ASTM E83-2010 8125 Standard Practice for Verification and Classification of Extensometer Systems.pdf

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1、Designation: E83 10Standard Practice forVerification and Classification of Extensometer Systems1This standard is issued under the fixed designation E83; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A n

2、umber in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This practice covers procedures for the verification an

3、dclassification of extensometer systems, but it is not intended tobe a complete purchase specification. The practice is applicableonly to instruments that indicate or record values that areproportional to changes in length corresponding to eithertensile or compressive strain. Extensometer systems ar

4、e clas-sified on the basis of the magnitude of their errors.1.2 Because strain is a dimensionless quantity, this docu-ment can be used for extensometers based on either SI or UScustomary units of displacement.NOTE 1Bonded resistance strain gauges directly bonded to a speci-men cannot be calibrated o

5、r verified with the apparatus described in thispractice for the verification of extensometers having definite gauge points.(See procedures as described in Test Methods E251.)1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibil

6、ity 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:2E6 Terminology Relating to Methods of Mechanical TestingE21 Test Methods for Elevated Temperature

7、Tension Testsof Metallic MaterialsE251 Test Methods for Performance Characteristics of Me-tallic Bonded Resistance Strain Gauges3. Terminology3.1 Definitions: In addition to the terms listed, see Termi-nology E6.3.1.1 calibrationa determination of the calibration factorfor a system using established

8、 procedures.3.1.2 calibration factorthe factor by which the change inextensometer reading must be multiplied to obtain the equiva-lent strain.3.1.2.1 DiscussionFor any extensometer, the calibrationfactor is equal to the ratio of change in length to the product ofthe gauge length and the change in th

9、e extensometer reading.For direct-reading extensometers the calibration factor is unity.3.1.3 compressometera specialized extensometer used forsensing negative or compressive strain.3.1.4 deflectometera specialized extensometer used forsensing of extension or motion, usually without reference to asp

10、ecific gauge length.3.1.5 error, in extensometer systemsthe value obtained bysubtracting the correct value of the strain from the indicatedvalue given by the extensometer system.3.1.6 extensometer, na device for sensing strain.3.1.7 extensometer systemsa system for sensing and indi-cating strain.3.1

11、.7.1 DiscussionThe system will normally include anextensometer, conditioning electronics and auxiliary device(recorder, digital readout, computer, etc.). However, com-pletely self-contained mechanical devices are permitted. Anextensometer system may be one of three types.3.1.8 Type 1 extensometer sy

12、stem, nan extensometer sys-tem which both defines gauge length and senses extension, forexample, a clip-on strain gauge type with conditioning elec-tronics.3.1.9 Type 2 extensometer system, nan extensometerwhich senses extension and the gauge length is defined byspecimen geometry or specimen feature

13、s such as ridges ornotches.3.1.9.1 DiscussionA Type 2 extensometer is used wherethe extensometer gauge length is determined by features on thespecimen, for example, ridges, notches, or overall height (incase of compression test piece). The precision associated withgauge length setting for a Type 2 e

14、xtensometer should bespecified in relevant test method or product standard. Theposition readout on a testing machine is not recommended foruse in a Type 2 extensometer system.1This practice is under the jurisdiction of ASTM Committee E28 on MechanicalTesting and is the direct responsibility of Subco

15、mmittee E28.01 on Calibration ofMechanical Testing Machines and Apparatus.Current edition approved Jan. 1, 2010. Published February 2010. Originallyapproved in 1950. Last previous edition approved in 2006 as E83 06. DOI:10.1520/E0083-10.2For referenced ASTM standards, visit the ASTM website, www.ast

16、m.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.10 Ty

17、pe 3 extensometer system, nan extensometersystem which intrinsically senses strain (ratiometric principle),for example, video camera system.3.1.11 gauge length (L), nthe original length of thatportion of the specimen over which strain or change of lengthis determined.3.1.11.1 DiscussionIf the device

18、 is used for sensingextension or motion, and gauge length is predetermined by thespecimen geometry or specific test method, then only resolu-tion and strain error for a specified gauge length shoulddetermine the class of extensometer system.3.1.12 resolution of the strain indicatorthe smallestchange

19、 in strain that can be estimated or ascertained on thestrain indicating apparatus of the testing system, at any appliedstrain.3.1.13 resolution of the digital type strain indicators (nu-meric displays, printouts, and so forth)the resolution is thesmallest change in strain that can be displayed on th

20、e strainindicator (may be a single digit or a combination of digits) atany applied strain.3.1.13.1 DiscussionIf the strain indication, for either typeof strain indicator, fluctuates more than twice the resolution, asdescribed in 3.1.12 or 3.1.13, the resolution expressed as astrain shall be equal to

21、 one-half the range of fluctuation.3.1.14 verificationa determination that a system meets therequirements of a given classification after calibration accord-ing to established procedures.3.1.15 verification apparatusa device for verifying exten-someter systems.3.1.15.1 DiscussionThis device is used

22、to simulate thechange in length experienced by a test specimen as a result ofthe applied force. The extensometer may either be attacheddirectly to the mechanism or interfaced with it in a mannersimilar to normal operation (that is, possibly without contactfor some optical extensometers).4. Verificat

23、ion Apparatus4.1 The apparatus for verifying extensometer systems shallprovide a means for applying controlled displacements to asimulated specimen and for measuring these displacementsaccurately. It may consist of a rigid frame, suitable coaxialspindles, or other fixtures to accommodate the extenso

24、meterbeing verified, a mechanism for moving one spindle or fixtureaxially with respect to the other, and a means for measuringaccurately the change in length so produced,3or any otherdevice or mechanism that will accomplish the purpose equallywell. The mechanism provided for moving one spindle relat

25、iveto the other shall permit sensitive adjustments. The changes inlength shall be measured, for example, by means of aninterferometer, calibrated standard gauge blocks and an indi-cator, a calibrated micrometer screw, or a calibrated lasermeasurement system. If standard gauge blocks and an indica-to

26、r, or a micrometer screw, are used, they shall be calibratedand their limits of accuracy and sensitivity stated. The errors ofthe verification apparatus shall not exceed one third of thepermissible error of the extensometer.4.2 The verification apparatus shall be calibrated at intervalsnot to exceed

27、 two years.NOTE 2He-Ne laser interferometer measurement systems based onthe 0.633 m wavelength line are considered to be primary-baseddisplacement standards and do not require recalibration.44.3 If the verification apparatus is to be used to verifyextensometers used for bidirectional tests, the erro

28、rs of theverification apparatus should be measured in both directions oftravel so as to include any backlash present.5. Verification Procedure for Extensometer Systems5.1 General RequirementsThe verification of an exten-someter system should not be done unless the components ofthe system are in good

29、 working condition. Thoroughly inspectall parts associated with smooth operation of the instrument toensure there are no excessively worn components. Repair orreplace parts as necessary. Remove any dirt particles whichmay have accumulated through normal use of the instrument.Verification of the syst

30、em shall be performed whenever partsare interchanged or replaced.5.1.1 The verification of an extensometer system refers to aspecific extensometer used with a specific readout device.Unless it can be demonstrated that autographic extensometersand recorders of a given type may be used interchangeably

31、without introducing errors that would affect the classificationof the extensometer, the extensometer shall be calibrated withthe readout device with which it is to be used.5.1.2 Prior to the initial verification, the extensometershould be calibrated according to the manufacturers instruc-tions or es

32、tablished procedures. The calibration procedure mayinclude adjustment of span or determination of calibrationfactor, or both.5.2 Gauge Length Measurement MethodMeasure thegauge length of self-setting instruments by either the direct orindirect method.NOTE 3The following is an example of an indirect

33、method. Set theextensometer to its starting position and mount it on a soft rod of thetypical specimen size or diameter. After the extensometer is removed,measure the distance between the marks left by the gauge points (or knifeedges). If there are four or more gauge points, take the average of thei

34、ndividual lengths as the gauge length. The differences between individualmeasurements shall not exceed the tolerance given for the class ofextensometer. If there are two gauge points (or knife edges), but onopposite sides of the specimen, attach the extensometer twice rotating it180 with respect to

35、the rod. Take the average of the lengths thusestablished on each side of the rod as the gauge length.5.2.1 Make two measurements of the gauge length. Deter-mine and record the error from each measurement, which is thedifference between the measured gauge length and the speci-fied gauge length, expre

36、ssed as a percent of the specified gaugelength.5.2.2 For extensometer devices that do not have a self-setting gauge length during use, such as deflectometers and3A review of some past, current, and possible future methods for calibratingstrain measuring devices is given in the paper by Watson, R. B.

37、, “CalibrationTechniques for Extensometry: Possible Standards of Strain Measurement,” Journalof Testing and Evaluation, JTEVA, Vol. 21, No. 6, November 1993, pp. 515521.4A letter from NIST (National Institute of Standards and Technology) has beenfiled at ASTM International Headquarters and may be ob

38、tained by requestingResearch Report RR: E28-1013.E83102some high-temperature tensile or creep extensometers, verifi-cation run errors should be calculated using the gauge lengthfor which the device is used. Separate classifications should beestablished for each gauge length or range used.5.2.3 Some

39、extensometers have the capability to measurethe gauge length set by or chosen by the user. If thismeasurement is used in the calculation of strain, then it is theinherent measurement accuracy that is the important factorrather than the error between the chosen length and the actual.NOTE 4An example

40、of an extensometer that is described by 5.2.3 isan optical extensometer that measures the position of “flags” attached tothe test specimen. The flags are positioned at the approximate requiredgauge length and the instrument measures the position of the flags (theactual gauge length) before and after

41、 the specimen is stressed. Althoughthis kind of device usually has a stated accuracy of gauge length, it mustbe verified by either direct or indirect methods at the appropriate gaugelengths.5.3 Position of ExtensometerCarefully position the exten-someter on or interface it to the verification device

42、 in the samemanner as it is normally used for typical specimens. Forextensometers that attach directly to the specimen, the verifi-cation device should allow attachment to pieces that are similarto the specimen on which the extensometer will be attached.5.4 Temperature ControlVerify the extensometer

43、 at ap-proximately the same temperature at which it will be used.Allow sufficient time for the verification device and extensom-eter to reach satisfactory temperature stability. Maintain tem-perature stability by excluding drafts throughout the subse-quent verification. Record the temperature during

44、 eachverification run.NOTE 5Extensometers used for high-temperature testing may beverified at ambient temperature to insure proper operation, but fixturesshould be designed to verify performance at the actual test temperature.This is especially true with optical extensometers which may be adverselya

45、ffected by air density changes associated with thermal gradients andturbulence, environmental chamber windows, or specimen changes due tothe environment. See Appendix X2.5.5 Method of ReadingRead the instrument or, in the caseof an autographic extensometer, measure the record in the samemanner as du

46、ring use.5.5.1 For extensometer with dial micrometers or digitalreadouts, the readings shall be recorded. Extensometers thatuse autographic methods shall have their charts read andrecorded using a suitable measuring device, such as a vernieror dial caliper. The use of an optical magnifying device is

47、recommended when reading and measuring autographicrecords.NOTE 6When autographic extensometer systems are used, careshould be taken to minimize errors introduced by variances in the graphpaper. These errors can be due to dimensional changes from reproductionor humidity changes. Direct measurement of

48、 the trace soon after it wasmade eliminates the graph paper errors and is desirable for systemsverification.NOTE 7If an extensometer is equipped with a dial micrometer, it maybe necessary to lightly tap the dial micrometer to minimize the effects offriction and to ensure that the most stable and rep

49、roducible readings areobtained. If the dial micrometer is tapped during the verification proce-dure, include this information in the report.5.6 Zero AdjustmentAfter temperature stability has beenachieved, displace the verification device (with extensometerin the test position) to a slightly negative value and return tozero. If the reading does not return to zero, adjust and repeatthe procedure until the reading does return to zero.5.7 Number of ReadingsFor any strain range, verify theextensometer system by applying at least five displacementvalu