New edition of DIN EN ISO 6892-1 – Metal tensile test at ambient temperature
In February 2017, the second edition of the standard DIN EN ISO 6892-1 for metal tensile tests was published as a German national standard. The national standard is the translation of the second edition of the international standard ISO 6892-1, which was already published in 2016. The new edition replaces the 2009 edition effective immediately. Labs and test institutions will not need to change their procedures with the update of this standard at this time. The main section of the standard, meaning the normative section, has not be changed in terms of metal tensile tests and the testing process. The main changes have been the addition of a new normative annex, which defines the determination of Young's modulus in a tensile test (Annex G), and the improved descriptions of setting standard-compliant test speeds to Methods A and B. ZwickRoell's products meet the requirements of the new edition of the standard DIN EN ISO 6892-1 without requiring any technical modifications. There are no technical modifications required for existing applications.
What Has Changed?
The first edition of DIN EN ISO 6892-1 from 2009 added a new option to the existing option for setting the test speed. The new option involves the strain rate-based setting of the test speed and the option to also use the extensometer signal, meaning the actual specimen strain, for controlling the test speed. The method was called strain rate control and given the name Method A. Up to this point, the only standardized method used, and still allowed, was called the strain speed-based method (Method B) and was not changed in its use and applicability. The second edition of DIN EN ISO 6892-1 from 2017 improves the language of the descriptions and thus the clarity of Method A as well as that of Method B. With Method A, it must be emphasized once more that it is important to adhere to the characteristic values from the tensile test, in particular those for yield and proof stress, and the strain rate in the normative tolerance limits as defined. This can be implemented with the extensometer signal in a closed-loop as well as with a constant crosshead speed that is selected in such a way that the normatively specified tolerance limit reaches and adheres to the characteristic values (open loop). To improve the language and to uniquely designate the two loop types for Method A, the closed loop method is named Method A1 and the open loop method is named A2 in the new edition.
Method A is explicitly recommended
Furthermore, in the second edition of DIN EN ISO 6892-1, Method A (test speed based on strain speed) is strongly recommended. This strong recommendation is now made in the introduction, that is in the main section of the standard. According to the second edition of the standard, the goal of Method A is to minimize differences in test speeds when determining characteristic values, in particular characteristics that depend on strain rate, and to minimize the measurement uncertainty of test results. The second edition of DIN EN ISO 6892-1 has been expanded by a new annex, Annex G. It defines in detail the procedure for determining Young's modulus in a tensile test. The approach is normative, but does not need to be used in a normal tensile test. Determining the initial gradient of the stress-strain measurement diagram mE is entirely sufficient for determining the characteristics of the tensile test. This means that test labs and institutions do not need to make any changes in order to implement the new edition of the standard DIN EN ISO 6892-1 in daily testing. The standard assumes that by following Annex G, the Young's modulus value is achieved in a separate test because of the measuring equipment and the test parameters required. Method B (test speed based on stress speed) has been revised in the second edition of DIN EN ISO 6892-1 so that the language is clearer. The content of Method B has not been amended, meaning that test labs and institutions do not need to make any changes to daily testing.
Significant changes to DIN EN ISO 6892-1:2017
1. A strong recommendation has been made for Method A.
2. "Parallel length" is used instead of "test length".
3. The description for setting the test speed for Rp determination in Method B is more precise and easier to understand.
4. New designations in Method A
- Method A closed loop has become Method A1
- Method A open loop has become Method A2. 5. Figures 8 and 9 have been edited so they are clearer.
6. Annex F has been revised and expanded, however the content remains the same.
7. Annex G (determination of Young's modulus) has been added.
8. Chapter 10 has been renumbered and the annexes G and above have been renamed.
