ASTM E1949-98

Designation: E 1949 – 98
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Ambient Temperature Fatigue Life of Metallic Bonded
1
Resistance Strain Gages
This standard is issued under the fixed designation E 1949; 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 their geometric design.
4.2 The determination of most strain gage parameters re-
1.1 This test method covers a uniform method for the
quires mechanical testing that is destructive. Since gages tested
determination of strain gage fatigue life at ambient tempera-
for fatigue life cannot be used again, it is necessary to treat data
ture. A suggested testing equipment design is included.
statistically. In general, longer and wider gages with lower
1.2 This test method does not apply to force transducers or
resistances will have greater fatigue life. Optional additions to
extensometers that use bonded resistance strain gages as
gages (integral leads are an example) will often reduce fatigue
sensing elements.
life.
1.3 Strain gages are part of a complex system that includes
4.3 To be used, strain gages must be bonded to a structure.
structure, adhesive, gage, leadwires, instrumentation, and (of-
Good results, particularly in a fatigue environment, depend
ten) environmental protection. As a result, many things affect
heavily on the materials used to clean the bonding surface, to
the performance of strain gages, including user technique. A
bond the gage, and to provide a protective coating. Skill of the
further complication is that strain gages, once installed, nor-
installer is another major factor in success. Finally, instrumen-
mally cannot be reinstalled in another location. Therefore, it is
tation systems must be carefully designed to ensure that they
not possible to calibrate individual strain gages; performance
do not unduly degrade the performance of the gages.
characteristics are normally presented on a statistical basis.
4.4 This test method encompasses only fully reversed strain
1.4 This standard does not purport to address all of the
cycles.
safety concerns, if any, associated with its use. It is the
4.5 Fatigue failure of a strain gage may not involve visible
responsibility of the user of this standard to establish appro-
cracking or fracture of the gage, but merely sufficient zero shift
priate safety and health practices and determine the applica-
to compromise the accuracy of the gage output for static strain
bility of regulatory limitations prior to its use.
components.
2. Referenced Documents
5. Interferences
2.1 ASTM Standards:
5.1 In order to ensure that strain gage test data are within a
E 1237 Guide for Installing Bonded Resistance Strain
2
defined accuracy, the gages must be properly bonded and
Gages
protected with acceptable materials. Aids in the strain gage
3. Terminology
installation and verification, thereof, can be found in Guide
E 1237. It is important to note that good performance in cyclic
3.1 strain gage fatigue life, n—the number of fully reversed
applications requires the best installations possible.
strain cycles corresponding to the onset of degraded gage
performance, whether due to excessive zero shift or other
6. Hazards
detectable failure mode (see Section 9.6).
6.1 Warning—In the specimen surface cleaning, gage bond-
4. Significance and Use ing, and protection steps of strain gage installations, hazardous
chemicals are often employed. Users of these test methods are
4.1 Strain gages are the most widely used devices for
responsible for contacting manufactures of these chemicals for
measuring strains and for evaluating stresses in structures. In
applicable Material Safety Data Sheets and to adhere to the
many applications there are often cyclic loads which can cause
required precautions.
strain gage failure. Performance parameters of strain gages are
affected by both the materials from which they are made and
7. Apparatus
7.1 Test Measurement Requirements:
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This test method is under the jurisdiction of ASTM Committee E-28 on 7.1.1 For fatigue life determination the uncertainty of the
Mechanical Testing and is the direct responsibility of Subcommittee E28.14 on
relative resistance change measurement shall not exceed 65
Strain Gages. Current edition approved April 10, 1998. Published June 1998.
μV/V or 60.1 % of the actual value, whichever is greater.
2
Annual Book of ASTM Standards, Vol 03.01.
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E 1949
7.1.2 Several methods are available for measuring the essential, there are several features that provide for a safer and
change of gage resistance with sufficient resolution and ac
...