1、Designation: E 1319 98 (Reapproved 2003)Standard Guide forHigh-Temperature Static Strain Measurement1This standard is issued under the fixed designation E 1319; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the selection and application of straingages for the measurement of static strain up to and includingthe temp
3、erature range from 425 to 650C (800 to 1200F). Thisguide reflects some current state-of-the-art techniques in hightemperature strain measurement, and will be expanded andupdated as new technology develops.1.2 This practice assumes that the user is familiar with theuse of bonded strain gages and asso
4、ciated signal conditioningand instrumentation as discussed in Refs. (1) and (2).2Thestrain measuring systems described are those that have proveneffective in the temperature range of interest and were availableat the time of issue of this practice. It is not the intent of thispractice to limit the u
5、ser to one of the gage types described noris it the intent to specify the type of system to be used for aspecific application. However, in using any strain measuringsystem including those described, the proposer must be able todemonstrate the capability of the proposed system to meet theselection cr
6、iteria provided in Section 5 and the needs of thespecific application.1.3 The devices and techniques described in this practicemay be applicable at temperatures above and below the rangenoted, and for making dynamic strain measurements at hightemperatures with proper precautions. The gage manufactur
7、ershould be consulted for recommendations and details of suchapplications.1.4 The references are a part of this practice to the extentspecified in the text.1.5 The values stated in metric (SI) units are to be regardedas the standard. The values given in parentheses are forinformation purposes only.1
8、.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. 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 Do
9、cuments2.1 ASTM Standards:E6 Terminology Relating to Methods of Mechanical Test-ing33. Terminology3.1 Definitions:3.1.1 Refer to Terminology E6 for definitions of termsrelating to stress and strain.3.2 Definitions of Terms Specific to This Standard:3.2.1 Terms pertinent to this guide are described a
10、s follows:3.2.2 capacitive strain gagea strain gage whose responseto strain is a change in electrical capacitance which is predict-ably related to that strain.3.2.3 conditioning circuita circuit or instrument sub-system that applies excitation to a strain gage, detects anelectrical change in the str
11、ain gage, and provides a means forconverting this change to an output that is related to strain inthe test article. The conditioning circuit may include one ormore of the following: bridge completion circuit, signal am-plification, zero adjustment, excitation adjustment, calibration,and gain (span)
12、adjustment.3.2.4 compensating gagea gage element that is subject tothe same environment as the active gage element, and which isplaced in the adjacent leg of a Wheatstone bridge to providethermal, pressure, or other compensation in the strain gagesystem.3.2.5 electrical simulationa method of calibra
13、tionwhereby a known voltage is generated at the input of anamplifier, equivalent to the voltage produced by a specificamount of strain.3.2.6 free filament gagea resistive strain gage made froma continuous wire or foil filament which is fixed to the testarticle along the entire length of the gage, an
14、d which issupplied without a permanent matrix.3.2.7 gage factorthe ratio between the unit change ofstrain gage resistance due to strain and the measurement. Thegage factor is dimensionless and is expressed as follows:K 5R 2 RoRo/L 2 LoLo5DRRo/e (1)1This practice is under the jurisdiction ofASTM Comm
15、ittee E28 on MechanicalTesting and is the direct responsibility of Subcommittee E28.01 on Calibration ofMechanical Testing Machines and Apparatus.Current edition approved June 10, 2003. Published January 2004. Originallyapproved in 1989. Last previous edition approved in 1998 as E 1319 - 98.2The bol
16、dface numbers in parentheses refer to the list of references at the end ofthis practice.3Annual Book of ASTM Standards, Vol 03.01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.where:K = gage factor,R = strain gage resistance at tes
17、t strain,Ro= strain gage resistance at zero or reference strain,L = test structure length under the strain gage at teststrain,Lo= test structure length under the strain gage at zero orreference strain,DR = change in strain gage resistance when strain ischanged from zero (or reference strain) to test
18、 strain,ande =mechanical strainL 2 LoLo3.2.8 integral lead wirea lead wire or portion of a leadwire that is furnished by a gage manufacturer as part of thegage assembly.3.2.9 linearitythe value measured as the maximum devia-tion between an actual instrument reading and the readingpredicted by a stra
19、ight line drawn between upper and lowercalibration points, usually expressed as a percent of the fullscale of the sensor range.3.2.10 lead wirea conductor used to connect a sensor toits instrumentation.3.2.11 matrixan electrically nonconductive layer of ma-terial used to support a strain gage grid.
20、The two mainfunctions of a matrix are to act as an aid for bonding the straingage to a structure and as an electrically insulating layer incases where the structure is electrically conductive.3.2.12 resistive strain gagea strain gage whose responseto strain is a change in electrical resistance that
21、is predictablyrelated to that strain.3.2.13 shunt calibrationa method of calibration wherebya resistor or capacitor of known value is placed electrically inparallel with another resistor or capacitor in a circuit, causinga calculable change in the total resistance or capacitance that ispredictably r
22、elated to a specific amount of strain.3.2.14 strain, linearthe unit elongation induced in aspecimen either by a stress field (mechanical strain) or by atemperature change (thermal expansion).3.2.15 strain gage systemthe sum total of all componentsused to obtain a strain measurement. May include a st
23、rain gage;a means of attaching the strain gage to the test articles; leadwires; splices; lead-wire attachments; signal-conditioning andread-out instrumentation; data-logging system; calibration andcontrol system; environmental protection; or any combinationof these and other elements required for th
24、e tests.3.2.16 static straina strain that is measured relative to aconstant reference value, as opposed to dynamic strain, whichis the peak-to-peak value of a cyclic phenomenon, withoutreference to a constant zero or reference value (Fig. 1).3.2.17 test articlean item to which a strain gage system i
25、sinstalled for the purpose of measuring strain in that item.3.2.18 thermal compensationthe process by which thethermal output of a gage system is counteracted through the useof one or more supplementary devices, such as a thermocoupleor compensating gage. The counteraction may be integral tothe gage
26、 system or may be accomplished by data processingmethods, or both.3.2.19 thermal outputthe reversible part of the tempera-ture induced indicated strain of a strain gage installed on anunrestrained test specimen when exposed to a change intemperature.3.2.20 thermal output-unmountedthe reversible part
27、 ofthe temperature induced indicated strain of an unmountedstrain gage when exposed to a change in temperature.4. Significance and Use4.1 The use of this guide is voluntary and is intended for useas a procedures guide for selection and application of specifictypes of strain gages for high-temperatur
28、e installations. Noattempt is made to restrict the type of strain gage types orconcepts to be chosen by the user. The provisions of this guidemay be invoked in specifications and procedures by specifyingthose which shall be considered mandatory for the purpose ofthe specific application. When so inv
29、oked, the user shallinclude in the work statement a notation that provisions of thisguide shown as recommendation shall be considered manda-tory for the purposes of the specification or procedure con-cerned, and shall include a statement of any exceptions to ormodifications of the affected provision
30、s of this guide.5. Gage Selection Criteria5.1 The factors listed in this section must be consideredwhen selecting a strain gage system for use in the temperaturerange specified in 1.1. It is recognized that no gage may haveall of the desired capabilities to meet all requirements of aparticular test.
31、 The risk of compromising certain test objectivesmust be evaluated, and some test objectives may have to bemodified to match the capabilities of the available gageselected. Guidelines for this evaluation are provided in Section9.5.2 Operating Temperature:5.2.1 Isothermal TestsStability of the refere
32、nce value withrespect to time is essential when tests are to be made atconstant temperature. The stability of the candidate gagesystem at the specified temperature must be such that any shiftthat occurs in the reference value is tolerable for the durationof the test.FIG. 1 Relationship Between Stati
33、c and Dynamic StrainE 1319 98 (2003)25.2.2 Thermal Compensation and TransientsThe ad-equacy of the thermal compensation must be considered whenthe measurement of strain during a thermal transient is re-quired. Thermal output is a function of temperature, thus itsvalue at a temperature depends not on
34、ly on temperature, but onthe temperature history followed in reaching that temperature.If significant hysteresis in the thermal response is present, largeerrors or uncertainties can result. This is especially true whenthe calibration procedure used to characterize the thermaloutput does not accurate
35、ly reflect the temperature sequence towhich the gages will be exposed during testing. If the responsetime of the compensation is exceeded, the resulting uncertaintymust be considered.The ability of the gage system to withstandthe transient without a detrimental shift of the reference valuemust be ve
36、rified. This is true whether or not strain is measuredduring the transient. Any gage factor change as a function oftemperature change must also be considered.5.2.3 Precalibration:5.2.3.1 Thermal output calibration on the structure is usu-ally not possible and precalibration of gages on a similarmate
37、rial is necessary. However, variations of up to 0.5 ppm/Fare possible within a material. Often, rolling direction willinfluence thermal expansion coefficient.5.2.3.2 Precalibration of resistive or capacitive strain gagesis performed using a calibration fixture made from materialsimilar to the test a
38、rticle. The calibration fixture must be madeto precisely fit the gage, especially if curvature is involved.Experience has shown mating parts must be lapped together toprovide uniform clamping pressure around the periphery of thegage weld area.5.2.3.3 The calibration test should be repeated to ensure
39、precise duplication of the calibration. Zero return should alsorepeat exactly. If calibration data does not repeat; either thecalibration set-up or the gages are faulty.5.2.4 Post Test Calibration:5.2.4.1 A more precise thermal output calibration can beachieved after the test by removing the test ga
40、ge (cut it out ofthe structure) and running a precision test on the test gage stillattached to the test article material. The test coupon is relievedof all induced stresses (thermal, mecahniacl, residual) and isfree to expand freely with temperature. The integral gage leadwire should be exposed to t
41、hermal gradients similar to thosethat occurred during the test program.5.3 Duration of TestThe ability of all parts of the gagesystem to function for the specified duration of test should bedemonstrated; if multiple tests are required on the same testarticle, the capability and effect of gage replac
42、ement must alsobe established.5.4 Strain RateThe time response of the candidate gagesystem must be adequate to meet test requirements if rapidchanges of load are anticipated. It may be necessary to designthe loading rate of the test to accommodate limitations of thestrain measurement system selected
43、.5.5 EnvironmentSome gages are limited to specific oper-ating environments and therefore, the gage system selectedmust be capable of withstanding the environment in which itwill operate. Such limitations must be carefully consideredwhen selecting the gage system to be used. Factors such aspressure,
44、vibration, radiation, magnetic fields, humidity, etc.,must be considered. The ambient and test environments of theelements of the strain gage system must be considered in theselection of lead wires, connectors, instrumentation, and seals(when required).5.6 Strain Range:5.6.1 Total Strain RangeThe ma
45、ximum strain ranges ofthe candidate gage types must be defined and must be adequatefor the test. Mechanical strain attenuators, when permissible,may be added to extend the strain range of a given strain gagesystem, subject to the limitation of 5.6.2.5.6.2 ResolutionThe ability of the candidate gage
46、tomeasure small increments of strain within the total strain rangeshould be compared with the incremental strain measurementrequirements of the test. When mechanical strain attenuatorsare used, the resulting loss of resolution must be considered.5.7 Strain GradientThe gage length of the candidate ga
47、geestablishes the length over which the unit strain is averaged.This factor must be considered.5.8 Uncertainty FactorUncertainty information that isavailable from the manufacturer must be considered, in con-junction with conditions which are unique to the test, in orderto estimate the total uncertai
48、nty.5.9 Space RequirementsIf space on or adjacent to the testarticle is limited, the space requirements for the complete straingage system may be a critical consideration in determining thesuitability of a particular gage system. Working space forinstallation of the system may also be limited and mu
49、st also beconsidered. Space adjacent to the installed strain gage shouldbe provided for installation of room-temperature strain gagesrequired for making in-place calibrations.5.10 Effects of the Strain Gage on the Test ArticleIn mostcases the reinforcing effect of the strain gage on the test articleis negligible, particularly in the case of capacitance gageswhere the spring rate is extremely low. If a weldable gage is tobe used on thin sections, an evaluation of the reinforcing effectshould be made. Technical data concerning this effect can beobtained fro
