ASTM E467-21

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Designation: E467 − 08 (Reapproved 2014) E467 − 21
Standard Practice for
Verification of Constant Amplitude Dynamic Forces in an
Axial Fatigue Testing System
This standard is issued under the fixed designation E467; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers procedures for the dynamic verification of cyclic force amplitude control or measurement accuracy during
constant amplitude testing in an axial fatigue testing system. It is based on the premise that force verification can be done with
the use of a strain gaged elastic element. Use of this practice gives assurance that the accuracies of forces applied by the machine
or dynamic force readings from the test machine, at the time of the test, after any user applied correction factors, fall within the
limits recommended in Section 9. It does not address static accuracy which must first be addressed using Practices E4 or
equivalent.
1.2 Verification is specific to a particular test machine configuration and specimen. This standard is recommended to be used for
each configuration of testing machine and specimen. Where dynamic correction factors are to be applied to test machine force
readings in order to meet the accuracy recommended in Section 9, the verification is also specific to the correction process used.
Finally, if the correction process is triggered or performed by a person, or both, then the verification is specific to that individual
as well.
1.3 It is recognized that performance of a full verification for each configuration of testing machine and specimen configuration
could be prohibitively time consuming and/or expensive. Annex A1 provides methods for estimating the dynamic accuracy impact
of test machine and specimen configuration changes that may occur between full verifications. Where test machine dynamic
accuracy is influenced by a person, estimating the dynamic accuracy impact of all individuals involved in the correction process
is recommended. This practice does not specify how that assessment will be done due to the strong dependence on owner/operators
of the test machine.
1.4 This practice is intended to be used periodically. Consistent results between verifications is expected. Failure to obtain
consistent results between verifications using the same machine configuration implies uncertain accuracy for dynamic tests
performed during that time period.
1.5 This practice addresses the accuracy of the testing machine’s force control or indicated forces, or both, as compared to a
dynamometer’s indicated dynamic forces. Force control verification is only applicable for test systems that have some form of
indicated force peak/valley monitoring or amplitude control. For the purposes of this verification, the dynamometer’s indicated
dynamic forces will be considered the true forces. Phase lag between dynamometer and force transducer indicated forces is not
within the scope of this practice.
This practice is under the jurisdiction of ASTM Committee E08 on Fatigue and Fractureand is the direct responsibility of Subcommittee E08.03 on Advanced Apparatus
and Techniques.
Current edition approved May 1, 2014April 15, 2021. Published September 2014April 2021. Originally approved in 1972. Last previous edition approved in 20082014
ε1
as E467E467–08(2014).–08 . DOI: 10.1520/E0467-08R14.10.1520/E0467-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E467 − 21
1.6 The results of either the Annex A1 calculation or the full experimental verification must be reported per Section 10 of this
standard.
1.7 This practice provides no assurance that the shape of the actual waveform conforms to the intended waveform within any
specified tolerance.
1.8 This standard is principally focused at room temperature operation. It is believed there are additional issues that must be
addressed when testing at high temperatures. At the present time, this standard practice must be viewed as only a partial solution
for high temperature testing.
1.9 The values stated in inch-pound units are to be regarded as standard. No other units of measurement are included in this
standard.
1.10 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.
1.10 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.11 This 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.
2. Referenced Documents
2.1 ASTM Standards:
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E1823 Terminology Relating to Fatigue and Fracture Testing
E1942 Guide for Evaluating Data Acquisition Systems Used in Cyclic Fatigue and Fracture Mechanics Testing
2.2 Military Standard:
1312-B Fastener Test Methods
2.3 ANSI Standard:
Z540-1-1994 Calibration Laboratories and Measuring and Test Equipment—General Requirements
2.4 NCSL Standard:
Publication 940830/1600 NCSL Glossary of Metrology—Related Terms
3. Terminology
3.1 Terminology used in this practice is in accordance with Terminology E1823. Definitions provided in this practice are
considered either unfamiliar or not included in Terminology E1823.
3.2 Definitions:
3.2.1 accuracy, n—The quantitative difference between a test measurement and a reference value.
3.2.2 amplitude, n—one-half the peak-to-peak measurement of the cyclic waveform.
3.2.3 cal factor, n—the conversion factor between the dynamometer force and the indicated force.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from the U.S. Government Printing Office, Washington, DC 20402.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
E467 − 21
3.2.4 conditioned force, n—the high level voltage or digital data available from the dynamometer or force transducer’s signal
conditioning instrumentation; it is frequently of value during dynamic verification as it can be more conveniently monitored by
stand alone measurement instrumentation.
3.2.5 corrected force, n—the force obtained after applying a dynamic correction factor to the force transducer’s indicated force.
3.2.6 data acquisition equipment, n—the equipment used to convert a conditioned force to an indicated force.
3.2.7 dynamic dynamometer forces, n—the maximum and minimum forces produced in the dynamometer during a portion of a
dynamic test.
3.2.8 dynamic errors, n—errors in the force transducer’s corrected force output that occur due to dynamic operation (with
specimen bending errors intentionally corrected out).
3.2.9 dynamic indicated forces, n—the maximum and minimum forces reported by the test machine during a portion of a dynamic
test. These values are typically obtained using an oscilloscope, peak-valley meter, or files generated by computerized data
acquisition.
3.2.10 dynamometer, n—an elastic calibration device used to indicate the forces applied by a fatigue testing system during dynamic
operation. A strain gaged specimen is often used as the dynamometer. Suitable transducer instrumentation is also required to
provide accurate readings over the intended frequency and force range. (Refer to Practice E467, Annex A2 for detailed information
about the dynamometer and instrumentation.)
3.2.11 dynamometer force, n—the force value provided by the dynamometer’s readout.
3.2.12 endlevel, n—either a maximum or minimum level for a cyclic waveform.
3.2.13 fatigue testing system, n—for the purpose of this practice, a device for applying repeated force cycles to a specimen or
component, which applies repeated force cycles of the same span, frequency, waveshape, mean level, and endlevels.
3.2.14 force command, n—the desired force to be applied to the specimen or dynamometer by the testing machine.
3.2.15 force transducer, n—a measuring device that can provide an output signal proportional to the force being applied.
3.2.16 indicated force, n—the force value provided by the force transducer or dynamometer’s readout (for example, a numeric or
graphical output for reading by a human including a peak picking capability); these values are typically obtained from a digital
volt meter (DVM) or files generated by a computerized data acquisition.
3.2.17 instrumentation, n—the electronics used with a transducer providing excitation for the transducer, conditioning of the
measured signal, and readout of that signal; typically the conditioned signal is a voltage and the readout is a numerical display or
printout.
3.2.18 peak, n—the maximum endlevel of a cycle.
3.2.19 peak picking, n—the process of determining the peak or valley of a cyclic waveform.
3.2.20 repeatability, n—the closeness of agreement among repeated measurements of the dynamic forces under the same
conditions.
3.2.21 span, n—the absolute value of the peak minus the valley for a cyclic waveform.
3.2.22 transducer, n—a measuring device which has an output signal proportional to the engineering quantity being measured.
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3.2.23 true force, n—the actual force applied to the specimen or dynamometer.
3.2.24 UUT, n—Unit Under Test
3.2.25 valley, n—the minimum endlevel of a cycle.
4. Significance and Use
4.1 It is well understood how to measure the forces applied to a specimen under static conditions. Practices E4 details the required
process for verifying the static force measurement capabilities of testing machines. During dynamic operation however, additional
errors may manifest themselves in a testing machine. Further verification is necessary to confirm the dynamic force measurement
capabilities of testing machines.
NOTE 1—The static machine verification accomplished by Practices E4 simply establishes the reference. Indicated forces measured from the force cell
are compared with the dynamometer conditioned forces statically for confirmation and then dynamically for dynamic verification of the fatigue testing
system’s force output.
NOTE 2—The dynamic accuracy of the force cell’s output will not always meet the accuracy requirement of this standard without correction. Dynamic
correction to the force cell output can be applied provided that verification is performed after the correction has been applied.
NOTE 3—Overall test accuracy is a combination of measurement accuracy and control accuracy. This practice provides methods to evaluate either or both.
As control accuracy is dependent on many more variables than measurement accuracy it is imperative that the test operator utilize appropriate
measurement tools to confirm that the testing machine’s control behavior is consistent between verification activities and actual testing activities.
4.2 Dynamic errors are primarily span dependent, not level dependent. That is, the error for a particular force endlevel during
dynamic operation is dependent on the immediately preceding force endlevel. Larger spans imply larger absolute errors for the
same force endlevel.
4.3 Due to the many test machine factors that influence dynamic force accuracy, verification is recommended for every new
combination of potential error producing factors. Primary factors are specimen design, machine configuration, test frequency, and
loading span. Clearly, performing a full verification for each configuration is often impractical. To address this problem, dynamic
verification is taken in two parts.
4.3.1 First, one or more full verifications are performed at least annually. The main body of this practice describes that procedure.
This provides the most accurate estimate of dynamic errors, as it will account for electronic as well as acceleration-induced sources
of error.
4.3.2 The second part, described in Annex A1, is a simplified verification procedure. It provides a simplified method of estimating
acceleration-induced errors only. This procedure is to be used for common configuration changes (that is, specimen/grip/crosshead
height changes).
4.4 Dynamic verification of the fatigue system is recommended over the entire range of force and frequency over which the
planned fatigue test series is to be performed. Endlevels are limited to the machine’s verified static force as defined by the current
static force verification when tested in accordance with Practices E4.
NOTE 4—There is uncertainty as to whether or not the vibration in a frame will be different when operating in compression as opposed to tension. As
a consequence, this practice recommends performing verifications at maximum tension and maximum compression endlevels. The total span does not
need to be between those two levels, but can be performed as two tests.
NOTE 5—Primary electronic characteristics affecting dynamic measurement accuracy are noise and bandwidth. Excessive noise is generally the dominant
effect at the minimum test frequency. Insufficient bandwidth-induced errors are generally most significant at the maximum test frequency.
5. Apparatus
5.1 Dynamometer Construction—A dynamometer is required. The strongly preferred dynamometer is an actual specimen, suitably
strain gaged to provide a signal when loaded axially. Where a strain gaged specimen is not practical, an alternative dynamometer
must be made. Annex A2 provides more detailed instructions on the preparation of a typical dynamometer.
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5.2 Dynamometer Instrumentation—Dynamometer instrumentation is also required. The overall accuracy of the dynamometer and
the associated instrumentation shall contribute less than 25 % of the total error of the dynamic measurement being made. Refer
to Annex A2 for guidance on suitable instrumentation for both the dynamometer and the machine being verified. Calibration of
the dynamometer instrumentation must be current and traceable to the National Institute of Standards and Technology (NIST) or
some other recognized national standards organization.
5.3 Dynamometer Static Calibration—An absolute calibration of the dynamometer as tested in accordance with Practices E4 is
not required. It is only necessary to statically calibrate the dynamometer indicated forces to the force transducer indicated forces
at the force levels corresponding to the desired dynamic force endlevels. It is this relationship that will be verified under dynamic
conditions to assure acceptable levels of additional errors due to dynamic operation. Details of the static calibration of the
dynamometer are included in Section 6 as an integral part of the practice.
6. Procedure—Full Verification
NOTE 6—The objective of a full verification is to show that the force transducer corrected force accuracy is within an acceptable range when all sources
of dynamic error have been taken into account.
6.1 Designing the Test—Prepare a matrix of configurations, test frequencies, and loading spans which address the following issues:
6.1.1 Machine Configurations—Ideally, the machine should be configured exactly as it will be used for material testing including
grips or fixturing, or both. Where it is not practical to test all expected configurations, test the configuration(s) with the largest
expected acceleration errors. In this case, Annex A1 must be used to verify additional test set-ups. It is recommended that at least
two machine configurations be verified, and that the ability to detect acceleration errors against the true errors measured with the
full verifications be tested.
6.1.2 Test Frequencies—Where the testing machine will only be used at a few discrete frequencies, perform the verification at
those frequencies. Where the machine will be used at a variety of frequencies, the minimum and maximum frequencies must be
verified using the full verification procedure. Any operating frequency between those frequencies may be verified using Annex A1.
A dynamic error graph may prove useful for identifying sources of dynamic errors and is recommended though not required. See
Annex A3 for an example.
6.1.3 Loading Spans—A recommended test would be with the machine configured for minimum motion and another would be
with the machine configured for maximum motion. Also, due to the uncertainty of differences in machine vibration when operating
in tension as opposed to compression, it is recommended that loading spans be applied in each region where the machine be
operated and through zero force if the machine is to be operated under that condition.
NOTE 7—In some tests, for example, a fatigue crack growth determination, the specimen stiffness may vary significantly during the test. To simulate this
situation, a range of specimens with differing notch or crack depths may be needed.
6.2 Conducting the Test:
6.2.1 Preliminary:
6.2.1.1 Assemble the test machine in the configuration to be tested.
6.2.1.2 Ensure that the force transducer indicated force accuracy has been statically verified meeting the requirements of Practices
E4.
NOTE 8—Some testing machines include a dynamic force compensation feature which is adjusted to correct the force transducer indicated force for effects
due to acceleration of the mass of the force transducer element and associated grips. This feature may be applied in the transducer instrumentation or
in the test machine’s data acquisition equipment. When present and required for acceptable dynamic accuracy, follow the manufacturer’s instructions for
this adjustment before performing any fatigue test or dynamic verification. After adjustment, verify that the dynamic force compensation has had no effect
on the static calibration.
6.2.2 Verification Method—Do 6.2.2.1 – 6.2.2.3 for each combination of machine configuration defined in 6.1.1. Do 6.2.2.7 –
6.2.2.9 for each combination of machine configuration, endlevels, and test frequency defined in 6.1.2.
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Basic Machine Configuration
6.2.2.1 Install the dynamometer in the system to be verified.
6.2.2.2 Connect the strain gage bridge of the dynamometer to the associated instrumentation. Connect the verification data
acquisition equipment to the dynamometer conditioned force output and the force transducer conditioned force output. Turn power
on to all devices and allow sufficient time for the dynamometer and associated instrumentation to stabilize.
NOTE 9—Where a separate verification system is used to perform the data acquisition of the force transducer conditioned force output, then the test
machine’s data acquisition and peak picking elements must be separately verified. Conversely, where the test machine’s data acquisition system is used
to perform the data acquisition of the dynamometer conditioned force output, that portion of the test machine’s data acquisition system must first be
verified as in 5.2.
6.2.2.3 Report the machine configuration in the final report, as in Section 10.
Static Calibration of the Dynamometer
6.2.2.4 Exercise the dynamometer three times to the maximum endlevel plus 5 % of the test span being verified, return to zero
force and zero the dynamometer indicated force and the force transducer indicated force outputs.
6.2.2.5 Using the Set-The-Force method defined in Practices E4, load the dynamometer to the maximum endlevel and calibrate
the dynamometer indicated force to the force transducer indicated force. Scale the dynamometer output to units appropriate for
performing the test. Although not necessary, it may be convenient to use the same scaling as on the test machine.
6.2.2.6 Using the Set-The-Force method defined in Practices E4, calibrate the dynamometer indicated force to the force transducer
indicated force at the six discrete points and in the order, defined below:
Maximum endlevel – 5 % of span
Maximum endlevel
Maximum endlevel + 5 % of span
Minimum endlevel + 5 % of span
Minimum endlevel
Minimum endlevel – 5 % of span
This provides a verified force range accounting for hysteresis at the minimum endlevel and compensating for a poorly controlled
machine. Record the force transducer indicated force and the dynamometer indicated force. When static calibration is performed
in accordance with Practices E4, the repeatability of the error associated with the maximum force of the dynamometer shall not
exceed 60.25 % of the maximum force applied by the testing machine.
NOTE 10—Assure that the value calibrated is within the machine’s current static verification range in accordance with Practices E4.
Cyclic Test
6.2.2.7 Set the machine controls to operate in the same manner as the actual test. Cycle the test machine at the desired test
frequency. Utilize peak/valley readout monitoring or amplitude control as appropriate to assure test endlevels are achieved.
(1) Force Indication Verification Method—Adjust the machine controls so that the dynamometer indicated force endlevels
during dynamic operation correspond to the maximum and minimum endlevels obtained statically as measured by the
dynamometer.
NOTE 11—Force indication verification is only applicable where real time output of the force transducer indicated force is available.
6.2.2.8 Wait for the system to stabilize. After stability has been achieved, record a minimum of 50 dynamometer indicated force
peaks and
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