direction (V), (in polarimeters transmitting the light in horizontal direction) or NS
26、, that is usually a symmetry axisof an instrument using a vertical light path, and polarizers are in a horizontal plane.7.1.2 Horizontal (H), or EW (perpendicular to the vertical or NS) (see Fig. 4)7.2 As usually employed, the polarimeter measures retardations in a sample that is placed in the polar
27、imeter and rotated untilthe measured stresses Sxand Syare oriented along V and H (vertical or a horizontal) direction. This is accomplished by setting thevibration direction of the polarizer at an angle of 45 to the vertical and clockwise to the horizontal (as shown in Fig. 2 and Fig.4). The vibrati
28、on direction of the analyzer must be “crossed” with respect to that of the polarizer; that is, the two directions mustbe at right angles to each other. In this relationship a minimum amount of light will pass through the combination. To check the45 angle at which the directions of the polarizer and
29、analyzer must be set, use may be made of a rectangular-shapedGlan-Thompson or Nicol prism. The prism is set so that its vibration direction is 45 to the vertical and horizontal. The polarizeris then rotated until extinction occurs between it and the prism. The position of the analyzer is then determ
30、ined in the same way,but by first rotating the Glan-Thompson or Nicol prism through 90; or, the analyzer may be rotated to extinction with respect tothe polarizer after the latter has been set in position with the prism.7.3 When a quarter-wave plate is used, its “slow” ray direction must be set 45 c
31、lockwise from the horizontal in anorthwest-southeast direction (see Fig. 2).Adjusted in this position, maximum extinction occurs when direction of axes of all threeelements (polarizer, analyzer and quarter-wave plate) are in agreement with Fig. 2.7.4 When the full-wave plate is used with the quarter
32、-wave plate, its “slow” ray direction must be placed in a horizontal position(see Fig. 2). Adjusted in this position, a violet-red background color is seen when the three elements (polarizer, full-wave plate,and analyzer) are placed in series.7.5 Sections 7.3 and 7.4 describe orientations of the qua
33、rter- and full-wave plates in the standard positions that have beengenerally adopted. However, the direction of the “ slow” rays may be rotated 90 without changing the functions of the apparatus.This does, however, cause the analyzer rotations (in the case of the quarter-wave plate) and the colors (
34、in the case of the full-waveplate) to have opposite meanings. Tables 1 and 2 define these meanings in whatever is being measured or observed with the “slow”ray directions in either the standard or the alternate positions.7.6 To assure proper orientation of the directions of the “slow” ray of the qua
35、rter-wave and full-wave plates with respect to thevibration directions of the polarizer and analyzer, use may be made of a U-shaped piece of annealed cane glass as illustrated inFig. 3. Squeezing the legs together slightly will develop a tensile stress on the outside and a compressive stress on the
36、inside. Aflat rectangular beam in bending, containing a region where the direction and sign of stresses is known can also be used. Then,if the “slow” ray directions of the quarter-wave and full-wave plates are oriented in the standard position, the stress conditions ofColumns 1 through 4 of Table 1
37、will be noted in the vertical and horizontal sides of the U-tube. If the opposite meaning of thecolor definition is preferred, it will be necessary to rotate the “slow” ray directions of the Full-Wave Plate 90 to the alternatepositions. The orientation of the full wave plate can be verified, compari
38、ng the observed colors to the expected colors shown inthe Table 2. The orientation of the quarter wave plate can be verified, checking that a clockwise rotation of the analyzer willdecrease the light intensity, whenever a black (zero-order) line is very near the point of interest.7.7 If a major stre
39、ss component lies in any direction other than vertical or horizontal, its measurement requires that either:7.7.1 The entire optical system be rotated so that the vibration directions of the polarizer and analyzer are set at 45 to the stressdirection, or7.7.2 That the part containing the stress direc
40、tion be rotated to suit assure the orientation shown in Fig. 4.8. Procedure8.1 Before proceeding with measurements, evaluate the stress field by observing the sample with and without the Full WavePlate (tint plate) in place. The colors observed when the tint plate is introduced provide an initial ev
41、aluation of the retardation.8.2 Identify directions and sign of stresses:8.2.1 Remove the tint-plate from the path of light. Rotate the sample in its plane. Observe the point of interest (POI) becomingdark (minimum transmitted light intensity) whenever the direction of stress Sxor Syis parallel to t
42、he polarizer. From the positionTABLE 1 Orientation of “Slow” Ray Direction of Full-Wave Platewith Corresponding StressesWhen orientationof“ slow” raywith respect tothe horizontal is:Standardand when stresscomponentlies in the: vertical horizontalthen theapproximatecolor: yellow green yellow greenind
43、icates: tension compression compression tensioncolumn:(see 3.5)12 34F218 124of extinction, rotate the sample 45, placing one of principal stresses, Sx, in vertical orientation, at 45 to the polarization axes. Inthis position, maximum brightness is observed. (See Fig. 4.)8.2.2 For a region near the P
44、OI exhibiting small retardation ( 0). If the colors observed are blueblue green, the stress Sxis compressive (or Sx-Sy150 nm), use the analyzer rotation to identify the sign of Sx,orSx Sy. Withthe Tint-Plate removed, rotate the Analyzer clockwise, and observe the sequence of changing colors.8.3.1 Th
45、e sequence Yellow-BlueGray-Brown-Yellow-BlueGray, or for larger retardation (approximately 300 nm) Yellow-Blue-Red-Orange-Yellow-LightYellow-Blue, indicates tensile stress (Sx0orSx Sy 0).8.3.2 The reverse sequence Yellow-Brown- BlueGray-Yellow, or for larger retardation (approximately300 nm) Yellow-
46、Orange-Red-Blue-Yellow-Orange-Red, indicates compressive stress (Sx0).8.4 Measure the retardation:8.4.1 To measure the retardation at any given point, remove the tint plate, place the monochromatic filter in the field of view,and rotate the analyzer with respect to its initial position until maximum
47、 extinction (darkness) occurs at the POI. The angle athrough which the analyzer must be rotated to the left or the right is a measure of the retardation at the point.8.4.1.1 In white light, the color of the fringe moving toward the POI will keep changing. To eliminate possible errors and toincrease
48、the contrast, the monochromatic filter, B, must be inserted for this operation, or the monochromatic lamp must be used.8.4.2 The rotation of the Analyzer must be clockwise. If the stress is tensile (Sxor Sx Sy0), the measured angle a is indicateddirectly on the dial, in degrees. When a fractional gr
49、aduation of the dial is used, the fraction f = a/180 is indicated on the dial.8.4.3 If the stress is compressive (Sxor Sx Sy0. In uniaxial stress, Sxis tension or Syis compression.Yellow 60Pale yellowA73 If the slow ray of the full wave plate is in vertical position:Yellow white 85WhiteA97 Sx Syis 0. In uniaxial stress, Sxis compression or Syis tension.Gray white 110Iron gray 172Black 180AMore distinctive color of pair.F218 1258.4.3.3 Instruments equipped with a dual scale, 0 to 180 CW and 0 to 180 CCW, the angle a is indicated direc
