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 18212;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 28212;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 38212;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.
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.
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.
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.
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).
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 48212;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 ...........
Copyright ©2024 All Rights Reserved