ASTM E467-21 Standard Practice for Verification of Constant-Amplitude Dynamic Forces in an Axial Fatigue Test System

The American Society for Testing and Materials (ASTM) standard "ASTM E467-21 Standard Practice for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System" describes procedures for dynamic verification of cyclic force amplitude control or measurement accuracy during constant amplitude testing in an axial fatigue testing system. This standard is based on the assumption that force verification can be performed using an elastic element with a strain gauge. Use of this practice provides assurance that the accuracy of the forces applied by the machine or the dynamic force readings from the testing machine remain within the limits recommended in this standard after correction factors applied by the user during testing.

Verification is specific to a particular testing machine configuration and specimen. It is recommended that this standard be used for each configuration of testing machine and specimen. When dynamic correction factors must be applied to testing machine force readings to meet the accuracy recommended in this standard, verification is also specific to the correction process used. Finally, if the correction process is triggered or performed by one or both persons, verification is also specific to that person.

It is recognized that performing a full verification for each test machine and specimen configuration may be prohibitively time consuming or expensive. The standard appendix provides methods for estimating the dynamic accuracy impact of test machine and specimen configuration changes that may occur between full verifications (Annex A1). If the dynamic accuracy of a test machine is affected by one individual, it is recommended that the dynamic accuracy impact of all individuals involved in the correction process be estimated. This practice does not specify how this assessment is to be made because of the strong dependency on the owner or operator of the test machine.

This application is designed to be used periodically. Consistent results are expected between validations. Failure to obtain consistent results between validations using the same machine configuration indicates uncertain accuracy for dynamic tests performed during that time period.

This application addresses the accuracy of the testing machine's force control or specified forces, or both, compared to a dynamometer's specified dynamic forces. Force control verification is only applicable to test systems that have some form of specified force peak/valley monitoring or amplitude control.

For the purposes of this standard, the following terms and definitions apply:

• Accuracy refers to the quantitative difference between a test measurement and a reference value.
• Amplitude refers to half the peak-to-peak measurement of the cyclic waveform.
• The Cal factor is the conversion factor between the dynamometer force and the indicated force.
• Conditioned force, n—high-level voltage or digital data obtained from the signal conditioning instrumentation of a dynamometer or force transducer, is often valuable during dynamic verification because it can be more conveniently monitored by independent measurement instrumentation.
• The corrected force is the force obtained after a dynamic correction factor is applied to the force transducer's displayed force.
• Data acquisition equipment is equipment used to convert a conditioned force into a displayed force.
• Dynamic dynamometer forces refer to the maximum and minimum forces produced on the dynamometer during a portion of a dynamic test.
• Dynamic errors are errors in the corrected force output of the force transducer that occur due to dynamic operation.
• Dynamic indicated forces are the maximum and minimum forces reported by the testing machine during a portion of a dynamic test. These values ​​are usually obtained using an oscilloscope, peak-valley meter, or files generated by computerized data acquisition.
• A dynamometer is an elastic calibration device used to indicate the forces exerted by a fatigue testing system during dynamic operation. A strain-gauge specimen is usually used as the dynamometer. Appropriate transducer instrumentation is also required to provide accurate readings over the intended frequency and force range.
• Dynamometer force is the force value provided by the dynamometer reading.
• The final level is the maximum or minimum level for a cyclic waveform.
• A fatigue testing system, for this application purpose, is a device that applies repeated force cycles to a specimen or component at the same range, frequency, waveform, average level, and final levels.
• The force command is the force desired to be applied to the sample or dynamometer by the testing machine.
• A force transducer is a measuring device that can provide an output signal proportional to the applied force.
• The indicated force is the force value provided by the force transducer or dynamometer reading.
• Peak picking is the process of determining the peak or valley of a cyclic waveform.

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