ASTM E1319-98(2009)

Standard Guide for High-Temperature Static Strain Measurement

SIGNIFICANCE AND USE
The use of this guide is voluntary and is intended for use as a procedures guide for selection and application of specific types of strain gages for high-temperature installations. No attempt is made to restrict the type of strain gage types or concepts to be chosen by the user. The provisions of this guide may be invoked in specifications and procedures by specifying those which shall be considered mandatory for the purpose of the specific application. When so invoked, the user shall include in the work statement a notation that provisions of this guide shown as recommendation shall be considered mandatory for the purposes of the specification or procedure concerned, and shall include a statement of any exceptions to or modifications of the affected provisions of this guide.
SCOPE
1.1 This guide covers the selection and application of strain gages for the measurement of static strain up to and including the temperature range from 425 to 650°C (800 to 1200°F). This guide reflects some current state-of-the-art techniques in high temperature strain measurement, and will be expanded and updated as new technology develops.
1.2 This practice assumes that the user is familiar with the use of bonded strain gages and associated signal conditioning and instrumentation as discussed in Refs. (1) and (2). The strain measuring systems described are those that have proven effective in the temperature range of interest and were available at the time of issue of this practice. It is not the intent of this practice to limit the user to one of the gage types described nor is it the intent to specify the type of system to be used for a specific application. However, in using any strain measuring system including those described, the proposer must be able to demonstrate the capability of the proposed system to meet the selection criteria provided in Section 5 and the needs of the specific application.
1.3 The devices and techniques described in this practice may be applicable at temperatures above and below the range noted, and for making dynamic strain measurements at high temperatures with proper precautions. The gage manufacturer should be consulted for recommendations and details of such applications.
1.4 The references are a part of this practice to the extent specified in the text.
1.5 The values stated in metric (SI) units are to be regarded as the standard. The values given in parentheses are for information purposes only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Mar-2009
• ICS: 19.060 - Mechanical testing
• Technical Committee: E28 - Mechanical Testing
• Drafting Committee: E28.01 - Calibration of Mechanical Testing Machines and Apparatus

Relations

• Replaces: ASTM E1319-98(2003) - Standard Guide for High-Temperature Static Strain Measurement
• Effective Date: 01-Apr-2009

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E1319 − 98(Reapproved 2009)
Standard Guide for
High-Temperature Static Strain Measurement
This standard is issued under the fixed designation E1319; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This guide covers the selection and application of strain
gages for the measurement of static strain up to and including
2. Referenced Documents
thetemperaturerangefrom425to650°C(800to1200°F).This
guide reflects some current state-of-the-art techniques in high 2.1 ASTM Standards:
temperature strain measurement, and will be expanded and E6Terminology Relating to Methods of MechanicalTesting
updated as new technology develops.
3. Terminology
1.2 This practice assumes that the user is familiar with the
use of bonded strain gages and associated signal conditioning 3.1 Definitions:
and instrumentation as discussed in Refs. (1) and (2). The 3.1.1 Refer to Terminology E6 for definitions of terms
strain measuring systems described are those that have proven relating to stress and strain.
effectiveinthetemperaturerangeofinterestandwereavailable 3.2 Definitions of Terms Specific to This Standard:
3.2.1 Termspertinenttothisguidearedescribedasfollows:
at the time of issue of this practice. It is not the intent of this
practicetolimittheusertooneofthegagetypesdescribednor 3.2.2 capacitive strain gage—a strain gage whose response
to strain is a change in electrical capacitance which is predict-
is it the intent to specify the type of system to be used for a
specific application. However, in using any strain measuring ably related to that strain.
system including those described, the proposer must be able to
3.2.3 conditioning circuit—a circuit or instrument subsys-
demonstrate the capability of the proposed system to meet the
temthatappliesexcitationtoastraingage,detectsanelectrical
selection criteria provided in Section 5 and the needs of the
change in the strain gage, and provides a means for converting
specific application.
this change to an output that is related to strain in the test
article.Theconditioningcircuitmayincludeoneormoreofthe
1.3 The devices and techniques described in this practice
following:bridgecompletioncircuit,signalamplification,zero
may be applicable at temperatures above and below the range
adjustment, excitation adjustment, calibration, and gain (span)
noted, and for making dynamic strain measurements at high
adjustment.
temperatures with proper precautions. The gage manufacturer
should be consulted for recommendations and details of such
3.2.4 compensating gage—a gage element that is subject to
applications.
thesameenvironmentastheactivegageelement,andwhichis
placed in the adjacent leg of a Wheatstone bridge to provide
1.4 The references are a part of this practice to the extent
thermal, pressure, or other compensation in the strain gage
specified in the text.
system.
1.5 The values stated in metric (SI) units are to be regarded
3.2.5 electrical simulation—a method of calibration
as the standard. The values given in parentheses are for
whereby a known voltage is generated at the input of an
information purposes only.
amplifier, equivalent to the voltage produced by a specific
1.6 This standard does not purport to address all of the
amount of strain.
safety concerns, if any, associated with its use. It is the
3.2.6 free filament gage—a resistive strain gage made from
responsibility of the user of this standard to establish appro-
a continuous wire or foil filament which is fixed to the test
article along the entire length of the gage, and which is
supplied without a permanent matrix.
ThispracticeisunderthejurisdictionofASTMCommitteeE28onMechanical
Testing and is the direct responsibility of Subcommittee E28.01 on Calibration of
Mechanical Testing Machines and Apparatus.
Current edition approved April 1, 2009. Published September 2009. Originally
approved in 1989. Last previous edition approved in 2003 as E1319-98 (2003). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/E1319-98R09. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
this practice. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1319 − 98 (2009)
3.2.7 gage factor—the ratio between the unit change of
strain gage resistance due to strain and the measurement. The
gage factor is dimensionless and is expressed as follows:
R 2 R L 2 L ∆R
o o
K 5 / 5 /ε (1)
R L R
o o o
where:
K = gage factor,
R = strain gage resistance at test strain,
R = strain gage resistance at zero or reference strain,
o
L = test structure length under the strain gage at test
strain,
L = test structure length under the strain gage at zero or
o
reference strain,
∆R = change in strain gage resistance when strain is
changedfromzero(orreferencestrain)toteststrain,
and
FIG. 1 Relationship Between Static and Dynamic Strain
ε =
L 2 L
o
mechanicalstrain
L
o
3.2.8 integral lead wire—a lead wire or portion of a lead
3.2.17 test article—an item to which a strain gage system is
wire that is furnished by a gage manufacturer as part of the
installed for the purpose of measuring strain in that item.
gage assembly.
3.2.18 thermal compensation—the process by which the
3.2.9 linearity—the value measured as the maximum devia-
thermaloutputofagagesystemiscounteractedthroughtheuse
tion between an actual instrument reading and the reading
ofoneormoresupplementarydevices,suchasathermocouple
predicted by a straight line drawn between upper and lower
or compensating gage. The counteraction may be integral to
calibration points, usually expressed as a percent of the full
the gage system or may be accomplished by data processing
scale of the sensor range.
methods, or both.
3.2.10 leadwire—aconductorusedtoconnectasensortoits
3.2.19 thermal output—the reversible part of the tempera-
instrumentation.
ture induced indicated strain of a strain gage installed on an
unrestrained test specimen when exposed to a change in
3.2.11 matrix—an electrically nonconductive layer of mate-
temperature.
rial used to support a strain gage grid.The two main functions
of a matrix are to act as an aid for bonding the strain gage to
3.2.20 thermaloutput-unmounted—thereversiblepartofthe
astructureandasanelectricallyinsulatinglayerincaseswhere
temperature induced indicated strain of an unmounted strain
the structure is electrically conductive.
gage when exposed to a change in temperature.
3.2.12 resistive strain gage—a strain gage whose response
4. Significance and Use
to strain is a change in electrical resistance that is predictably
related to that strain.
4.1 Theuseofthisguideisvoluntaryandisintendedforuse
as a procedures guide for selection and application of specific
3.2.13 shunt calibration—a method of calibration whereby
types of strain gages for high-temperature installations. No
a resistor or capacitor of known value is placed electrically in
attempt is made to restrict the type of strain gage types or
parallel with another resistor or capacitor in a circuit, causing
concepts to be chosen by the user.The provisions of this guide
acalculablechangeinthetotalresistanceorcapacitancethatis
maybeinvokedinspecificationsandproceduresbyspecifying
predictably related to a specific amount of strain.
those which shall be considered mandatory for the purpose of
3.2.14 strain,linear—theunitelongationinducedinaspeci-
the specific application. When so invoked, the user shall
men either by a stress field (mechanical strain) or by a
include in the work statement a notation that provisions of this
temperature change (thermal expansion).
guide shown as recommendation shall be considered manda-
3.2.15 strain gage system—the sum total of all components tory for the purposes of the specification or procedure
usedtoobtainastrainmeasurement.Mayincludeastraingage;
concerned, and shall include a statement of any exceptions to
a means of attaching the strain gage to the test articles; lead or modifications of the affected provisions of this guide.
wires; splices; lead-wire attachments; signal-conditioning and
5. Gage Selection Criteria
read-out instrumentation; data-logging system; calibration and
control system; environmental protection; or any combination
5.1 The factors listed in this section must be considered
of these and other elements required for the tests.
when selecting a strain gage system for use in the temperature
3.2.16 static strain—a strain that is measured relative to a range specified in 1.1. It is recognized that no gage may have
constant reference value, as opposed to dynamic strain, which all of the desired capabilities to meet all requirements of a
is the peak-to-peak value of a cyclic phenomenon, without particulartest.Theriskofcompromisingcertaintestobjectives
reference to a constant zero or reference value (Fig. 1). must be evaluated, and some test objectives may have to be
E1319 − 98 (2009)
modified to match the capabilities of the available gage 5.4 Strain Rate—The time response of the candidate gage
selected.GuidelinesforthisevaluationareprovidedinSection system must be adequate to meet test requirements if rapid
9. changes of load are anticipated. It may be necessary to design
the loading rate of the test to accommodate limitations of the
5.2 Operating Temperature:
strain measurement system selected.
5.2.1 Isothermal Tests—Stabilityofthereferencevaluewith
respect to time is essential when tests are to be made at 5.5 Environment—Some gages are limited to specific oper-
constant temperature. The stability of the candidate gage
ating environments and therefore, the gage system selected
system at the specified temperature must be such that any shift must be capable of withstanding the environment in which it
that occurs in the reference value is tolerable for the duration
will operate. Such limitations must be carefully considered
of the test. when selecting the gage system to be used. Factors such as
5.2.2 Thermal Compensation and Transients—The ad- pressure, vibration, radiation, magnetic fields, humidity, etc.,
equacy of the thermal compensation must be considered when must be considered. The ambient and test environments of the
the measurement of strain during a thermal transient is re- elements of the strain gage system must be considered in the
quired. Thermal output is a function of temperature, thus its selection of lead wires, connectors, instrumentation, and seals
valueatatemperaturedependsnotonlyontemperature,buton (when required).
the temperature history followed in reaching that temperature.
5.6 Strain Range:
Ifsignificanthysteresisinthethermalresponseispresent,large
5.6.1 Total Strain Range—The maximum strain ranges of
errors or uncertainties can result. This is especially true when
thecandidategagetypesmustbedefinedandmustbeadequate
the calibration procedure used to characterize the thermal
for the test. Mechanical strain attenuators, when permissible,
output does not accurately reflect the temperature sequence to
may be added to extend the strain range of a given strain gage
whichthegageswillbeexposedduringtesting.Iftheresponse
system, subject to the limitation of 5.6.2.
timeofthecompensationisexceeded,theresultinguncertainty
5.6.2 Resolution—The ability of the candidate gage to
mustbeconsidered.Theabilityofthegagesystemtowithstand
measuresmallincrementsofstrainwithinthetotalstrainrange
the transient without a detrimental shift of the reference value
should be compared with the incremental strain measurement
must be verified.This is true whether or not strain is measured
requirements of the test. When mechanical strain attenuators
during the transient. Any gage factor change as a function of
are used, the resulting loss of resolution must be considered.
temperature change must also be considered.
5.7 Strain Gradient—Thegagelengthofthecandidategage
5.2.3 Precalibration:
establishes the length over which the unit strain is averaged.
5.2.3.1 Thermal output calibration on the structure is usu-
This factor must be considered.
ally not possible and precalibration of gages on a similar
material is necessary. However, variations of up to 0.5 ppm/°F
5.8 Uncertainty Factor—Uncertainty information that is
are possible within a material. Often, rolling direction will
available from the manufacturer must be considered, in con-
influence thermal expansion coefficient.
junction with conditions which are unique to the test, in order
5.2.3.2 Precalibration of resistive or capacitive strain gages
to estimate the total uncertainty.
is performed using a calibration fixture made from material
5.9 Space Requirements—If space on or adjacent to the test
similar to the test article.The calibration fixture must be made
articleislimited,thespacerequirementsforthecompletestrain
to precisely fit the gage, especially if curvature is involved.
gage system may be a critical consideration in determining the
Experience has shown mating parts must be lapped together to
suitability of a particular gage system. Working space for
provideuniformclampingpressurearoundtheperipheryofthe
installationofthesystemmayalsobelimitedandmustalsobe
gage weld area.
considered. Space adjacent to the installed strain gage should
5.2.3.3 The calibration test should be repeated to ensure
be provided for installation of room-temperature strain gages
precise duplication of the calibration. Zero return should also
required for making in-place calibrations.
repeat exactly. If calibration data does not repeat; either the
5.10 Effects of the Strain Gage on the Test Article—In most
calibration set-up or the gages are faulty.
cases the reinforcing effect of the strain gage on the test article
5.2.4 Post Test Calibration:
is negligible, particularly in the case of capacitance gages
5.2.4.1 A more precise thermal output calibration can be
wherethespringrateisextremelylow.Ifaweldablegageisto
achieved after the test by removing the test gage (cut it out of
beusedonthinsections,anevaluationofthereinforcingeffect
the structure) and running a precision test on the test gage still
should be made. Technical data concerning this effect can be
attached to the test article material.The test coupon is relieved
obtained from a strain gage manufacturer.
of all indu
...