ASTM E83-2006 Standard Practice for Verification and Classification of Extensometer Systems《伸长仪系统检验和分类标准实施规程》.pdf

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1、Designation: E 83 06Standard Practice forVerification and Classification of Extensometer Systems1This standard is issued under the fixed designation E 83; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A

2、 number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) 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

3、 andclassification 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

4、 are 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 gages directly bonded to a specimencannot be calibrated o

5、r verified with the apparatus described in thispractice for the verification of extensometers having definite gage points.(See procedures as described in Test Methods E 251.)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 Test-ingE21 Test Methods for Elevated Temperature

7、 Tension Testsof Metallic MaterialsE 251 Test Methods for Performance Characteristics ofMetallic Bonded Resistance Strain Gages3. 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 gage length and the change in the

9、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 aspec

10、ific gage 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.3.1.7.

11、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 syste

12、m, nan extensometer sys-tem which both defines gage length and senses extension, forexample, a clip-on strain gage type with conditioning electron-ics.3.1.9 Type 2 extensometer system, nan extensometerwhich senses extension and the gage length is defined byspecimen geometry or specimen features such

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

14、ter 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 Subcommittee

15、E28.01 on Calibration ofMechanical Testing Machines and Apparatus.Current edition approved May 1, 2006. Published June 2006. Originallyapproved in 1950. Last previous edition approved in 2002 as E 83 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Ser

16、vice 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 Type 3 extensometer system, nan exte

17、nsometersystem which intrinsically senses strain (ratiometric principle),for example, video camera system.3.1.11 gage length (L), nthe original length of that portionof the specimen over which strain or change of length isdetermined.3.1.11.1 DiscussionIf the device is used for sensingextension or mo

18、tion, and gage length is predetermined by thespecimen geometry or specific test method, then only resolu-tion and strain error for a specified gage length shoulddetermine the class of extensometer system.3.1.12 resolution of the strain indicatorthe smallestchange in strain that can be estimated or a

19、scertained 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 the strainindicator (may be a single di

20、git 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 3.1.11 or 3.1.12, the resolution expressed as astrain shall be equal to one-half the range of fluctuation.3.

21、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 to simulate thechange in length exper

22、ienced 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. Verification Apparatus4.1 The apparatus for ve

23、rifying 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 extensometerbeing verified, a mechanism for

24、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 relativeto the other shall permit sensitiv

25、e adjustments. The changes inlength shall be measured, for example, by means of aninterferometer, calibrated standard gage blocks and an indica-tor, a calibrated micrometer screw, or a calibrated lasermeasurement system. If standard gage blocks and an indicator,or a micrometer screw, are used, they

26、shall be calibrated andtheir limits of accuracy and sensitivity stated. The errors of theverification apparatus shall not exceed one third of the permis-sible error of the extensometer.4.2 The verification apparatus shall be calibrated at intervalsnot to exceed two years.NOTE 2He-Ne laser interferom

27、eter 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 errors of theverification apparatus should

28、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 working condition. Thoroughly inspecta

29、ll 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 system shall be performed whenever partsare

30、 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 interchangeablywithout introducing errors that would a

31、ffect 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 established procedures. The calibration p

32、rocedure mayinclude adjustment of span or determination of calibrationfactor, or both.5.2 Gage Length Measurement Method Measure the gagelength of self-setting instruments by either the direct or indirectmethod.NOTE 3The following is an example of an indirect method. Set theextensometer to its start

33、ing 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 gage points (or knifeedges). If there are four or more gage points, take the average of theindividual lengths as the gage length. The

34、differences between individualmeasurements shall not exceed the tolerance given for the class ofextensometer. If there are two gage points (or knife edges), but on oppositesides of the specimen, attach the extensometer twice rotating it 180 withrespect to the rod. Take the average of the lengths thu

35、s established on eachside of the rod as the gage length.5.2.1 Make two measurements of the gage length. Deter-mine and record the error from each measurement, which is thedifference between the measured gage length and the specifiedgage length, expressed as a percent of the specified gagelength.3A r

36、eview of some past, current, and possible future methods for calibratingstrain measuring devices is given in the paper by Watson, R. B., “CalibrationTechniques for Extensometry: Possible Standards of Strain Measurement,” Journalof Testing and Evaluation, JTEVA, Vol. 21, No. 6, November 1993, pp. 515

37、521.4A letter from NIST (National Institute of Standards and Technology) has beenfiled at ASTM International Headquarters and may be obtained by requestingResearch Report RR: E 28-1013.E830625.2.2 For extensometer devices that do not have a self-setting gage length during use, such as deflectometers

38、 andsome high-temperature tensile or creep extensometers, verifi-cation run errors should be calculated using the gage length forwhich the device is used. Separate classifications should beestablished for each gage length or range used.5.2.3 Some extensometers have the capability to measurethe gage

39、length set by or chosen by the user. If this measure-ment is used in the calculation of strain, then it is the inherentmeasurement accuracy that is the important factor rather thanthe error between the chosen length and the actual.NOTE 4An example of an extensometer that is described by 5.2.3 isan o

40、ptical extensometer that measures the position of “flags” attached tothe test specimen. The flags are positioned at the approximate requiredgage length and the instrument measures the position of the flags (theactual gage length) before and after the specimen is stressed.Although thiskind of device

41、usually has a stated accuracy of gage length, it must beverified by either direct or indirect methods at the appropriate gagelengths.5.3 Position of ExtensometerCarefully position the exten-someter on or interface it to the verification device in the samemanner as it is normally used for typical spe

42、cimens. 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 at ap-proximately the same temperature at which it will

43、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 eachverification run.NOTE 5Extensometers used for high-t

44、emperature 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 adverselyaffected by air density changes associated with thermal gr

45、adients 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 during use.5.5.1 For extensometer with dial micrometers or

46、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 isrecommended when reading and measuring autographicrecords

47、.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 the trace soon after it wasmade eliminates the graph pap

48、er 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 reproducible readings areobtained. If the dial micrometer is

49、 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 displacementvalues, not including zero, at least two times, with thediffer