1、Designation:F21812F21813 Standard Test Method for Measuring Optical Retardation and Analyzing Stress in Glass 1 ThisstandardisissuedunderthexeddesignationF218;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthes
2、esindicatestheyearoflastreapproval.Asuperscript epsilon () indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 ThistestmethodcoverstheanalysisofstressinglassbymeansofapolarimeterbasedontheprinciplesdevelopedbyJessop andFriedel(1,2). 2 Stressisevaluatedasafunctionofoptic
3、alretardation,thatisexpressedastheangleofrotationofananalyzing polarizer 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 all of the safety concerns, if any, associated with its use. It is the responsibility of
4、the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: 3 C162Terminology of Glass and Glass Products C770Test Method for Measurement of Glass StressOptical Coef
5、ficient C978Test Method for Photoelastic Determination of Residual Stress in a Transparent Glass Matrix Using a Polarizing Microscope and Optical Retardation Compensation Procedures C1426Practices for Verication and Calibration of Polarimeters E691Practice for Conducting an Interlaboratory Study to
6、Determine the Precision of a Test Method E177Practice for Use of the Terms Precision and Bias in ASTM Test Methods 3. Terminology 3.1 For denitions of terms used in this standard, refer to Terminology C162. 4. Signicance and Use 4.1 The performance of glass products may be affected by presence of re
7、sidual stresses due to process, differential thermal expansion between fused components, and by inclusions. This test method provides means of quantitative evaluation of stresses. 5. Calibration and Standardization 5.1 Whenevercalibrationofthepolarimeterisrequiredbyproductspecication,PracticesC1426f
8、orvericationandcalibration should be used. 6. Polarimeter 6.1 The polarimeter shall consist of an arrangement similar to that shown in Fig. 1.Adescription of each component follows: 6.1.1 SourceofLightEitherawhitelightoramonochromaticsourcesuchassodiumlight(l589nm)orawhitelightcovered with a narrow-
9、band interferential lter B, (see Fig. 1,) transmitting the desired monochromatic wavelength. NOTE 1The white light should provide a source of illumination with solar temperature of at least that of Illuminant A. 1 This test method is under the jurisdiction ofASTM Committee C14 on Glass and Glass Pro
10、ducts and is the direct responsibility of Subcommittee C14.04 on Physical and Mechanical Properties. Current edition approved March 1, 2012Oct. 1, 2013. Published March 2012October 2013. Originally approved in 1950. Last previous edition approved in 20052012 as F21805.F21812. DOI: 10.1520/F0218-12.1
11、0.1520/F0218-13. 2 The boldface numbers in parentheses refer to the reports and papers appearing in the list of references at the end of this test method. 3 ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatserviceastm.org.ForAnnualBookofASTMStandards volume i
12、nformation, refer to the standards Document Summary page on the ASTM website. This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because it may not be technically possible to adequatel
13、y depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version of 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
14、, PA 19428-2959. United States 16.1.2 FilterTheltershouldbeplacedbetweenthelightsourceandthepolarizer,orbetweentheanalyzerandtheviewer(see Fig. 1). 6.1.3 DiffuserA piece of opal glass or a ground glass of photographic quality. 6.1.4 PolarizerA polarizing element housed in a rotatable mount capable o
15、f being locked in a xed position shown in Fig. 2 and Fig. 4. 6.1.5 ImmersionCellRectangularglassjarwithstrain-free,retardation-freeviewingsideslledwithaliquidhavingthesame index of refraction as the glass specimen to be measured. It may be surmounted with a suitable device for holding and rotating t
16、he 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 phosphate (index 1.555) may be mixed to produce any desired refractive index between the two limits, the refractive in
17、dex being a linear function of the proportion of one liquid to the other. Other liquids that may be used are: Liquid Refractive Index Cinnamic aldehyde 1.62 Oil of cassia 1.61 Monochlorobenzene 1.525 Carbon tetrachloride 1.463 Dipentene (Eastman) 1.473 NOTE 3Cases may arise where the refraction liqu
18、id may contaminate the specimen. When the sample is viewed through faces that are essentially parallel,eliminationoftheliquidwillcauseonlyaminorerror.However,whenviewingthroughfacesofthesamplethatarenotparallel,theuseofliquid of same refraction index is essential. 6.1.6 Full-Wave(SensitiveTint)Plate
19、,havingaretardationof56565nm,whichproduces,withwhitelight,aviolet-redcolor. It should be housed in a rotatable mount capable of being locked in a xed position shown in Fig. 2. ALight source (white, sodium vapor, or mercury vapor arc) BFilter (used only with mercury arc light) (used with white light)
20、 CDiffuser DPolarizer EImmersion cell FFull-wave plate (used only with white light) GQuarter-wave plate HAnalyzer ITelescope FIG. 1 Polarimeter The direction of vibration of the polarizer and analyzer may be oriented 90 from indicated positions. FIG. 2 Orientation of Polarimeter in Standard Position
21、 F21813 26.1.7 Quarter-WavePlate,havingaretardationequivalenttoonequarterofthewavelengthofmonochromaticlightbeingused, or14165nmwhenwhitelightisused.Itshouldbehousedinarotatablemountcapableofbeinglockedinaxedpositionshown in Fig. 2. 6.1.8 AnalyzerIdentical to the polarizer. It should be housed in a
22、rotatable mount capable of being rotated 360, and a graduated dial indicating the angular rotation a of the analyzer from its standard position. The polarizer must be lockable in position shown in Fig. 2. 6.1.9 Telescope, short-focus, having a suitable magnifying power over the usable focusing range
23、. 7. Setup of Polarimeter 7.1 The standard setup of the polarimeter is illustrated in Fig. 2. Two reference directions must be identied: 7.1.1 Verticaldirection(V),(inpolarimeterstransmittingthelightinhorizontaldirection)orNS,thatisusuallyasymmetryaxis of an instrument using a vertical light path, a
24、nd 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 polarimeter and rotated until the measured stresses S x and S y are oriented alongV
25、and H (vertical or a horizontal) direction.This is accomplished by setting the vibration 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 vibration direction of the analyzer must be crossed with respect to that of the p
26、olarizer; that is, the two directions must be at right angles to each other. In this relationship a minimum amount of light will pass through the combination. To check the 45 angle at which the directions of the polarizer and analyzer must be set, use may be made of a rectangular-shaped Glan-Thompso
27、n or Nicol prism. The prism is set so that its vibration direction is 45 to the vertical and horizontal. The polarizer is then rotated until extinction occurs between it and the prism. The position of the analyzer is then determined in the same way, but by rst rotating the Glan-Thompson or Nicol pri
28、sm through 90; or, the analyzer may be rotated to extinction with respect to the 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 clockwise from the horizontal in a northwest-southeastdirection(seeFig.2).
29、Adjustedinthisposition,maximumextinctionoccurswhendirectionofaxesofallthree elements (polarizer, analyzer and quarter-wave plate) are in agreement with Fig. 2. 7.4 Whenthefull-waveplateisusedwiththequarter-waveplate,itsslowraydirectionmustbeplacedinahorizontalposition (see Fig. 2). Adjusted in this
30、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 quarter- and full-wave plates in the standard positions that have been generally adopted. However, the direct
31、ion of the slow rays may be rotated 90 without changing the functions of the apparatus. Thisdoes,however,causetheanalyzerrotations(inthecaseofthequarter-waveplate)andthecolors(inthecaseofthefull-wave plate)tohaveoppositemeanings.Tables1and2denethesemeaningsinwhateverisbeingmeasuredorobservedwiththes
32、low ray directions in either the standard or the alternate positions. NOTE 1When the legs are squeezed together, Sides A and C become tensile and Sides B and D become compressive. NOTE 2MaterialCane glass of approximately 7 mm diameter, annealed after forming. NOTE 3When viewed in the polarimeter, i
33、mmerse in a liquid having the same refractive index as the glass. FIG. 3Reference Specimen F21813 37.6 To assure proper orientation of the directions of the slow ray of the quarter-wave and full-wave plates with respect to the vibration directions of the polarizer and analyzer, use may be made of a
34、U-shaped piece of annealed cane glass as illustrated in Fig. 3. Squeezing the legs together slightly will develop a tensile stress on the outside and a compressive stress on the inside.A at rectangular beam in bending, containing a region where the direction and sign of stresses is known can also be
35、 used. Then, if the slow ray directions of the quarter-wave and full-wave plates are oriented in the standard position, the stress conditions of Columns 1 through 4 of Table 1 will be noted in the vertical and horizontal sides of the U-tube. If the opposite meaning of the color denition is preferred
36、, it will be necessary to rotate the slow ray directions of the Full-Wave Plate 90 to the alternate positions. The orientation of the full wave plate can be veried, comparing the observed colors to the expected colors shown in the Table 2. The orientation of the quarter wave plate can be veried, che
37、cking that a clockwise rotation of the analyzer will decrease the light intensity, whenever a black (zero-order) line is very near the point of interest. 7.7 If a major stress component lies in any direction other than vertical or horizontal, its measurement requires that either: 7.7.1 Theentireopti
38、calsystemberotatedsothatthevibrationdirectionsofthepolarizerandanalyzeraresetat45tothestress direction, or 7.7.2 That the part containing the stress direction be rotated to suit assure the orientation shown in Fig. 4. 8. Procedure 8.1 Before proceeding with measurements, evaluate the stress eld by o
39、bserving the sample with and without the Full Wave Plate (tint plate) in place. The colors observed when the tint plate is introduced provide an initial evaluation of the retardation. NOTE 1Stress S x in Vertical (NS) Position. FIG. 4Orientation of the Polarizer, Analyzer, Quarter-Wave Plate, Full-W
40、ave Plate, and of Stresses S x and S y in the Region of Interest TABLE 1 Orientation of Slow Ray Direction of Full-Wave Plate with Corresponding Stresses When orientation of slow ray with respect to the horizontal is: Standard and when stress component lies in the: vertical horizontal then the appro
41、ximate color: yellow green yellow green indicates: tension compression compression tension column: (see 3.5) 1 2 3 4 F21813 48.2 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) becoming
42、dark (minimum transmitted light intensity) whenever the direction of stress S x or S y is parallel to the polarizer. From the position of extinction, rotate the sample 45, placing one of principal stresses, S x , in vertical orientation, at 45 to the polarization axes. In this position, maximum brig
43、htness is observed. (See Fig. 4.) 8.2.2 For a region near the POI exhibiting small retardation ( 0). If the colors observed are blueblue green, the stress S x is compressive (or S x -S y 150 nm), use the analyzer rotation to identify the sign of S x , or S x S y . With the Tint-Plate removed, rotate
44、 the Analyzer clockwise, and observe the sequence of changing colors. 8.3.1 The sequence Yellow-BlueGray-Brown-Yellow-BlueGray, or for larger retardation (approximately 300 nm) Yellow- Blue-Red-Orange-Yellow-LightYellow-Blue, indicates tensile stress (S x 0 or S x S y 0). 8.3.2 The reverse sequence
45、Yellow-Brown- BlueGray-Yellow, or for larger retardation (approximately300 nm) Yellow- Orange-Red-Blue-Yellow-Orange-Red, indicates compressive stress (S x0). 8.4 Measure the retardation: 8.4.1 To measure the retardation at any given point, remove the tint plate, place the monochromatic lter in the
46、eld of view, and rotate the analyzer with respect to its initial position until maximum extinction (darkness) occurs at the POI. The angle a through 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 frin
47、ge moving toward the POI will keep changing. To eliminate possible errors and to increase the contrast, the monochromatic lter, B, must be inserted for this operation, or the monochromatic lamp must be used. 8.4.2 TherotationoftheAnalyzermustbeclockwise.Ifthestressistensile(S x orS x S y 0),themeasu
48、redangle aisindicated directly on the dial, in degrees. When a fractional graduation of the dial is used, the fraction f = a/180 is indicated on the dial. 8.4.3 If the stress is compressive (S x or S x S y0. In uniaxial stress, S x is tension or S y is compression. Yellow 60 Pale yellow A 73 If the
49、slow ray of the full wave plate is in vertical position: Yellow white 85 White A 97 S x S y is 0. In uniaxial stress, S x is compression or S y is tension. Gray white 110 Iron gray 172 Black 180 A More distinctive color of pair. F21813 58.4.3.2 Similarly, the indicated fraction is a compliment, and the measured fraction is: f512indicatedfraction 8.4.3.3 Instruments equipped with a dual scale, 0 to 180 CW and 0 to 180 CCW, the angle a is indicated directly when the analyzer is rotated CCW. 8.
