ASTM E 251 : 2020
Superseded
A superseded Standard is one, which is fully replaced by another Standard, which is a new edition of the same Standard.
A superseded Standard is one, which is fully replaced by another Standard, which is a new edition of the same Standard.
Standard Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
Hardcopy , PDF
14-08-2020
English
01-05-2020
1.1The purpose of these test methods are to provide uniform test methods for the determination of strain gage performance characteristics. Suggested testing equipment designs are included.
1.2Test Methods E251 describes methods and procedures for determining five strain gage parameters:
| Section | |
| Part I—General Requirements | 7 |
| Part II—Resistance at a Reference Temperature | 8 |
| Part III—Gage Factor at a Reference Temperature | 9 |
| Part IV—Temperature Coefficient of Gage Factor | 10 |
| Part V—Transverse Sensitivity | 11 |
| Part VI—Thermal Output | 12 |
1.3Strain gages are very sensitive devices with essentially infinite resolution. Their response to strain, however, is low and great care must be exercised in their use. The performance characteristics identified by these test methods must be known to an acceptable accuracy to obtain meaningful results in field applications.
1.3.1Strain gage resistance is used to balance instrumentation circuits and to provide a reference value for measurements since all data are related to a change in the gage resistance from a known reference value.
1.3.2Gage factor is the transfer function of a strain gage. It relates resistance change in the gage and strain to which it is subjected. Accuracy of strain gage data can be no better than the precision of the gage factor.
1.3.3Changes in gage factor as temperature varies also affect accuracy although to a much lesser degree since variations are usually small.
1.3.4Transverse sensitivity is a measure of the strain gage's response to strains perpendicular to its measurement axis. Although transverse sensitivity is usually much less than 10 % of the gage factor, large errors can occur if the value is not known with reasonable precision.
1.3.5Thermal output is the response of a strain gage to temperature changes. Thermal output is an additive (not multiplicative) error. Therefore, it can often be much larger than the gage output from structural loading. To correct for these effects, thermal output must be determined from gages bonded to specimens of the same material on which the tests are to run, often to the test structure itself.
1.4Bonded resistance strain gages differ from extensometers in that they measure average unit elongation (ΔL/L) over a nominal gage length rather than total elongation between definite gauge points. Practice E83 is not applicable to these gages.
1.5These test methods do not apply to transducers, such as load cells and extensometers, that use bonded resistance strain gages as sensing elements.
1.6Strain gages are part of a complex system that includes structure, adhesive, gage, lead wires, instrumentation, and (often) environmental protection. As a result, many things affect the performance of strain gages, including user technique. A further complication is that strain gages once installed normally cannot be reinstalled in another location. Therefore, gage characteristics can be stated only on a statistical basis.
1.7This 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.8This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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