ASTM E1319-98

Standard Guide for High-Temperature Static Strain Measurement

SCOPE
1.1 This practice covers the selection and application of strain gages and associated instrumentation for the measurement of static strain up to and including the temperature range from 425 to 650°C (800 to 1200°F). This practice 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 and Appendixes X1 through X5.
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: 09-May-1998
• ICS: 19.060 - Mechanical testing
• Technical Committee: E28 - Mechanical Testing

Relations

• Replaced By: ASTM E1319-98(2003) - Standard Guide for High-Temperature Static Strain Measurement
• Effective Date: 10-May-1998

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 1319 – 98
Standard Guide for
High-Temperature Static Strain Measurement
This standard is issued under the fixed designation E 1319; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This guide covers the selection and application of strain 2.1 ASTM Standards:
gages for the measurement of static strain up to and including E 6 Terminology Relating to Methods of Mechanical Test-
the temperature range from 425 to 650°C (800 to 1200°F). This ing
guide reflects some current state-of-the-art techniques in high
3. Terminology
temperature strain measurement, and will be expanded and
updated as new technology develops. 3.1 Definitions:
3.1.1 Refer to Terminology E 6 for definitions of terms
1.2 This practice assumes that the user is familiar with the
use of bonded strain gages and associated signal conditioning relating to stress and strain.
3.2 Definitions of Terms Specific to This Standard:
and instrumentation as discussed in Refs. (1) and (2). The
strain measuring systems described are those that have proven 3.2.1 Terms pertinent to this guide are described as follows:
3.2.2 capacitive strain gage—a strain gage whose response
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 to strain is a change in electrical capacitance which is predict-
ably related to that strain.
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 3.2.3 conditioning circuit—a circuit or instrument sub-
system that applies excitation to a strain gage, detects an
specific application. However, in using any strain measuring
system including those described, the proposer must be able to electrical change in the strain gage, and provides a means for
converting this change to an output that is related to strain in
demonstrate the capability of the proposed system to meet the
selection criteria provided in Section 5 and the needs of the the test article. The conditioning circuit may include one or
more of the following: bridge completion circuit, signal am-
specific application.
1.3 The devices and techniques described in this practice plification, zero adjustment, excitation adjustment, calibration,
and gain (span) adjustment.
may be applicable at temperatures above and below the range
noted, and for making dynamic strain measurements at high 3.2.4 compensating gage—a gage element that is subject to
the same environment as the active gage element, and which is
temperatures with proper precautions. The gage manufacturer
should be consulted for recommendations and details of such placed in the adjacent leg of a Wheatstone bridge to provide
thermal, pressure, or other compensation in the strain gage
applications.
system.
1.4 The references are a part of this practice to the extent
specified in the text. 3.2.5 electrical simulation—a method of calibration
whereby a known voltage is generated at the input of an
1.5 The values stated in metric (SI) units are to be regarded
as the standard. The values given in parentheses are for amplifier, equivalent to the voltage produced by a specific
amount of strain.
information purposes only.
1.6 This standard does not purport to address all of the 3.2.6 free filament gage—a resistive strain gage made from
a continuous wire or foil filament which is fixed to the test
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- article along the entire length of the gage, and which is
supplied without a permanent matrix.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. 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:
This practice is under the jurisdiction of ASTM Committee E-28 on Mechanical
Testing and is the direct responsibility of Subcommittee E28.14 on Strain Gages.
Current edition approved May 10, 1998. Published March 1999. Originally
e1
published as E 1319 - 89. Last previous edition E 1319 - 89 (1996) .
The boldface numbers in parentheses refer to the list of references at the end of
this practice. Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1319
R 2 R L 2 L DR
o o
K 5 / 5 /e (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,
DR = change in strain gage resistance when strain is
changed from zero (or reference strain) to test strain,
and
e = L 2 L
o
mechanical strain
L
o
FIG. 1 Relationship Between Static and Dynamic Strain
3.2.8 integral lead wire—a lead wire or portion of a lead
wire that is furnished by a gage manufacturer as part of the
gage assembly.
or compensating gage. The counteraction may be integral to
3.2.9 linearity—the value measured as the maximum devia-
the gage system or may be accomplished by data processing
tion between an actual instrument reading and the reading
methods, or both.
predicted by a straight line drawn between upper and lower
3.2.19 thermal output—the reversible part of the tempera-
calibration points, usually expressed as a percent of the full
ture induced indicated strain of a strain gage installed on an
scale of the sensor range.
unrestrained test specimen when exposed to a change in
3.2.10 lead wire—a conductor used to connect a sensor to
temperature.
its instrumentation.
3.2.20 thermal output-unmounted—the reversible part of
3.2.11 matrix—an electrically nonconductive layer of ma-
the temperature induced indicated strain of an unmounted
terial used to support a strain gage grid. The two main
strain gage when exposed to a change in temperature.
functions of a matrix are to act as an aid for bonding the strain
gage to a structure and as an electrically insulating layer in
4. Significance and Use
cases where the structure is electrically conductive.
4.1 The use of this guide is voluntary and is intended for use
3.2.12 resistive strain gage—a strain gage whose response
as a procedures guide for selection and application of specific
to strain is a change in electrical resistance that is predictably
types of strain gages for high-temperature installations. No
related to that strain.
attempt is made to restrict the type of strain gage types or
3.2.13 shunt calibration—a method of calibration whereby
concepts to be chosen by the user. The provisions of this guide
a resistor or capacitor of known value is placed electrically in
may be invoked in specifications and procedures by specifying
parallel with another resistor or capacitor in a circuit, causing
those which shall be considered mandatory for the purpose of
a calculable change in the total resistance or capacitance that is
the specific application. When so invoked, the user shall
predictably related to a specific amount of strain.
include in the work statement a notation that provisions of this
3.2.14 strain, linear—the unit elongation induced in a
guide shown as recommendation shall be considered manda-
specimen either by a stress field (mechanical strain) or by a
tory for the purposes of the specification or procedure con-
temperature change (thermal expansion).
cerned, and shall include a statement of any exceptions to or
3.2.15 strain gage system—the sum total of all components
modifications of the affected provisions of this guide.
used to obtain a strain measurement. May include a strain gage;
a means of attaching the strain gage to the test articles; lead 5. Gage Selection Criteria
wires; splices; lead-wire attachments; signal-conditioning and
5.1 The factors listed in this section must be considered
read-out instrumentation; data-logging system; calibration and
when selecting a strain gage system for use in the temperature
control system; environmental protection; or any combination
range specified in 1.1. It is recognized that no gage may have
of these and other elements required for the tests.
all of the desired capabilities to meet all requirements of a
3.2.16 static strain—a strain that is measured relative to a
particular test. The risk of compromising certain test objectives
constant reference value, as opposed to dynamic strain, which
must be evaluated, and some test objectives may have to be
is the peak-to-peak value of a cyclic phenomenon, without
modified to match the capabilities of the available gage
reference to a constant zero or reference value (Fig. 1).
selected. Guidelines for this evaluation are provided in Section
3.2.17 test article—an item to which a strain gage system is
9.
installed for the purpose of measuring strain in that item. 5.2 Operating Temperature:
3.2.18 thermal compensation—the process by which the 5.2.1 Isothermal Tests—Stability of the reference value with
thermal output of a gage system is counteracted through the use respect to time is essential when tests are to be made at
of one or more supplementary devices, such as a thermocouple constant temperature. The stability of the candidate gage
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1319
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
pressure, vibration, radiation, magnetic fields, humidity, etc.,
5.2.2 Thermal Compensation and Transients—The ad-
must be considered. The ambient and test environments of the
equacy of the thermal compensation must be considered when
elements of the strain gage system must be considered in the
the measurement of strain during a thermal transient is re-
selection of lead wires, connectors, instrumentation, and seals
quired. Thermal output is a function of temperature, thus its
(when required).
value at a temperature depends not only on temperature, but on
5.6 Strain Range:
the temperature history followed in reaching that temperature.
5.6.1 Total Strain Range—The maximum strain ranges of
If significant hysteresis in the thermal response is present, large
the candidate gage types must be defined and must be adequate
errors or uncertainties can result. This is especially true when
for the test. Mechanical strain attenuators, when permissible,
the calibration procedure used to characterize the thermal
may be added to extend the strain range of a given strain gage
output does not accurately reflect the temperature sequence to
system, subject to the limitation of 5.6.2.
which the gages will be exposed during testing. If the response
5.6.2 Resolution—The ability of the candidate gage to
time of the compensation is exceeded, the resulting uncertainty
measure small increments of strain within the total strain range
must be considered. The ability of the gage system to withstand
the transient without a detrimental shift of the reference value should be compared with the incremental strain measurement
requirements of the test. When mechanical strain attenuators
must be verified. This is true whether or not strain is measured
during the transient. Any gage factor change as a function of are used, the resulting loss of resolution must be considered.
5.7 Strain Gradient—The gage length of the candidate gage
temperature change must also be considered.
establishes the length over which the unit strain is averaged.
5.2.3 Precalibration:
This factor must be considered.
5.2.3.1 Thermal output calibration on the structure is usu-
5.8 Uncertainty Factor—Uncertainty information that is
ally not possible and precalibration of gages on a similar
available from the manufacturer must be considered, in con-
material is necessary. However, variations of up to 0.5 ppm/°F
junction with conditions which are unique to the test, in order
are possible within a material. Often, rolling direction will
to estimate the total uncertainty.
influence thermal expansion coefficient.
5.9 Space Requirements—If space on or adjacent to the test
5.2.3.2 Precalibration of resistive or capacitive strain gages
article is limited, the space requirements for the complete strain
is performed using a calibration fixture made from material
gage system may be a critical consideration in determining the
similar to the test article. The calibration fixture must be made
suitability of a particular gage system. Working space for
to precisely fit the gage, especially if curvature is involved.
installation of the system may also be limited and must also be
Experience has shown mating parts must be lapped together to
considered. Space adjacent to the installed strain gage should
provide uniform clamping pressure around the periphery of the
be provided for installation of room-temperature strain gages
gage weld area.
required for making in-place calibrations.
5.2.3.3 The calibration test should be repeated to ensure
5.10 Effects of the Strain Gage on the Test Article—In most
precise duplication of the calibration. Zero return should also
cases the reinforcing effect of the strain gage on the test article
repeat exactly. If calibration data does not repeat; either the
is negligible, particularly in the case of capacitance gages
calibration set-up or the gages are faulty.
where the spring rate is extremely low. If a weldable gage is to
5.2.4 Post Test Calibration:
be used on thin sections, an evaluation of the reinforcing effect
5.2.4.1 A more precise thermal output calibration can be
should be made. Technical data concerning this effect can be
achieved after the test by removing the test gage (cut it out of
obtained from a strain gage manufacturer.
the structure) and running a precision test on the test gage still
attached to the test article material. The test coupon is relieved 6. Characteristics of
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